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Chandrasekhar Nataraj and Turki Haj MOHAMAD "Fault diagnostics systems and methods"

[Abstract] [Patent URL]
Abstract: This disclosure relates to diagnosing a nature and magnitude of faults within electrical and mechanical systems.
Amir A,Prashant N,Parham S and Nataraj C "Physics-informed machine learning for modeling multidimensional dynamics"

[Abstract] [BibTeX] [DOI] [URL]
Abstract: This study presents a hybrid modeling approach that integrates physics and machine learning for modeling multi-dimensional dynamics of a coupled nonlinear dynamical system. This approach leverages principles from classical mechanics, such as the Euler-Lagrange and Hamiltonian formalisms, to facilitate the process of learning from data. The hybrid model incorporates single or multiple artificial neural networks within a customized computational graph designed based on the physics of the problem. The customization minimizes the potential of violating the underlying physics and maximizes the efficiency of information flow within the model. The capabilities of this approach are investigated for various multidimensional modeling scenarios using different configurations of a coupled nonlinear dynamical system. It is demonstrated that, in addition to improving modeling criteria such as accuracy and consistency with physics, this approach provides additional modeling benefits. The hybrid model implements a physics-based architecture, enabling the direct alteration of both conservative and non-conservative components of the dynamics. This allows for an expansion in the model’s input dimensionality and optimal allocation of input variable effects on conservative or non-conservative components of dynamics.
BibTeX: 
    @Article{2024 Amir,
      author   = {Amir A,Prashant N,Parham S and Nataraj C},
      title    = {Physics-informed machine learning for modeling multidimensional dynamics},
      journal  = {Nonlinear Dynamics},
      year     = {2024},
      month    = {08},
      pages    = {1-21},
      doi      = {https://doi.org/10.1007/s11071-024-10163-3},
      keywords = {Hybrid modeling ,Multidimensionaldynamics ,Euler-Lagrange ,Hamiltonian ,Dynamicalsystem},
      url      = {https://www.researchgate.net/publication/383455829_Physics-informed_machine_learning_for_modeling_multidimensional_dynamics},
}
McKelvey S, Abassi A, Nataraj C and Duran M, "Data-driven modeling techniques for prediction of settled water turbidity in drinking water treatment." Front. Environ. Eng. 3:1401180.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Drinking water treatment is a complex system of chemical, physical, and biological processes that is highly dependent on water quality and the design of the treatment process. To create decision-support tools, the prediction of key performance indicators, such as settled water turbidity, is needed. A variety of data-driven modeling techniques is available to formulate such predictions. Data-driven models provide valuable tools for formulating predictions where there is a lack of mechanistic models or the mechanisms are not fully understood, as in surface water treatment. The objective of this paper is to evaluate and compare the effectiveness of various data-driven techniques for this important, but difficult, problem. Recognizing that the size and quality of the dataset are most critical in this kind of analysis, this work uses one of the largest datasets used in this context consisting of 2,527 vectors of water quality and operational data (2,527 X nine data frame) from a full-scale water treatment plant. The paper constructs and compares the performance of the several data-driven models including k-nearest neighbor (KNN) regression, polynomial regression, and artificial neural networks (ANN). Based on test scaled root mean square error (RMSE), the ANN model was the most predictive (0.124). Similarly, the ANN model had the best predictive performance based on total scaled RMSE (0.086). These results show that ANNs have a high potential for the development of a future decision support system in selecting appropriate coagulant doses based on settled water turbidity.
BibTeX: 
    @Article{2024 McKelvey,
      author   = {2024 McKelvey, Abassi, Nataraj and Duran},
      journal  = {ORIGINAL RESEARCH article},
      title    = {Data-driven modeling techniques for prediction of settled water turbidity in drinking water treatment},
      year     = {2024},
      note     = {Sec. Water, Waste and Wastewater Engineering},
      volume   = {3 - 2024},
      doi      = {doi: 10.3389/fenve.2024.1401180},
      keywords = {water treatment, data-driven modeling, artificial neural network, k-nearest neighbor, linear regression, polynomial regression},
      url      = {https://www.frontiersin.org/journals/environmental-engineering/articles/10.3389/fenve.2024.1401180/full#h1},
}
Will J. Pivik, Garrett M. Clayton, Gerard F. Jones and C. Nataraj, "Dynamic Modeling of a Low-cost Mechanical Ventilator", IFAC-PapersOnLine. Vol. 55, pp. 81-85.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: In this paper, we develop a dynamic model for a low-cost ventilator, Novavent, developed at Villanova University. Since 2020, several academic institutions have focused on developing a less expensive ventilator system with the goal of increasing accessibility of medical ventilation for low-income countries. This is mainly a response to the ongoing Covid-19 pandemic. Due to the demand the pandemic has created, the development process of these new designs have prioritized development and implementation speed over model validation. In order to increase the understanding and aid in the controller design process of these new ventilator designs, an empirical model was developed for a low-cost ventilator design, developed at Villanova University. The process of this model design was systematically documented with the intention that other institutions can use this process as a template for modeling their own designs. After developing expressions of the different responses in the system observed through empirical data, Simulink was then used to combine all expressions into a holistic model. This model was then validated using data collected from the response of the ventilator design observed.
BibTeX: 
    @Article{Pivik2022,
      author   = {Will J. Pivik,Garrett M. Clayton, Gerard F. Jones and C. Nataraj},
      journal  = {IFAC-PapersOnLine},
      title    = {Dynamic Modeling of a Low-cost Mechanical Ventilator},
      year     = {2022},
      issn     = {2405-8963},
      note     = {2nd Modeling, Estimation and Control Conference MECC 2022},
      number   = {37},
      pages    = {81-85},
      volume   = {55},
      doi      = {https://doi.org/10.1016/j.ifacol.2022.11.165},
      keywords = {Ventilator, system dynamics, healthcare technology},
      url      = {https://www.sciencedirect.com/science/article/pii/S2405896322028087},
}
Barbara Nara Teixeira Cunha,Aldemir Ap. Cavallini, Jr. and Valder Steffen, Jr. and Prashant N. Kambali and C. Nataraj, "Numerical Analysis of Rotordynamic Systems Using the Harmonic Balance Method"

[BibTeX]

BibTeX: 
    @Conference{Cunha2023,
      author    = {Brbara Nara Teixeira Cunha,Aldemir Ap. Cavallini, Jr. and Valder Steffen, Jr. and Prashant N. Kambali and C. Nataraj},
      booktitle = {COBEM - 27th International Congress of Mechanical Engineering},
      title     = {Numerical Analysis of Rotordynamic Systems Using the Harmonic Balance Method},
      year      = {2023},
      address   = {Florianopolis, Brazil},
    }
Alexandre Henrique Pereira Tavares,Aldemir Ap. Cavallini, Jr. and Antonio Claudio Paschoarelli Veiga,Amirhassan Abbasi and C. Nataraj, "Wavenet-based autoencoder for real-time and unsupervised condition monitoring of rotary machines"

[BibTeX]

BibTeX: 
    @Conference{Tavares2023,
      author    = {Alexandre Henrique Pereira Tavares, Aldemir Ap. Cavallini, Jr. and Antonio Claudio Paschoarelli Veiga,Amirhassan Abbasi and C. Nataraj},
      booktitle = {CODEM: 27th International Congress of Mechanical Engineering},
      title     = {Wavenet-based autoencoder for real-time and unsupervised condition monitoring of rotary machines},
      year      = {2023},
      address   = {Florianopolis, Brazil},
    }
Mohseni, Mohamad and Santhanam, Sridhar and Williams, Jesse and Thakker, Ash and Nataraj, C., "Systematic fatigue spectrum editing by fast wavelet transform and genetic algorithm", Fatigue \& Fracture of Engineering Materials \& Structures. Vol. 45, pp. 69-83.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Abstract Fatigue testing is critical in order to establish the service life of load-bearing components and structures. The extensive time associated with full fatigue spectrum testing can lead to prohibitive costs. A significant need exists for a fatigue load spectrum editing methodology, based on the mechanics of fatigue, that produces load spectra that can replicate service damage in laboratory testing and can lead to compressed testing times and reduced costs. In this work, a wavelet genetic (WAVEGEN) algorithm is developed to edit fatigue loading spectra using wavelet analysis to greatly reduce the length of a spectrum while retaining the same damage accumulation characteristics. In addition, an optimization protocol using a genetic algorithm is included within this process to automatically select the best wavelet editing parameters. The algorithm is designed to identify the most suitable wavelet type, filter, and level to optimally edit a given fatigue spectrum and ensure equivalence between edited and unedited spectra from a damage perspective. The algorithm was applied to two well-known aircraft fatigue spectra: Fighter Aircraft Loading Standard for Fatigue evaluation (FALSTAFF) and Transport Wing Standard (TWIST). The proposed approach has demonstrated that both spectra can be compressed significantly even while ensuring equivalence from a damage perspective.
BibTeX: 
    @Article{Mohseni2021j,
      author   = {Mohseni, Mohamad and Santhanam, Sridhar and Williams, Jesse and Thakker, Ash and Nataraj, C.},
      journal  = {Fatigue \& Fracture of Engineering Materials \& Structures},
      title    = {Systematic fatigue spectrum editing by fast wavelet transform and genetic algorithm},
      year     = {2021},
      pages    = {69-83},
      volume   = {45},
      doi      = {10.1111/ffe.13583},
      eprint   = {https://onlinelibrary.wiley.com/doi/pdf/10.1111/ffe.13583},
      keywords = {fatigue analysis, genetic algorithm, signal processing, wavelet transform},
      url      = {https://onlinelibrary.wiley.com/doi/abs/10.1111/ffe.13583},
}
Sanchirico, M. J. and Jiao, X. and Nataraj, C, "AMITE: A Novel Polynomial Expansion for Analyzing Neural Network Nonlinearities"

[BibTeX]

BibTeX: 
    @Article{Sanchirico2021j,
      author  = {Sanchirico, M. J. and Jiao, X. and Nataraj, C.},
      journal = {{IEEE} Transactions on Neural Networks and Learning Systems},
      title   = {{AMITE}: A Novel Polynomial Expansion for Analyzing Neural Network Nonlinearities},
      year    = {2021},
      issn    = {2162-2388},
      pages   = {1--13},
      doi     = {10.1109/TNNLS.2021.3130904},
    }
Lacarbonara, Walter and Tenreiro Machado, J. and Ma, Jun and Nataraj, C, "Preface to Special Issue on Complex dynamics of {COVID}-19: modeling, prediction and control", Nonlinear Dynamics. Vol. 106, pp. 1129--1131.

[BibTeX] [DOI] [URL]
BibTeX: 
    @Article{Lacarbonara2021j,
      author  = {Lacarbonara, Walter and Tenreiro Machado, J. and Ma, Jun and Nataraj, C.},
      journal = {Nonlinear Dynamics},
      title   = {Preface to Special Issue on Complex dynamics of {COVID}-19: modeling, prediction and control},
      year    = {2021},
      issn    = {1573-269X},
      note    = {Special Issue on Complex dynamics of {COVID}-19: modeling, prediction and control},
      number  = {2},
      pages   = {1129--1131},
      volume  = {106},
      refid   = {Lacarbonara2021},
      url     = {https://doi.org/10.1007/s11071-021-06900-7},
    }
C. Nataraj, "2021 Benjamin Franklin Medal in Mechanical Engineering presented to C. Daniel Mote, Jr., Ph.D"

[BibTeX]

BibTeX: 
    @Article{Nataraj2022j,
      author  = {C. Nataraj},
      journal = {Journal of the Franklin Institute},
      title   = {2021 {B}enjamin {F}ranklin {M}edal in {M}echanical Engineering presented to {C}. {Daniel Mote, Jr., Ph.D}},
      year    = {2022},
    }
Lebbad, Anderson and Clayton, Garrett M. and Nataraj, C., "Convolutional Networks for Classification of Mortars", ASME. Letters Dyn. Sys. Control. July 2022; 2(3): 031003.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: The task of classifying unexploded mortars is critical in both humanitarian and military explosive ordnance disposal (EOD) operations. Classification needs to be completed quickly and accurately and is the first step toward disarming the ordnance because it provides information about the fuzing mechanism, or the stage in the arming cycle that the ordnance is currently in. To assist EOD technicians with mortar identification, this article presents an automated image-based algorithm and the database of images used in its development. The algorithm utilizes convolutional networks with variations to training to improve performance for ordnance found in varying states of disassembly. The classifier developed was found to be 98.5\\% accurate for these lab condition photos; future work will focus on more cluttered environments.
BibTeX: 
    @Article{Lebbad2022,
      author   = {Lebbad, Anderson and Clayton, Garrett M. and Nataraj, C.},
      journal  = {ASME Letters in Dynamic Systems and Control},
      title    = {{Convolutional Networks for Classification of Mortars}},
      year     = {2022},
      issn     = {2689-6117},
      month    = {03},
      note     = {031003},
      number   = {3},
      volume   = {2},
      doi      = {10.1115/1.4053886},
      eprint   = {https://asmedigitalcollection.asme.org/lettersdynsys/article-pdf/2/3/031003/6866044/aldsc\_2\_3\_031003.pdf},
      url      = {https://doi.org/10.1115/1.4053886},
}
Bender, Dieter and Licht, Daniel J. and Nataraj, C., "A Novel Embedded Feature Selection and Dimensionality Reduction Method for an SVM Type Classifier to Predict Periventricular Leukomalacia (PVL) in Neonates", Appl. Sci. 2021, 11(23), 11156.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: This paper is concerned with the prediction of the occurrence of periventricular leukomalacia (PVL) in neonates after heart surgery. Our prior work shows that the Support Vector Machine (SVM) classifier can be a powerful tool in predicting clinical outcomes of such complicated and uncommon diseases, even when the number of data samples is low. In the presented work, we first illustrate and discuss the shortcomings of the traditional automatic machine learning (aML) approach. Consequently, we describe our methodology for addressing these shortcomings, while utilizing the designed interactive ML (iML) algorithm. Finally, we conclude with a discussion of the developed method and the results obtained. In sum, by adding an additional (Genetic Algorithm) optimization step in the SVM learning framework, we were able to (a) reduce the dimensionality of an SVM model from 248 to 53 features, (b) increase generalization that was confirmed by a 100% accuracy assessed on an unseen testing set, and (c) improve the overall SVM model’s performance from 65% to 100% testing accuracy, utilizing the proposed iML method.
BibTeX: 
    @Article{Bender2021a,
      author   = {Bender, Dieter and Licht, Daniel J. and Nataraj, C.},
      journal  = {Applied Sciences},
      title    = {A Novel Embedded Feature Selection and Dimensionality Reduction Method for an SVM Type Classifier to Predict Periventricular Leukomalacia (PVL) in Neonates},
      year     = {2021},
      issn     = {2076-3417},
      number   = {23},
      volume   = {11},
      doi      = {10.3390/app112311156},
      keywords = {periventricular leukomalacia, active learning, interactive machine learning, support vector machine, feature selection, dimensionality reduction, congenital heart disease, pediatric},
}
Watkins, R. and Phelan, J. and Clayton, G. M. and Ortega, A. and Nataraj, C. and Poler, S. M., "Instrumenting a Simple Lung Simulator for Digital Data Acquisition and Simulation of Spontaneous Breathing"

[BibTeX]

BibTeX: 
    @Article{Watkins2021,
      author  = {Watkins, R. and Phelan, J. and Clayton, G. M. and Ortega, A. and Nataraj, C. and Poler, S. M.},
      journal = {Anesthesia and Analgesia},
      title   = {Instrumenting a Simple Lung Simulator for Digital Data Acquisition and Simulation of Spontaneous Breathing},
      year    = {2021},
      month   = mar,
      pages   = {65-66},
      volume  = {132},
    }
Hershey, Marc and Burris, Heather H. and Cereceda, David and Nataraj, C., "Predicting the risk of spontaneous premature births using clinical data and machine learning", Informatics in Medicine Unlocked. Vol. 32, pp. 101053.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Background: Spontaneous preterm birth (sPTB) is a worldwide public health issue that affects millions of infants per year and causes long-lasting effects. Prediction of sPTB is critical for clinical management and patient referral to centers capable of treating preterm infants. The outstanding capabilities of machine learning to detect patterns and make predictions have motivated recent studies to improve the prediction of sPTB. However, there is still a high level of uncertainty, especially among patients without a prior sPTB. Objective: The objectives of this study were to formulate more effective and accurate predictions of sPTB and to identify relevant sPTB risk factors. Methods: From the data set collected by the NICHD Maternal Fetal Medicine Units (MFMU) Network between 1992 and 1994, we selected a cohort of women with no previous preterm birth (n = 2390). We then developed a pre-processing protocol that prioritized original information by limiting interpolation criteria to individual feature averages, reducing complexity and cross-feature correlation to increase generalization. Next we created a machine learning model based on support vector machines and a radial basis function kernel to: (i) predict the occurrence of spontaneous preterm birth, and (ii) accommodate clinical considerations for treatment. Results: In clinically conservative, moderate, and aggressively models, prediction of sPTB reached average true positive rate of 0.36, 0.62, and 0.82, respectively, and corresponding average false positive rate of 0.03, 0.38, and 0.56, respectively in an independent testing partition. The area under the receiver operating characteristics curve (AUC) was 0.75. The models benefited most from features collected in the earlier stages of the study protocol and pregnancy, generally 26 weeks gestational age, and involved a combination of socioeconomic and biological contributors identified as risk factors in previous studies. Conclusions: Our findings provide a framework for improving clinical decision support system models to assist providers in predicting sPTB. Updating such models with more recent data that include multiple levels of individual and contextual factors could prove useful to predict sPTB.
BibTeX: 
    @Article{Hershey2022,
      author   = {Hershey, Marc and Burris, Heather H. and Cereceda, David and Nataraj, C.},
      journal  = {Informatics in Medicine Unlocked},
      title    = {Predicting the risk of spontaneous premature births using clinical data and machine learning},
      year     = {2022},
      issn     = {2352-9148},
      pages    = {101053},
      volume   = {32},
      doi      = {10.1016/j.imu.2022.101053},
      keywords = {Spontaneous preterm birth, Machine learning, Nulliparous women},
      url      = {https://www.sciencedirect.com/science/article/pii/S2352914822001927},
}
Amirhassan Abbasi and Foad Nazari and C. Nataraj, "Adaptive Modeling of Vibrations and Structural Fatigue for Analyzing Crack Propagation in a Rotating System"

[BibTeX]

BibTeX: 
    @Article{Abbasi2022,
      author  = {Amirhassan Abbasi and Foad Nazari and C. Nataraj},
      journal = {Journal of Sound and Vibration},
      title   = {Adaptive Modeling of Vibrations and Structural Fatigue for Analyzing Crack Propagation in a Rotating System},
      year    = {2022},
      note    = {In Print},
    }
Abbasi, Amirhassan and Nataraj, C., "Physics-Informed Machine Learning for Uncertainty Reduction in Time Response Reconstruction of a Dynamic System", IEEE Internet Computing. Vol. 26, pp. 35-44.

[BibTeX] [DOI]

BibTeX: 
    @Article{Abbasi2022a,
      author  = {Abbasi, Amirhassan and Nataraj, C.},
      journal = {IEEE Internet Computing},
      title   = {Physics-Informed Machine Learning for Uncertainty Reduction in Time Response Reconstruction of a Dynamic System},
      year    = {2022},
      number  = {4},
      pages   = {35-44},
      volume  = {26},
      doi     = {10.1109/MIC.2022.3170736},
    }
AL-Shudeifat, Mohammad A., "Impact of non-synchronous whirl on post-resonance backward whirl in vertical cracked rotors", Journal of Sound and Vibration. Vol. 520, pp. 116605.

[Abstract] [BibTeX] [URL]
Abstract: Certain heavy-duty industrial machinery uses vertical rotating shafts. Such rotating systems typically undergo transient operation phases to reach their nominal speeds; recurrent passage through resonance generally occurs during startup and coast down operations. The Non-synchronous whirl between the shaft rotational speed and its whirling in the whirl orbit in the vicinity of the resonance zones, significantly affecting the breathing mechanism of a propagating transverse crack. Therefore, the appearance of Non-synchronous whirl during the passage through resonance rotational speed activates the crack breathing mechanism. To verify this observation, Jeffcott rotor and finite element models with induced breathing cracks are considered here for geometrically symmetrical and asymmetrical vertical rotor configurations. The mathematical models associated with these systems yield linear time-varying equations of motion incorporating the angular acceleration rate. The appearance of a Non-synchronous is found activating the crack breathing mechanism, which immediately excites the post-resonance backward whirl even with small crack depths in the rotor system. Accordingly, the excitation of post-resonance backward whirl can be considered as a strong indicator of an early crack propagation phase in vertical rotors.
BibTeX: 
    @Article{ALShudeifat2022,
      author   = {AL-Shudeifat, Mohammad A.},
      journal  = {Journal of Sound and Vibration},
      title    = {Impact of non-synchronous whirl on post-resonance backward whirl in vertical cracked rotors},
      year     = {2022},
      issn     = {0022-460X},
      pages    = {116605},
      volume   = {520},
      keywords = {Rotor systems, Breathing crack, Cracked shaft, Post-resonance backward whirl, Jeffcott rotor},
      url      = {https://www.sciencedirect.com/science/article/pii/S0022460X21006179},
}
Tyler Alexander and C. Nataraj and Chengyuan Wu, "A machine learning approach to predict quality of life changes in patients with {P}arkinson's {D}isease"

[BibTeX]

BibTeX: 
    @Article{Alexander2022,
      author  = {Tyler Alexander and C. Nataraj and Chengyuan Wu},
      journal = {Annals of Clinical and Translational Neurology},
      title   = {A machine learning approach to predict quality of life changes in patients with {P}arkinson's {D}isease},
      year    = {2022},
      note    = {In Print.},
    }
Walter Lacarbonara and Jun Ma and C. Nataraj, "Complex dynamics of COVID-19: modeling, prediction and control (part II)", Nonlinear Dynamics.

[BibTeX] [DOI]

BibTeX: 
    @Article{Walter,
      author  = {Walter Lacarbonara and Jun Ma and C. Nataraj},
      journal = {Nonlinear Dynamics},
      title   = {Complex dynamics of COVID-19: modeling, prediction and control (part II)},
      year    = {2022},
      note    = {Special Issue},
      doi     = {10.1007/s11071-022-07588-z},
    }
Kambali, Prashant N. and Abbasi, Amirhassan and Nataraj, C., "Nonlinear dynamic epidemiological analysis of effects of vaccination and dynamic transmission on COVID-19", Nonlinear Dynamics. Vol. 111, pp. 951--963.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: This paper is concerned with nonlinear modeling and analysis of the COVID-19 pandemic. We are especially interested in two current topics: effect of vaccination and the universally observed oscillations in infections. We use a nonlinear Susceptible, Infected, & Immune model incorporating a dynamic transmission rate and vaccination policy. The US data provides a starting point for analyzing stability, bifurcations and dynamics in general. Further parametric analysis reveals a saddle-node bifurcation under imperfect vaccination leading to the occurrence of sustained epidemic equilibria. This work points to the tremendous value of systematic nonlinear dynamic analysis in pandemic modeling and demonstrates the dramatic influence of vaccination, and frequency, phase, and amplitude of transmission rate on the persistent dynamic behavior of the disease.
BibTeX: 
    @Article{Kambali2023,
      author   = {Kambali, Prashant N. and Abbasi, Amirhassan and Nataraj, C.},
      journal  = {Nonlinear Dynamics},
      title    = {Nonlinear dynamic epidemiological analysis of effects of vaccination and dynamic transmission on COVID-19},
      year     = {2023},
      issn     = {1573-269X},
      number   = {1},
      pages    = {951--963},
      volume   = {111},
      doi      = {10.1007/s11071-022-08125-8},
      refid    = {Kambali2023},
      url      = {https://doi.org/10.1007/s11071-022-08125-8},
}
Kambali, Prashant N. and Nataraj, C., "Nonlinear dynamics of yaw motion of surface vehicles", Nonlinear Dynamics. Vol. 111, pp. 5047--5062.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: The dynamics of surface vehicles such as boats and ships, when modeled as a rigid body, is complex as it is strongly nonlinear and involves six degrees of freedom. We are particularly interested in the steering dynamics decoupled from pitching and rolling as the basis of our research on unmanned boats and autonomy. Steering dynamics has been traditionally modeled using a linear Nomoto s model, which however does a poor job of capturing real nonlinear phenomena. On the other hand, there exists a somewhat simplified three-degree-of-freedom nonlinear model derived by Abkowitz, which, although better than the Nomoto s model, is still too intractable for analytical methods. In this paper, we derive a nonlinear single-degree-of-freedom model with a cubic nonlinearity that is conditionally equivalent to the Abkowitz model. Using this model, we analyze the yaw motion of an autopilot ship with a PD controller under the influence of an external wave force. Analytical and numerical investigations of the nonlinear dynamics are performed using parameters of an example container ship for various sea states. We employ the harmonic balance method to investigate the nonlinear frequency response of the ship under the influence of different parameters and demonstrate that the external wave force is balanced by stiffer ships. We also numerically investigate the nonlinear dynamic behavior to understand the different mechanisms involved in transitions from periodic to chaotic behavior under the influence of various parameters and different sea state conditions. The analysis reveals periodic response of the ship for a calm sea state. It is noteworthy that for lower values of linear stiffness, higher values of nonlinear stiffness, and higher values of external wave force corresponding to higher sea states, the bifurcation structure reveals mixed dynamic response in which periodic solutions evolve into period doubled, period tripled, and chaotic-like solutions even with high levels of damping. This work aims to demonstrate the utility of a simple nonlinear model and nonlinear behavior of steering motion of the ships to gain better insight into the nonlinear dynamics of autonomous surface vehicles. Further, the model stands out as an accessible nonlinear model for steering motion of the ship adequately representing the dynamics of real ships. It hence provides a basis for much improved controller design to implement smarter autopilots on manned ships but also aids in the development of robust autonomy in surface vehicles.
BibTeX: 
    @Article{Kambali2023a,
      author   = {Kambali, Prashant N. and Nataraj, C.},
      journal  = {Nonlinear Dynamics},
      title    = {Nonlinear dynamics of yaw motion of surface vehicles},
      year     = {2023},
      issn     = {1573-269X},
      number   = {6},
      pages    = {5047--5062},
      volume   = {111},
      doi      = {10.1007/s11071-022-08089-9},
      refid    = {Kambali2023},
      url      = {https://doi.org/10.1007/s11071-022-08089-9},
}
Amirhassan Abbasi and Prashant N. Kambali and C. Nataraj, "Physics-informed machine learning for modeling multidimensional dynamics"

[BibTeX]

BibTeX: 
    @Article{Abbasi2023,
      author  = {Amirhassan Abbasi and Prashant N. Kambali and C. Nataraj},
      journal = {Nonlinear Dynamics},
      title   = {Physics-informed machine learning for modeling multidimensional dynamics},
      year    = {2023},
      note    = {[Under review]},
    }
Mohamad, T. Haj and Abbasi, A. and Kappaganthu, K. and Nataraj, C., "On extraction, ranking and selection of data-driven and physics-informed features for bearing fault diagnostics", Knowledge-Based Systems. Vol. 276, pp. 110744.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Many traditional bearing fault detection techniques rely on pattern recognition using black box machine learning models, which lack generalizability to out of sample cases and are generally only effective for an a priori defined operating condition set. Therefore, the developed models are required to be retrained each time the operating condition changes because of the dependence of the dynamic response on them. The lack of effective techniques that can be applied and adapted to different operation domains of the system is a well-established need, which motivates the development of hybrid approaches which integrate both physics and data based techniques. This paper discusses the development of a hybrid physics-informed method that integrates information from physics and data for fault diagnostics of a rotor-bearing system. A physics-based model is used to simulate the dynamics of the system in a defect free condition and a machine fault simulator is used to generate experimental data. Physics-informed features are extracted by residual-based and cross-sample entropy techniques, while the data-based features are obtained using Proper and Smooth Orthogonal Decomposition techniques. Subsequently, these two collections of extracted features are fused into a hybrid feature set. Then, the features are ranked using the Shapley values ranking technique. Comparing the accuracy of classifications upon using the features of physics-informed, data-based and hybrid sets shows improved capability of the proposed framework to generalize diagnostics for various operating conditions.
BibTeX: 
    @Article{Mohamad2023,
      author   = {Mohamad, T. Haj and Abbasi, A. and Kappaganthu, K. and Nataraj, C.},
      journal  = {Knowledge-Based Systems},
      title    = {On extraction, ranking and selection of data-driven and physics-informed features for bearing fault diagnostics},
      year     = {2023},
      issn     = {0950-7051},
      pages    = {110744},
      volume   = {276},
      doi      = {10.1016/j.knosys.2023.110744},
      keywords = {Condition-based maintenance, Diagnostics, Rigid rotor, Rolling element bearings, Residual analysis, Statistical techniques, Cross-sample entropy technique, Proper orthogonal decomposition technique, Smooth orthogonal decomposition technique},
      url      = {https://www.sciencedirect.com/science/article/pii/S095070512300494X},
}
Abbasi, Amirhassan and Kambali, Prashant N. and Nataraj, C., "Hybrid modeling of a multidimensional coupled nonlinear system with integration of Hamiltonian mechanics", Nonlinear Dynamics. Vol. 111, pp. 15011--15022.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: This study concerns hybrid modeling of a multidimensional coupled nonlinear system. The underlying basis for the model is derived from Hamiltonian mechanics capitalizing on the broad utility and efficiency of energy-based reasoning in modeling high-dimensional systems. The hybrid model is essentially an artificial neural network with a computational graph that is modified from conventional neural networks in a few significant ways. The first modification includes incorporating an intermediate scalar function representing the Hamiltonian learned from data. The second modification enhances input/output channels for capturing the multidimensional dynamics of the system. The main goal of such hybrid reasoning is to improve the extrapolation capability of the model by enforcing conformance with some key aspects of the underlying physics in the form of a bias. The results demonstrate that incorporating this physics-based bias into the hybrid model empowers it to produce long-term and physically plausible predictions. The proposed modeling approach also shows high scalability for energy-based modeling of multidimensional dynamic systems in general.
BibTeX: 
    author   = {Abbasi, Amirhassan and Kambali, Prashant N. and Nataraj, C.},
    journal  = {Nonlinear Dynamics},
    title    = {Hybrid modeling of a multidimensional coupled nonlinear system with integration of Hamiltonian mechanics},
    year     = {2023},
    issn     = {1573-269X},
    number   = {16},
    pages    = {15011--15022},
    volume   = {111},
    doi      = {10.1007/s11071-023-08618-0},
    refid    = {Abbasi2023},
    url      = {https://doi.org/10.1007/s11071-023-08618-0},  
}
Liu, Zihan and Mohamad, T Haj and Ilbeigi, Shahab and Nataraj, C, "Early Detection of Cracks in a Gear-Train System Using Proper and Smooth Orthogonal Decompositions"

[BibTeX]

BibTeX: 
    @InProceedings{liu2021early,
      author       = {Liu, Zihan and Mohamad, T Haj and Ilbeigi, Shahab and Nataraj, C},
      booktitle    = {Advances in Nonlinear Dynamics: Proceedings of the Second International Nonlinear Dynamics Conference (NODYCON 2021), Volume 2},
      title        = {Early Detection of Cracks in a Gear-Train System Using Proper and Smooth Orthogonal Decompositions},
      year         = {2021},
      organization = {Springer},
      pages        = {451--461},
    }
Bender D, Morgan RW, Nadkarni VM, Berg RA, Zhang B, Kilbaugh TJ, Sutton RM and Nataraj C (2021), "MLWAVE: A novel algorithm to classify primary versus secondary asphyxia-associated ventricular fibrillation", Resuscitation Plus. Vol. 5, pp. 100052.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Introduction/Hypothesis
The outcome of cardiopulmonary resuscitation (CPR) depends on timely recognition of the underlying cause of cardiac arrest. Ventricular fibrillation (VF) waveform analysis to differentiate primary VF from secondary asphyxia-associated VF may allow tailoring of therapies to improve cardiac arrest outcomes. Therefore, the primary goal of this investigation was to develop a novel technique utilizing wavelet synchrosqueezed transform (WSST) and decision-tree classifier that was specifically adapted to discriminate between these two incidents of VF.
Methods
Secondary analytical investigation of electrocardiography (ECG) data obtained from swine models of either primary VF (n=18) or secondary asphyxia-associated VF (7min of asphyxia prior to VF induction; n=12). In the primary analysis, WSST technique was applied to the first 35s of the VF ECG signal to identify the most differentiating characteristics of the signal for use as features to develop a machine learning algorithm to classify the arrest as either primary VF vs. secondary asphyxia-associated VF. The performance of this new interactive Machine Learning algorithm with Wavelet Energy features of ECG (MLWAVE) was assessed using both classification accuracy and area under the receiver operating characteristic curve (AUCROC). To evaluate the validity of the new technique, the amplitude spectrum area (AMSA)-based technique, a well-established defibrillation classification method, was also applied to the same ECG signals. The classification accuracy and AUCROC were then compared between the two techniques.
Results
For the primary analysis evaluating the first 35s of the VF waveform, the MLWAVE technique classified the type of VF with high accuracy (28/28 [100%], AUCROC: 1.00). The MLWAVE technique performed better than the AMSA technique across all comparisons, but given the small sample sizes, differences were not statistically significant (accuracy: 100% vs. 85.7%; p=0.24; AUCROC: 1.00 vs. 0.82; p=0.24).
Conclusion
This analytical investigation illustrates the advantages of the MLWAVE signal processing method which was associated with 100% accuracy in classifying the type of VF waveform: primary vs. asphyxia-associated. Such classification could lead to personalized tailoring of resuscitation (e.g., immediate defibrillation vs. continued CPR and treatment of reversible cardiac arrest causes before defibrillation) to improve outcomes for cardiac arrest.
BibTeX: 
@article{Bender2021,
  author = {Dieter Bender and Ryan W. Morgan and Vinay M. Nadkarni and Robert A. Berg and Bingqing Zhang and Todd J. Kilbaugh and Robert M. Sutton and C. Nataraj},
  title = {MLWAVE: A novel algorithm to classify primary versus secondary asphyxia-associated ventricular fibrillation},
  journal = {Resuscitation Plus},
  year = {2021},
  volume = {5},
  pages = {100052},
  url = {https://www.sciencedirect.com/science/article/pii/S2666520420300539},
  doi = {10.1016/j.resplu.2020.100052}
}
Mohamad TH and Nataraj C (2021), "Fault identification and severity analysis of rolling element bearings using phase space topology", Journal of Vibration and Control. Vol. 27(3-4), pp. 295-310.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: This article presents the application of phase space topology and time-domain statistical features for rolling element bearing diagnostics in rotating machines under variable operating conditions. The results indicate very promising performance in identifying various faults with virtually perfect accuracy, recall, and precision. A comparison with the envelope analysis method is performed to show the superior performance of the proposed approach. In addition, the results demonstrate an outstanding prediction rate for the fault diameter of bearing defects.
BibTeX: 
@article{doi:10.1177/1077546320926293,
  author = {T Haj Mohamad and C Nataraj},
  title = {Fault identification and severity analysis of rolling element bearings using phase space topology},
  journal = {Journal of Vibration and Control},
  year = {2021},
  volume = {27},
  number = {3-4},
  pages = {295-310},
  url = {https://doi.org/10.1177/1077546320926293},
  doi = {10.1177/1077546320926293}
}
Singh SJ, Nataraj C and Harsha SP (2021), "Nonlinear dynamic analysis of a sandwich plate with S-FGM face sheets and homogeneous core subjected to harmonic excitation", Journal of Sandwich Structures & Materials. Vol. 23(6), pp. 1831-1869.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: In the present paper, for a sandwich plate with homogeneous core, the nonlinear dynamic response is analyzed in which material properties of functionally graded facesheets are varied in accordance with sigmoid law. The sandwich plate of various configurations is presumed to be built on Pasternak foundation and subjected to harmonic load. Equilibrium and compatibility equations are derived by taking into consideration the geometrical non-linearity in von Karman sense. The Airy�s stress function and Galerkin method are used to solve geometric nonlinearity and implement the different edge conditions, respectively, for sandwich sigmoid function plate. A few numerical examples validate the accuracy of the present formulation with the results of available theory for different geometric parameters, elastic foundation, and plate configuration. A convergence study is performed to determine the number of terms in order to converge the solution, and it is deduced that considering the first four terms provides sufficient accuracy with average error less than 0.22% which is acceptable for any computation. The present paper is the first proposal to analyze the nonlinear dynamic characteristics of sandwich sigmoid function plate with homogeneous core and functionally graded material face sheets in ambient conditions. This article is also new in its assessment of the plate behavior in terms of predicting the periodicity such as periodic, quasi-periodic, chaotic, etc. and analyzing the frequency-amplitude relation. The aforementioned prediction aids researchers in active control of plates and shells under dynamic loading. It is found that core thickness in the sandwich plate reduces the effect of the nonlinearity. Also, the plate configurations 1-0-1 and 1-8-1 show the sensitive features in the dynamic response with varying aspect factors and span-to-thickness ratios.
BibTeX: 
@article{Singh2021,
  author = {Simran J Singh and C Nataraj and Suraj P Harsha},
  title = {Nonlinear dynamic analysis of a sandwich plate with S-FGM face sheets and homogeneous core subjected to harmonic excitation},
  journal = {Journal of Sandwich Structures & Materials},
  year = {2021},
  volume = {23},
  number = {6},
  pages = {1831-1869},
  url = {https://doi.org/10.1177/1099636220904338},
  doi = {10.1177/1099636220904338}
}
AL-Shudeifat MA and Alhammadi FK (2021), "Negative potential energy content analysis in cracked rotors whirl response", Scientific Reports. Vol. 11(1), pp. 15294.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Appearance of transverse cracks in rotor systems mainly affects their stiffness content. The stability of such systems at steady-state running is usually analyzed by using the Floquet�s theory. Accordingly, the instability zones of rotational speeds are dominated by negative stiffness content in the whirl response in the vicinity of critical rotational speeds. Consequently, an effective stiffness measure is introduced here to analyze the effect of the crack and the unbalance force vector orientation on the intensity of negative potential and stiffness content in the whirl response. The effective stiffness expression is obtained from the direct integration of the equations of motion of the considered cracked rotor system. The proposed effective stiffness measure is applied for steady-state and transient operations using the Jeffcott rotor model with open and breathing crack models. The intensity of negative potential and stiffness content in the numerical and experimental whirl responses is found to be critically depending on the propagation level of the crack and the unbalance force vector orientation. Therefore, this can be proposed as a crack detection tool in cracked rotor systems that either exhibit recurrent passage through the critical rotational speeds or steady-state running.
BibTeX: 
@article{ALShudeifat2021,
  author = {AL-Shudeifat, Mohammad A. and Alhammadi, Fatima K.},
  title = {Negative potential energy content analysis in cracked rotors whirl response},
  journal = {Scientific Reports},
  year = {2021},
  volume = {11},
  number = {1},
  pages = {15294},
  url = {https://doi.org/10.1038/s41598-021-94836-8},
  doi = {10.1038/s41598-021-94836-8}
}
AL-Shudeifat M, Hammadi FA, Alzarooni T and Nataraj C (2020), "Post-Resonance Backward Whirl in Accelerating Cracked Rotor Systems", European Journal of Mechanics A / Solids.

[BibTeX]
BibTeX: 
@article{ALShudeifat2020bj,
  author = {Mohammad AL-Shudeifat and Fatima Al Hammadi and Tariq Alzarooni and C Nataraj},
  title = {Post-Resonance Backward Whirl in Accelerating Cracked Rotor Systems},
  journal = {European Journal of Mechanics A / Solids},
  year = {2020}
}
Alzarooni T, AL-Shudeifat M, Shiryayev O and Nataraj C (2020), "Breathing Crack Model Effect on Rotors Post-Resonance Backward Whirl", Journal of Computational and Nonlinear Dynamics.

[BibTeX]
BibTeX: 
@article{Alzarooni2020j,
  author = {Alzarooni, Tariq and AL-Shudeifat, Mohammad and Shiryayev, Oleg and Nataraj, C.},
  title = {Breathing Crack Model Effect on Rotors Post-Resonance Backward Whirl},
  journal = {Journal of Computational and Nonlinear Dynamics},
  year = {2020},
  note = {[To appear]}
}
Haj Mohamad T, Nazari F and Nataraj C (2020), "Diagnostic Signal Phase Space Topology Method for Fault Identification of Electro-Hydraulic Servo Actuators", Journal of Vibration and Control.

[BibTeX]
BibTeX: 
@article{HajMohamad2020,
  author = {Haj Mohamad, Turki and Nazari, Foad and Nataraj, C},
  title = {Diagnostic Signal Phase Space Topology Method for Fault Identification of Electro-Hydraulic Servo Actuators},
  journal = {Journal of Vibration and Control},
  year = {2020},
  note = {[To appear]}
}
Hosseiny H, Nazari F, Smith V and Nataraj C (2020), "A Framework for Modeling Flood Depth Using a Hybrid of Hydraulics and Machine Learning", Scientific Reports. Vol. 10(1), pp. 8222.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Solving river engineering problems typically requires river flow characterization, including the prediction of flow depth, flow velocity, and flood extent. Hydraulic models use governing equations of the flow in motion (conservation of mass and momentum principles) to predict the flow characteristics. However, solving such equations can be substantially expensive, depending upon their spatial extension. Moreover, modeling two- or three-dimensional river flows with high-resolution topographic data for large-scale regions (national or continental scale) is next to impossible. Such simulations are required for comprehensive river modeling, where a system of connected rivers is to be simulated simultaneously. Machine Learning (ML) approaches have shown promise for different water resources problems, and they have demonstrated an ability to learn from current data to predict new scenarios, which can enhance the understanding of the systems. The aim of this paper is to present an efficient flood simulation framework that can be applied to large-scale simulations. The framework outlines a novel, quick, efficient and versatile model to identify flooded areas and the flood depth, using a hybrid of hydraulic model and ML measures. To accomplish that, a two-dimensional hydraulic model (iRIC), calibrated by measured water surface elevation data, was used to train two ML models to predict river depth over the domain for an arbitrary discharge. The first ML model included a random forest (RF) classification model, which was used to identify wet or dry nodes over the domain. The second was a multilayer perceptron (MLP) model that was developed and trained by the iRIC simulation results, in order to estimate river depth in wet nodes. For the test data the overall accuracy of 98.5 percent was achieved for the RF classification. The regression coefficient for the MLP model for depth was 0.88. The framework outlined in this paper can be used to couple hydraulics and ML models to reduce the computation time, resources and expenses of large-scale, real-time simulations, specifically for two- or three-dimensional hydraulic modeling, where traditional hydraulic models are infeasible or prohibitively expensive.
BibTeX: 
@article{Hosseiny2020,
  author = {Hosseiny, Hossein and Nazari, Foad and Smith, Virginia and Nataraj, C.},
  title = {A Framework for Modeling Flood Depth Using a Hybrid of Hydraulics and Machine Learning},
  journal = {Scientific Reports},
  year = {2020},
  volume = {10},
  number = {1},
  pages = {8222},
  url = {https://doi.org/10.1038/s41598-020-65232-5},
  doi = {10.1038/s41598-020-65232-5}
}
Kwuimy CAK, Nazari F, Jiao X, Rohani P and Nataraj C (2020), "Nonlinear dynamic analysis of an epidemiological model for COVID-19 including public behavior and government action", Nonlinear Dynamics. Vol. 101(3), pp. 1545-1559.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: This paper is concerned with nonlinear modeling and analysis of the COVID-19 pandemic currently ravaging the planet. There are two objectives: to arrive at an appropriate model that captures the collected data faithfully and to use that as a basis to explore the nonlinear behavior. We use a nonlinear susceptible, exposed, infectious and removed transmission model with added behavioral and government policy dynamics. We develop a genetic algorithm technique to identify key model parameters employing COVID-19 data from South Korea. Stability, bifurcations and dynamic behavior are analyzed. Parametric analysis reveals conditions for sustained epidemic equilibria to occur. This work points to the value of nonlinear dynamic analysis in pandemic modeling and demonstrates the dramatic influence of social and government behavior on disease dynamics.
BibTeX: 
@article{Kwuimy2020,
  author = {Kwuimy, C. A. K. and Nazari, Foad and Jiao, Xun and Rohani, Pejman and Nataraj, C.},
  title = {Nonlinear dynamic analysis of an epidemiological model for COVID-19 including public behavior and government action},
  journal = {Nonlinear Dynamics},
  year = {2020},
  volume = {101},
  number = {3},
  pages = {1545--1559},
  url = {https://doi.org/10.1007/s11071-020-05815-z},
  doi = {10.1007/s11071-020-05815-z}
}
Mohamad TH, Nazari F and Nataraj C (2020), "A Review of Phase Space Topology Methods for Vibration-Based Fault Diagnostics in Nonlinear Systems", Journal of Vibration Engineering & Technologies. Vol. 8(3), pp. 393-401.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: In general, diagnostics can be defined as the procedure of mapping the information obtained in the measurement space to the presence and magnitude of faults in the fault space. These measurements, and especially their nonlinear features, have the potential to be exploited to detect changes in dynamics due to the faults.
BibTeX: 
@article{Mohamad2020,
  author = {Mohamad, T. Haj and Nazari, Foad and Nataraj, C.},
  title = {A Review of Phase Space Topology Methods for Vibration-Based Fault Diagnostics in Nonlinear Systems},
  journal = {Journal of Vibration Engineering & Technologies},
  year = {2020},
  volume = {8},
  number = {3},
  pages = {393--401},
  url = {https://doi.org/10.1007/s42417-019-00157-6},
  doi = {10.1007/s42417-019-00157-6}
}
Bender, Dieter and Nadkarni, Vinay M. and Nataraj, C., "A machine learning algorithm to improve patient-centric pediatric cardiopulmonary resuscitation", Informatics in Medicine Unlocked., May, 2020. Vol. 19, pp. 100339.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Background Several studies suggest that the outcome of pediatric cardiopul-monary resuscitation depends strongly on timely recognition of the underlying cause for cardiac arrest, the prominent ones being primary ventricular fibril-lation and secondary asphyxia-associated ventricular fibrillation. If the cause could be determined within the first minute of cardiopulmonary resuscitation, the administration could be appropriately modified in order to achieve optimal outcome. However, distinguishing the two causes has been a difficult challenge. Objective To derive a robust algorithm with acceptable accuracy that distinguishes primary ventricular fibrillation and secondary asphyxia-associated ventricular fibrillation within the first minute of starting cardiopulmonary resus-citation. Methods We address this problem with MACWAVE, a new computa-tional technique integrating advanced signal processing and machine learning. MACWAVE is an algorithm that uses wavelet transforms with electrocardiog-raphy data to identify the most differentiating characteristics of the signal and uses them as features to develop a support vector machine classification model. Results The developed algorithm shows an average classification accuracy of 85%, this being the first result ever achieved for this critical pediatric problem. Conclusion Being the first research effort to ever analyze this critical pediatric problem, the MACWAVE method can improve patient-centric cardiopulmonary resuscitation treatment and significantly increase positive outcomes for pediatric cardiac arrest.
BibTeX: 
  @Article{Bender2020j,
    author   = {Bender, Dieter and Nadkarni, Vinay M. and Nataraj, C.},
    journal  = {Informatics in Medicine Unlocked},
    title    = {A machine learning algorithm to improve patient-centric pediatric cardiopulmonary resuscitation},
    year     = {2020},
    issn     = {2352-9148},
    pages    = {100339},
    volume   = {19},
    doi      = {10.1016/j.imu.2020.100339},
    keywords = {Electrocardiography, Wavelet transform, Support vector machine, Cardiac arrest, Cardiopulmonary resuscitation, Ventricular fibrillation, Asphyxia},
    url      = {https://www.sciencedirect.com/science/article/pii/S2352914820300381},
}
Alzarooni, Tariq and AL-Shudeifat, Mohammad and Shiryayev, Oleg and Nataraj, C., "Post-resonance backward whirl analysis in cracked overhung rotors", Scientific Reports. Vol. 12, pp. 8517.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Overhung rotors usually exhibit recurrent transitions through critical whirl rotational speeds during startup and coast down operations, which significantly differ from their steady-state whirl responses. The presence of angular acceleration results in a linear-time-varying (LTV) system, which, although technically linear, still presents complexities often evinced by a nonlinear system. In general, backward whirl zones can either precede the critical forward whirl speed (termed as pre-resonance backward whirl, Pr-BW), or immediately follow the critical forward whirl speed (termed as post-resonance backward whirl, Po-BW). The Po-BW in the whirl response of a cracked overhung rotor with a breathing crack is studied here as distinct from that of geometrically symmetric configurations of other rotor systems. The equations of motion from the finite element (FE) model of an overhung rotor system with a breathing crack are numerically integrated to obtain the whirl response. The transient whirl responses with different bearing conditions are thoroughly investigated for excitation of Po-BW. The Po-BW zones of rotational speeds are determined via the wavelet transform method and full spectrum analysis (FSA) and applied to signals with added noise. The results of this work confirm the excitation of the Po-BW in cracked overhung rotors and confirm the robustness of the employed methods.
BibTeX: 
  @Article{Alzarooni2022,
    author   = {Alzarooni, Tariq and AL-Shudeifat, Mohammad and Shiryayev, Oleg and Nataraj, C.},
    journal  = {Scientific Reports},
    title    = {Post-resonance backward whirl analysis in cracked overhung rotors},
    year     = {2022},
    issn     = {2045-2322},
    number   = {1},
    pages    = {8517},
    volume   = {12},
    doi      = {10.1038/s41598-022-12068-w},
    refid    = {Alzarooni2022},
    url      = {https://doi.org/10.1038/s41598-022-12068-w},
}
Maraini, D. & Nataraj, C. (2018), "Nonlinear Dynamic Analysis of a Rotor-Bearing System Using Describing Functions", Journal of Sound and Vibration.

[Abstract] [BibTeX]
Abstract: This paper presents a model for studying the nonlinear behavior of a rotor-bearing system with clearance and rotating unbalance. The rotor-bearing system is separated into linear and nonlinear components, and the nonlinear bearing force is replaced with an equivalent describing function gain. The describing function captures the relationship between the amplitude of the fundamental input to the nonlinearity and the fundamental output. The frequency response is constructed for various values of the clearance parameter, and the results show the presence of a jump resonance in bearings with both clearance and preload. Nonlinear hardening type behavior is observed in the case with clearance and softening behavior is observed for the case with preload. Numerical integration is also carried out on the nonlinear equations of motion showing strong agreement with the approximate solution. This work could easily be modified to include additional nonlinearities that arise from defects, providing a powerful diagnostic tool.
BibTeX: 
@article{Maraini2018j,
  author = {Daniel Maraini and C. Nataraj},
  title = {Nonlinear Dynamic Analysis of a Rotor-Bearing System Using Describing Functions},
  journal = {Journal of Sound and Vibration},
  year = {2018},
  note = {In Print.}
}
Mohamad, T.H., Aldemir Ap Cavalini, J., Valder Steffen, J. & Nataraj, C. (2018), "Detection of Cracks in Rotating Shafts Using Extended Phase Space Topology", In 10th IFToMM International Conference on Rotordynamics.

[BibTeX]
BibTeX: 
@inproceedings{Mohamad2018,
  author = {T. Haj Mohamad and Aldemir Ap Cavalini, Jr. and Valder Steffen, Jr. and C. Nataraj},
  title = {Detection of Cracks in Rotating Shafts Using Extended Phase Space Topology},
  booktitle = {10th IFToMM International Conference on Rotordynamics},
  year = {2018}
}
Sutton RM, Morgan RW, Kilbaugh TJ, Nadkarni VM and Berg RA (2017), "Cardiopulmonary Resuscitation in Pediatric and Cardiac Intensive Care Units.", Pediatric clinics of North America. United States, October, 2017. Vol. 64, pp. 961-972.

[Abstract] [BibTeX]
Abstract: Approximately 5000 to 10,000 children suffer an in-hospital cardiac arrest requiring cardiopulmonary resuscitation (CPR) each year in the United States. Importantly, 2% to 6% of all children admitted to pediatric intensive care units (ICUs) receive CPR, as do 4% to 6% of children admitted to pediatric cardiac ICUs. Survival from pediatric ICU cardiac arrest has improved substantially during the past 20�years presumably due to improved training methods, CPR quality, and post-resuscitation care. Extracorporeal life support CPR remains an important treatment option for both cardiac and noncardiac ICU patients.
BibTeX: 
@article{Sutton2017,
  author = {Sutton, Robert M. and Morgan, Ryan W. and Kilbaugh, Todd J. and Nadkarni, Vinay M. and Berg, Robert A.},
  title = {Cardiopulmonary Resuscitation in Pediatric and Cardiac Intensive Care Units.},
  journal = {Pediatric clinics of North America},
  year = {2017},
  volume = {64},
  pages = {961-972}
}
Bender, D., Morgan, R.W., M.Nadkarni, V. & Nataraj, C. (2017), "Classification of Asphyxia & Ventricular Fibrillation Induced Cardiac Arrest During Cardiopulmonary Resuscitation", In IEEE-NIH Conference on Healthcare Innovations and Point-of-Care Technologies. Bethesda, MD, November 6-8, 2017.

[BibTeX]
BibTeX: 
@inproceedings{Bender2017,
  author = {Dieter Bender and Ryan W. Morgan and Vinay M.Nadkarni and C. Nataraj},
  title = {Classification of Asphyxia & Ventricular Fibrillation Induced Cardiac Arrest During Cardiopulmonary Resuscitation},
  booktitle = {IEEE-NIH Conference on Healthcare Innovations and Point-of-Care Technologies},
  year = {2017}
}
Jalali, A., Nadkarni, V., Berg, R. & Nataraj, C. (2017), "A novel nonlinear mathematical model of thoracic wall mechanics during cardiopulmonary resuscitation based on a porcine model of cardiac arrest", Journal of Medical Systems., February, 2017. Vol. 41(20)

[Abstract] [BibTeX] [DOI]
Abstract: Cardiopulmonary resuscitation (CPR) is used widely to rescue cardiac arrest patients, yet some physiological aspects of the procedure remain poorly understood. We conducted this study to characterize the dynamic mechanical properties of the thorax during CPR in a swine model. This is an important step toward determining optimal CPR chest compression mechanics with the goals of improving the fidelity of CPR simulation manikins and ideally chest compression delivery in real-life resuscitations. This paper presents a novel nonlinear model of the thorax that captures the complex behavior of the chest during CPR. The proposed model consists of nonlinear elasticity and damping properties along with frequency dependent hysteresis. An optimization technique was used to estimate the model coefficients for force-compression using data collected from experiments conducted on swine. To track clinically relevant, time-dependent changes of the chests properties, the data was divided into two time periods, from 1 to 10 min (early) and greater than 10 min (late) after starting CPR. The results showed excellent agreement between the actual and the estimated forces, and energy dissipation due to viscous damping in the late stages of CPR was higher when compared to the earlier stages. These findings provide insight into improving chest compression mechanics during CPR, and may provide the basis for developing CPR simulation manikins that more accurately represent the complex real world changes that occur in the chest during CPR.
BibTeX: 
@article{Jalali2017j,
  author = {Ali Jalali and Vinay Nadkarni and Robert Berg and C. Nataraj},
  title = {A novel nonlinear mathematical model of thoracic wall mechanics during cardiopulmonary resuscitation based on a porcine model of cardiac arrest},
  journal = {Journal of Medical Systems},
  year = {2017},
  volume = {41},
  number = {20},
  doi = {http://dx.doi.org/10.1007/s10916-016-0676-1}
}
Jalali, A., Nadkarni, V., Rehman, M. & Nataraj, C. (2017), "Integrating Clinical Physiological Knowledge at the Feature and Classifier Levels for Improved Prediction of Outcomes in Intensive Care Units", In Biomedical Signal Processing in Big Data. CRC Press.

[BibTeX]
BibTeX: 
@incollection{Jalali2017x,
  author = {Jalali, A. and Nadkarni, V. and Rehman, M. and Nataraj, C.},
  title = {Integrating Clinical Physiological Knowledge at the Feature and Classifier Levels for Improved Prediction of Outcomes in Intensive Care Units},
  booktitle = {Biomedical Signal Processing in Big Data},
  publisher = {CRC Press},
  year = {2017}
}
Kwuimy, C.A.K., Adewusi, S.A. & Nataraj, C. (2017), "Characterization of the vibration transmitted in human arm using selected recurrence quantification parameters", Nonlinear Dynamics. Vol. 88(4), pp. 2873-2887.

[Abstract] [BibTeX] [DOI]
Abstract: This paper deals with the analysis of the time series signals extracted from the vibration of a human arm. The data are extracted at the wrist, elbow and shoulder of three male subjects with different vibration pre-exposure levels. The method of recurrence analysis is used to extract features in order to characterize the nature of the vibration transmitted from the wrist to the elbow and the shoulder. A comparative analysis among the individual levels of pre-exposure is carried out. It is shown that some recurrence parameters, namely the recurrence rate, the entropy, the mean diagonal and the trapping time appear to be efficient in characterizing the nature of the vibration. Overall, the analysis performed in this paper shows that the method of recurrence analysis can effectively be used to quantitatively discriminate between the nature of the vibration transmitted in the human arm and illustrate the effects of the vibration pre-exposure. © 2017, Springer Science+Business Media Dordrecht.
BibTeX: 
@article{Kwuimy2017aj,
  author = {C. A. Kitio Kwuimy and S. A. Adewusi and C. Nataraj},
  title = {Characterization of the vibration transmitted in human arm using selected recurrence quantification parameters},
  journal = {Nonlinear Dynamics},
  year = {2017},
  volume = {88},
  number = {4},
  pages = {2873-2887},
  doi = {http://dx.doi.org/10.1007/s11071-017-3417-1}
}
Kwuimy, C.A.K. & Nataraj, C. (2017), "Nonlinear analysis of the yaw motion of a mariner vehicle under PD$^ control", Journal of Applied Nonlinear Dynamics. Vol. 6(4), pp. 531-545.

[Abstract] [BibTeX] [DOI]
Abstract: This paper considers a mariner under PD$^mu$ controller and analyses the effects of controller parameters on the yaw rate by using the Nomoto model. The Nomoto model describing the time evolution of the yaw rate of the steering dynamics of a mariner is reduced to an asymmetric Duffing oscillator with fractional order derivative. Under the approximation of calm water, the steady behavior of the mariner shows an "imperfect"' supercritical pitchfork bifurcation. Region of safe behavior is identified and strategy to reduce the yaw rate by an appropriated selection of controller parameters are discussed. The frequency analysis of the mariner shows the prominence of hysteresis is reduced for small order of the fractional derivative as well as the amplitude of the yaw rate. Evidence of chaotic response is illustrated using robust chaotic indicators such as the Lyapunov exponent and the fast Fourier transform.
BibTeX: 
@article{Kwuimy2017j,
  author = {C. A. Kitio Kwuimy and C. Nataraj},
  title = {Nonlinear analysis of the yaw motion of a mariner vehicle under PD$^ control},
  journal = {Journal of Applied Nonlinear Dynamics},
  year = {2017},
  volume = {6},
  number = {4},
  pages = {531-545},
  doi = {http://dx.doi.org/10.5890/JAND.2019.12.008}
}
Lebbad, A., Anderson, J.W., Clayton, G.M. & Nataraj., C. (2017), "Novel algorithms for color analysis and data fusion with a LIDAR/Video Vision System for Autonomous Surface Vehicles", In RobotX Forum. Sydney, Australia, December, 2017.

[BibTeX]
BibTeX: 
@inproceedings{Lebbad2017,
  author = {Anderson Lebbad and J. Wesley Anderson and Garrett M. Clayton and C. Nataraj.},
  title = {Novel algorithms for color analysis and data fusion with a LIDAR/Video Vision System for Autonomous Surface Vehicles},
  booktitle = {RobotX Forum},
  year = {2017}
}
Lebbad, A., Clayton, G. & Nataraj, C. (2017), "Classification of UXO using Convolutional Networks Trained on a Limited Dataset", In International Conference on
Machine Learning and Applications. Cancun, Mexico, December, 2017.

[BibTeX]
BibTeX: 
@inproceedings{Lebbad2017a,
  author = {A. Lebbad and G. Clayton and C. Nataraj},
  title = {Classification of UXO using Convolutional Networks Trained on a Limited Dataset},
  booktitle = {International Conference on
Machine Learning and Applications},
  year = {2017}
}
Mohamad, T.H. & Nataraj, C. (2017), "Discrimination of Multiple Faults in Bearings Using Density-Based Orthogonal Functions of The Time Response", In ASME International Design Engineering Technology Conference. Cleveland, Ohio, August 6-9, 2017.

[BibTeX]
BibTeX: 
@inproceedings{Mohamad2017,
  author = {T. Haj Mohamad and C. Nataraj},
  title = {Discrimination of Multiple Faults in Bearings Using Density-Based Orthogonal Functions of The Time Response},
  booktitle = {ASME International Design Engineering Technology Conference},
  year = {2017}
}
Mohamad, T.H. & Nataraj, C. (2017), "Gear Fault Diagnostics Using Extended Phase Space Topology", In Annual Conference of the Prognostics and Health Management Society. St. Petersburg, Florida, October 2-5, 2017.

[BibTeX]
BibTeX: 
@inproceedings{Mohamad2017a,
  author = {T. Haj Mohamad and C. Nataraj},
  title = {Gear Fault Diagnostics Using Extended Phase Space Topology},
  booktitle = {Annual Conference of the Prognostics and Health Management Society},
  year = {2017}
}
Naseradinmousavi, P., Machiani, S.G., Ayoubi, M.A. & Nataraj, C. (2017), "Coupled Operational Optimization of Smart Valve System Subject to Different Approach Angles of a Pipe Contraction", Structural and Multidisciplinary Optimization., March, 2017. Vol. 55(3), pp. 1001-1015.

[Abstract] [BibTeX] [DOI]
Abstract: In this paper, we focus on interconnected trajectory optimization of two sets of solenoid actuated butterfly valves dynamically coupled in series. The system undergoes different approach angles of a pipe contraction as a typical profile of the so-called Smart Valves network containing tens of actuated valves. A high fidelity interconnected mathematical modeling process is derived to reveal the expected complexity of such a multiphysics system dealing with electromagnetics, fluid mechanics, and nonlinear dynamic effects. A coupled operational optimization scheme is formulated in order to seek the most efficient trajectories of the interconnected valves minimizing the energy consumed enforcing stability and physical constraints. We examine various global optimization methods including Particle Swarm, Simulated Annealing, Genetic, and Gradient based algorithms to avoid being trapped in several possible local minima. The effect of the approach angles of the pipeline contraction on the amount of energy saved is discussed in detail. The results indicate that a substantial amount of energy can be saved by an intelligent operation that uses flow torques to augment the closing efforts.
BibTeX: 
@article{Naseradinmousavi2017j,
  author = {Peiman Naseradinmousavi and Sahar Ghanipoor Machiani and Mohammad A. Ayoubi and C. Nataraj},
  title = {Coupled Operational Optimization of Smart Valve System Subject to Different Approach Angles of a Pipe Contraction},
  journal = {Structural and Multidisciplinary Optimization},
  year = {2017},
  volume = {55},
  number = {3},
  pages = {1001-1015},
  doi = {http://dx.doi.org/10.1007/s00158-016-1554-7}
}
Nataraj, C. (2017), "2014 Benjamin Franklin Medal in Mechanical Engineering presented to Ali Hasan Nayfeh, Ph.D. of Virginia Polytechnic Institute and State University Blacksburg, Virginia, USA, University of Jordan Amman, Jordan", Journal of the Franklin Institute. Vol. 354(1), pp. 32-38.

[Abstract] [BibTeX] [DOI]
Abstract: It is now well recognized that all natural and many man-made systems are dynamic, and also that many of them exhibit nonlinear phenomena. Mathematical models for these systems, which are approximate representations, could be linear or nonlinear. Nonlinear models are significantly different from more conventional linear models both qualitatively and quantitatively. Typical nonlinear phenomena not predictable by linear analysis include multiple equilibria, instabilities, limit cycles, bifurcations and chaotic motion. Hence, in order to be able to analyze and design practical systems accurately and safely, nonlinear modeling and analysis techniques are necessary
BibTeX: 
@article{Nataraj2017j,
  author = {C. Nataraj},
  title = {2014 Benjamin Franklin Medal in Mechanical Engineering presented to Ali Hasan Nayfeh, Ph.D. of Virginia Polytechnic Institute and State University Blacksburg, Virginia, USA, University of Jordan Amman, Jordan},
  journal = {Journal of the Franklin Institute},
  year = {2017},
  volume = {354},
  number = {1},
  pages = {32-38},
  doi = {http://dx.doi.org/10.1016/j.jfranklin.2015.05.019}
}
Asare, P., Chowdhury, M.A., Rajah, T., Poler, S.M., Shah, M., Guion, P., Martin, J., Driscoll, K., Wu, Q., Mannes, A. & Nataraj, C. (2016), "A system for semi-automated management of blood loss during surgery: Preliminary results", In IEEE Healthcare Innovation Point-Of-Care Technologies Conference (HI-POCT)., November 9-11, 2016.

[BibTeX] [DOI]
BibTeX: 
@inproceedings{Asare2016,
  author = {Philip Asare and Mahmood Arifin Chowdhury and Taimoore Rajah and S. Mark Poler and Mohammed Shah and Peter Guion and Jeffrey Martin and Kevin Driscoll and Qianhong Wu and Andrew Mannes and C. Nataraj},
  title = {A system for semi-automated management of blood loss during surgery: Preliminary results},
  booktitle = {IEEE Healthcare Innovation Point-Of-Care Technologies Conference (HI-POCT)},
  year = {2016},
  doi = {http://dx.doi.org/10.1109/HIC.2016.7797735}
}
Bender, D., Jalali, A. & Nataraj, C. (2016), "Pilot Study to Predict Cardiac Arrest Using Continuous Wavelet Trasform Measures as Predictors for an Artificial Neural Network", In IEEE Engineering in Medicine and Biology Society Conference.

[BibTeX]
BibTeX: 
@inproceedings{Bender2016,
  author = {Dieter Bender and Ali Jalali and C. Nataraj},
  title = {Pilot Study to Predict Cardiac Arrest Using Continuous Wavelet Trasform Measures as Predictors for an Artificial Neural Network},
  booktitle = {IEEE Engineering in Medicine and Biology Society Conference},
  year = {2016}
}
Jalali, A., Rehman, M., Nadkarni, V. & Nataraj, C. (2016), "Intensive Care Unit Outcome Prediction Using Machine Learning Modeling", In Society for Technology in Anesthesia Meeting.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2016a,
  author = {Ali Jalali and Mohamed Rehman and Vinay Nadkarni and C. Nataraj},
  title = {Intensive Care Unit Outcome Prediction Using Machine Learning Modeling},
  booktitle = {Society for Technology in Anesthesia Meeting},
  year = {2016}
}
Jalali, A., Rehman, M., Nadkarni, V. & Nataraj, C. (2016), "Advanced Analytics for Outcome Prediction in Intensive Care Units", In IEEE Engineering in Medicine and Biology Soceity Conference (EMBC).

[BibTeX]
BibTeX: 
@inproceedings{Jalali2016b,
  author = {Ali Jalali and Mohamed Rehman and Vinay Nadkarni and C. Nataraj},
  title = {Advanced Analytics for Outcome Prediction in Intensive Care Units},
  booktitle = {IEEE Engineering in Medicine and Biology Soceity Conference (EMBC)},
  year = {2016}
}
Jalali, A., Lingappan, A.M., Rehman, M. & Nataraj, C. (2016), "Automatic Detection of Endotracheal Intubation During the Anesthesia Procedure", Journal of Dynamic Systems, Measurement and Control., August, 2016. Vol. 138(11), pp. 111013-111013-8.

[Abstract] [BibTeX] [DOI]
Abstract: This paper is concerned with the mathematical modeling and detection of endotracheal (ET) intubation in children under general anesthesia during surgery. In major pediatric surgeries, the airway is often secured with an endotracheal tube (ETT) followed by initiation of mechanical ventilation. Clinicians utilize auscultation of breath sounds and capnography to verify correct ETT placement. However, anesthesia providers often delay timely charting of ET intubation. This latency in event documentation results in decreased efficacy of clinical decision support systems. In order to target this problem, we collected real inpatient data and designed an algorithm to accurately detect the intubation time within the clinically valid range; the results show that we are able to achieve high accuracy in more than 96% of the cases. Automatic detection of ET intubation time would thus enhance better real-time data capture to support future improvement in clinical decision support systems.
BibTeX: 
@article{Jalali2016j,
  author = {Ali Jalali and Arul M. Lingappan and Mohamed Rehman and C. Nataraj},
  title = {Automatic Detection of Endotracheal Intubation During the Anesthesia Procedure},
  journal = {Journal of Dynamic Systems, Measurement and Control},
  year = {2016},
  volume = {138},
  number = {11},
  pages = {111013-111013-8},
  doi = {http://dx.doi.org/10.1115/1.4033864}
}
Lingappan, A., Jalali, A., Nataraj, C. & Rehman, M. (2016), "A Clinical Decision Support System for Automatic Documentation of Intubation", In Society for Technology in Anesthesia Meeting.

[BibTeX]
BibTeX: 
@inproceedings{Lingappan2016,
  author = {A Lingappan and A Jalali and C Nataraj and M Rehman},
  title = {A Clinical Decision Support System for Automatic Documentation of Intubation},
  booktitle = {Society for Technology in Anesthesia Meeting},
  year = {2016}
}
Naseradinmousavi, P., Krstic, M. & Nataraj, C. (2016), "Design Optimization of Dynamically Coupled Actuated Butterfly Valves Subject to a Sudden Contraction", ASME Journal of Mechanical Design. Vol. 138(4), pp. 041402-1:041402-11.

[Abstract] [BibTeX] [DOI]
Abstract: In this effort, we present novel nonlinear modeling of two solenoid actuated butterfly valves subject to a sudden contraction and then develop an optimal configuration in the presence of highly coupled nonlinear dynamics. The valves are used in the so-called "smart systems" employed in a wide range of applications including bioengineering, medicine, and engineering fields. Typically, thousands of the actuated valves operate together to regulate the amount of flow and also to avoid probable catastrophic disasters which have been observed in practice. We focus on minimizing the amount of energy used in the system as one of the most critical design criteria to yield an efficient operation. We optimize the actuation subsystems interacting with the highly nonlinear flow loads in order to minimize the amount of energy consumed. The contribution of this work is the inclusion of coupled nonlinearities of electromechanical valve systems to optimize the actuation units. Stochastic, heuristic, and gradient based algorithms are utilized in seeking the optimal design of two sets. The results indicate that substantial amount of energy can be saved by an intelligent design that helps select parameters carefully and also uses flow torques to augment the closing efforts.
BibTeX: 
@article{Naseradinmousavi2016aj,
  author = {Peiman Naseradinmousavi and Miroslav Krstic and C. Nataraj},
  title = {Design Optimization of Dynamically Coupled Actuated Butterfly Valves Subject to a Sudden Contraction},
  journal = {ASME Journal of Mechanical Design},
  year = {2016},
  volume = {138},
  number = {4},
  pages = {041402-1:041402-11},
  doi = {http://dx.doi.org/10.1115/1.4032215}
}
Naseradinmousavi, P., Segala, D. & Nataraj, C. (2016), "Chaotic and Hyperchaotic Dynamics of Coupled Actuated Butterfly Valves Subject to a Sudden Contraction", Journal of Computational and Nonlinear Dynamics. Vol. 11(5), pp. 051025.

[Abstract] [BibTeX] [DOI]
Abstract: In this paper, we focus on determining the safe operational domain of a coupled actuator-valve configuration. The so-called smart valves system has increasingly been used in critical applications and missions including municipal piping networks, oil and gas fields, petrochemical plants, and more importantly, the U.S. Navy ships. A comprehensive dynamic analysis is hence needed to be carried out for capturing dangerous behaviors observed repeatedly in practice. Using some powerful tools of nonlinear dynamic analysis including Lyapunov exponents and Poincaré map, a comprehensive stability map is provided in order to determine the safe operational domain of the network in addition to characterizing the responses obtained. Coupled chaotic and hyperchaotic dynamics of two coupled solenoid-actuated butterfly valves are captured by running the network for some critical values through interconnected flow loads affected by the coupled actuators' variables. The significant effect of an unstable configuration of the valve-actuator on another set is thoroughly investigated to discuss the expected stability issues of a remote set due to others and vice versa.
BibTeX: 
@article{Naseradinmousavi2016j,
  author = {Peiman Naseradinmousavi and David Segala and C. Nataraj},
  title = {Chaotic and Hyperchaotic Dynamics of Coupled Actuated Butterfly Valves Subject to a Sudden Contraction},
  journal = {Journal of Computational and Nonlinear Dynamics},
  year = {2016},
  volume = {11},
  number = {5},
  pages = {051025},
  doi = {http://dx.doi.org/10.1115/1.4033610}
}
Samadani, M., Mohammad, T.H. & Nataraj, C. (2016), "Feature Extraction for Bearing Diagnostics Based on the Characterization of Orbit Plots with Orthogonal Functions", In ASME International Design Engineering Technology Conference. Charlotte, NC, August 21-24, 2016.

[BibTeX]
BibTeX: 
@inproceedings{Samadani2016,
  author = {M. Samadani and T. Haj Mohammad and C. Nataraj},
  title = {Feature Extraction for Bearing Diagnostics Based on the Characterization of Orbit Plots with Orthogonal Functions},
  booktitle = {ASME International Design Engineering Technology Conference},
  year = {2016}
}
Samadani, M., Kwuimy, C.A.K. & Nataraj, C. (2016), "Characterization of the nonlinear response of defective multi-DOF oscillators using the method of phase space topology (PST)", Nonlinear Dynamics., November, 2016. Vol. 86(3), pp. 2023-2034.

[Abstract] [BibTeX] [DOI]
Abstract: Most engineered systems are nonlinear and exhibit phenomena that can only be predicted by nonlinear models. However, the application of model-based approaches for diagnostics has been constrained mostly to linearized or simplified models. This paper introduces a fundamentally new approach (“PST”) for characterization of nonlinear response of systems based on the topology of the phase space trajectory. The method uses the density distribution of the system states to quantify this topology and extracts features that can be used for system diagnostics. The various parameters of the PST method have been analyzed to explore the effectiveness of the method, and it has been employed in the non-trivial diagnostics problem of a multiple degree of freedom oscillator system with various defects occurring simultaneously.
BibTeX: 
@article{Samadani2016j,
  author = {Mohsen Samadani and C. A. Kitio Kwuimy and C. Nataraj},
  title = {Characterization of the nonlinear response of defective multi-DOF oscillators using the method of phase space topology (PST)},
  journal = {Nonlinear Dynamics},
  year = {2016},
  volume = {86},
  number = {3},
  pages = {2023-2034},
  doi = {http://dx.doi.org/10.1007/s11071-016-3012-x}
}
Bender, D., Jalali, A., Licht, D.J. & Nataraj, C. (2015), "Prediction of Periventricular Leukomalacia Occurrence in Neonates Using a Novel Support Vector Machine Classifier Optimization Method", In ASME Dynamic Systems and Control Conference.

[BibTeX]
BibTeX: 
@inproceedings{Bender2015,
  author = {D. Bender and A. Jalali and D. J. Licht and C. Nataraj},
  title = {Prediction of Periventricular Leukomalacia Occurrence in Neonates Using a Novel Support Vector Machine Classifier Optimization Method},
  booktitle = {ASME Dynamic Systems and Control Conference},
  year = {2015}
}
Bender, D., Jalali, A., Licht, D.J. & Nataraj, C. (2015), "A Novel Optimized Learning Approach to Predict Periventricular Leukomalacia Occurrence in Neonates", In Biomedical Engineering Society.

[BibTeX]
BibTeX: 
@inproceedings{Bender2015a,
  author = {D. Bender and A. Jalali and D. J. Licht and C. Nataraj},
  title = {A Novel Optimized Learning Approach to Predict Periventricular Leukomalacia Occurrence in Neonates},
  booktitle = {Biomedical Engineering Society},
  year = {2015}
}
Jalali, A., Lingappan, A., Rehman, M. & Nataraj, C. (2015), "Mathematical modeling of endotracheal intubation in children", In Society for Technology in Anesthesia Conference.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2015,
  author = {Ali Jalali and Arul Lingappan and Mohammed Rehman and C. Nataraj},
  title = {Mathematical modeling of endotracheal intubation in children},
  booktitle = {Society for Technology in Anesthesia Conference},
  year = {2015}
}
Jalali, A., Lingappan, A., Rehman, M. & Nataraj, C. (2015), "A Novel Algorithm for Detection of Endotracheal Tube Placement during Surgery", In 8th Annual Healthcare Informatics Symposium. Philadelphia

[BibTeX]
BibTeX: 
@inproceedings{Jalali2015a,
  author = {A Jalali and A Lingappan and M Rehman and C Nataraj},
  title = {A Novel Algorithm for Detection of Endotracheal Tube Placement during Surgery},
  booktitle = {8th Annual Healthcare Informatics Symposium},
  year = {2015}
}
Jalali, A., Nadkarni, V.M., Berg, R.M. & Nataraj, C. (2015), "Mathematical modeling of cardiopulmonary resuscitation", In Proceedings of the 8th Annual Dynamic Systems and Control Conference. Palo Alto, California, October 21-23, 2015.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2015b,
  author = {Jalali, A. and Nadkarni, V. M. and Berg, R. M. and Nataraj, C.},
  title = {Mathematical modeling of cardiopulmonary resuscitation},
  booktitle = {Proceedings of the 8th Annual Dynamic Systems and Control Conference},
  year = {2015}
}
Jalali, A., Jones, G.F., Licht, D. & Nataraj, C. (2015), "Application of Mathematical Modeling for Simulation and Analysis of Hypoplastic Left Heart Syndrome (HLHS) in Pre and Post Surgery Conditions", Biomed Research International.

[Abstract] [BibTeX] [DOI]
Abstract: This paper is concerned with the mathematical modeling of a severe and common congenital defect called hypoplastic left heart syndrome (HLHS). Surgical approaches are utilized for palliating this heart condition; however, a brain white matter injury called periventricular leukomalacia (PVL) occurs with high prevalence at or around the time of surgery, the exact cause of which is not known presently. Our main goal in this paper is to study the hemodynamic conditions under which HLHS physiology may lead to the occurrence of PVL. A lumped parameter model of the HLHS circulation has been developed integrating diffusion modeling of oxygen and carbon dioxide concentrations in order to study hemodynamic variables such as pressure, flow, and blood gas concentration. Results presented include calculations of blood pressures and flow rates in different parts of the circulation. Simulations also show changes in the ratio of pulmonary to systemic blood flow rates when the sizes of the patent ductus arteriosus and atrial septal defect are varied. These changes lead to unbalanced blood circulations and, when combined with low oxygen and carbon dioxide concentrations in arteries, result in poor oxygen delivery to the brain. We stipulate that PVL occurs as a consequence.
BibTeX: 
@article{Jalali2015j,
  author = {A. Jalali and G. F. Jones and D.J. Licht and C. Nataraj},
  title = {Application of Mathematical Modeling for Simulation and Analysis of Hypoplastic Left Heart Syndrome (HLHS) in Pre and Post Surgery Conditions},
  journal = {Biomed Research International},
  year = {2015},
  note = {Article ID 987293},
  doi = {http://dx.doi.org/10.1155/2015/987293}
}
Karagiannis, D.A., Clayton, G.M. & Nataraj, C. (2015), "Boundary control of harmonic disturbances on flexible cantilever beams using piezoelectric patch actuators", Journal of Vibration and Control., February, 2015. Vol. 22(18), pp. 3916-3929.

[Abstract] [BibTeX] [DOI]
Abstract: This work addresses the control of vibrations in flexible structures caused by external harmonic disturbances using a boundary control method. The research is motivated by practical systems where beam-like structures require vibration suppression to prevent fatigue and system damage, or to increase efficiency. Importantly, this paper addresses a practical constraint of the actuation points being at the boundaries only. The method presented here is an open-loop control scheme which requires knowledge of the harmonic disturbance and a model of the flexible system. The controller uses the model, developed using the Rayleigh Ritz method, to predict the reaction of the beam to the known input disturbance and compute an optimized control input which reduces the steady state vibration in the system. By properly choosing the cost function, the controller can be used to reduce the total vibration or to reduce the vibration in certain spatial locations. The method's vibration reduction capabilities are studied over a range of frequencies; data collected from experiments on a physical beam model is used to validate the predicted behavior of the system.
BibTeX: 
@article{Karagiannis2015j,
  author = {Dimitrios A. Karagiannis and Garrett M. Clayton and C Nataraj},
  title = {Boundary control of harmonic disturbances on flexible cantilever beams using piezoelectric patch actuators},
  journal = {Journal of Vibration and Control},
  year = {2015},
  volume = {22},
  number = {18},
  pages = {3916-3929},
  doi = {http://dx.doi.org/10.1177/1077546314567723}
}
Kwuimy, C.A., Samadani, M., Kankar, P.K. & Nataraj, C. (2015), "Recurrence analysis of experimental time series of a rotor response with bearing outer race faults", In ASME International Design Engineering Technical Conferences.

[BibTeX]
BibTeX: 
@inproceedings{Kwuimy2015,
  author = {Kwuimy, C. A. and M. Samadani and P. K. Kankar and C. Nataraj},
  title = {Recurrence analysis of experimental time series of a rotor response with bearing outer race faults},
  booktitle = {ASME International Design Engineering Technical Conferences},
  year = {2015}
}
Kwuimy, C.A.K., Kankar, P.K., Chen, Y., Chaudhry, Z. & Nataraj, C. (2015), "Development of recurrence analysis for fault discrimination in gears", In ASME International Design Engineering Technical Conferences.

[BibTeX]
BibTeX: 
@inproceedings{Kwuimy2015a,
  author = {C. A. K. Kwuimy and P. K. Kankar and Y. Chen and Z. Chaudhry and C. Nataraj},
  title = {Development of recurrence analysis for fault discrimination in gears},
  booktitle = {ASME International Design Engineering Technical Conferences},
  year = {2015}
}
Kwuimy, C.K., Samadani, M., Kappaganthu, K. & Nataraj, C. (2015), "Sequential recurrence analysis of experimental time series of a rotor response with bearing outer race faults", In Vibration Engineering and Technology of Machinery. , pp. 663-672. Springer Verlag.

[BibTeX] [DOI]
BibTeX: 
@incollection{Kwuimy2015ax,
  author = {C.A. Kitio Kwuimy and M. Samadani and K. Kappaganthu and C. Nataraj},
  title = {Sequential recurrence analysis of experimental time series of a rotor response with bearing outer race faults},
  booktitle = {Vibration Engineering and Technology of Machinery},
  publisher = {Springer Verlag},
  year = {2015},
  pages = {663-672},
  doi = {http://dx.doi.org/10.1007/978-3-319-09918-7_59}
}
Kwuimy, C.A.K., Litak, G. & Nataraj, C. (2015), "Nonlinear analysis of energy harvesting systems with fractional order physical properties", Nonlinear Dynamics., April, 2015. Vol. 80(1), pp. 491-501.

[Abstract] [BibTeX] [DOI]
Abstract: An electromechanical energy harvesting system with a fractional order current–voltage relationship for the electrical circuit and fractional power law in the restoring force of its mechanical part is considered to act as an energy harvester. Our results show that, under a single-well potential configuration, for a small amplitude of the perturbation, as the order of derivative increases, the resonant amplitude of mechanical vibration decreases while the bending degree (hardening case) remains fairly constant. For a large amplitude of the perturbation, the output power is increased due to the hardening effects. Under a double-well configuration, the fractional power stiffness (Formula presented) strongly affects the crossing well dynamics (large amplitude motion) and consequently the output electrical power. The harvested electric power appears to be maximal for deterministic and random excitation for small (Formula presented). High-level noise intensity is found to reduce the output power in the region of resonance and surprisingly increases the output in other regions of (Formula presented). For sufficiently large amplitude of harmonic excitation, this effect is realized in a stochastic resonance.
BibTeX: 
@article{Kwuimy2015j,
  author = {C. A. Kitio Kwuimy and G. Litak and C. Nataraj},
  title = {Nonlinear analysis of energy harvesting systems with fractional order physical properties},
  journal = {Nonlinear Dynamics},
  year = {2015},
  volume = {80},
  number = {1},
  pages = {491-501},
  doi = {http://dx.doi.org/10.1007/s11071-014-1883-2}
}
Kwuimy, C.K. & Nataraj, C. (2015), "Recurrence and Joint Recurrence Analysis of Multiple Attractors Energy Harvesting System", In Structural Nonlinear Dynamics and Diagnosis. Springer Verlag.

[BibTeX]
BibTeX: 
@incollection{Kwuimy2015x,
  author = {C.A. Kitio Kwuimy and C. Nataraj},
  title = {Recurrence and Joint Recurrence Analysis of Multiple Attractors Energy Harvesting System},
  booktitle = {Structural Nonlinear Dynamics and Diagnosis},
  publisher = {Springer Verlag},
  year = {2015}
}
Lebbad, A. & Nataraj, C. (2015), "A Bayesian Algorithm for Vision Based Navigation of Autonomous Surface Vehicles", In 7th IEEE International Conference on Cybernetics and Intelligent Systems (CIS) and Robotics, Automation and Mechatronics (RAM).

[BibTeX]
BibTeX: 
@inproceedings{Lebbad2015,
  author = {A. Lebbad and C. Nataraj},
  title = {A Bayesian Algorithm for Vision Based Navigation of Autonomous Surface Vehicles},
  booktitle = {7th IEEE International Conference on Cybernetics and Intelligent Systems (CIS) and Robotics, Automation and Mechatronics (RAM)},
  year = {2015}
}
Maraini, D. & Nataraj, C. (2015), "Freight Car Roller Bearing Fault Detection Using Artificial Neural Networks and Support Vector Machines", In Vibration Engineering and Technology of Machinery. , pp. 663-672. Springer Verlag.

[BibTeX] [DOI]
BibTeX: 
@incollection{Maraini2015x,
  author = {Maraini, Daniel and C. Nataraj},
  title = {Freight Car Roller Bearing Fault Detection Using Artificial Neural Networks and Support Vector Machines},
  booktitle = {Vibration Engineering and Technology of Machinery},
  publisher = {Springer Verlag},
  year = {2015},
  pages = {663-672},
  doi = {http://dx.doi.org/10.1007/978-3-319-09918-7_59}
}
Samadani, M., Kuimy, C.A.K. & Nataraj, C. (2015), "Characterization of phase space topology using density: application to fault diagnosticsc", In Annual Conference of the Prognostics and Health Management Society.

[BibTeX]
BibTeX: 
@inproceedings{Samadani2015,
  author = {M. Samadani and C. A. K. Kuimy and C. Nataraj},
  title = {Characterization of phase space topology using density: application to fault diagnosticsc},
  booktitle = {Annual Conference of the Prognostics and Health Management Society},
  year = {2015}
}
Samadani, M., Kwuimy, C.K. & Nataraj, C. (2015), "Model-based fault diagnostics of nonlinear systems using the features of the phase space response", Communications in Nonlinear Science and Numerical Simulation. Vol. 20(2), pp. 583-593.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: A novel algorithm is presented in this paper for the diagnostics of nonlinear systems based on the idea of estimating the parameters of the system using features of the nonlinear response. The method combines statistical features of the nonlinear response and capabilities of artificial neural networks in data fitting with the objective of estimating the parameters of a defective nonlinear system. New features extracted from the density distribution of position and velocity signals are introduced to characterize the complex topologies of the phase plane response in periodic and multi-periodic domains. A nonlinear pendulum is used for experimental validation of the procedure. The results show that, with appropriately selected features of the response, the parameters of the nonlinear system can be estimated with an acceptable accuracy.
BibTeX: 
@article{Samadani2015j,
  author = {M. Samadani and C.A. Kitio Kwuimy and C. Nataraj},
  title = {Model-based fault diagnostics of nonlinear systems using the features of the phase space response},
  journal = {Communications in Nonlinear Science and Numerical Simulation},
  year = {2015},
  volume = {20},
  number = {2},
  pages = {583-593},
  url = {http://www.sciencedirect.com/science/article/pii/S1007570414002731},
  doi = {http://dx.doi.org/10.1016/j.cnsns.2014.06.010}
}
Temel, T., Ashrafiuon, H., Nataraj, C. & Yildrim, S. (2015), "A New Sliding-mode Model Predictive Controller for Output Tracking of Nonlinear Systems with Online Optimization", International Journal of Advanced Research., September, 2015. Vol. 3(9), pp. 660-664.

[Abstract] [BibTeX]
Abstract: A model predictive control method for nonlinear systems is presented
resulting from a new sliding manifold definition. The sliding-mode control
with new manifold drives dynamics of a given nonlinear system to a stable
sliding surface faster compared to standard counterparts. The new manifold
definition is further exploited for a straightforward derivation of discretetime
predictive controller with on-line optimization in dynamics of both
deterministic and stochastic components. Simulation results for a secondorder
nonlinear system show that new predictive controller leads to more
successful tracking of a given target trajectory compared to conventional
sliding-mode controller for the system studied with suitably determined realtime
operational conditions such as time and control update terms.
BibTeX: 
@article{Temel2015j,
  author = {Turgay Temel and Hashem Ashrafiuon and C. Nataraj and Sahin Yildrim},
  title = {A New Sliding-mode Model Predictive Controller for Output Tracking of Nonlinear Systems with Online Optimization},
  journal = {International Journal of Advanced Research},
  year = {2015},
  volume = {3},
  number = {9},
  pages = {660-664}
}
Anderson, J.W., Lebbad, A., Nataraj, C. & Clayton, G.M. (2014), "An Integrated LIDAR/Video Vision System for Autonomous Surface Vehicles", Naval Engineers Journal., December, 2014. Vol. 126(4), pp. 169-172.

[Abstract] [BibTeX]
Abstract: In this paper, the design and implementation of an integrated LIDAR/Video vision system for autonomous surface vehicles (ASVs) is presented. This system consists of a gimbaled LIDAR and an RGB webcam, which enables the acquisition of 3-D information about the environment as well as ASV motion. Details of the systems mechanical and electronic design, LIDAR/Video fusion, and an experimental buoy identification example are presented.
BibTeX: 
@article{Anderson2014j,
  author = {J. Wesley Anderson and Anderson Lebbad and C. Nataraj and Garrett M. Clayton},
  title = {An Integrated LIDAR/Video Vision System for Autonomous Surface Vehicles},
  journal = {Naval Engineers Journal},
  year = {2014},
  volume = {126},
  number = {4},
  pages = {169-172}
}
Bender, D., Jalali, A. & Nataraj, C. (2014), "Prediction of Periventricular Leukomalacia Occurrence in Neonates Using a Novel Unsupervised Learning Method", In Proceedings of ASME 2014 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE)., October 22-24, 2014.

[BibTeX]
BibTeX: 
@inproceedings{Bender2014,
  author = {Bender, D. and Jalali, A. and Nataraj, C.},
  title = {Prediction of Periventricular Leukomalacia Occurrence in Neonates Using a Novel Unsupervised Learning Method},
  booktitle = {Proceedings of ASME 2014 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE)},
  year = {2014}
}
Jalali, A., Nadkarni, V.M. & Nataraj, C. (2014), "IModeling Mechanical Properties of the Chest During the Cardiopulmonary Resuscitation Procedure", In Proceedings of Computing in Cardiology Conference. Palo Alto, California, October 21-23, 2014.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2014,
  author = {Jalali, A. and Nadkarni, V. M. and Nataraj, C.},
  title = {IModeling Mechanical Properties of the Chest During the Cardiopulmonary Resuscitation Procedure},
  booktitle = {Proceedings of Computing in Cardiology Conference},
  year = {2014}
}
Jalali, A., Buckley, E.M., Lynch, J.M., Schwab, P.J., Licht, D.J. & Nataraj, C. (2014), "Prediction of periventricular leukomalacia occurrence in neonates after heart surgery.", IEEE Journal of Biomedical and Health Informatics., Jul, 2014. Vol. 18(4), pp. 1453-1460.

[Abstract] [BibTeX] [DOI]
Abstract: This paper is concerned with predicting the occurrence of periventricular leukomalacia (PVL) using vital and blood gas data which are collected over a period of 12 h after the neonatal cardiac surgery. A data mining approach has been employed to generate a set of rules for classification of subjects as healthy or PVL affected. In view of the fact that blood gas and vital data have different sampling rates, in this study we have divided the data into two categories: 1) high resolution (vital), and 2) low resolution (blood gas), and designed a separate classifier based on each data category. The developed algorithm is composed of several stages; first, a feature pool has been extracted from each data category and the extracted features have been ranked based on the data reliability and their mutual information content with the output. An optimal feature subset with the highest discriminative capability has been formed using simultaneous maximization of the class separability measure and mutual information of a set. Two separate decision trees (DTs) have been developed for the classification purpose and more importantly to discover hidden relationships that exist among the data to help us better understand PVL pathophysiology. The DT result shows that high amplitude 20 min variations and low sample entropy in the vital data and the defined out of range index as well as maximum rate of change in blood gas data are important factors for PVL prediction. Low sample entropy represents lack of variability in hemodynamic measurement, and constant blood pressure with small fluctuations is an important indicator of PVL occurrence. Finally, using the different time frames of data collection, we show that the first 6 h of data contain sufficient information for PVL occurrence prediction.
BibTeX: 
@article{Jalali2014j,
  author = {Ali Jalali and Erin M Buckley and Jennifer M Lynch and Peter J Schwab and Daniel J Licht and C. Nataraj},
  title = {Prediction of periventricular leukomalacia occurrence in neonates after heart surgery.},
  journal = {IEEE Journal of Biomedical and Health Informatics},
  year = {2014},
  volume = {18},
  number = {4},
  pages = {1453--1460},
  note = {Selected as one of top 5 papers in the category of decision support systems for a complex clinical condition out of 1,254 papers compiled by International Medical Informatics Association.},
  doi = {http://dx.doi.org/10.1109/JBHI.2013.2285011}
}
Kuimy, C.A.K., Samadani, M., Kappaganthu, K. & Nataraj, C. (2014), "Sequential recurrence analysis of experimental time series of a rotor response with bearing outer race faults", In 10th International Conference on Vibration Engineering and Technology of Machinery.

[BibTeX]
BibTeX: 
@inproceedings{Kuimy2014,
  author = {Kuimy, C. A. K. and M. Samadani and Karthik Kappaganthu and C. Nataraj},
  title = {Sequential recurrence analysis of experimental time series of a rotor response with bearing outer race faults},
  booktitle = {10th International Conference on Vibration Engineering and Technology of Machinery},
  year = {2014}
}
Kuimy, C.A.K., Samadani, M. & Nataraj, C. (2014), "Initial diagnostics of dynamic systems from time series", In Proceedings of ASME 2014 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE).

[BibTeX]
BibTeX: 
@inproceedings{Kuimy2014a,
  author = {C. A. K. Kuimy and M. Samadani and C. Nataraj},
  title = {Initial diagnostics of dynamic systems from time series},
  booktitle = {Proceedings of ASME 2014 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE)},
  year = {2014}
}
Kwuimy, C.A.K., Samadani, M. & Nataraj, C. (2014), "Bifurcation analysis of a nonlinear pendulum using recurrence and statistical methods: Applications to fault diagnostics", Nonlinear Dynamics., June, 2014. Vol. 76(4), pp. 1963-1975.

[Abstract] [BibTeX] [DOI]
Abstract: The problem of maintenance of expensive and heavy systems has increased the need for powerful tools to analyze their performance. The methods of recurrence plots (RPs) and statistical measurement have been used as data-driven tools for diagnostics with no possibility of classifying the nature of defect and poor ability to localize it. In order to enhance the efficiency of the forecast, innovative approaches consist of using physics-based features to train a data-based assessment methods. This requires proper analysis of the physical system using appropriate methods. For this purpose, this paper focusses on the bifurcation dynamics of nonlinear systems using the recurrence and statistical methods. Considering the nonlinear pendulum as a model, the qualitative behavior of the system is discussed through the bifurcation diagram of some recurrence quantification analysis (RQA) parameters, namely the recurrence rate, determinism, and laminarity. These parameters are used to measure the level of complexity and transition from regular to chaotic motion and vice versa. Statistical parameters such as crest factor, skewness, and kurtosis are used to identify various bifurcation and amplitudes in the system, and to measure the orientation and the level of asymmetry. Plots of recurrence diagrams and histograms are presented to support our observations. Examples of detection of dynamic changes using these two methods are provided. The interesting results obtained in this paper show that statistical methods complement results obtained from RPs. In addition, the paper demonstrates how the RPs can be employed in conjunction with the physics-based model.
BibTeX: 
@article{Kwuimy2014j,
  author = {Kwuimy, C A. Kitio and Samadani, M. and Nataraj, C},
  title = {Bifurcation analysis of a nonlinear pendulum using recurrence and statistical methods: Applications to fault diagnostics},
  journal = {Nonlinear Dynamics},
  year = {2014},
  volume = {76},
  number = {4},
  pages = {1963-1975},
  doi = {http://dx.doi.org/10.1007/s11071-014-1261-0}
}
Lebbad, A., Anderson, W., Benson, M. & Nataraj, C. (2014), "Vison Based Navigation of Autonomous Vehicles", In NEEC Annual Program Conference.

[BibTeX]
BibTeX: 
@inproceedings{Lebbad2014,
  author = {Lebbad, A. and Anderson, W. and Benson, M. and C. Nataraj},
  title = {Vison Based Navigation of Autonomous Vehicles},
  booktitle = {NEEC Annual Program Conference},
  year = {2014}
}
Lebbad, A., DiLeo, N., Shivananda, C.M., Nataraj, C. & Ferrese, F. (2014), "Probabilistic Vision Based Guidance & SLAM for Autonomous Surface Vehicles", Naval Engineers Journal., December, 2014. Vol. 126(4), pp. 95-99.

[Abstract] [BibTeX]
Abstract: This article presents novel methods for robust vision-based navigation and control of autonomous surface vehicles. The algorithms employ probabilistic methods for recursive color analysis, Simultaneous Localization and Mapping, and for path-planning. These algorithms are motivated by Villanova's selection for the International Maritime RobotX Challenge, but the algorithms could be extended to vision based mobile robots of many types, and especially for those operating in an uncertain environment.
BibTeX: 
@article{Lebbad2014j,
  author = {Anderson Lebbad and Nicholas DiLeo and Chidananda Matada Shivananda and C. Nataraj and Frank Ferrese},
  title = {Probabilistic Vision Based Guidance & SLAM for Autonomous Surface Vehicles},
  journal = {Naval Engineers Journal},
  year = {2014},
  volume = {126},
  number = {4},
  pages = {95-99}
}
Maraini, D. & Nataraj, C. (2014), "Freight car roller bearing fault detection using artificial neural networks and support vector machines", In Proceedings of VETOMAC-X. Manchester, UK, September 9-11, 2014.

[BibTeX]
BibTeX: 
@inproceedings{Maraini2014,
  author = {Maraini, Daniel and Nataraj, C.},
  title = {Freight car roller bearing fault detection using artificial neural networks and support vector machines},
  booktitle = {Proceedings of VETOMAC-X},
  year = {2014}
}
Samadani, M., Kuimy, C.A.K. & Nataraj, C. (2014), "Fault Detection and Severity Analysis of Servo Valves Using Recurrence Quantfication Analysis", In Annual Conference of the Prognostics and Health Management Society.

[BibTeX]
BibTeX: 
@inproceedings{Samadani2014,
  author = {M. Samadani and C. A. K. Kuimy and C. Nataraj},
  title = {Fault Detection and Severity Analysis of Servo Valves Using Recurrence Quantfication Analysis},
  booktitle = {Annual Conference of the Prognostics and Health Management Society},
  year = {2014}
}
Zhu, E., DeGaetano, D., Shah, P., Jenkins, G. & Nataraj, C. (2014), "The Maritime RobotX Challenge", In NEEC Annual Program Conference.

[BibTeX]
BibTeX: 
@inproceedings{Zhu2014,
  author = {Zhu, E. and DeGaetano, D. and Shah, P. and Jenkins, G. and C. Nataraj},
  title = {The Maritime RobotX Challenge},
  booktitle = {NEEC Annual Program Conference},
  year = {2014}
}
Zhu, E., DeGaetano, D., Cheng, G., Shah, P., Benson, M., Jenkins, G., Ferrese, F. & Nataraj, C. (2014), "An Experimental Autonomous Surface Vehicle With Vision-Based Navigation, Obstacle Avoidance & SLAM", Naval Engineers Journal., December, 2014. Vol. 126(4), pp. 173-177.

[Abstract] [BibTeX]
Abstract: This article presents a system overview of SeaCat, an autonomous surface vehicle (ASV), developed by a student team at Villanova University. Designed for various autonomous tasks, emphasis has been placed on robustness in various operating conditions. Using an extensive sensor suite, a depth-based, lighting invariant vision system and complex algorithms, SeaCat carries out mapping, path planning, obstacle avoidance and navigation. In addition, dual hydrophones enable the potential for acoustic localization tasks. Mission-level control is provided by a hierarchical structure and programmed using a finite state machine, allowing for the development of modular routines that can be quickly implemented and tested.
BibTeX: 
@article{Zhu2014j,
  author = {Edward Zhu and Dylan DeGaetano and GinSiu Cheng and Priya Shah and Michael Benson and Gus Jenkins and Frank Ferrese and C. Nataraj},
  title = {An Experimental Autonomous Surface Vehicle With Vision-Based Navigation, Obstacle Avoidance & SLAM},
  journal = {Naval Engineers Journal},
  year = {2014},
  volume = {126},
  number = {4},
  pages = {173-177}
}
Jalali, A., Licht, D.J. & Nataraj, C. (2013), "Discovering hidden relationships in physiological signals for prediction of Periventricular Leukomalacia", In Proceedings of the 35th Annual International Conference of the IEEE Conference Engineering in Medicine and Biology Society (EMBC). Osaka, Japan, July 3-7, 2013.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2013,
  author = {Jalali, A. and Licht, D. J. and Nataraj, C.},
  title = {Discovering hidden relationships in physiological signals for prediction of Periventricular Leukomalacia},
  booktitle = {Proceedings of the 35th Annual International Conference of the IEEE Conference Engineering in Medicine and Biology Society (EMBC)},
  year = {2013}
}
Jalali, A., Nadkarni, V.M., Berg, R.M. & Nataraj, C. (2013), "Improving Cardiopulmonary Resuscitation (CPR) by Dynamic Variation of CPR Parameters", In Proceedings of the 6th Annual Dynamic Systems and Control Conference. Palo Alto, California, October 21-23, 2013.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2013a,
  author = {Jalali, A. and Nadkarni, V. M. and Berg, R. M. and Nataraj, C.},
  title = {Improving Cardiopulmonary Resuscitation (CPR) by Dynamic Variation of CPR Parameters},
  booktitle = {Proceedings of the 6th Annual Dynamic Systems and Control Conference},
  year = {2013}
}
Kitio Kwuimy, C.A.K., Litak, G. & Nataraj, C. (2013), "Performance of an energy harvester system with fractional order deflection", In Proceedings of the 6th Annual Dynamic Systems and Control Conference. Palo Alto, California, October 21-23, 2013.

[BibTeX]
BibTeX: 
@inproceedings{KitioKwuimy2013,
  author = {Kitio Kwuimy, C. A. K. and Litak, G. and Nataraj, C.},
  title = {Performance of an energy harvester system with fractional order deflection},
  booktitle = {Proceedings of the 6th Annual Dynamic Systems and Control Conference},
  year = {2013}
}
Kwuimy, C.A.K., Das, A.S. & Nataraj, C. (2013), "Stability analysis of a fault-free balance rotor supported on rolling element bearings with clearance and static load", In Proceedings of the ASME International Design Engineering Technical Conferences & Computers and Information in Engineering Conference. Portland, Oregon, August 4-7, 2013.

[BibTeX]
BibTeX: 
@inproceedings{Kwuimy2013,
  author = {Kwuimy, C. A. K. and Das, A. S. and Nataraj, C.},
  title = {Stability analysis of a fault-free balance rotor supported on rolling element bearings with clearance and static load},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conferences & Computers and Information in Engineering Conference},
  year = {2013}
}
Kwuimy, C.A.K. & Nataraj, C. (2013), "Bistability and Bursting Oscillations in Electromechanical Butterfly Valves", Journal of Applied Nonlinear Dynamics. Vol. 2(3), pp. 303-314.

[Abstract] [BibTeX] [DOI]
Abstract: This papers considers an electromechanical butterfly valve and discusses the conditions for appearance of bistability and bursting oscillations. The critical nonlinear stiffness coefficient and inlet velocities leading to such dynamics are obtained as a function of the system parameters, and the effects of external perturbation on the bursting response of the system are illustrated. It is observed that the driving parameters and the direct current voltage strongly affect the sharpness, the number of strikes, the amplitude of the strikes and the time interval between the strikes. Combinations of large-amplitude oscillations and small-amplitude oscillations are obtained for the electric circuit, while combination of fast-slow dynamics is obtained for the mechanical part. The results of the paper provide potential criteria for evaluating and optimizing system performance.
BibTeX: 
@article{Kwuimy2013aj,
  author = {Kwuimy, C A. Kitio and Nataraj, C},
  title = {Bistability and Bursting Oscillations in Electromechanical Butterfly Valves},
  journal = {Journal of Applied Nonlinear Dynamics},
  year = {2013},
  volume = {2},
  number = {3},
  pages = {303-314},
  doi = {http://dx.doi.org/10.5890/JAND.2013.08.005}
}
Kwuimy, C.A.K., Ramakrishnan, S. & Nataraj, C. (2013), "On the nonlinear on-off dynamics of an electromechanically actuated butterfly valve", Journal of Sound and Vibration. Vol. 332(24), pp. 6488-6504.

[Abstract] [BibTeX] [DOI]
Abstract: In this paper, we study the nonlinear dynamics of a butterfly valve actuated by the induced electromotive force (emf) of a permanent magnet, with a focus on the on-off dynamics of the valve and its nonlinear response under ambient perturbation. The complex interplay between the electromagnetic, hydrodynamic and mechanical forces leads to a fundamentally multiphysical, nonlinear dynamical model for the problem. First, we analyze the stability of the on-off conditions in terms of three critical dynamical parameters - the actuating DC voltage, inlet velocity and the opening angle. Next, the response of the system to perturbations around the equilibrium points is studied in terms of the frequency response using the method of multiple scales. Finally, evidence of fractality is established using Melnikov analysis and a plot of the basins of attraction. The results reported in the article, in addition to being of fundamental theoretical interest, are expected to impact practical design considerations of electromechanical butterfly valves
BibTeX: 
@article{Kwuimy2013j,
  author = {C. A. Kitio Kwuimy and S. Ramakrishnan and C. Nataraj},
  title = {On the nonlinear on-off dynamics of an electromechanically actuated butterfly valve},
  journal = {Journal of Sound and Vibration},
  year = {2013},
  volume = {332},
  number = {24},
  pages = {6488-6504},
  doi = {http://dx.doi.org/10.1016/j.jsv.2013.07.014}
}
Naseradinmousavi, P. & Nataraj, C. (2013), "Optimal design of solenoid actuators driving butterfly valves", ASME Journal of Mechanical Design., September, 2013. Vol. 135(9), pp. 094501.

[Abstract] [BibTeX] [DOI]
Abstract: Smart valves are used in cooling applications and are responsible for regulating and supplying the coolant, which is critical for safe and effective operation of many components on naval and commercial ships. In order to be operated under local power (for various mission-critical reasons) they need to consume as little energy as possible in order to ensure continued operability. This paper focuses on optimized design of a typical system using high fidelity nonlinear dynamic models for all the subsystems with full consideration of stability constraints. A simulated annealing algorithm is applied to explore optimal design using two sets of design variables. The results indicate that substantial amount of energy can be saved by an intelligent design that helps select parameters carefully, but also uses hydrodynamic loads to augment the closing effort.
BibTeX: 
@article{Naseradinmousavi2013j,
  author = {P. Naseradinmousavi and C. Nataraj},
  title = {Optimal design of solenoid actuators driving butterfly valves},
  journal = {ASME Journal of Mechanical Design},
  year = {2013},
  volume = {135},
  number = {9},
  pages = {094501},
  note = {Paper No: MD-12-1011},
  doi = {http://dx.doi.org/10.1115/1.4024720}
}
Samadani, M., Kwuimy, C.A.K. & Nataraj, C. (2013), "Diagnostics of a nonlinear pendulum using computational intelligence", In Proceedings of the 6th Annual Dynamic Systems and Control Conference. Palo Alto, CA, October 21-23, 2013.

[BibTeX]
BibTeX: 
@inproceedings{Samadani2013,
  author = {Samadani, M. and Kwuimy, C. A. K. and Nataraj, C.},
  title = {Diagnostics of a nonlinear pendulum using computational intelligence},
  booktitle = {Proceedings of the 6th Annual Dynamic Systems and Control Conference},
  year = {2013}
}
Samadani, M., Behbahani, S. & Nataraj, C. (2013), "A reliability-based manufacturing process planning method for the components of a complex mechatronic system", Applied Mathematical Modelling. Vol. 37(24), pp. 9829-9845.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Abstract Uncertainties in the values of the parameters of a system can originate from the manufacturing tolerances of the system components, which can produce a degree of unreliability in the performance of the system. A systematic framework for realistic reliability assessment of an electro-hydraulic servo system has been presented in this paper with the objective of providing adequate information for the selection of the best manufacturing process for each of the servo valve components. Monte Carlo simulation has been employed to evaluate the effect of these uncertainties of the servo valve parameters on the statistical performance of the system. Possible manufacturing processes have been introduced for each component and the justifiability of using each one has been discussed based on the estimated reliability of the system.
BibTeX: 
@article{Samadani2013j,
  author = {Mohsen Samadani and Saeed Behbahani and C. Nataraj},
  title = {A reliability-based manufacturing process planning method for the components of a complex mechatronic system},
  journal = {Applied Mathematical Modelling},
  year = {2013},
  volume = {37},
  number = {24},
  pages = {9829-9845},
  url = {http://www.sciencedirect.com/science/article/pii/S0307904X1300351X},
  doi = {http://dx.doi.org/10.1016/j.apm.2013.05.030}
}
StFleur, C. & Nataraj, C. (2013), "The Science Of Unmanned Aerial Vehicles With Flexible Flying Surfaces", In proceedings of the Second Anual KAUVSI Mini-Symposium. Philadelphia, PA, June 4, 2013.

[BibTeX]
BibTeX: 
@inproceedings{StFleur2013,
  author = {StFleur, C. and Nataraj, C.},
  title = {The Science Of Unmanned Aerial Vehicles With Flexible Flying Surfaces},
  booktitle = {proceedings of the Second Anual KAUVSI Mini-Symposium},
  year = {2013}
}
Ghorbanian, P., Ghaffari, A., Jalali, A. & Nataraj, C. (2012), "An Improved Procedure for Detection of Heart Arrhythmias with Novel Preprocessing Techniques", Expert Systems., November, 2012. Vol. 29(5), pp. 478-491.

[Abstract] [BibTeX] [DOI]
Abstract: The objective of this study is to develop an algorithm to detect and classify six types of electrocardiogram (ECG) signal beats including normal beats (N), atrial pre-mature beats (A), right bundle branch block beats (R), left bundle branch block beats (L), paced beats (P), and pre-mature ventricular contraction beats (PVC or V) using a neural network classifier. In order to prepare an appropriate input vector for the neural classifier several pre-processing stages have been applied. Initially, a signal filtering method is used to remove the ECG signal baseline wandering. Continuous wavelet transform is then applied in order to extract features of the ECG signal. Next, principal component analysis is used to reduce the size of the data. A well-known neural network architecture called the multi-layered perceptron neural network is then utilized as the final classifier to classify each ECG beat as one of six groups of signals under study. Finally, the MIT-BIH database is used to evaluate the proposed algorithm, resulting in 99.5% sensitivity, 99.66% positive predictive accuracy and 99.17% total accuracy.
BibTeX: 
@article{Ghorbanian2012j,
  author = {P. Ghorbanian and A. Ghaffari and A. Jalali and C. Nataraj},
  title = {An Improved Procedure for Detection of Heart Arrhythmias with Novel Preprocessing Techniques},
  journal = {Expert Systems},
  year = {2012},
  volume = {29},
  number = {5},
  pages = {478-491},
  doi = {http://dx.doi.org/10.1111/j.1468-0394.2011.00606.x}
}
Jalali, A., Berg, R., Nadkarni, V. & Nataraj, C. (2012), "Model Based Optimization of The Cardiopulmonary Resuscitation (CPR) Procedure", In 34th International Conference of the IEEE Engineering in Medicine & Biology in Medicine. San Diego, August 28 - September 1, 2012.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2012,
  author = {Ali Jalali and Robert Berg and Vinay Nadkarni and C. Nataraj},
  title = {Model Based Optimization of The Cardiopulmonary Resuscitation (CPR) Procedure},
  booktitle = {34th International Conference of the IEEE Engineering in Medicine & Biology in Medicine},
  year = {2012}
}
Jalali, A., Licht, D.J. & Nataraj, C. (2012), "Application of Decision Tree in the Prediction of Periventricular Leukomalacia (PVL) Occurrence in Neonates After Neonatal Heart Surgery", In 34th International Conference of the IEEE Engineering in Medicine & Biology in Medicine. San Diego, August 28 - September 1, 2012.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2012a,
  author = {Ali Jalali and Daniel J. Licht and C. Nataraj},
  title = {Application of Decision Tree in the Prediction of Periventricular Leukomalacia (PVL) Occurrence in Neonates After Neonatal Heart Surgery},
  booktitle = {34th International Conference of the IEEE Engineering in Medicine & Biology in Medicine},
  year = {2012}
}
Jalali, A. & Nataraj, C. (2012), "Prediction of occurrence of Periventricular Leukomalacia in Neonates after Heart Surgery Using A Decision Tree Algorithm", In ASME International Design Engineering Technical Conferences & Computers and Information in Engineering Conference., September, 2012.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2012b,
  author = {Ali Jalali and C. Nataraj},
  title = {Prediction of occurrence of Periventricular Leukomalacia in Neonates after Heart Surgery Using A Decision Tree Algorithm},
  booktitle = {ASME International Design Engineering Technical Conferences & Computers and Information in Engineering Conference},
  year = {2012}
}
Jalali, A. & Nataraj, C. (2012), "Application of computational intelligence techniques in the prediction of occurrence and severity of periventricular leukomalacia (PVL)", In 5th Annual ASME Dynamic Systems and Control Conference., October 17-19, 2012. ASME.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2012c,
  author = {Ali Jalali and C. Nataraj},
  title = {Application of computational intelligence techniques in the prediction of occurrence and severity of periventricular leukomalacia (PVL)},
  booktitle = {5th Annual ASME Dynamic Systems and Control Conference},
  publisher = {ASME},
  year = {2012}
}
Jalali, A., Ghorbanian, P., Ghaffari, A. & Nataraj, C. (2012), "A Novel Technique for Identifying Patients With ICU Needs Using Hemodynamic Features", Advances in Fuzzy Systems. Vol. 12(Article ID 696194)

[Abstract] [BibTeX] [DOI]
Abstract: Identification of patients requiring intensive care is a critical issue in clinical treatment. The objective of this study is to develop a novel methodology using hemodynamic features for distinguishing such patients requiring intensive care from a group of healthy subjects. In this study, based on the hemodynamic features, subjects are divided into three groups: healthy, risky and patient. For each of the healthy and patient subjects, the evaluated features are based on the analysis of existing differences between hemodynamic variables: Blood Pressure and Heart Rate. Further, four criteria from the hemodynamic variables are introduced: circle criterion, estimation error criterion, Poincare plot deviation, and autonomic response delay criterion. For each of these criteria, three fuzzy membership functions are defined to distinguish patients from healthy subjects. Furthermore, based on the evaluated criteria, a scoring method is developed. In this scoring method membership degree of each subject is evaluated for the three classifying groups. Then, for each subject, the cumulative sum of membership degree of all four criteria is calculated. Finally, a given subject is classified with the group which has the largest cumulative sum. In summary, the scoring method results in 86% sensitivity, 94.8% positive predictive accuracy and 82.2% total accuracy.
BibTeX: 
@article{Jalali2012j,
  author = {A. Jalali and P. Ghorbanian and A. Ghaffari and C. Nataraj},
  title = {A Novel Technique for Identifying Patients With ICU Needs Using Hemodynamic Features},
  journal = {Advances in Fuzzy Systems},
  year = {2012},
  volume = {12},
  number = {Article ID 696194},
  doi = {http://dx.doi.org/10.1155/2012/696194}
}
Kwuimy, C.A.K. & Nataraj, C. (2012), "Combined resonances in a rotor supported on rolling element bearings", In Fourteenth Conference on Nonlinear Vibrations, Dynamics and Multi-Body Systems., July 16-19, 2012.

[BibTeX]
BibTeX: 
@inproceedings{Kwuimy2012,
  author = {C. A. Kitio Kwuimy and C. Nataraj},
  title = {Combined resonances in a rotor supported on rolling element bearings},
  booktitle = {Fourteenth Conference on Nonlinear Vibrations, Dynamics and Multi-Body Systems},
  year = {2012}
}
Kwuimy, C.K. & Nataraj, C. (2012), "Modeling and nonlinear dynamics analysis of a magnetically actuated butterfly valve", Nonlinear Dynamics. Vol. 70, pp. 435-451.

[Abstract] [BibTeX] [DOI]
Abstract: Recent progress in the analysis of butterfly valve presented accurate information for mathematical modeling and analysis. In this work, a magnetically actuated butterfly valve is considered and an innovative and accurate mathematical model is derived. Static analysis of the system is investigated and the effects of the inlet velocity and direct current voltage (DC) on the stable tilt angle of the valve are presented. Considering a time periodic perturbation, the effects of operating angle, inlet velocity and driving parameters on the periodic and chaotic dynamics of the system are highlighted. It is observed that, for an opening angle less than the cut-off angle, there exists a unique DC voltage for a stable equilibrium. The stability of this equilibrium nonlinearly depends on the inlet velocity and seating torque. The expression of the threshold bound for the stability of the valve is derived. Under periodic perturbation, the inlet velocity and stable angle induced backward shift on the resonant frequency; jump phenomena and sub-harmonic are observed for some values of the driving amplitude. The highest amplitudes of vibration are detected for a full open valve or large rotational valve, and large inlet velocity. Using the bifurcation diagram and Lyapunov exponent, the system shows a route to chaos with windows of period doubling and unbounded motion. Some guidance for design of future magnetically actuated butterfly valves is proposed as well as recommendations for future work.
BibTeX: 
@article{Kwuimy2012aj,
  author = {C.A. Kitio Kwuimy and C. Nataraj},
  title = {Modeling and nonlinear dynamics analysis of a magnetically actuated butterfly valve},
  journal = {Nonlinear Dynamics},
  year = {2012},
  volume = {70},
  pages = {435-451},
  doi = {http://dx.doi.org/10.1007/s11071-012-0466-3}
}
Kwuimy, C.K., Nataraj, C. & Belhaq, M. (2012), "Chaos Control in a Magnetic Pendulum Subjected to a Tilted Excitation and Parametric Damping", Mathematical Problems in Engineering. Vol. 2012

[Abstract] [BibTeX] [DOI] [URL]
Abstract: The effect of tilted harmonic excitation and of parametric damping on the chaotic dynamic in an asymmetric magnetic pendulum is investigated in this paper. The Melnikov method is used to derive a criterion for transition to non-periodic motion in terms of the hyper-geometric function. The regular and fractal shapes of the basin of attraction are used to validate the Melnikov predictions. In the absence of parametric damping, the results show that an increase of the tilt angle of the excitation causes the lower bound for horseshoes chaos to increase and produces a singularity at the vertical position of the excitation. It is also shown that the presence of a parametric damping without a periodic fluctuation can enhance or suppress horseshoes chaos while a parametric damping with a periodic fluctuation can increase the region of regular motions significantly.
BibTeX: 
@article{Kwuimy2012bj,
  author = {C.A. Kitio Kwuimy and C. Nataraj and M. Belhaq},
  title = {Chaos Control in a Magnetic Pendulum Subjected to a Tilted Excitation and Parametric Damping},
  journal = {Mathematical Problems in Engineering},
  year = {2012},
  volume = {2012},
  note = {Article ID 546364},
  url = {http://www.hindawi.com/journals/mpe/aip/546364/},
  doi = {http://dx.doi.org/10.1155/2012/546364}
}
Kwuimy, C.A.K., Litak, G., Borowiec, M. & Nataraj, C. (2012), "Performance of a piezoelectric energy harvester driven by air flow", Applied Physics Letters., January 9, 2012. Vol. 100(2), pp. 024103.

[Abstract] [BibTeX] [DOI]
Abstract: A turbulent wind source for possible energy harvesting is considered. To increase the amplitude of vibration we apply a magnetopiezoelastic oscillator having a double well Duffing potential. The output voltage response of the system for different level of wind excitations is analyzed. The energy harvesting appeared to be the most efficient for the conditions close to the stochastic resonance region where the potential well was overcame.
BibTeX: 
@article{Kwuimy2012j,
  author = {C. A. Kitio Kwuimy and G. Litak and M. Borowiec and C. Nataraj},
  title = {Performance of a piezoelectric energy harvester driven by air flow},
  journal = {Applied Physics Letters},
  year = {2012},
  volume = {100},
  number = {2},
  pages = {024103},
  doi = {http://dx.doi.org/10.1063/1.3676272}
}
Lee, D. & Nataraj, C. (2012), "Linear Time-varying Control of Adaptive Model-Based System", In Proceedings of the American Control Conference.

[BibTeX]
BibTeX: 
@conference{Lee2012,
  author = {DongBin Lee and C. Nataraj},
  title = {Linear Time-varying Control of Adaptive Model-Based System},
  booktitle = {Proceedings of the American Control Conference},
  year = {2012}
}
Lee, D., Nataraj, C., Burg, T.C. & Dawson, D.M. (2012), "Coordinated Control of Flying Robotic Arm", In 5th Annual ASME Dynamic Systems and Control Conference., Ocgtober 17-19, 2012.

[BibTeX]
BibTeX: 
@inproceedings{Lee2012a,
  author = {DongBin Lee and C. Nataraj and Timothy C. Burg and Darren M. Dawson},
  title = {Coordinated Control of Flying Robotic Arm},
  booktitle = {5th Annual ASME Dynamic Systems and Control Conference},
  year = {2012}
}
Lee, D. & Nataraj, C. (2012), "Model-based Adaptive Tracking Control of Linear Time-varying System with Uncertainties (in press)", In Numerical Simulation - From Theory to Industry., September 19, 2012. , pp. 35-48. InTech.

[BibTeX] [DOI]
BibTeX: 
@incollection{Lee2012cx,
  author = {DongBin Lee and C. Nataraj},
  title = {Model-based Adaptive Tracking Control of Linear Time-varying System with Uncertainties (in press)},
  booktitle = {Numerical Simulation - From Theory to Industry},
  publisher = {InTech},
  year = {2012},
  pages = {35-48},
  doi = {http://dx.doi.org/10.5772/51625}
}
Lee, D., Nataraj, C. & Naseradinmousavi, P. (2012), "Nonlinear Dynamic Model-based Adaptive Control of a Solenoid-Valve System", Journal of Control Science and Engineering. Vol. 17(11), pp. 4336-4345.

[Abstract] [BibTeX] [DOI]
Abstract: In this paper, a nonlinear model-based adaptive control approach is proposed for a solenoid-valve system. The challenge is that solenoids and butterfly valves have uncertainties in multiple parameters in the nonlinear model; various kinds of physical appearance such as size and stroke, dynamic parameters including inertia, damping, and torque coefficients, and operational parameters especially, pipe diameters and flow velocities. These uncertainties are making the system not only difficult to adjust to the environment, but also further complicated to develop the appropriate control approach for meeting the system objectives. The main contribution of this research is the application of adaptive control theory and Lyapunov-type stability approach to design a controller for a dynamic model of the solenoid-valve system in the presence of those uncertainties. The control objectives such as set-point regulation, parameter compensation, and stability are supposed to be simultaneously accomplished. The error signals are first formulated based on the nonlinear dynamicmodels and then the control input is developed using the Lyapunov stability-type analysis to obtain the error bounded while overcoming the uncertainties. The parameter groups are updated by adaptation laws using a projection algorithm.Numerical simulation results are shown to demonstrate good performance of the proposed nonlinear model based adaptive approach and to compare the performance of the same solenoid-valve system with a non-adaptive method as well.
BibTeX: 
@article{Lee2012j,
  author = {Lee, D. and Nataraj, C. and Naseradinmousavi, P.},
  title = {Nonlinear Dynamic Model-based Adaptive Control of a Solenoid-Valve System},
  journal = {Journal of Control Science and Engineering},
  year = {2012},
  volume = {17},
  number = {11},
  pages = {4336-4345},
  doi = {http://dx.doi.org/10.1155/2012/846458}
}
Naseradinmousavi, P. & Nataraj, C. (2012), "Nonlinear Modeling And Analysis Of Electromagnetic Bearings With Permanent Magnets For Bias", In ASME International Design Engineering Technical Conferences & Computers and Information in Engineering Conference., September, 2012.

[BibTeX]
BibTeX: 
@inproceedings{Naseradinmousavi2012,
  author = {Peiman Naseradinmousavi and C. Nataraj},
  title = {Nonlinear Modeling And Analysis Of Electromagnetic Bearings With Permanent Magnets For Bias},
  booktitle = {ASME International Design Engineering Technical Conferences & Computers and Information in Engineering Conference},
  year = {2012}
}
Naseradinmousavi, P. & Nataraj, C. (2012), "Transient chaos and crisis phenomena in butterfly valves driven by solenoid actuators", Communications in Nonlinear Science and Numerical Simulation. Vol. 17(11), pp. 4336-4345.

[Abstract] [BibTeX] [DOI]
Abstract: Chilled water systems used in the industry and on board ships are critical for safe andreliable operation. It is hence important to understand the fundamental physics of these systems. This paper focuses in particular on a critical part of the automation system, namely, actuators and valves that are used in so-called smart valve systems. The system is strongly nonlinear, and necessitates a nonlinear dynamic analysis to be able to predict all critical phenomena that affect effective operation and efficient design. The derived mathematical model includes electromagnetics, fluid mechanics, and mechanical dynamics. Nondimensionalization has been carried out in order to reduce the large number of parameters to a few critical independent sets to help carry out a broad parametric analysis. The system stability analysis is then carried out with the aid of the tools from nonlinear dynamic analysis. This reveals that the system is unstable in a certain region of the parameter space. The system is also shown to exhibit crisis and transient chaotic responses; this is characterized using Lyapunov exponents and power spectra. Knowledge and avoidance of these dangerous regimes is necessary for successful and safe operation.
BibTeX: 
@article{Naseradinmousavi2012j,
  author = {P. Naseradinmousavi and C. Nataraj},
  title = {Transient chaos and crisis phenomena in butterfly valves driven by solenoid actuators},
  journal = {Communications in Nonlinear Science and Numerical Simulation},
  year = {2012},
  volume = {17},
  number = {11},
  pages = {4336-4345},
  doi = {http://dx.doi.org/10.1016/j.cnsns.2012.01.034}
}
Nataraj, C. (2012), "Nonlinear Analysis of Magnetic Bearings (keynote)", In The International Conference on Nonlinear Dynamics and Complexity. Jinan, Shandong, China, July 23-29, 2012.

[BibTeX]
BibTeX: 
@inproceedings{Nataraj2012,
  author = {C. Nataraj},
  title = {Nonlinear Analysis of Magnetic Bearings (keynote)},
  booktitle = {The International Conference on Nonlinear Dynamics and Complexity},
  year = {2012}
}
Nataraj, C., Jalali, A. & Ghorbanian, P. (2012), "The Cardiovascular System - Physiology, Diagnostics and Clinical Implications", In Application of Computational Intelligence Techniques for Cardiovascular Diagnostics. , pp. 211-241. InTech.

[BibTeX] [DOI]
BibTeX: 
@incollection{Nataraj2012ax,
  author = {C. Nataraj and Ali Jalali and Parham Ghorbanian},
  title = {The Cardiovascular System - Physiology, Diagnostics and Clinical Implications},
  booktitle = {Application of Computational Intelligence Techniques for Cardiovascular Diagnostics},
  publisher = {InTech},
  year = {2012},
  pages = {211-241},
  doi = {http://dx.doi.org/10.5772/38032}
}
Ferrese, F., Dong, Q., Nataraj, C. & Biswas, S. (2011), "Optimal Feedback Control of Power Systems Using Eigenstructure Assignment and Particle Swarm Optimization", Naval Engineers Journal., March, 2011. Vol. 123(1), pp. 67-75.

[Abstract] [BibTeX] [DOI]
Abstract: The U.S. Navy has a continuing interest and investment in basic and applied research in
the area of automation and control. The potential naval applications for this research are
numerous and wide ranging. The need for advances in control and automation systems
exists from missile defense, to shipboard auxiliary systems, to naval aircraft, and virtually
everywhere in between. This research is performed in industry, academia, and in naval
laboratories across the nation. This paper will detail particular research in control theory
being performed in the area of automation and controls in the naval laboratories. A
Particle Swarm Optimization (PSO) algorithm is used to manipulate the state and control
weighting matrices of a Linear Quadratic Regulator (LQR) to achieve an optimal control
for a desired eigenstructure. The algorithm is demonstrated on a non-linear power system
model, and is found to be highly effective in the stabilization of the system output
performance, showing both rapid convergence and a closed loop eigenstructure very close
to the specified eigenstructure.
BibTeX: 
@article{Ferrese2011j,
  author = {Frank Ferrese and Qing Dong and C. Nataraj and Saroj Biswas},
  title = {Optimal Feedback Control of Power Systems Using Eigenstructure Assignment and Particle Swarm Optimization},
  journal = {Naval Engineers Journal},
  year = {2011},
  volume = {123},
  number = {1},
  pages = {67-75},
  doi = {http://dx.doi.org/10.1111/j.1559-3584.2010.00300.x}
}
Jalali, A., Nataraj, C., Butchy, M. & Ghaffari, A. (2011), "Feature Extraction and Abnormality Detection in Autonomic Regulation of Cardiovascular System", In Proceedings of the ASME International Design Engineering Technical Conference (IDETC).

[BibTeX]
BibTeX: 
@inproceedings{Jalali2011,
  author = {A. Jalali and C. Nataraj and Margaret Butchy and A. Ghaffari},
  title = {Feature Extraction and Abnormality Detection in Autonomic Regulation of Cardiovascular System},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference (IDETC)},
  year = {2011}
}
Jalali, A., Nataraj, C., Jones, G.F. & Licht, D.J. (2011), "Computational Modeling of Hypoplastic Left Heart Syndrome (HLHS) in Newborn Babies", In Proceedings of the ASME International Design Engineering Technical Conference (IDETC).

[BibTeX]
BibTeX: 
@inproceedings{Jalali2011a,
  author = {A. Jalali and C. Nataraj and G. F. Jones and D. J. Licht},
  title = {Computational Modeling of Hypoplastic Left Heart Syndrome (HLHS) in Newborn Babies},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference (IDETC)},
  year = {2011}
}
Jalali, A., Ghaffari, A., Ghorbanian, P. & Nataraj, C. (2011), "Identification of Sympathetic and Parasympathetic Nerves Function in Cardiovascular Regulation using ANFIS Approximation", Artificial Intelligence in Medicine., In Journal of Artifical Intelligence in Medicine. Vol. 52(1), pp. 27-32.

[Abstract] [BibTeX] [DOI]
Abstract: In this paper a new nonlinear system identification approach is developed for dynamical quantification of cardiovascular regulation. This approach is specifically focused on the identification of the heart rate (HR) baroreflex mechanism. The principal objective of this paper is to improve the model accuracy in the estimation of HR by proposing a modified nonlinear model.
BibTeX: 
@article{Jalali2011j,
  author = {A. Jalali and A. Ghaffari and P. Ghorbanian and C. Nataraj},
  title = {Identification of Sympathetic and Parasympathetic Nerves Function in Cardiovascular Regulation using ANFIS Approximation},
  booktitle = {Journal of Artifical Intelligence in Medicine},
  journal = {Artificial Intelligence in Medicine},
  year = {2011},
  volume = {52},
  number = {1},
  pages = {27--32},
  doi = {http://dx.doi.org/10.1016/j.artmed.2011.01.002}
}
Kappaganthu, K. & Nataraj, C. (2011), "Modeling and analysis of outer race defects in rolling element bearings", Advances in Vibration Engineering. Vol. 11(4)

[BibTeX]
BibTeX: 
@article{Kappaganthu2010j,
  author = {Karthik Kappaganthu and C. Nataraj},
  title = {Modeling and analysis of outer race defects in rolling element bearings},
  journal = {Advances in Vibration Engineering},
  year = {2011},
  volume = {11},
  number = {4}
}
Kappaganthu, K. & Nataraj, C. (2011), "Mutual Information Based Feature Selection From Data Driven And Model Based Techniques For Fault Detection In Rolling Element Bearings", In Proceedings of the ASME IDETC/CIE.

[BibTeX]
BibTeX: 
@conference{Kappaganthu2011,
  author = {Karthik Kappaganthu and C. Nataraj},
  title = {Mutual Information Based Feature Selection From Data Driven And Model Based Techniques For Fault Detection In Rolling Element Bearings},
  booktitle = {Proceedings of the ASME IDETC/CIE},
  year = {2011}
}
Kappaganthu, K. & Nataraj, C. (2011), "Feature selection for fault detection in rolling element bearings using mutual information", ASME Journal of Vibration and Acoustics., December, 2011. Vol. 133(6)

[Abstract] [BibTeX] [DOI]
Abstract: Rolling element bearings are among the key components in many rotating machineries. It is hence necessary to determine the condition of the bearing with a reasonable degree of confidence. Many techniques have been developed for bearing fault detection. Each of these techniques has its own strengths and weaknesses. In this paper, various features are compared for detecting inner and outer race defects in rolling element bearings. Mutual information between the feature and the defect is used as a quantitative measure of quality. Various time, frequency, and time-frequency domain features are compared and ranked according to their cumulative mutual information content, and an optimal feature set is determined for bearing classification. The performance of this optimal feature set is evaluated using an artificial neural network with one hidden layer. An overall classification accuracy of 97% was obtained over a range of rotating speeds.
BibTeX: 
@article{Kappaganthu2011ej,
  author = {Karthik Kappaganthu and Nataraj, C},
  title = {Feature selection for fault detection in rolling element bearings using mutual information},
  journal = {ASME Journal of Vibration and Acoustics},
  year = {2011},
  volume = {133},
  number = {6},
  doi = {http://dx.doi.org/10.1115/1.4003400}
}
Kappaganthu, K. & Nataraj, C. (2011), "Optimal Biped Design Using a Moving Torso: Theory and Experiments", In Biped Robots. , pp. 35-54. Intech International.

[BibTeX] [DOI]
BibTeX: 
@incollection{Kappaganthu2011gx,
  author = {Karthik Kappaganthu and Nataraj, C.},
  title = {Optimal Biped Design Using a Moving Torso: Theory and Experiments},
  booktitle = {Biped Robots},
  publisher = {Intech International},
  year = {2011},
  pages = {35-54},
  doi = {http://dx.doi.org/10.5772/13791}
}
Kappaganthu, K. & Nataraj, C. (2011), "Nonlinear Modeling and Analysis of a Rolling Element Bearing With a Clearance", Communications in Nonlinear Science and Numerical Simulation., October, 2011. Vol. 16(10), pp. 4134-4145.

[Abstract] [BibTeX] [DOI]
Abstract: Rolling element bearings are the key components in many rotating machinery. For efficient performance of the machine it is necessary to accurately predict the effect of various parameters and operating conditions on the machines behavior. This paper deals with the development of a nonlinear model of the rotor-bearing system on rolling element bearings with clearance. Clearance is an important nonlinearity which can cause bifurcations and chaos as has been shown in this paper. In this paper a detailed model for clearance is developed. In this model the inner race center and the outer race center are not assumed to be collinear when relations for deflections in the rolling element are developed. The model is non-dimensionalized and then analyzed to reveal rich nonlinear phenomena. Further, for better performance of any machine it is necessary to identify and stay out of chaotic regimes of operation. Hence, Lyapunov exponents and Poincar mappings are used to analyze the system and determine the regions of chaotic response.
BibTeX: 
@article{Kappaganthu2011j,
  author = {Karthik Kappaganthu and Nataraj, C},
  title = {Nonlinear Modeling and Analysis of a Rolling Element Bearing With a Clearance},
  journal = {Communications in Nonlinear Science and Numerical Simulation},
  year = {2011},
  volume = {16},
  number = {10},
  pages = {4134-4145},
  doi = {http://dx.doi.org/10.1016/j.cnsns.2011.02.001}
}
Kwuimy, C.K., Litak, G., Borowiec, M. & Nataraj, C. (2011), "On the performance of piezoelectric energy harvesting driven by air fow", In 11th conference on dynamical systems theory and applications. Loodoz, Poland, December 5-8, 2011.

[Abstract] [BibTeX]
Abstract: A wind source for possible energy harvesting is proposed. To increase
the amplitude of vibration we apply a magnetopiezoelastic oscillator possessing
a double well Dung potential. We show the output voltage response of the
system for di erent choice of wind excitations including the combination of
harmonic and noisy components. The energy harvesting appeared to be the
most ecient for the conditions close to the stochastic resonance region where
the potential well was overcame.
BibTeX: 
@inproceedings{Kwuimy2011,
  author = {C.A. Kitio Kwuimy and G. Litak and M. Borowiec and C. Nataraj},
  title = {On the performance of piezoelectric energy harvesting driven by air fow},
  booktitle = {11th conference on dynamical systems theory and applications},
  year = {2011}
}
Kwuimy, C.K. & Nataraj, C. (2011), "Prediction of horseshoes chaos in active magnetic bearings with time-varying stiffness", In Proceedings of ASME 2011 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 2011. Washington, DC, USA, August 29-31, 2011, 2011. Vol. DETC2011-48317

[Abstract] [BibTeX]
Abstract: The paper considers a model of an active magnetic bearing with
time-varying stiffness and investigates the effects of the control
gain parameters on the appearance of horseshoes chaos. The
Melnikov method is used to derive the critical conditions for
chaos and numerical simulations are performed to determine the
basins of attraction. It is shown that the domain of chaotic mo-
tion strongly depends on the gain parameters and that this do-
main increases with the magnetic force and decrease with the
static current. The controller frequency w is found to be a key
parameter and has a critical effect on the enlargement of the
chaotic domain.
BibTeX: 
@inproceedings{Kwuimy2011a,
  author = {C.A. Kitio Kwuimy and C. Nataraj},
  title = {Prediction of horseshoes chaos in active magnetic bearings with time-varying stiffness},
  booktitle = {Proceedings of ASME 2011 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 2011},
  year = {2011},
  volume = {DETC2011-48317}
}
Kwuimy, C.A.K., Nataraj, C. & Litak, G. (2011), "Melnikov's criteria, parametric control of chaos, and stationary chaos occurrence in systems with asymmetric potential subjected to multiscale type excitation", Chaos: An Interdisciplinary Journal of Nonlinear Science (American Institute of Physics). Vol. 21(043113)

[Abstract] [BibTeX] [DOI]
Abstract: We consider the problems of chaos and parametric control in nonlinear systems under an asymmetric potential subjected to a multiscale type excitation. The lower bound line for horseshoes chaos is analyzed using the Melnikovs criterion for a transition to permanent or transient nonperiodic motions, complement by the fractal or regular shape of the basin of attraction. Numerical simulations based on the basins of attraction, bifurcation diagrams, Poincare sections, Lyapunov exponents, and phase portraits are used to show how stationary dissipative chaos occurs in the system. Our attention is focussed on the effects of the asymmetric potential term and the driven frequency. It is shown that the threshold amplitude jccj of the excitation decreases for small values of the driven frequency x and increases for large values of x. This threshold value decreases with the asymmetric parameter a and becomes constant for sufficiently large values of a. cc has its maximum value for asymmetric load in comparison with the symmetric load. Finally, we apply the Melnikov theorem to the controlled system to explore the gain control parameter dependencies
BibTeX: 
@article{Kwuimy2011fj,
  author = {C A. Kitio Kwuimy and C. Nataraj and G. Litak},
  title = {Melnikov's criteria, parametric control of chaos, and stationary chaos occurrence in systems with asymmetric potential subjected to multiscale type excitation},
  journal = {Chaos: An Interdisciplinary Journal of Nonlinear Science (American Institute of Physics)},
  year = {2011},
  volume = {21},
  number = {043113},
  doi = {http://dx.doi.org/10.1063/1.3650699}
}
Lee, D., Burg, T.C., Xu, P. & Nataraj, C. (2011), "Modeling and Coordinated Control of Flying Robotic Arm", In American Control Conference.

[BibTeX]
BibTeX: 
@inproceedings{Lee2011,
  author = {DongBin Lee and Timothy C. Burg and Peng Xu and C. Nataraj},
  title = {Modeling and Coordinated Control of Flying Robotic Arm},
  booktitle = {American Control Conference},
  year = {2011}
}
Lee, D. & Nataraj, C. (2011), "Design and Control of an Autonomous Surface Vehicle Demonstrator", In American Control Conference.

[BibTeX]
BibTeX: 
@inproceedings{Lee2011a,
  author = {DongBin Lee and Nataraj, C},
  title = {Design and Control of an Autonomous Surface Vehicle Demonstrator},
  booktitle = {American Control Conference},
  year = {2011}
}
Lee, D. & Nataraj, C. (2011), "Adaptive Control of a Nonlinear Model-based Solenoid-Valve System with Uncertainties", In Intelligent Ships Symposium IX.

[BibTeX] [URL]
BibTeX: 
@inproceedings{Lee2011b,
  author = {DongBin Lee and C. Nataraj},
  title = {Adaptive Control of a Nonlinear Model-based Solenoid-Valve System with Uncertainties},
  booktitle = {Intelligent Ships Symposium IX},
  year = {2011},
  url = {https://admin.navalengineers.org/SiteCollectionDocuments/2011%20Proceedings%20Documents/ISSIX/Abstracts/1Track1_Nataraj.pdf}
}
Lee, D. & Nataraj, C. (2011), "Adaptive Tracking Control of Linear Time-varying Unmanned Surface Vehicles with Disturbances", In Intelligent Ships Symposium IX.

[BibTeX]
BibTeX: 
@conference{Lee2011c,
  author = {DongBin Lee and C. Nataraj},
  title = {Adaptive Tracking Control of Linear Time-varying Unmanned Surface Vehicles with Disturbances},
  booktitle = {Intelligent Ships Symposium IX},
  year = {2011}
}
Lee, D., Nataraj, C. & Burg, T.C. (2011), "Adaptive Tracking Control of an Underactuated Aerial Vehicle", In American Control Conference.

[BibTeX]
BibTeX: 
@inproceedings{Lee2011d,
  author = {DongBin Lee and C. Nataraj and Timothy C. Burg},
  title = {Adaptive Tracking Control of an Underactuated Aerial Vehicle},
  booktitle = {American Control Conference},
  year = {2011}
}
Lee, D., Nataraj, C. & Burg, T.C. (2011), "Robust Control Of A Surface Vehicle With Disturbances", In Proceedings of the ASME Dynamic Systems and Control Conference.

[BibTeX]
BibTeX: 
@conference{Lee2011e,
  author = {DongBin Lee and C. Nataraj and Timothy C. Burg},
  title = {Robust Control Of A Surface Vehicle With Disturbances},
  booktitle = {Proceedings of the ASME Dynamic Systems and Control Conference},
  year = {2011}
}
Lee, D., Nataraj, C., Burg, T.C. & Dawson, D.M. (2011), "Adaptive Tracking Control of an Underactuated Aerial Vehicle", In American Control Conference.

[BibTeX]
BibTeX: 
@conference{Lee2011f,
  author = {DongBin Lee and C. Nataraj and Timothy C. Burg and Darren M. Dawson},
  title = {Adaptive Tracking Control of an Underactuated Aerial Vehicle},
  booktitle = {American Control Conference},
  year = {2011}
}
Lee, D., Sullivan, R. & Nataraj, C. (2011), "Design and Control of a Surface Vehicle Demonstrator", In 2nd IEEE Workshop on Model-based Engineering for Real-Time Embedded Systems (MoBE-RTES 2011).

[BibTeX]
BibTeX: 
@inproceedings{Lee2011g,
  author = {DongBin Lee and Ralph Sullivan and Nataraj, C},
  title = {Design and Control of a Surface Vehicle Demonstrator},
  booktitle = {2nd IEEE Workshop on Model-based Engineering for Real-Time Embedded Systems (MoBE-RTES 2011)},
  year = {2011}
}
Lee, D., Sullivan, R., Nataraj, C. & Loeb, H. (2011), "Model-based Control Systems For an Autonomous Surface Vehicle", In ASNE Intelligent Ship Symposium IX., May, 2011.

[BibTeX]
BibTeX: 
@inproceedings{Lee2011h,
  author = {D. Lee and R. Sullivan and C. Nataraj and H. Loeb},
  title = {Model-based Control Systems For an Autonomous Surface Vehicle},
  booktitle = {ASNE Intelligent Ship Symposium IX},
  year = {2011}
}
Lee, D., Sullivan, R., Nataraj, C. & Loeb, H. (2011), "Model-based Control Systems For an Autonomous Surface Vehicle", In Intelligent Ships Symposium IX.

[BibTeX]
BibTeX: 
@conference{Lee2011i,
  author = {DongBin Lee and Ralph Sullivan and C. Nataraj and Helen Loeb},
  title = {Model-based Control Systems For an Autonomous Surface Vehicle},
  booktitle = {Intelligent Ships Symposium IX},
  year = {2011}
}
Loeb, H., Holihan, R. & Nataraj, C. (2011), "Design of an Intelligent Collision Avoidance System based on a Scanning Range Finder", In Intelligent Ships Symposium IX.

[BibTeX]
BibTeX: 
@conference{Loeb2011,
  author = {Helen Loeb and Ryan Holihan and C. Nataraj},
  title = {Design of an Intelligent Collision Avoidance System based on a Scanning Range Finder},
  booktitle = {Intelligent Ships Symposium IX},
  year = {2011}
}
Naseradinmousavi, P. & Nataraj, C. (2011), "A chaotic blue sky catastrophe of butterfly valves driven by solenoid actuators", In Proceedings of the ASME 2011 International Mechanical Engineering Congress & Exposition. (IMECE2011/62608)

[BibTeX] [URL]
BibTeX: 
@inproceedings{Naseradinmousavi2011,
  author = {Peiman Naseradinmousavi and C. Nataraj},
  title = {A chaotic blue sky catastrophe of butterfly valves driven by solenoid actuators},
  booktitle = {Proceedings of the ASME 2011 International Mechanical Engineering Congress & Exposition},
  year = {2011},
  number = {IMECE2011/62608},
  url = {http://www.asmeconferences.org/Congress2011/TechnicalProgramOverview.cfm#696}
}
Naseradinmousavi, P. & Nataraj, C. (2011), "Nonlinear mathematical modeling of butterfly valves driven by solenoid actuators", Applied Mathematical Modelling. Vol. 35(5), pp. 2324-2335.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: This paper describes high fidelity modeling and analysis of the opening and closing processes of butterfly valves driven by solenoid actuators using multiphysics models. The equations are derived and solved numerically. The variable of primary interest is the butterfly valve rotation angle. The coupled model for electromagnetics, fluid dynamics and mechanical dynamics are derived by making some simplifying assumptions. It is shown that the behavior of hydrodynamic torque plays an important role in the closing and opening processes. A discussion is presented with an explanation of the results and a comparison has been made for both the processes.
BibTeX: 
@article{Naseradinmousavi2011cj,
  author = {Peiman Naseradinmousavi and C. Nataraj},
  title = {Nonlinear mathematical modeling of butterfly valves driven by solenoid actuators},
  journal = {Applied Mathematical Modelling},
  year = {2011},
  volume = {35},
  number = {5},
  pages = {2324-2335},
  url = {http://www.sciencedirect.com/science/article/pii/S0307904X10004464},
  doi = {http://dx.doi.org/10.1016/j.apm.2010.11.036}
}
Nataraj, C. & Kappaganthu, K. (2011), "Vibration-based diagnostics of rolling element bearings: state of the art and challenges", In 13th World Congress in Mechanism and Machine Science, Guanajuato, Mexico., June 19-25, 2011.

[Abstract] [BibTeX]
Abstract: Fault identification and estimation is an important and necessary step in Condition Based Maintenance. In general, there are two prevalent methods that are used for this purpose, data driven techniques and model based techniques. Data driven techniques use data collected from experiments, learn about the system and then use this knowledge to infer the system's current state of health; these tend to be more in the applied arena and are favored for implementation in the industry. Model based techniques use models to derive the knowledge that can be used to determine the machine's condition; these tend to be more fundamental and are pursued often as a research topic to gain insights into the physics underlying the observed phenomena. Each of these methods has its own strengths and limitations. This paper reviews the state of the art in this area focusing on defects in rolling element bearings, and identifies the challenges to be tackled. Finally, a new paradigm is proposed using an illustrative example.
BibTeX: 
@inproceedings{Nataraj2011,
  author = {C. Nataraj and Karthik Kappaganthu},
  title = {Vibration-based diagnostics of rolling element bearings: state of the art and challenges},
  booktitle = {13th World Congress in Mechanism and Machine Science, Guanajuato, Mexico},
  year = {2011}
}
O Brien, J.C., Stein, R.A., Clayton, G.M., Wemhoff, A.P. & Nataraj, C. (2011), "Exchange Sea Perch/Mate Science Learning Modules", In American Society for Engineering Education Annual Conference.

[BibTeX]
BibTeX: 
@conference{O Brien2011,
  author = {James C. O Brien and Rebecca A Stein and Garrett M. Clayton and Aaron P. Wemhoff and C. Nataraj},
  title = {Exchange Sea Perch/Mate Science Learning Modules},
  booktitle = {American Society for Engineering Education Annual Conference},
  year = {2011}
}
Ghorbanian, P., Ghaffari, A., Jalali, A. & Nataraj, C. (2010), "Heart Arrhythmia detection Using Continuous Wavelet Transform and Principal Component Analysis with Neural Network Classifier", In Computing in Cardiology 2010. Vol. 37, pp. 669-672.

[BibTeX]
BibTeX: 
@inproceedings{Ghorbanian2010,
  author = {P. Ghorbanian and A. Ghaffari and A. Jalali and C. Nataraj},
  title = {Heart Arrhythmia detection Using Continuous Wavelet Transform and Principal Component Analysis with Neural Network Classifier},
  booktitle = {Computing in Cardiology 2010},
  year = {2010},
  volume = {37},
  pages = {669--672}
}
Jalali, A., Ghaffari, A., Ghorbanian, P., Jalali, F. & Nataraj, C. (2010), "Quantitative Analysis of Heart Rate Baroreflex in Healthy Subjects Using Adaptive Neuro Fuzzy Inference System Approximation", In Computing in Cardiology 2010. Vol. 37, pp. 951-954.

[BibTeX]
BibTeX: 
@inproceedings{Jalali2010,
  author = {Ali Jalali and Ali Ghaffari and Parham Ghorbanian and Fatemeh Jalali and C Nataraj},
  title = {Quantitative Analysis of Heart Rate Baroreflex in Healthy Subjects Using Adaptive Neuro Fuzzy Inference System Approximation},
  booktitle = {Computing in Cardiology 2010},
  year = {2010},
  volume = {37},
  pages = {951--954}
}
Kappaganthu, K. & Nataraj, C. (2010), "Nonlinear modeling of a rigid rotor supported on rolling element bearings with localized defects", In Proceedings of the ASME IDETC/CIE 2009.

[BibTeX]
BibTeX: 
@conference{Kappaganthu2010,
  author = {Karthik Kappaganthu and C. Nataraj},
  title = {Nonlinear modeling of a rigid rotor supported on rolling element bearings with localized defects},
  booktitle = {Proceedings of the ASME IDETC/CIE 2009},
  year = {2010}
}
Kappaganthu, K. & Nataraj, C. (2010), "Feature Selection for Bearing Fault Detection Based on Mutual Information", In Emerging Trends in Rotor Dynamics. Springer Verlag.

[BibTeX]
BibTeX: 
@incollection{Kappaganthu2010fx,
  author = {Karthik Kappaganthu and Nataraj, C},
  title = {Feature Selection for Bearing Fault Detection Based on Mutual Information},
  booktitle = {Emerging Trends in Rotor Dynamics},
  publisher = {Springer Verlag},
  year = {2010}
}
Lee, D., Nataraj, C., Burg, T.C. & Dawson, D.M. (2010), "Robust and Adaptive Tracking Control of a Surface Vessel", In American Control Conference.

[BibTeX]
BibTeX: 
@inproceedings{Lee2010,
  author = {DongBin Lee and C. Nataraj and Timothy C. Burg and Darren M. Dawson},
  title = {Robust and Adaptive Tracking Control of a Surface Vessel},
  booktitle = {American Control Conference},
  year = {2010}
}
Lee, D., Nataraj, C. & Naseradinmousavi, P. (2010), "Nonlinear Model-based Adaptive Control Of A Solenoid-Valve System", In Proceedings of the ASME Dynamic Systems and Control Conference.

[BibTeX] [URL]
BibTeX: 
@inproceedings{Lee2010a,
  author = {Lee, D. and Nataraj, C. and Naseradinmousavi, P.},
  title = {Nonlinear Model-based Adaptive Control Of A Solenoid-Valve System},
  booktitle = {Proceedings of the ASME Dynamic Systems and Control Conference},
  year = {2010},
  url = {https://asme-dscd.papercept.net/conferences/scripts/abstract.pl?ConfID=4&Number=4283}
}
Nataraj, C. & Lee, D. (2010), "Model-based Adaptive Control of A Solenoid-Valve System", In ASME Intl Mechanical Engineering Congress and Exposition (IMECE-39371).

[BibTeX]
BibTeX: 
@inproceedings{Nataraj2010,
  author = {Nataraj, C. and Lee, D.},
  title = {Model-based Adaptive Control of A Solenoid-Valve System},
  booktitle = {ASME Intl Mechanical Engineering Congress and Exposition (IMECE-39371)},
  year = {2010}
}
Nataraj, C., Reddy, S., Woods, M. & Nataraj, C. (2010), "Swarm robotics: a research project with high school students as active participants", In ASEE Annual Conference. (AC 2010-1655)

[BibTeX]
BibTeX: 
@inproceedings{Nataraj2010a,
  author = {Chiraag Nataraj and Sanjeev Reddy and Mark Woods and C. Nataraj},
  title = {Swarm robotics: a research project with high school students as active participants},
  booktitle = {ASEE Annual Conference},
  year = {2010},
  number = {AC 2010-1655}
}
Nataraj, C. & Thimmaraya, R. (2010), "Tracking control of unmanned surface vehicles with Abkowitz steering model", In ASME Dynamic Systems & Control Conference.

[BibTeX]
BibTeX: 
@inproceedings{Nataraj2010b,
  author = {C. Nataraj and Ramesh Thimmaraya},
  title = {Tracking control of unmanned surface vehicles with Abkowitz steering model},
  booktitle = {ASME Dynamic Systems & Control Conference},
  year = {2010}
}
Nataraj, C. & Kappaganthu, K. (2010), "Nonlinear Response in a Rotor System with a Coulomb Spline", In Dynamical Systems: Discontinuity, Stochasticity and Time-Delay. Springer Verlag.

[BibTeX]
BibTeX: 
@incollection{Nataraj2010bx,
  author = {Nataraj, C and Karthik Kappaganthu},
  title = {Nonlinear Response in a Rotor System with a Coulomb Spline},
  booktitle = {Dynamical Systems: Discontinuity, Stochasticity and Time-Delay},
  publisher = {Springer Verlag},
  year = {2010}
}
Thimmaraya, R., Nataraj, C. & Lee, D. (2010), "Linear Time-Varying Tracking Control With Application to Unmanned Aerial Vehicles", In American Control Conference.

[BibTeX]
BibTeX: 
@inproceedings{Thimmaraya2010,
  author = {Ramesh Thimmaraya and C. Nataraj and DongBin Lee},
  title = {Linear Time-Varying Tracking Control With Application to Unmanned Aerial Vehicles},
  booktitle = {American Control Conference},
  year = {2010}
}
Feresse, F., Kappaganthu, K. & Nataraj, C. (2009), "Eigenstructure assignment using a linear quadratic regulator and particle swarm optimization", In 7th IEEE International Conference on Control & Automation, IEEE.

[BibTeX]
BibTeX: 
@conference{Feresse2009,
  author = {F. Feresse and Karthik Kappaganthu and C. Nataraj},
  title = {Eigenstructure assignment using a linear quadratic regulator and particle swarm optimization},
  booktitle = {7th IEEE International Conference on Control & Automation, IEEE},
  year = {2009}
}
Harsha, S.P. & Nataraj, C. (2009), "Intermittent chaotic dynamics of rail axle supported by roller bearings", In Proceedings of the International Design Engineering Technical Conferences (IDETC2009)., August 30 - September 2, 2009. (DETC2009-87183)

[BibTeX]
BibTeX: 
@inproceedings{Harsha2009,
  author = {S. P. Harsha and C. Nataraj},
  title = {Intermittent chaotic dynamics of rail axle supported by roller bearings},
  booktitle = {Proceedings of the International Design Engineering Technical Conferences (IDETC2009)},
  year = {2009},
  number = {DETC2009-87183}
}
Kappaganthu, K., Nataraj, C. & Samanta, B. (2009), "Fault parameter identification for model based prognostics of a ball bearing with an outer race defect", In Proceedings of IDETC/CIE 2009., August 30 - September 2, 2009. (DETC2009-87599)

[BibTeX]
BibTeX: 
@inproceedings{Kappaganthu2009,
  author = {Karthik Kappaganthu and C. Nataraj and B. Samanta},
  title = {Fault parameter identification for model based prognostics of a ball bearing with an outer race defect},
  booktitle = {Proceedings of IDETC/CIE 2009},
  year = {2009},
  number = {DETC2009-87599}
}
Kappaganthu, K., Nataraj, C. & Samanta, B. (2009), "Optimal Feature Set for Detection of Inner Race Defect in Rolling Element Bearings", In Annual Conference of the Prognostics and Health Management Society.

[BibTeX]
BibTeX: 
@conference{Kappaganthu2009a,
  author = {Karthik Kappaganthu and C. Nataraj and B. Samanta},
  title = {Optimal Feature Set for Detection of Inner Race Defect in Rolling Element Bearings},
  booktitle = {Annual Conference of the Prognostics and Health Management Society},
  year = {2009}
}
Kappaganthu, K., Nataraj, C. & Samanta, B. (2009), "Model Based Bearing Fault Detection Using Support Vector Machines", In Annual Conference of the Prognostics and Health Management Society.

[BibTeX]
BibTeX: 
@conference{Kappaganthu2009b,
  author = {Karthik Kappaganthu and C. Nataraj and B. Samanta},
  title = {Model Based Bearing Fault Detection Using Support Vector Machines},
  booktitle = {Annual Conference of the Prognostics and Health Management Society},
  year = {2009}
}
Kappaganthu, K. & Nataraj, C. (2009), "A Biped with a Moving Torso", International Journal of Humanoid Robotics., December, 2009. Vol. 6(4), pp. 657-674.

[Abstract] [BibTeX] [DOI]
Abstract: The moving torso plays an important role in the dynamics of bipeds like human beings, the exploitation of which is the essential focus of this paper. A design is presented where the torso is actuated to make the biped walk with the required step-length while allowing the legs to move passively. A periodic response excitation is achieved and the motion of the torso is optimized with respect to the external energy input. A working model of the biped is designed and built in which only the torso is actuated and the legs are passive. This laboratory model is used to test and validate the analytical solutions.
BibTeX: 
@article{Kappaganthu2009j,
  author = {Karthik Kappaganthu and C. Nataraj},
  title = {A Biped with a Moving Torso},
  journal = {International Journal of Humanoid Robotics},
  year = {2009},
  volume = {6},
  number = {4},
  pages = {657-674},
  doi = {http://dx.doi.org/10.1142/S0219843609001887}
}
Naseradinmousavi, P. & Nataraj, C. (2009), "Nonlinear Analysis of Solenoid Actuators and Butterfly Valve Systems", In Intelligent Ships Symposium VIII.

[BibTeX]
BibTeX: 
@inproceedings{Naseradinmousavi2009,
  author = {Peiman Naseradinmousavi and C. Nataraj},
  title = {Nonlinear Analysis of Solenoid Actuators and Butterfly Valve Systems},
  booktitle = {Intelligent Ships Symposium VIII},
  year = {2009}
}
Nataraj, C., Bolla, S. & Samanta, B. (2009), "Analysis & Design Of An Adaptive Autopilot: Theory & Experiments", In International Ship Symposium 7., May, 2009.

[BibTeX]
BibTeX: 
@inproceedings{Nataraj2009,
  author = {C. Nataraj and Sreekanth Bolla and B. Samanta},
  title = {Analysis & Design Of An Adaptive Autopilot: Theory & Experiments},
  booktitle = {International Ship Symposium 7},
  year = {2009}
}
Nataraj, C. & Mousavi, P.N. (2009), "Nonlinear analysis of solenoid actuators and butterfly valve systems", In International Ship Control Systems Symposium (SCSS 2009). Ottawa, Canada, September, 2009.

[BibTeX]
BibTeX: 
@inproceedings{Nataraj2009a,
  author = {C. Nataraj and Mousavi, Peiman Naseradin},
  title = {Nonlinear analysis of solenoid actuators and butterfly valve systems},
  booktitle = {International Ship Control Systems Symposium (SCSS 2009)},
  year = {2009}
}
Nataraj, C. (2009), "Accurate Analytical Determination Of Electromagnetic Bearing Coefficients", In Emerging Trends in Rotor Dynamics. Springer Verlag.

[BibTeX]
BibTeX: 
@incollection{Nataraj2009ax,
  author = {C. Nataraj},
  title = {Accurate Analytical Determination Of Electromagnetic Bearing Coefficients},
  booktitle = {Emerging Trends in Rotor Dynamics},
  publisher = {Springer Verlag},
  year = {2009},
  note = {Was also the subject of a keynote speech at IUTAM Conference, March 2009.}
}
Nataraj, C. & Ehrich, F. (2009), "Nonlinear Vibration", In Harris' Shock and Vibration Handbook. McGraw Hill.

[BibTeX]
BibTeX: 
@incollection{Nataraj2009x,
  author = {C. Nataraj and F. Ehrich},
  title = {Nonlinear Vibration},
  booktitle = {Harris' Shock and Vibration Handbook},
  publisher = {McGraw Hill},
  year = {2009},
  edition = {Sixth},
  note = {Standard international handbook on vibrations.}
}
Nersesov, S., Nataraj, C. & Avis, J. (2009), "Design of finite-time stabilizing controllers for nonlinear dynamical systems", International Journal of Robust and Nonlinear Control. UK Vol. 19(8), pp. 900-918.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Finite-time stability involves dynamical systems whose trajectories converge to an equilibrium state in finite time. Since finite-time convergence implies nonuniqueness of system solutions in reverse time, such systems possess non-Lipschitzian dynamics. Sufficient conditions for finite-time stability have been developed in the literature using Holder continuous Lyapunov functions. In this paper, we extend the finite-time stability theory to revisit time-invariant dynamical systems and to address time-varying dynamical systems. Specifically, we develop a Lyapunov-based stability and control design framework for finite-time stability as well as finite-time tracking for time-varying nonlinear dynamical systems. Furthermore, we use the vector Lyapunov function approach to study finite-time stabilization of compact sets for large-scale dynamical systems. Copyright © 2008 John Wiley & Sons, Ltd.
BibTeX: 
@article{Nersesov2009j,
  author = {Nersesov, S.G. and Nataraj, C. and Avis, J.M.},
  title = {Design of finite-time stabilizing controllers for nonlinear dynamical systems},
  journal = {International Journal of Robust and Nonlinear Control},
  year = {2009},
  volume = {19},
  number = {8},
  pages = {900-918},
  url = {http://dx.doi.org/10.1002/rnc.1359},
  doi = {http://dx.doi.org/10.1002/rnc.1359}
}
Samanta, B. & Nataraj, C. (2009), "Intrinsic mode decompostion of physiological signals for feature extraction", In Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007. San Diego, CA, August 30 - September 2, 2009. (DETC2009-86806)

[BibTeX]
BibTeX: 
@inproceedings{Samanta2009,
  author = {B. Samanta and C. Nataraj},
  title = {Intrinsic mode decompostion of physiological signals for feature extraction},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007},
  year = {2009},
  number = {DETC2009-86806}
}
Samanta, B. & Nataraj, C. (2009), "Health Indices Based on Morphology and Complexity Measures of Vibration Signals for Machine Condition Monitoring and Prognostics", In Annual Conference of the Prognostics and Health Management Society., October, 2009.

[BibTeX]
BibTeX: 
@inproceedings{Samanta2009a,
  author = {B. Samanta and C. Nataraj},
  title = {Health Indices Based on Morphology and Complexity Measures of Vibration Signals for Machine Condition Monitoring and Prognostics},
  booktitle = {Annual Conference of the Prognostics and Health Management Society},
  year = {2009}
}
Samanta, B., Bird, G., Kuijpers, M., Zimmerman, R., Jarvik, G., Wernovsky, G., Clancy, R., Licht, D., Gaynor, J. & Nataraj, C. (2009), "Prediction of periventricular leukomalacia. Part I. Selection of hemodynamic features using logistic regression and decision tree algorithms", Artificial Intelligence in Medicine. Netherlands Vol. 46(3), pp. 201-215.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: Objective: Periventricular leukomalacia (PVL) is part of a spectrum of cerebral white matter injury which is associated with adverse neurodevelopmental outcome in preterm infants. While PVL is common in neonates with cardiac disease, both before and after surgery, it is less common in older infants with cardiac disease. Pre-, intra-, and postoperative risk factors for the occurrence of PVL are poorly understood. The main objective of the present work is to identify potential hemodynamic risk factors for PVL occurrence in neonates with complex heart disease using logistic regression analysis and decision tree algorithms. Methods: The postoperative hemodynamic and arterial blood gas data (monitoring variables) collected in the cardiac intensive care unit of Children's Hospital of Philadelphia were used for predicting the occurrence of PVL. Three categories of datasets for 103 infants and neonates were used-(1) original data without any preprocessing, (2) partial data keeping the admission, the maximum and the minimum values of the monitoring variables, and (3) extracted dataset of statistical features. The datasets were used as inputs for forward stepwise logistic regression to select the most significant variables as predictors. The selected features were then used as inputs to the decision tree induction algorithm for generating easily inter- pretable rules for prediction of PVL. Results: Three sets of data were analyzed in SPSS for identifying statistically significant predictors (p < 0.05) of PVL through stepwise logistic regression and their correlations. The classification success of the Case 3 dataset of extracted statistical features was best with sensitivity (SN), specificity (SP) and accuracy (AC) of 87, 88 and 87%, respectively. The identified features, when used with decision tree algorithms, gave SN, SP and AC of 90, 97 and 94% in training and 73, 58 and 65% in test. The identified variables in Case 3 dataset mainly included blood pressure, both systolic and diastolic, partial pressures pO2 and pCO2, and their statistical features like average, variance, skewness (a measure of asymmetry) and kurtosis (a measure of abrupt changes). Rules for prediction of PVL were generated automatically through the decision tree algorithms. Conclusions: The proposed approach combines the advantages of statistical approach (regression analysis) and data mining techniques (decision tree) for generation of easily interpretable rules for PVL prediction. The present work extends an earlier research [Galli KK, Zimmerman RA, Jarvik GP, Wernovsky G, Kuijpers M, Clancy RR, et al. Periventricular leukomalacia is common after cardiac surgery. J Thorac Car- diovasc Surg 2004;127:692-704] in the form of expanding the feature set, identifying additional prognostic factors (namely pCO2) emphasizing the temporal variations in addition to upper or lower values, and generating decision rules. The Case 3 dataset was further investigated in Part II for feature selection through computational intelligence.[All rights reserved Elsevier].
BibTeX: 
@article{Samanta2009aj,
  author = {Samanta, B. and Bird, G.L. and Kuijpers, M. and Zimmerman, R.A. and Jarvik, G.P. and Wernovsky, G. and Clancy, R.R. and Licht, D.J. and Gaynor, J.W. and Nataraj, C.},
  title = {Prediction of periventricular leukomalacia. Part I. Selection of hemodynamic features using logistic regression and decision tree algorithms},
  journal = {Artificial Intelligence in Medicine},
  year = {2009},
  volume = {46},
  number = {3},
  pages = {201-215},
  url = {http://dx.doi.org/10.1016/j.artmed.2008.12.005},
  doi = {http://dx.doi.org/10.1016/j.artmed.2008.12.005}
}
Samanta, B. & Nataraj, C. (2009), "Particle swarm optimization for chaotic system parameter estimation", In 2009 IEEE Swarm Intelligence Symposium., March 30 - April 2, 2009.

[BibTeX]
BibTeX: 
@inproceedings{Samanta2009b,
  author = {B. Samanta and C. Nataraj},
  title = {Particle swarm optimization for chaotic system parameter estimation},
  booktitle = {2009 IEEE Swarm Intelligence Symposium},
  year = {2009}
}
Samanta, B., Bird, G., Kuijpers, M., Zimmerman, R., Jarvik, G., Wernovsky, G., Clancy, R., Licht, D., Gaynor, J. & Nataraj, C. (2009), "Prediction of periventricular leukomalacia. Part II. Selection of hemodynamic features using computational intelligence", Artificial Intelligence in Medicine. Netherlands Vol. 46(3), pp. 217-231.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: For pt. I see ibid.,p. 201-15 (2009). Objective: The objective of Part II is to analyze the dataset of extracted hemodynamic features (Case 3 of Part I) through computational intelligence (CI) techniques for identification of potential prognostic factors for periventricular leukomalacia (PVL) occurrence in neonates with congenital heart disease. Methods: The extracted features (Case 3 dataset of Part I) were used as inputs to CI based classifiers, namely, multi-layer perceptron (MLP) and probabilistic neural network (PNN) in combination with genetic algorithms (GA) for selection of the most suitable features predicting the occurrence of PVL. The selected features were next used as inputs to a decision tree (DT) algorithm for generating easily interpretable rules of PVL prediction. Results: Prediction performance for two CI based classifiers, MLP and PNN coupled with GA are presented for different number of selected features. The best prediction performances were achieved with 6 and 7 selected features. The prediction success was 100% in training and the best ranges of sensitivity (SN), specificity (SP) and accuracy (AC) in test were 60-73%, 74-84% and 71-74%, respectively. The identified features when used with the DT algorithm gave best SN, SP and AC in the ranges of 87-90% in training and 80-87%, 74-79% and 79-82% in test. Among the variables selected in CI, systolic and diastolic blood pressures, and pCO2 figured prominently similar to Part I. Decision tree based rules for prediction of PVL occurrence were obtained using the CI selected features. Conclusions: The proposed approach combines the generalization capability of CI based feature selection approach and generation of easily interpretable classification rules of the decision tree. The combination of CI techniques with DT gave substantially better test prediction performance than using CI and DT separately. [All rights reserved Elsevier].
BibTeX: 
@article{Samanta2009bj,
  author = {Samanta, B. and Bird, G.L. and Kuijpers, M. and Zimmerman, R.A. and Jarvik, G.P. and Wernovsky, G. and Clancy, R.R. and Licht, D.J. and Gaynor, J.W. and Nataraj, C.},
  title = {Prediction of periventricular leukomalacia. Part II. Selection of hemodynamic features using computational intelligence},
  journal = {Artificial Intelligence in Medicine},
  year = {2009},
  volume = {46},
  number = {3},
  pages = {217-231},
  url = {http://dx.doi.org/10.1016/j.artmed.2008.12.004},
  doi = {http://dx.doi.org/10.1016/j.artmed.2008.12.004}
}
Samanta, B. & Nataraj, C. (2009), "Estimation Of States And Parameters In Chaotic Systems Using Particle Swarm Optimization", In Proceedings of the ASME IDETC/CIE 2009.

[BibTeX]
BibTeX: 
@conference{Samanta2009c,
  author = {B. Samanta and C. Nataraj},
  title = {Estimation Of States And Parameters In Chaotic Systems Using Particle Swarm Optimization},
  booktitle = {Proceedings of the ASME IDETC/CIE 2009},
  year = {2009}
}
Samanta, B. & Nataraj, C. (2009), "Use of Particle swarm optimization for machinery fault detection", Engineering Applications of Artificial Intelligence. Vol. 22(2), pp. 308-316.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: A study is presented on the application of particle swarm optimization (PSO) combined with other computational intelligence (CI) techniques for bearing fault detection in machines. The performance of two CI based classifiers, namely, artificial neural networks (ANNs) and support vector machines (SVMs) are compared. The time domain vibration signals of a rotating machine with normal and defective bearings are processed for feature extraction. The extracted features from original and preprocessed signals are used as inputs to the classifiers for detection of machine condition. The classifier parameters, e.g., the number of nodes in the hidden layer for ANNs and the kernel parameters for SVMs are selected along with input features using PSO algorithms. The classifiers are trained with a subset of the experimental data for known machine conditions and are tested using the remaining set of data. The procedure is illustrated using the experimental vibration data of a rotating machine. The roles of the number of features, PSO parameters and CI classifiers on the detection success are investigated. Results are compared with other techniques such as genetic algorithm (GA) and principal component analysis (PCA). The PSO based approach gave a test classification success rate of 98.6 100% which were comparable with GA and much better than with PCA. The results show the effectiveness of the selected features and the classifiers in the detection of the machine condition.
BibTeX: 
@article{Samanta2009cj,
  author = {Samanta, B. and Nataraj, C},
  title = {Use of Particle swarm optimization for machinery fault detection},
  journal = {Engineering Applications of Artificial Intelligence},
  year = {2009},
  volume = {22},
  number = {2},
  pages = {308-316},
  url = {http://dx.doi.org/10.1016/j.engappai.2008.07.006},
  doi = {http://dx.doi.org/10.1016/j.engappai.2008.07.006}
}
Samanta, B., Nataraj, C., Reddy, S., Woods, M. & Nataraj, C. (2009), "Swarm robotics: research experience for high school students", In ASEE Midatlantic Conference., October, 2009.

[BibTeX]
BibTeX: 
@inproceedings{Samanta2009d,
  author = {B. Samanta and Chiraag Nataraj and Sanjeev Reddy and Mark Woods and C. Nataraj},
  title = {Swarm robotics: research experience for high school students},
  booktitle = {ASEE Midatlantic Conference},
  year = {2009}
}
Samanta, B. & Nataraj, C. (2009), "Prognostics of machine condition using energy based monitoring index and computational intelligence", Journal of Computing and Information Science in Engineering., December, 2009. Vol. 9

[Abstract] [BibTeX] [DOI]
Abstract: A study is presented on applications of computational intelligence (CI) techniques for monitoring and prognostics of machinery conditions. The machine condition is assessed through an energybased feature, termed as "energy index, "extracted from the vibration signals. The progression of the "monitoring index" is predicted using the CI techniques, namely, recursive neural network (RNN), adaptive neurofuzzy inference system (ANFIS), and support vector regression (SVR). The proposed procedures have been evaluated through benchmark data sets for one-step-ahead prediction. The prognostic effectiveness of the techniques has been illustrated through vibration data set of a helicopter drivetrain system gearbox. The prediction performance of SVR was better than RNN and ANFIS. The improved performance of SVR can be attributed to its inherently better generalization capability. The training time of SVR was substantially higher than RNN and ANFIS. The results are helpful in understanding the relationship of machine conditions, the corresponding indicating feature, the level of damage or degradation, and their progression.
BibTeX: 
@article{Samanta2009jj,
  author = {Samanta, B. and Nataraj, C.},
  title = {Prognostics of machine condition using energy based monitoring index and computational intelligence},
  journal = {Journal of Computing and Information Science in Engineering},
  year = {2009},
  volume = {9},
  doi = {http://dx.doi.org/10.1115/1.3249574}
}
Samanta, B. & Nataraj, C. (2009), "Application of particle swarm optimization and proximal support vector machines for fault detection", Swarm Intelligence. Vol. 3(4), pp. 303-325.

[Abstract] [BibTeX] [DOI]
Abstract: This paper presents a novel application of particle swarm optimization (PSO) in combination with another computational intelligence (CI) technique, namely, proximal support vector machine (PSVM) for machinery fault detection. Both real-valued and binary PSO algorithms have been considered along with linear and nonlinear versions of PSVM. The time domain vibration signals of a rotating machine with normal and defective bearings are processed for feature extraction. The features extracted from original and preprocessed signals are used as inputs to the classifiers (PSVM) for detection of machine condition. Input features are selected using a PSO algorithm. The classifiers are trained with a subset of experimental data for known machine conditions and are tested using the remaining data. The procedure is illustrated using the experimental vibration data of a rotating machine. The influences of the number of features, PSO algorithms and type of classifiers (linear or nonlinear PSVM) on the detection success are investigated. Results are compared with a genetic algorithm (GA) and principal component analysis (PCA). The PSO based approach gave test classification success above 90% which were comparable with the GA and much better than PCA. The results show the effectiveness of the selected features and classifiers in detection of machine condition.
BibTeX: 
@article{Samanta2009oj,
  author = {B. Samanta and C. Nataraj},
  title = {Application of particle swarm optimization and proximal support vector machines for fault detection},
  journal = {Swarm Intelligence},
  year = {2009},
  volume = {3},
  number = {4},
  pages = {303-325},
  doi = {http://dx.doi.org/10.1007/s11721-009-0028-6}
}
Samanta, B. & Nataraj, C. (2009), "Morphological signal processing and computational intelligence for engineering system prognostics", Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering. Vol. 223(8), pp. 1095-1109.

[Abstract] [BibTeX] [DOI]
Abstract: A computational intelligence (CI)-based approach is presented for prognostics of machine conditions using morphological signal processing (MSP). The machine vibration signals are processed using MSP to extract a novel entropy-based health index (HI) characterizing the signal shape-size complexity for system prognostics. The progression of HI is predicted using CI techniques, namely, recursive neural network (RNN), adaptive neuro-fuzzy inference system (ANFIS), and support vector regression (SVR). Both single- and multi-step ahead predictions were evaluated through benchmark datasets of non-linear, non-stationary, and chaotic time series solutions of Mackey-Glass and Lorenz equations. The prognostic effectiveness of the CI techniques was illustrated using a vibration dataset of a helicopter drive-train system gearbox. For each CI predictor, both training datasets gave almost similar prediction performance. In training, the performance of ANFIS was the best, followed by SVR and RNN. In test, the best performance was obtained with SVR for both single- and multi-step ahead predictions. The results are helpful in understanding the relationship between the system conditions, the corresponding indicating feature, the level of degradation, and their progression.
BibTeX: 
@article{Samanta2009qj,
  author = {B. Samanta and C. Nataraj},
  title = {Morphological signal processing and computational intelligence for engineering system prognostics},
  journal = {Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering},
  year = {2009},
  volume = {223},
  number = {8},
  pages = {1095-1109},
  doi = {http://dx.doi.org/10.1243/09596518JSCE722}
}
Fahimi, F., Rineesh, S.V.S. & Nataraj, C. (2008), "Formation controllers for underactuated surface vessels and zero dynamics stability", Control and Intelligent Systems. Calgary, AB, T3E 7J9, Canada Vol. 36(3), pp. 277-287.

[Abstract] [BibTeX] [DOI]
Abstract: Nonlinear feedback control laws for controlling multiple robotic vessels in arbitrary formations are proposed. The presented leader-follower formation control approach uses only the inertial information obtained from the immediate neighbours of each vehicle via communication for control calculations. A three-degree-of-freedom (3DOF) surface vessel dynamic model and the method of Lyapunov has been used to derive the nonlinear control laws that stabilize the relative distance and orientation of neighboring vessels. It is shown that the internal dynamics of the 3DOF vessel as an underactuated system is also stable. The performance of these control laws is demonstrated in the presence of sea disturbances by computer simulations using a 6DOF dynamic model of the surface vessel. These controllers can be utilized to control an arbitrary number of robotic vessels moving in very general formations.
BibTeX: 
@article{Fahimi2008aj,
  author = {Fahimi, Fahimi and Rineesh, S. V. S. and Nataraj, C.},
  title = {Formation controllers for underactuated surface vessels and zero dynamics stability},
  journal = {Control and Intelligent Systems},
  year = {2008},
  volume = {36},
  number = {3},
  pages = {277-287},
  doi = {http://dx.doi.org/10.2316/Journal.201.2008.3.201-1909}
}
Fahimi, F., Nataraj, C. & Ashrafiuon, H. (2008), "Real-time obstacle avoidance for multiple mobile robots", Robotica., In Press, 2008. Vol. 27, pp. 189-198.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: An efficient, simple, and practical real time path planning method for multiple mobile robots in dynamic environments is introduced. Harmonic potential functions are utilized along with the panel method known in fluid mechanics. First, a complement to the traditional panel method is introduced to generate a more effective harmonic potential field for obstacle avoidance in dynamically changing environments. Second, a group of mobile robots working in an environment containing stationary and moving obstacles is considered. Each robot is assigned to move from its current position to a goal position. The group is not forced to maintain a formation during the motion. Every robot considers the other robots of the group as moving obstacles and hence the physical dimensions of the robots are also taken into account. The path of each robot is planned based on the changing position of the other robots and the position of stationary and moving obstacles. Finally, the effectiveness of the scheme is shown by modeling an arbitrary number of mobile robots and the theory is validated by several computer simulations and hardware experiments.
BibTeX: 
@article{Fahimi2008j,
  author = {Farbod Fahimi and C. Nataraj and Hashem Ashrafiuon},
  title = {Real-time obstacle avoidance for multiple mobile robots},
  journal = {Robotica},
  year = {2008},
  volume = {27},
  pages = {189-198},
  url = {http://dx.doi.org/10.1017/S0263574708004438},
  doi = {http://dx.doi.org/10.1017/S0263574708004438}
}
Harsha, S.P. & Nataraj, C. (2008), "Nonlinear Vibration Analysis of a Rotor Bearing System Due to Surface Imperfection of Rolling Elements", Mechanics Based Design of Structure and Machines., In Press, 2008.

[BibTeX]
BibTeX: 
@article{Harsha2008aj,
  author = {Harsha, S. P. and C. Nataraj},
  title = {Nonlinear Vibration Analysis of a Rotor Bearing System Due to Surface Imperfection of Rolling Elements},
  journal = {Mechanics Based Design of Structure and Machines},
  year = {2008}
}
Mousavi, P.N., Nataraj, C., Bagheri, A. & Entezari, M.A. (2008), "Mathematical simulation of combined trajectory paths of a seven link biped robot", Applied Mathematical Modelling. New York, NY 10010, United States Vol. 32(7), pp. 1445-1462.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: The following article focuses on biped robot simulation and control over combined trajectory paths with the aid of mathematical modeling methods focusing on the effects of hip height over torso's modified motion. The mathematical simulation has been exploited to interpolate the combined trajectory of the robot path with the given breakpoints using inverse kinematic and dynamic methods to determine ZMP and stability treatments. After the robot's combined path determination, a third-order spline is utilized because of its high precision and ability to calculate the kinematic, dynamic and control parameters. With the aid of this software, common parameters such as joint angles and inertial forces for the given specifications and nominal conditions are calculated and simulated. © 2007 Elsevier Inc. All rights reserved.
BibTeX: 
@article{Mousavi2008j,
  author = {Mousavi, Peiman Naseradin and Nataraj, C. and Bagheri, Ahmad and Entezari, Mahdi Alizadeh},
  title = {Mathematical simulation of combined trajectory paths of a seven link biped robot},
  journal = {Applied Mathematical Modelling},
  year = {2008},
  volume = {32},
  number = {7},
  pages = {1445-1462},
  url = {http://dx.doi.org/10.1016/j.apm.2007.11.026},
  doi = {http://dx.doi.org/10.1016/j.apm.2007.11.026}
}
Nataraj, C. & Marx, S. (2008), "Bifurcation analysis of a one DOF rotor on electromagnetic bearings", 2007 Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007., In Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007. New York, NY 10016-5990, United States Vol. 1 PART C, pp. 1775 - 1782.

[Abstract] [BibTeX]
Abstract: This paper considers a one degree of freedom rotor supported on an electromagnetic bearing in a feedback control loop. A nonlinear model of an electromagnetic bearing is developed and a nondimensional model is derived for the system with two distinct parameters corresponding to the controller gain and the static load. Nonlinear analysis is carried out as a function of these two parameters and bifurcation diagrams are derived. The results reveal a very interesting panoply of fixed points with varying stability conditions. Numerical simulations are carried out to confirm the results of nonlinear analysis. Practical implications of the nonlinear analysis results are discussed. Copyright © 2007 by ASME.
BibTeX: 
@inproceedings{Nataraj2008,
  author = {Nataraj, C. and Marx, Steven},
  title = {Bifurcation analysis of a one DOF rotor on electromagnetic bearings},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007},
  journal = {2007 Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007},
  year = {2008},
  volume = { 1 PART C},
  pages = {1775 - 1782}
}
Nataraj, C. & Marx, S. (2008), "Optimal Control of a Nonlinear Magnetic Bearing System Using the Trigonometric Collocation Method", In Proceedings of ASME 2008 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2008). Ellicott City, MD, October 28-30, 2008.

[BibTeX]
BibTeX: 
@inproceedings{Nataraj2008a,
  author = {C. Nataraj and Steven Marx},
  title = {Optimal Control of a Nonlinear Magnetic Bearing System Using the Trigonometric Collocation Method},
  booktitle = {Proceedings of ASME 2008 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2008)},
  year = {2008}
}
Nataraj, C. & Harsha, S.P. (2008), "The effect of bearing cage run-out on the nonlinear dynamics of a rotating shaft", Communications in Nonlinear Science and Numerical Simulation. Amsterdam, 1000 AE, Netherlands Vol. 13( 4), pp. 822-838.

[Abstract] [BibTeX] [DOI]
Abstract: This paper presents an analytical model to investigate the nonlinear dynamic behavior of an unbalanced rotor-bearing system due to cage run-out. Due to run-out of the cage, the rolling elements no longer stay equally spaced. The mathematical model takes into account the sources of nonlinearity such as Hertzian contact forces and cage run-out, and the resulting transition from a state of no contact to contact between the rolling elements and the races. The contact between the rolling elements and races is treated as nonlinear springs and the system is analyzed for varying numbers of balls. The results are presented in the form of fast Fourier transformations and Poincare maps. The results show that the ball passage frequency is modulated with the rotational frequency. The response falls into three regimes: periodic motion, quasi-periodic oscillations, and chaotic response. © 2006 Elsevier B.V. All rights reserved.
BibTeX: 
@article{Nataraj2008j,
  author = {Nataraj, C. and Harsha, S. P.},
  title = {The effect of bearing cage run-out on the nonlinear dynamics of a rotating shaft},
  journal = {Communications in Nonlinear Science and Numerical Simulation},
  year = {2008},
  volume = {13},
  number = { 4},
  pages = {822-838},
  doi = {http://dx.doi.org/10.1016/j.cnsns.2006.07.010}
}
Nersesov, S.G., Nataraj, C. & Avis, J.M. (2008), "Design of finite-time stabilizing controllers for nonlinear dynamical systems", Proceedings of the IEEE Conference on Decision and Control., In Proceedings of the IEEE Conference on Decision and Control. Piscataway, NJ 08855-1331, United States , pp. 1740 - 1745.

[Abstract] [BibTeX] [URL]
Abstract: Finite-time stability involves dynamical systems whose trajectories converge to an equilibrium state in finite time. Since finite-time convergence implies nonuniqueness of system solutions in reverse time, such systems possess nonLipschitzian dynamics. Sufficient conditions for finite-time stability have been developed in the literature using Holder continuous Lyapunov functions. In this paper, we extend the finite-time stability theory to revisit time-invariant dynamical systems and to address time-varying systems. Specifically, we develop a Lyapunov based stability and control design framework for finite-time stability as well as finite-time tracking for time-varying nonlinear dynamical systems. Furthermore, we use vector Lyapunov function approach to study finite-time stabilization of sets for large-scale dynamical systems which is essential in formation control of multiple agents. © 2007 IEEE.
BibTeX: 
@inproceedings{Nersesov2008,
  author = {Nersesov, Sergey G. and Nataraj, C. and Avis, Jevon M.},
  title = {Design of finite-time stabilizing controllers for nonlinear dynamical systems},
  booktitle = {Proceedings of the IEEE Conference on Decision and Control},
  journal = {Proceedings of the IEEE Conference on Decision and Control},
  year = {2008},
  pages = {1740 - 1745},
  url = {http://dx.doi.org/10.1109/CDC.2007.4434736}
}
Samanta, B. & Nataraj, C. (2008), "Design of Intelligent Ship Autopilots using Particle Swarm Optimization", 2008 IEEE Swarm Intelligence Symposium, SIS 2008., In IEEE Swarm Intelligence Symposium (SIS2008). Piscataway, NJ 08855-1331, United States , pp. 4668327 - .

[Abstract] [BibTeX] [URL]
Abstract: A study is presented on the application of particle swarm optimization (PSO) to design intelligent autopilots for ship steering. Two versions of PSO - conventional and anti-predatory (APSO)- have been used. The autopilot consists of a fuzzy logic controller (FLC) emulating the characteristics of manual ship steering. The parameters for the FLC are optimized using PSO and APSO. The robustness of the autopilot based on the optimized FLC is illustrated through the simulation of a realistic nonlinear ship model. The steering performance of the optimal FLC is compared with a PID type autopilot designed with and without PSO. © 2008 IEEE.
BibTeX: 
@inproceedings{Samanta2008,
  author = {Samanta, B. and Nataraj, C.},
  title = {Design of Intelligent Ship Autopilots using Particle Swarm Optimization},
  booktitle = {IEEE Swarm Intelligence Symposium (SIS2008)},
  journal = {2008 IEEE Swarm Intelligence Symposium, SIS 2008},
  year = {2008},
  pages = {4668327 - },
  url = {http://dx.doi.org/10.1109/SIS.2008.4668327}
}
Samanta, B. & Nataraj, C. (2008), "Cracked rotor diagnostics using soft computing", 2007 Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007., In Proceedings of the ASME International Design Engineering Technical Conference (IDETC2008). New York, NY 10016-5990, United States Vol. 1 PART C, pp. 1731 - 1740.

[Abstract] [BibTeX]
Abstract: A study is presented for detection and diagnostics of cracked rotors using soft computing techniques like adaptive neuro-fuzzy inference system (ANFIS), artificial neural networks (ANN) and genetic algorithms (GA). A simple model for a cracked rotor is used to simulate its transient response during startup for different levels of cracks. The transient response is processed through continuous wavelet transform (CWT) to extract time-frequency features for the normal and cracked conditions of the rotor. Several features including the wavelet energy distributions and the grey moment vectors (GMV) of the CWT scalograms are used as inputs for diagnosis of crack level. The parameters of the classifiers, ANFIS and ANN, along with the features from wavelet energy distribution and grey moment vectors are selected using GA maximizing the diagnostic success. The classifiers are trained with a subset of the data with known crack levels and tested using the other set of data (testing data), not used in training. The procedure is illustrated using the simulation data of a simple de Laval rotor with a 'breathing' crack for different crack levels during run-up through its critical speed. A comparison of diagnostic performance for the classifiers is presented. Results show the effectiveness of the proposed approach in detection and diagnosis of cracked rotors. Copyright © 2007 by ASME.
BibTeX: 
@inproceedings{Samanta2008a,
  author = {Samanta, B. and Nataraj, C.},
  title = {Cracked rotor diagnostics using soft computing},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference (IDETC2008)},
  journal = {2007 Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007},
  year = {2008},
  volume = {1 PART C},
  pages = {1731 - 1740}
}
Samanta, B. & Nataraj, C. (2008), "Prognostics of machine condition using soft computing", Robotics and Computer-Integrated Manufacturing. Oxford, OX5 1GB, United Kingdom Vol. 24(6), pp. 816-823.

[Abstract] [BibTeX] [DOI]
Abstract: This paper presents a system for monitoring and prognostics of machine conditions using soft computing (SC) techniques. The machine condition is assessed through a suitable 'monitoring index' extracted from the vibration signals. The progression of the monitoring index is predicted using an SC technique, namely adaptive neuro-fuzzy inference system (ANFIS). Comparison with a machine learning method, namely support vector regression (SVR), is also presented. The proposed prediction procedures have been evaluated through benchmark data sets. The prognostic effectiveness of the techniques has been illustrated through previously published data on several types of faults in machines. The performance of SVR was found to be better than ANFIS for the data sets used. The results are helpful in understanding the relationship of machine conditions, the corresponding indicating features, the level of damage/degradation and their progression.
BibTeX: 
@article{Samanta2008aj,
  author = {Samanta, B. and Nataraj, C.},
  title = {Prognostics of machine condition using soft computing},
  journal = {Robotics and Computer-Integrated Manufacturing},
  year = {2008},
  volume = { 24},
  number = {6},
  pages = {816-823},
  doi = {http://dx.doi.org/10.1016/j.rcim.2008.03.011}
}
Samanta, B. & Nataraj, C. (2008), "Prognostics using morphological signal processing and computational intelligence", Proceedings of the 1st IEEE International Conference on Prognostics and Health Management (PHM2008)., In Proceedings of the 1st IEEE International Conference on Prognostics and Health Management (PHM2008). Denver, CO, October 6-9, 2008.

[BibTeX] [URL]
BibTeX: 
@inproceedings{Samanta2008b,
  author = {Samanta, B. and Nataraj, C.},
  title = {Prognostics using morphological signal processing and computational intelligence},
  booktitle = {Proceedings of the 1st IEEE International Conference on Prognostics and Health Management (PHM2008)},
  journal = {Proceedings of the 1st IEEE International Conference on Prognostics and Health Management (PHM2008)},
  year = {2008},
  url = {http://dx.doi.org/10.1109/PHM.2008.4711461}
}
Samanta, B. & Nataraj, C. (2008), "Prognostics of machine condition using energy based monitoring index and computational intelligence", In Proceedings of ASME 2008 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE 2008). Brooklyn, NY, Aug. 3-6, 2008.

[BibTeX]
BibTeX: 
@inproceedings{Samanta2008c,
  author = {Samanta, B. and Nataraj, C},
  title = {Prognostics of machine condition using energy based monitoring index and computational intelligence},
  booktitle = {Proceedings of ASME 2008 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE 2008)},
  year = {2008}
}
Samanta, B. & Nataraj, C. (2008), "Automated diagnosis of cardiac state in healthcare systems using computational intelligence", International Journal of Services Operations and Informatics. Geneve 15, CH-1215, Switzerland Vol. 3(2), pp. 162-177.

[Abstract] [BibTeX] [DOI]
Abstract: A study is presented for the diagnosis of a patient's heart conditions using recorded heart sounds and Computational Intelligence (CI) techniques. The digitally recorded heart sound signals are processed through Continuous Wavelet Transform (CWT) to extract time frequency features for normal and abnormal heart conditions. The wavelet energy distributions are used as inputs to classifiers based on soft computing techniques such as Adaptive Neuro-Fuzzy Inference Systems (ANFIS) and Genetic Algorithms (GAs) for diagnosis of heart conditions. The number and the parameters of Membership Functions (MFs) used in ANFIS along with the features from wavelet energy distribution are selected using GAs, maximising the diagnosis success. ANFIS with GAs (GA-ANFIS) are trained with a subset of data with known heart conditions. The trained GA-ANFIS are tested using the other set of data (testing data), not used in training. The results are compared with Artificial Neural Network (ANN) and GA (GA-ANN). The results show the effectiveness of the proposed approach in automated diagnosis of cardiac state in healthcare systems.
BibTeX: 
@article{Samanta2008cj,
  author = {Samanta, Biswanath and Nataraj, C.},
  title = {Automated diagnosis of cardiac state in healthcare systems using computational intelligence},
  journal = {International Journal of Services Operations and Informatics},
  year = {2008},
  volume = { 3},
  number = {2},
  pages = {162-177},
  doi = {http://dx.doi.org/10.1504/IJSOI.2008.019331}
}
Samanta, B. & Nataraj, C. (2008), "Surface roughness prediction in machining using computational intelligence", International Journal of Manufacturing Research. Olney, Bucks, MK46 5WB, United Kingdom Vol. 3(4), pp. 379-392.

[Abstract] [BibTeX] [DOI]
Abstract: A study is presented to model surface roughness in turning using Genetic Programming (GP). The machining parameters, namely, the spindle speed, feed rate, depth of cut and the workpiece tool vibration amplitudes in three orthogonal directions have been used as inputs to model the workpiece surface roughness. The input parameters and the corresponding functional relationship are automatically selected using GP and maximising the modelling accuracy. The effects of different GP parameters on the prediction accuracy and training time are studied. The results of the GP-based approach are compared with other Computational Intelligence (CI) techniques like Artificial Neural Networks (ANN).
BibTeX: 
@article{Samanta2008dj,
  author = {Samanta, Biswanath and Nataraj, C.},
  title = {Surface roughness prediction in machining using computational intelligence},
  journal = {International Journal of Manufacturing Research},
  year = {2008},
  volume = { 3},
  number = {4},
  pages = {379-392},
  doi = {http://dx.doi.org/10.1504/IJMR.2008.020900}
}
Harsha, S.P. & Nataraj, C. (2007), "Dynamic Analysis of High-Speed Ball Bearings Due to Geometrical Imperfections", In Arctic Summer Conference on Dynamics, Vibrations and Control. Saariselka, Finland, August 6-10, 2007.

[BibTeX]
BibTeX: 
@inproceedings{Harsha2007,
  author = {S. P. Harsha and C. Nataraj},
  title = {Dynamic Analysis of High-Speed Ball Bearings Due to Geometrical Imperfections},
  booktitle = {Arctic Summer Conference on Dynamics, Vibrations and Control},
  year = {2007}
}
Harsha, S.P. & Nataraj, C. (2007), "The effect of surface waviness and number of rolling elements on the dynamic behavior of a rotor-bearing system", 2007 Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007., In Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007. New York, NY 10016-5990, United States Vol. 1 PART C, pp. 1755-1762.

[Abstract] [BibTeX]
Abstract: In the paper, the effects of the number of rolling elements and wave number of surface waviness on the nonlinear dynamic analysis of a rotor-bearing system has been studied. In the analytical formulation, the contacts between rolling elements and races are considered as nonlinear springs, whose stiffnesses are obtained by using Hertzian elastic contact deformation theory. The results are presented in the form of Fast Fourier Transformations (FFT) and Poincare maps, which show that the vibration characteristics of the rotor and its bearings change when the bearings operate in different regions of their nonlinear load deflection characteristics. The appearance of regions of periodic, sub-harmonic and chaotic behavior has been observed to be strongly dependent on number of rolling elements. Copyright © 2007 by ASME.
BibTeX: 
@inproceedings{Harsha2007a,
  author = {Harsha, S. P. and Nataraj, C.},
  title = {The effect of surface waviness and number of rolling elements on the dynamic behavior of a rotor-bearing system},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007},
  journal = {2007 Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2007},
  year = {2007},
  volume = {1 PART C},
  pages = {1755-1762}
}
Harsha, S. & Nataraj, C. (2007), "Nonlinear dynamic analysis of a rotor bearing system due to distributed defects using factorial design of experiments", International Journal of Applied Mechanics and Engineering. Poland Vol. 12(2), pp. 379-399.

[Abstract] [BibTeX]
Abstract: This paper focuses on accurate performance prediction which is essential to the design of high performance rotor bearing system. It considers distributed defects such as internal radial clearance and surface waviness of the bearing components. In the analytical formulation the contacts between the rolling elements and the races are considered as nonlinear springs, whose stiffnesses are obtained by using Hertzian elastic contact deformation theory. The governing differential equations of motion are obtained by using Lagrange's equations. In terms of the feature that the nonlinear bearing forces act on the system, a reduction method and corresponding integration technique is used to increase the numerical stability and decrease computer time for system analysis. Poincard maps are used to elucidate and to illustrate the diversity of the system behavior. For investigating the nonlinear behavior of a rotor bearing system, effects of distributed defects are considered simultaneously. It is shown that the system dynamic behavior is sensitive to small variations of distributed defects.
BibTeX: 
@article{Harsha2007aj,
  author = {Harsha, S.P. and Nataraj, C.},
  title = {Nonlinear dynamic analysis of a rotor bearing system due to distributed defects using factorial design of experiments},
  journal = {International Journal of Applied Mechanics and Engineering},
  year = {2007},
  volume = { 12},
  number = {2},
  pages = {379-399}
}
Marx, S. & Nataraj, C. (2007), "Suppression of base excitation of rotors on magnetic bearings", International Journal of Rotating Machinery. New York, NY 10022, United States Vol. 2007(91276)

[Abstract] [BibTeX] [DOI] [URL]
Abstract: This paper deals with rotor systems that suffer harmonic base excitation when supported on magnetic bearings. Magnetic bearings using conventional control techniques perform poorly in such situations mainly due to their highly nonlinearcharacteristics. The compensation method presented here is a novel optimal control procedure with a combination of conventional, proportional, and differential feedback control. A four-degree-of-freedom model is used for the rotor system, and the bearings are modeled by nonlinear expressions. Each disturbance frequency is expected to produce a multiharmonic system response, a characteristic of nonlinear systems. We apply optimal control choosing to minimize a performance index, which leads to the optimization of the trigonometric coefficients in the correction current function. Results show that the control technique suppresses rotor vibration to amplitudes that were significantly smaller than the disturbance amplitudes for the entire range ofdisturbance frequencies applied. The control technique explored in this paper is a promising step towards the successful application of magnetic bearings to systems mounted on moving platforms.
BibTeX: 
@article{Marx2007j,
  author = {Marx, Steven and Nataraj, C.},
  title = {Suppression of base excitation of rotors on magnetic bearings},
  journal = {International Journal of Rotating Machinery},
  year = {2007},
  volume = { 2007},
  number = {91276},
  url = {http://dx.doi.org/10.1155/2007/91276},
  doi = {http://dx.doi.org/10.1155/2007/91276}
}
Nataraj, C. & Harsha, S.P. (2007), "Intermittent Chaos in Steering Dynamics of Ships", In Arctic Summer Conference on Dynamics, Vibrations and Control. Saariselka Finland, August 6-10, 2007.

[BibTeX]
BibTeX: 
@inproceedings{Nataraj2007,
  author = {C. Nataraj and S. P. Harsha},
  title = {Intermittent Chaos in Steering Dynamics of Ships},
  booktitle = {Arctic Summer Conference on Dynamics, Vibrations and Control},
  year = {2007}
}
Samanta, B. & Nataraj, C. (2007), "Automated Diagnosis of Cardiac State in Healthcare Systems", In The 17th International Conference on Flexible Automation and Intelligent Manufacturing. Philadelphia, PA, June 18-20, 2007.

[BibTeX]
BibTeX: 
@inproceedings{Samanta2007,
  author = {B. Samanta and C. Nataraj},
  title = {Automated Diagnosis of Cardiac State in Healthcare Systems},
  booktitle = {The 17th International Conference on Flexible Automation and Intelligent Manufacturing},
  year = {2007}
}
Samanta, B. & Nataraj, C. (2007), "Machinery Prognostics Using Soft Computing", In The 17th International Conference on Flexible Automation and Intelligent Manufacturing. Philadelphia, PA, June 18-20, 2007.

[BibTeX]
BibTeX: 
@inproceedings{Samanta2007a,
  author = {B. Samanta and C. Nataraj},
  title = {Machinery Prognostics Using Soft Computing},
  booktitle = {The 17th International Conference on Flexible Automation and Intelligent Manufacturing},
  year = {2007}
}
Harsha, S.P. & Nataraj, C. (2006), "Nonlinear Vibration Analysis Of A Balanced Rotor Supported By Roller Bearings", In 2nd Annual AIAA-ASME Symposium. Philadelphia, PA

[BibTeX]
BibTeX: 
@inproceedings{Harsha2006,
  author = {S. P. Harsha and C. Nataraj},
  title = {Nonlinear Vibration Analysis Of A Balanced Rotor Supported By Roller Bearings},
  booktitle = {2nd Annual AIAA-ASME Symposium},
  year = {2006}
}
Harsha, S.P. & Nataraj, C. (2006), "Intermittent Chaotic Behavior of an Unbalanced Rotor Supported by Rolling Element Bearings with to Race Waviness", In Eleventh conference on Nonlinear vibrations, stability and dynamics of structures., August 13-17, 2006.

[BibTeX]
BibTeX: 
@inproceedings{Harsha2006a,
  author = {S. P. Harsha and C. Nataraj},
  title = {Intermittent Chaotic Behavior of an Unbalanced Rotor Supported by Rolling Element Bearings with to Race Waviness},
  booktitle = {Eleventh conference on Nonlinear vibrations, stability and dynamics of structures},
  year = {2006}
}
Harsha, S.P. & Nataraj, C. (2006), "Nonlinear Dynamic Analysis of High-Speed Ball Bearings Due to Surface Waviness and Unbalanced Rotor", International Journal of Nonlinear Sciences and Numerical Simulation. Vol. 7(2), pp. 163-167.

[Abstract] [BibTeX] [DOI]
Abstract: This paper studies the nonlinear dynamic analysis of high speed ball bearings due to waviness and
unbalanced rotor. In the analytical formulation, the contacts between balls and races are modeled as
nonlinear springs, whose stiffnesses are obtained by using Hertzian elastic contact deformation theory. The
numerical integration technique Newmark-b with Newton-Raphson method is used to solve the nonlinear
differential equations iteratively. The results are presented in the form of FFTs. From the analysis, for the
even wave-number, the response shows that the interaction of ball passage and unbalanced force results in
low amplitude regions of instability and chaos.
BibTeX: 
@article{Harsha2006bj,
  author = {Harsha, S. P. and Nataraj, C.},
  title = {Nonlinear Dynamic Analysis of High-Speed Ball Bearings Due to Surface Waviness and Unbalanced Rotor},
  journal = {International Journal of Nonlinear Sciences and Numerical Simulation},
  year = {2006},
  volume = {7},
  number = {2},
  pages = {163-167},
  doi = {http://dx.doi.org/10.1515/IJNSNS.2006.7.2.163}
}
Harsha, S., Nataraj, C. & Kankar, P. (2006), "The effect of ball waviness on nonlinear vibration associated with rolling element bearings", International Journal of Acoustics and Vibrations. Auburn, AL 36849-3501, United States Vol. 11(2), pp. 56-66.

[Abstract] [BibTeX] [DOI]
Abstract: An analytical model was developed to investigate the nonlinear vibrations of a rotor bearing system due to ball waviness. In the analytical formulation the contacts between the balls and the races are modelled as nonlinear springs, whose stiffnesses are obtained by using Hertzian elastic contact deformation theory. The governing differential equations of motion are obtained by using Lagrange's equations. The implicit type of numerical integration technique Newmark-β with Newton-Raphson method is used to solve the nonlinear differential equations iteratively. A computer program was developed to simulate the effect of ball waviness. The formulation predicts the discrete spectra with specific frequency components for each order of ball waviness. Numerical results obtained from the simulation are compared with those of prior researchers.
BibTeX: 
@article{Harsha2006j,
  author = {Harsha, S.P. and Nataraj, C. and Kankar, P.K.},
  title = {The effect of ball waviness on nonlinear vibration associated with rolling element bearings},
  journal = {International Journal of Acoustics and Vibrations},
  year = {2006},
  volume = {11},
  number = {2},
  pages = {56-66},
  doi = {http://dx.doi.org/10.20855/ijav.2006.11.2191}
}
Nataraj, C. & Harsha, S.P. (2006), "Nonlinear Vibration Analysis of an Unbalanced Rotor on Rolling Element Bearing Due to Cage Run-out", In Transaction of Nonlinear Science and Complexity (NSC). , pp. 213-221. World Scientific.

[BibTeX]
BibTeX: 
@incollection{Nataraj2006x,
  author = {C. Nataraj and Harsha, S. P.},
  title = {Nonlinear Vibration Analysis of an Unbalanced Rotor on Rolling Element Bearing Due to Cage Run-out},
  booktitle = {Transaction of Nonlinear Science and Complexity (NSC)},
  publisher = {World Scientific},
  year = {2006},
  pages = {213--221}
}
Samanta, B. & Nataraj, C. (2006), "Detection and diagnostics of cracked rotors using soft computing", In Proc. 10th Mechatronics Forum Biennial International Conference - Mechatronics 2006 (MX2006). Penn State Great Valley, Malvern, PA, June 19-21, 2006.

[BibTeX]
BibTeX: 
@inproceedings{Samanta2006,
  author = {B. Samanta and C. Nataraj},
  title = {Detection and diagnostics of cracked rotors using soft computing},
  booktitle = {Proc. 10th Mechatronics Forum Biennial International Conference - Mechatronics 2006 (MX2006)},
  year = {2006}
}
Cartes, D., Nataraj, C., Metzer, J. & Castelin, S. (2005), "Path Planning and Nonlinear Model Selective Control Using Neural Networks: Precision Maneuvering of Unmanned Surface Vehicles", In Intelligent Ships Symposium VI. Villanova, PA

[BibTeX]
BibTeX: 
@inproceedings{Cartes2005,
  author = {David Cartes and C. Nataraj and John Metzer and Steve Castelin},
  title = {Path Planning and Nonlinear Model Selective Control Using Neural Networks: Precision Maneuvering of Unmanned Surface Vehicles},
  booktitle = {Intelligent Ships Symposium VI},
  year = {2005}
}
Fahimi, F., Rineesh, S.V.S. & Nataraj, C. (2005), "Formation control of under-actuated robotic boats", American Society of Mechanical Engineers, Dynamic Systems and Control Division (Publication) DSC., In Proceedings of International Mechanical Engineering Congress and Exposition (IMECE2005). New York, NY 10016-5990, United States, November 5-11, 2005. (IMECE2005-81561), pp. 1607-1615.

[Abstract] [BibTeX]
Abstract: Feedback control laws for controlling multiple robotic boats in arbitrary formations are proposed. The presented formation control method uses only local sensor-based information. The method of input-output linearization has been used to exponentially stabilize the relative distance and orientation of neighboring boats with a three-degree-of-freedom dynamic model. It is shown that the internal dynamics of the system is also stable. The use of these control laws is demonstrated by computer simulations. These controllers can be utilized to control an arbitrarily large number of robotic boats moving in very general formations. Copyright © 2005 by ASME.
BibTeX: 
@inproceedings{Fahimi2005,
  author = {Fahimi, Farbod and Rineesh, S. V. Sudhil and Nataraj, C.},
  title = {Formation control of under-actuated robotic boats},
  booktitle = {Proceedings of International Mechanical Engineering Congress and Exposition (IMECE2005)},
  journal = {American Society of Mechanical Engineers, Dynamic Systems and Control Division (Publication) DSC},
  year = {2005},
  number = {IMECE2005-81561},
  pages = {1607-1615}
}
Fahimi, F., SiddaReddy, R. & Nataraj, C. (2005), "Controlling Formation of Unmanned Surface Vehicles", In Intelligent Ships Symposium VI. Villanova, PA

[BibTeX]
BibTeX: 
@inproceedings{Fahimi2005a,
  author = {Farbod Fahimi and Rineesh SiddaReddy and C. Nataraj},
  title = {Controlling Formation of Unmanned Surface Vehicles},
  booktitle = {Intelligent Ships Symposium VI},
  year = {2005}
}
Harsha, S.P. & Nataraj, C. (2005), "Nonlinear Dynamic Analysis of a Unbalanced Rotor Supported by High-Speed Rolling Element Bearings with Effect of Surface Waviness", In International Symposium on Nonlinear Dynamics. Shanghai, China, December 20-21, 2005.

[BibTeX]
BibTeX: 
@inproceedings{Harsha2005,
  author = {Harsha, S. P. and Nataraj, C.},
  title = {Nonlinear Dynamic Analysis of a Unbalanced Rotor Supported by High-Speed Rolling Element Bearings with Effect of Surface Waviness},
  booktitle = {International Symposium on Nonlinear Dynamics},
  year = {2005}
}
Marx, S. & Nataraj, C. (2005), "An optimal control algorithm for suppression of harmonic base excitation in nonlinear magnetic bearings", Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference - DETC2005., In Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2005. New York, NY 10016-5990, United States Vol. 1 B, pp. 1239 - 1248.

[Abstract] [BibTeX]
Abstract: The paper deals with rotor systems that suffer harmonic base excitation when supported on magnetic bearings. Magnetic bearings using conventional control techniques perform poorly in such situations mainly due to their highly nonlinear characteristics. The compensation method presented here is a novel optimal control procedure with a combination of conventional, proportional and differential feedback control. A four degree of freedom model is used for the rotor system, and the bearings are modeled by nonlinear expressions. Each disturbance frequency is exprcted to produce a multi-harmonic system response, a characteristic of nonlinear systems. We apply optimal control choosing to minimize a performance index, which leads to the optimization of the trigonometric coefficients in the correction current function. Results show that the control technique suppresses rotor vibration to amplitudes that were significantly smaller than the disturbance amplitudes for the entire range of disturbance frequencies applied. The control technique explored in this paper is a promising step towards the successful application of magnetic bearings to systems mounted on moving platforms.
BibTeX: 
@inproceedings{Marx2005,
  author = {Marx, Steven and Nataraj, C.},
  title = {An optimal control algorithm for suppression of harmonic base excitation in nonlinear magnetic bearings},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2005},
  journal = {Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference - DETC2005},
  year = {2005},
  volume = { 1 B},
  pages = {1239 - 1248}
}
Marx, S. & Nataraj, C. (2005), "A Combined PD and Optimal Control of a Nonlinear Magnetic Bearing Rotor Subject to Harmonic Base Motion", In Intelligent Ships Symposium VI. Villanova, PA

[BibTeX]
BibTeX: 
@inproceedings{Marx2005a,
  author = {Steven Marx and C. Nataraj},
  title = {A Combined PD and Optimal Control of a Nonlinear Magnetic Bearing Rotor Subject to Harmonic Base Motion},
  booktitle = {Intelligent Ships Symposium VI},
  year = {2005}
}
Nataraj, C. & Kasliwal, P. (2005), "Comparison of ship models for nonlinear dynamic steering response", In Intelligent Ships Symposium VI. Villanova, PA

[Abstract] [BibTeX]
Abstract: This paper considers the path planning control
of an unmanned surface vehicle. The nonlinear
equations have been derived assuming one
control input (rudder). The equations have been
written assuming that the ship is moving with
a large forward velocity. A steering input has
been provided and then the error equations have
been derived. The error equations have been linearized
assuming small errors; this leads to time
varying equations, the control of which is a nontrivial
problem.
Lyapunov transformations have been applied
to change the error equation into a canonical
form. A desired closed-loop PD-spectrum and
the desired right PD-modal matrix have been
chosen and the resulting Sylvester equation has
been solved to obtain the parameter matrix.
This leads to the closed loop equations for controlling
the ship steering of an unmanned ship.
Using the kinematic equations and the closed
loop control equations the steering motion of the
ship has been simulated. An example circular
trajectory has been investigated and presented.
The control algorithm is shown to be quite
effective for tracking of unmanned surface vehicles.
BibTeX: 
@inproceedings{Nataraj2005,
  author = {Nataraj, C. and Kasliwal, Pritesh},
  title = {Comparison of ship models for nonlinear dynamic steering response},
  booktitle = {Intelligent Ships Symposium VI},
  year = {2005}
}
Nataraj, C. & Kasliwal, P. (2005), "Linear Time Varying Control of Unmanned Surface Vehicles", In Intelligent Ships Symposium VI. Villanova, PA

[Abstract] [BibTeX]
Abstract: This paper considers the path planning control
of an unmanned surface vehicle. The nonlinear
equations have been derived assuming one
control input (rudder). The equations have been
written assuming that the ship is moving with
a large forward velocity. A steering input has
been provided and then the error equations have
been derived. The error equations have been linearized
assuming small errors; this leads to time
varying equations, the control of which is a nontrivial
problem.
Lyapunov transformations have been applied
to change the error equation into a canonical
form. A desired closed-loop PD-spectrum and
the desired right PD-modal matrix have been
chosen and the resulting Sylvester equation has
been solved to obtain the parameter matrix.
This leads to the closed loop equations for controlling
the ship steering of an unmanned ship.
Using the kinematic equations and the closed
loop control equations the steering motion of the
ship has been simulated. An example circular
trajectory has been investigated and presented.
The control algorithm is shown to be quite
effective for tracking of unmanned surface vehicles.
BibTeX: 
@inproceedings{Nataraj2005a,
  author = {Nataraj, C. and Kasliwal, Pritesh},
  title = {Linear Time Varying Control of Unmanned Surface Vehicles},
  booktitle = {Intelligent Ships Symposium VI},
  year = {2005}
}
Nataraj, C. & Pietrusko, R.G. (2005), "Dynamic response of rigid rotors supported on rolling element bearings with an outer raceway defect", Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference - DETC2005., In Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2005. New York, NY 10016-5990, United States Vol. 1 B, pp. 1249 - 1261.

[Abstract] [BibTeX]
Abstract: This paper is concerned with the nonlinear dynamical response of a rigid rotor supported on rolling element bearings with defects in the outer raceway. The rotor is modeled with five degrees of freedom, and the bearings are modeled with nonlinear forces arising from Hertzian contact stresses. Then we introduce a defect into the roller bearings with a controllable parameter, and analyze the effect of the growth of this defect on the dynamic response of the system using serveral signal processing tools such as spectrum, cepstrum and envelope methods. Numerical results are obtained for a screw compressor rotor. We examine these results with the idea a potential application towards the development of automated condition assessment tools for machinery diagnostics and prognostics. It appears from the results that no single tool is ideal, and that a combination of existing tools could possibly lead to a good strategy.
BibTeX: 
@inproceedings{Nataraj2005b,
  author = {Nataraj, C. and Pietrusko, Robert Gerard},
  title = {Dynamic response of rigid rotors supported on rolling element bearings with an outer raceway defect},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference, DETC2005},
  journal = {Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference - DETC2005},
  year = {2005},
  volume = { 1 B},
  pages = {1249 - 1261}
}
Nataraj, C. & Muske, K.R. (2005), "Nonlinear Dynamics in Chemical Processes", In Encylopedia of Chemical Processing. Taylor & Francis.

[BibTeX] [DOI]
BibTeX: 
@incollection{Nataraj2006ax,
  author = {C. Nataraj and Kenneth R. Muske},
  title = {Nonlinear Dynamics in Chemical Processes},
  booktitle = {Encylopedia of Chemical Processing},
  publisher = {Taylor & Francis},
  year = {2005},
  doi = {http://dx.doi.org/10.1081/E-ECHP-120039236}
}
Fahimi, F., Nataraj, C. & Ashrafiuon, H. (2004), "Obstacle avoidance for groups of mobile robots using potential field technique", American Society of Mechanical Engineers, Dynamic Systems and Control Division (Publication) DSC. New York, NY 10016-5990, United States Vol. 73( 2 PART B), pp. 1179 - 1186.

[Abstract] [BibTeX]
Abstract: An efficient real time path planning method for groups of mobile robots in dynamic environments is introduced. Harmonic potential functions are utilized along with the panel method known in fluid mechanics. First, a complement to the traditional panel method is introduced to generate a more effective harmonic potential field for obstacle avoidance in dynamically changing environments. Second, a group of mobile robots working in an environment containing stationary and moving obstacles is considered. Each robot is assigned to move from its current position to a goal position. The group is not forced to maintain a formation during the motion. Every robot considers the other robots of the group as moving obstacles and hence the physical dimensions of the robots are also taken into account. The path of each robot is planned based on the changing position of the other robots and the position of stationary and moving obstacles. Finally, the effectiveness of the scheme is shown by modeling groups of an arbitrary number of mobile robots and the theory is validated by several computer simulations and hardware experiments. Copyright © 2004 by ASME.
BibTeX: 
@inproceedings{Fahimi2004,
  author = {Fahimi, F. and Nataraj, C. and Ashrafiuon, H.},
  title = {Obstacle avoidance for groups of mobile robots using potential field technique},
  journal = {American Society of Mechanical Engineers, Dynamic Systems and Control Division (Publication) DSC},
  year = {2004},
  volume = { 73},
  number = { 2 PART B},
  pages = {1179 - 1186}
}
Marx, S. & Nataraj, C. (2004), "A Control Technique used to Compensate for Magnetic Bearing Responses to Base Motion", In ASNE EMTS 2004 Symposium. Philadelphia, PA, January 27-29, 2004.

[BibTeX]
BibTeX: 
@inproceedings{Marx2004,
  author = {Steven Marx and C. Nataraj},
  title = {A Control Technique used to Compensate for Magnetic Bearing Responses to Base Motion},
  booktitle = {ASNE EMTS 2004 Symposium},
  year = {2004}
}
Fahimi, F., Ashrafiuon, H. & Nataraj, C. (2003), "Obstacle avoidance for spatial hyper-redundant manipulators using harmonic potential functions and the mode shape technique", Journal of Robotic Systems. Vol. 20( 1), pp. 23-33.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: This paper deals with the obstacle avoidance problem for spatial hyper-redundant manipulators in known environments. The manipulators is divided into two sections, a proximal section that has not entered the space among the obstacles and a distal section among the obstacles. Harmonic potential functions are employed to achieve obstacle avoidance for the distal section in three-dimensional space in order to avoid local minima in cluttered environments. A modified panel method is used to generate the potential of any arbitrary shaped obstacle in three-dimensional space. An alternative backbone curve concept and an efficient fitting method are introduced to control the trajectory of proximal links. The fitting method is recursive and avoids the complications involved with solving large systems of nonlinear algebraic equations. The combination of a three-dimensional safe path derived from the harmonic potential field and the backbone curve concept leads to an elegant kinematic control strategy that guarantees obstacle avoidance.
BibTeX: 
@article{Fahimi2003j,
  author = {Fahimi, F. and Ashrafiuon, H. and Nataraj, C.},
  title = {Obstacle avoidance for spatial hyper-redundant manipulators using harmonic potential functions and the mode shape technique},
  journal = {Journal of Robotic Systems},
  year = {2003},
  volume = { 20},
  number = { 1},
  pages = {23-33},
  url = {http://dx.doi.org/10.1002/rob.10067},
  doi = {http://dx.doi.org/10.1002/rob.10067}
}
Nataraj, C. & Calvert, T.E. (2003), "Compensation of base motion in magnetic-bearing supported rotors for Navy applications", In Intelligent Ships Symposium V., May, 2003.

[BibTeX]
BibTeX: 
@inproceedings{Nataraj2003,
  author = {C. Nataraj and Thomas E. Calvert},
  title = {Compensation of base motion in magnetic-bearing supported rotors for Navy applications},
  booktitle = {Intelligent Ships Symposium V},
  year = {2003}
}
Wenzel, B. & Nataraj, C. (2003), "Effect of dynamics on path planning of mobile robots", Proceedings of the ASME Design Engineering Technical Conference., In Proceedings of the ASME International Design Engineering Technical Conference (IDETC2003). New York, NY 10016-5990, United States Vol. 5 B, pp. 1705 - 1713.

[Abstract] [BibTeX]
Abstract: This paper deals with accurate path planning of two kinds of mobile robots: conventionally steered and differentially steered. In particular, we are concerned with the effect of dynamics. Dynamic models are derived, and numerical and experimental results are presented. The effects of varying mass, velocity and manipulator arms on the mobile robots are presented.
BibTeX: 
@inproceedings{Wenzel2003,
  author = {Wenzel, Bryan and Nataraj, C.},
  title = {Effect of dynamics on path planning of mobile robots},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference (IDETC2003)},
  journal = {Proceedings of the ASME Design Engineering Technical Conference},
  year = {2003},
  volume = { 5 B},
  pages = {1705 - 1713}
}
Asl, F.M., Ashrafiuon, H. & Nataraj, C. (2002), "A general solution for the position, velocity, and acceleration of hyperredundant planar manipulators", Journal of Robotic Systems. Vol. 19( 1), pp. 1-12.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: A new approach for the solution of the position, velocity, and acceleration of hyperredundant planar manipulators following any twice-differentiable desired path is presented. The method is singularity free, and provides a robust solution even in the event of mechanical failure of some of the robot actuators. The approach is based on defining virtual layers, and dividing them into virtual/real three-link or four-link subrobots. It starts by solving the inverse kinematic problem for the subrobot located in the lowest virtual layer, which is then used to solve the inverse kinematic equations for the subrobots located in the upper virtual layers. An algorithm is developed that provides a singularity-free solution up to the full extension through a configuration index. The configuration index can be interpreted as the average of the determinants of the Jacobians of the subrobots. The equations for the velocities and accelerations of the manipulator are solved by extending the same approach, and it is shown that the value of the configuration index is critical in maintaining joint velocity continuity. The inverse dynamic problem of the robot is also solved to obtain the torques required for the robot actuators to accomplish their tasks. Computer simulations of several hyperredundant manipulators using the proposed method are presented as numerical examples.
BibTeX: 
@article{Asl2002j,
  author = {Asl, F. M. and Ashrafiuon, H. and Nataraj, C.},
  title = {A general solution for the position, velocity, and acceleration of hyperredundant planar manipulators},
  journal = {Journal of Robotic Systems},
  year = {2002},
  volume = { 19},
  number = { 1},
  pages = {1-12},
  url = {http://dx.doi.org/10.1002/rob.8117},
  doi = {http://dx.doi.org/10.1002/rob.8117}
}
Fahimi, F., Ashrafiuon, H. & Nataraj, C. (2002), "Inverse kinematic solution for universal-jointed hyper-redundant robots", Proceedings of the ASME Design Engineering Technical Conference., In Proceedings of the ASME International Design Engineering Technical Conference. Vol. 5 B, pp. 1447 - 1454.

[Abstract] [BibTeX]
Abstract: A new and efficient kinematic position and velocity solution scheme for spatial hyper-redundant manipulators is presented. The manipulator's arm has discrete links and universal joints. Backbone curve concepts and a modal approach are used to resolve the manipulator's redundancy. The effects of the mode shapes and the slope of backbone curve at the starting point on the workspace are studied. It is shown that the usage of conventional mode shapes limits the workspace of the hyper-redundant arm. By introducing new mode shapes, an improved workspace is obtained. A simple and efficient recursive fitting method is introduced to avoid complications involved with solving systems of nonlinear algebraic equations. This method also guarantees the existence of solutions for the inverse kinematic problem at the velocity level. Velocity properties of the backbone curve are investigated and the inverse velocity propagation is solved for the spatial hyper-redundant arm. The velocity propagation scheme is recursive and is efficiently applicable to any number of links.
BibTeX: 
@inproceedings{Fahimi2002,
  author = {Fahimi, Farbod and Ashrafiuon, Hashem and Nataraj, C.},
  title = {Inverse kinematic solution for universal-jointed hyper-redundant robots},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference},
  journal = {Proceedings of the ASME Design Engineering Technical Conference},
  year = {2002},
  volume = { 5 B},
  pages = {1447 - 1454}
}
Fahimi, F., Ashrafiuon, H. & Nataraj, C. (2002), "An improved inverse kinematic and velocity solution for spatial hyper-redundant robots", IEEE Transactions on Robotics and Automation. Vol. 18( 1), pp. 103-107.

[Abstract] [BibTeX] [DOI] [URL]
Abstract: A new and efficient kinematic position and velocity solution scheme for spatial hypers-redundant manipulators is presented. The manipulator's arm has discrete links and universal joints. Backbone curve concepts and a modal approach are used to resolve the manipulator's redundancy. The effects of the mode shapes and the slope of the backbone curve at the starting point on the workspace are studied. It is shown that the usage of conventional mode shapes limits the workspace of the hyper-redundant arm. By introducing new mode shapes, an improved workspace is obtained. A simple and efficient recursive fitting method is introduced to avoid complications involved with solving systems of nonlinear algebraic equations. This method also guarantees the existence of solution for the inverse kinematic problem at the velocity level. Velocity properties of the backbone curve are investigated and the inverse velocity propagation is solved for the spatial hyper-redundant arm. The velocity propagation scheme is recursive and is efficiently applicable to any number of links.
BibTeX: 
@article{Fahimi2002j,
  author = {Fahimi, Farbod and Ashrafiuon, Hashem and Nataraj, C.},
  title = {An improved inverse kinematic and velocity solution for spatial hyper-redundant robots},
  journal = {IEEE Transactions on Robotics and Automation},
  year = {2002},
  volume = {18},
  number = { 1},
  pages = {103-107},
  url = {http://dx.doi.org/10.1109/70.988980},
  doi = {http://dx.doi.org/10.1109/70.988980}
}
Fahimi, F., Ashrafiuon, H. & Nataraj, C. (2001), "Obstacle avoidance for 2D hyper-redundant manipulators using harmonic potential functions and the mode shape technique", Proceedings of the ASME Design Engineering Technical Conference., In Proceedings of the ASME International Design Engineering Technical Conference. Vol. 6 B, pp. 1919 - 1925.

[Abstract] [BibTeX]
Abstract: Obstacle avoidance for discrete-link two-dimensional (2D) hyper-redundant manipulators in known environments is considered. The manipulator is divided into two sections, a proximal section that has not entered the space among obstacles and a distal section among the obstacles. Harmonic potential functions were used, in order to avoid local minima in cluttered environments. A modified panel method is used to generate the potential of any arbitrary shaped obstacle in two-dimensional space. An alternative backbone curve concept and an efficient fitting method are introduced to control the trajectory of proximal links. The fitting method is recursive and avoids the complications involved with solving large systems of nonlinear algebraic equations. Combination of the safe path derived from the harmonic potential field and the backbone curve concept leads to an elegant kinematic control strategy that guarantees obstacle avoidance for planar hyper-redundant robotic manipulators.
BibTeX: 
@inproceedings{Fahimi2001,
  author = {Fahimi, F. and Ashrafiuon, H. and Nataraj, C.},
  title = {Obstacle avoidance for 2D hyper-redundant manipulators using harmonic potential functions and the mode shape technique},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference},
  journal = {Proceedings of the ASME Design Engineering Technical Conference},
  year = {2001},
  volume = { 6 B},
  pages = {1919 - 1925}
}
Hailu, G., Nataraj, C. & Ashrafiuon, H. (2001), "Is reduction in task space a condition for accelerated learning?", Proceedings of the IEEE International Conference on Systems, Man and Cybernetics., In Proceedings of the IEEE International Conference on Systems, Man and Cybernetics. Vol. 1, pp. 628 - 633.

[Abstract] [BibTeX] [URL]
Abstract: The effect of two different biases on the learning time of a reinforcement learning agent was studied. Generally, results indicate that different biases affect learning differently. It was concluded that learning speed is not a mere function of search size and large state space should be viewed only as a potential indication of slow learning.
BibTeX: 
@inproceedings{Hailu2001,
  author = {Hailu, G. and Nataraj, C. and Ashrafiuon, H.},
  title = {Is reduction in task space a condition for accelerated learning?},
  booktitle = {Proceedings of the IEEE International Conference on Systems, Man and Cybernetics},
  journal = {Proceedings of the IEEE International Conference on Systems, Man and Cybernetics},
  year = {2001},
  volume = { 1},
  pages = {628 - 633},
  url = {http://dx.doi.org/10.1109/ICSMC.2001.969922}
}
Arakere, N.K. & Nataraj, C. (1999), "Numerical simulation of nonlinear spur gear dynamics", In Proceedings of DETC99 Deisgn Engineering Technical Conferences. Las Vegass, Nevada, September 12-15, 1999.

[BibTeX]
BibTeX: 
@inproceedings{Arakere1999,
  author = {Nagaraj K. Arakere and C. Nataraj},
  title = {Numerical simulation of nonlinear spur gear dynamics},
  booktitle = {Proceedings of DETC99 Deisgn Engineering Technical Conferences},
  year = {1999}
}
Asl, F., Ashrafiuon, H. & Nataraj, C. (1999), "Analysis of Hyper-redundant manipulators", In 17th ASME Biennial Conference on Mechanical Vibration and Noise., September, 1999.

[BibTeX]
BibTeX: 
@inproceedings{Asl1999,
  author = {Farshid Asl and Hashem Ashrafiuon and C. Nataraj},
  title = {Analysis of Hyper-redundant manipulators},
  booktitle = {17th ASME Biennial Conference on Mechanical Vibration and Noise},
  year = {1999}
}
Nataraj, C. & Arakere, N.K. (1999), "Dynamic response and stability of a spur gear pair", In 17th ASME Biennial Conference on Mechanical Vibration and Noise., September, 1999.

[BibTeX]
BibTeX: 
@inproceedings{Nataraj1999,
  author = {C. Nataraj and N. K. Arakere},
  title = {Dynamic response and stability of a spur gear pair},
  booktitle = {17th ASME Biennial Conference on Mechanical Vibration and Noise},
  year = {1999}
}
Arakere, N. & Nataraj, C. (1998), "Vibration of high-speed spur gear webs", Journal of Vibration and Acoustics, Transactions of the ASME. Fairfield, NJ, USA Vol. 120( 3), pp. 791-800.

[Abstract] [BibTeX] [DOI]
Abstract: This paper presents an analytical treatment of the in-plane vibration of high-speed gear webs resulting from rotational effects and periodic excitation from dynamic tooth loading. Dynamic tooth loads result from the combined effect of inertia forces of gear wheels which are significant at high speeds, the periodic variation of gear mesh stiffness, and involute tooth profile errors. The in-plane vibration equations are solved by an approximate method of weighted residuals.
BibTeX: 
@article{Arakere1998j,
  author = {Arakere, N.K. and Nataraj, C.},
  title = {Vibration of high-speed spur gear webs},
  journal = {Journal of Vibration and Acoustics, Transactions of the ASME},
  year = {1998},
  volume = {120},
  number = { 3},
  pages = {791-800},
  doi = {http://dx.doi.org/10.1115/1.2893899}
}
Nataraj, C. & Calvert, T.E. (1998), "Optimal Design of Radial Magnetic Bearings", In Proceedings of the Sixth International Symposium on Magnetic Bearings. , pp. 296-305.

[BibTeX]
BibTeX: 
@inproceedings{Nataraj1998,
  author = {C. Nataraj and T. E. Calvert},
  title = {Optimal Design of Radial Magnetic Bearings},
  booktitle = {Proceedings of the Sixth International Symposium on Magnetic Bearings},
  year = {1998},
  pages = {296-305}
}
Jones, G.F. & Nataraj, C. (1997), "Heat transfer in an electromagnetic bearing", Journal of Heat Transfer, Transactions ASME. New York, NY, USA Vol. 119( 3), pp. 611-616.

[Abstract] [BibTeX] [DOI]
Abstract: An exact solution for two-dimensional, full transient, and steady periodic heat conduction in an electromagnetic bearing is obtained. Classical methods are used to obtain an analytical expression for the temperature distribution that arises from power dissipated in the pole windings. Among the key findings is the need for cooling in the immediate neighborhood of the bearing support due to the relatively large thermal resistance of the supporting structure. The results presented prove the existence of large temperature gradients in the bearing in both the radial and circumferential directions. This demands the need for a fine mesh when performing the commonly used nodal-network thermal analysis. Conditions are described under which the temperature distribution is independent of the frequency of the time-dependent current supplied to the poles. For these cases the problem reduces to steady state, and the solution is given. A peak circumferential temperature difference of about 55 °C in the bearing is possible under certain conditions that are discussed. Attention to proper thermal design is critical to reduce the dimensional distortion of the bearing caused by thermal expansion. The effects of thermal expansion can range from catastrophic, should the shaft come in contact with the bearing, to an undesirable change in the force and dynamic control characteristics caused by a variation in the critical shaft-to-bearing clearance, which is of the order of a fraction of a millimeter.
BibTeX: 
@article{Jones1997j,
  author = {Jones, G. F. and Nataraj, C.},
  title = {Heat transfer in an electromagnetic bearing},
  journal = {Journal of Heat Transfer, Transactions ASME},
  year = {1997},
  volume = { 119},
  number = { 3},
  pages = {611-616},
  doi = {http://dx.doi.org/10.1115/1.2824149}
}
Nataraj, C. & Whitman, A.M. (1997), "Parameter Excitation Effects in Gear Dynamics", In 16th ASME Biennial Conference on Vibration and Noise. Sacramento, CA

[BibTeX]
BibTeX: 
@inproceedings{Nataraj1997,
  author = {C. Nataraj and Alan M. Whitman},
  title = {Parameter Excitation Effects in Gear Dynamics},
  booktitle = {16th ASME Biennial Conference on Vibration and Noise},
  year = {1997}
}
Arakere, N.K. & Nataraj, C. (1995), "In-plane vibration of high-speed spur gear webs", American Society of Mechanical Engineers, Design Engineering Division (Publication) DE., In Proceedings of the ASME International Design Engineering Technical Conference. Vol. 84( 3 Pt A/1), pp. 259 - 275.

[Abstract] [BibTeX]
Abstract: This paper presents an analytical treatment of the in-plane vibration of high-speed gear webs resulting from rotational effects and excitation from dynamic tooth loading. The gear web is modeled as a thin rotating disc and the governing differential equations of motion and the associated boundary conditions are derived from first principles. A comprehensive tooth stiffness model for spur gear is used that accounts for periodic variation of mesh stiffness.
BibTeX: 
@inproceedings{Arakere1995,
  author = {Arakere, N. K. and Nataraj, C.},
  title = {In-plane vibration of high-speed spur gear webs},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference},
  journal = {American Society of Mechanical Engineers, Design Engineering Division (Publication) DE},
  year = {1995},
  volume = { 84},
  number = { 3 Pt A/1},
  pages = {259 - 275}
}
Nataraj, C. (1995), "Nonlinear analysis of a rigid rotor on magnetic bearings", American Society of Mechanical Engineers (Paper)., In Proceedings of the ASME International Design Engineering Technical Conference. New York, NY, USA , pp. 7 - .

[Abstract] [BibTeX]
Abstract: A simple model of a rigid rotor supported on magnetic bearings is considered. A proportional control architecture is assumed, the nonlinear equations of motion are derived and some essential nondimensional parameters are identified. The free and forced response of the system is analyzed using techniques of nonlinear analysis. Both qualitative and quantitative results are obtained and stability criteria are derived for safe operation of the system.
BibTeX: 
@inproceedings{Nataraj1995,
  author = {Nataraj, C.},
  title = {Nonlinear analysis of a rigid rotor on magnetic bearings},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference},
  journal = {American Society of Mechanical Engineers (Paper)},
  year = {1995},
  pages = {7 - }
}
Sampath, A.M., Nataraj, C. & Ashrafiuon, H. (1995), "Optimal design of coupled structures subjected to random excitation", American Society of Mechanical Engineers, Design Engineering Division (Publication) DE., In Proceedings of the ASME International Design Engineering Technical Conference (IDETC1995). Vol. 82( 1), pp. 323 - 330.

[Abstract] [BibTeX]
Abstract: This paper presents optimization of the response of coupled structures subjected to random excitation. The dynamic system involves discrete and continuous models of coupled structures. The structures are assumed to be subjected to white noise excitation of known power spectral density. The mean square response of the structure is taken as the objective function. The physical properties such as length, thickness, stiffness and damping are taken as the design variables. The discrete system is assumed to be subjected to two kinds of excitation; band-limited white noise excitation and ideal white noise excitation. Coupling stiffness and damping characteristics are used as design variables. For the case of continuous coupled beam model, band-limited white noise excitation is considered and the root mean square response of the structure is minimized for a range of excitation frequency. Geometric properties of the structure are used as design variables.
BibTeX: 
@inproceedings{Sampath1995,
  author = {Sampath, Arun M. and Nataraj, C. and Ashrafiuon, H.},
  title = {Optimal design of coupled structures subjected to random excitation},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference (IDETC1995)},
  journal = {American Society of Mechanical Engineers, Design Engineering Division (Publication) DE},
  year = {1995},
  volume = { 82},
  number = { 1},
  pages = {323 - 330}
}
Nataraj, C., Ashrafiuon, H. & Arakere, N.K. (1994), "Effect of fluid inertia on journal bearing parameters", Tribology Transactions. Park Ridge, IL, USA Vol. 37( 4), pp. 784-792.

[Abstract] [BibTeX] [DOI]
Abstract: In the modeling and analysis of rotordynamic systems with journal bearings, the stiffness and damping parameters are usually obtained from the Reynolds equation of hydrodynamic lubrication. The Reynolds equation is derived from the continuity and momentum equations with several assumptions; the principal one among them being that the inertia terms are negligible since the lubricant flow is viscosity-dominated. Some previous work has shown, however, that the effect of fluid inertia on the static and dynamic properties of a bearing is not negligible in many circumstances. This paper uses a perturbation approach to present a rigorous derivation of the correction terms to be added to account for the effect of inertia in the case of a journal on a short bearing. The governing equation for pressure correction is derived and the corrected stiffness, damping, and inertia coefficients to the first order are displayed as a function of the equilibrium position.
BibTeX: 
@article{Nataraj1994j,
  author = {Nataraj, C. and Ashrafiuon, Hashem and Arakere, Nagaraj K.},
  title = {Effect of fluid inertia on journal bearing parameters},
  journal = {Tribology Transactions},
  year = {1994},
  volume = { 37},
  number = { 4},
  pages = {784-792},
  doi = {http://dx.doi.org/10.1080/10402009408983360}
}
Nataraj, C. (1993), "Flexibility effects in a single link robotic manipulator", American Society of Mechanical Engineers, Design Engineering Division (Publication) DE., In Proceedings of the ASME International Design Engineering Technical Conference. New York, NY, USA Vol. 57, pp. 115 - 122.

[Abstract] [BibTeX]
Abstract: A single link robotic manipulator is modeled as a rotating flexible beam with a rigid mass at the tip and accurate energy expressions are derived. The resulting partial differential equations are solved using an approximate method of weighted residuals. From the solutions, coupling between axial and flexural deformations and the interactions with rigid body motions are rigorously analyzed. The emphasis in the current paper is not on a exhaustive analysis of existing systems but it is rather intended to compare and highlight the various flexibility effects in a relatively simple system. Hence, a nondimensional parametric analysis is performed to determine the effect of several parameters ( including the rotating speed) on the errors and the individual interaction effects are discussed. Comparison with previous work in the field shows important phenomena often ignored or buried in large scale numerical analyses. Future work including application to multi-link robots is outlined.
BibTeX: 
@inproceedings{Nataraj1993,
  author = {Nataraj, C.},
  title = {Flexibility effects in a single link robotic manipulator},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference},
  journal = {American Society of Mechanical Engineers, Design Engineering Division (Publication) DE},
  year = {1993},
  volume = { 57},
  pages = {115 - 122}
}
Nataraj, C. (1993), "On the interaction of torsion and bending in rotating shafts", Journal of Applied Mechanics, Transactions ASME. Vol. 60( 1), pp. 239-241.

[Abstract] [BibTeX]
Abstract: The problem of torsional and transverse deformations of a shaft rotating at a constant speed is considered. The displacements are expressed in a perturbation series in terms of a small parameter. Energy expressions are derived to each order and Hamilton's principle is applied to obtain the equations of motion and the boundary conditions governing the displacement functions of different orders. It is clearly shown that the interaction of torsion and transverse vibration occurs at second order. Previous work reporting results of torsional vibration caused at a frequency equal to twice the rotational speed due to this interaction is confirmed.
BibTeX: 
@article{Nataraj1993aj,
  author = {Nataraj, C.},
  title = {On the interaction of torsion and bending in rotating shafts},
  journal = {Journal of Applied Mechanics, Transactions ASME},
  year = {1993},
  volume = { 60},
  number = { 1},
  pages = {239-241},
  note = {Impact factor: 1.232.}
}
Nataraj, C. & Ashrafiuon, H. (1993), "Optimal design of centered squeeze film dampers", Journal of Vibration, Acoustics, Stress, and Reliability in Design. Vol. 115( 2), pp. 210-214.

[Abstract] [BibTeX] [DOI]
Abstract: A two degree-of-freedom model, consisting of a rigid rotor supported on rigid bearings which are in turn supported on squeeze film dampers, is considered. Isotropic centering springs are assumed resulting in a steady synchronous centered circular response for the rotor. The resulting nonlinear system is modeled in nondimensional form. The transmissibility ratio of the system as well as the power dissipated are minimized for various values of unbalance and at several speeds, with the squeeze film bearing parameter as the primary design variable. Expressions are derived for linear variational stability of the circular orbit, and are imposed as constraints in the optimization process. The dependence of the optimal configuration on speed and unbalance is discussed.
BibTeX: 
@article{Nataraj1993bj,
  author = {Nataraj, C. and Ashrafiuon, H.},
  title = {Optimal design of centered squeeze film dampers},
  journal = {Journal of Vibration, Acoustics, Stress, and Reliability in Design},
  year = {1993},
  volume = { 115},
  number = { 2},
  pages = {210-214},
  doi = {http://dx.doi.org/10.1115/1.2930332}
}
Ashrafiuon, H. & Nataraj, C. (1992), "Dynamic analysis of engine-mount systems", Journal of Vibration, Acoustics, Stress, and Reliability in Design. Vol. 114( 1), pp. 79-83.

[Abstract] [BibTeX] [DOI]
Abstract: This paper examines the forced response of an airplane engine supported by an elastic foundation. It is assumed that the vibrations of the engine and the foundation are small enough such that the equations of motion are linear. The engine is modeled as a rigid body connected to the foundation by standard industrial rubber mounts which act as three-dimensional springs with a significant amount of hysteresis damping. There fundamental models of the foundation are considered: rigid, stutically flexible, and dynamically flexible. In the flexible cases, the foundation is modeled as a clamped circular plate, infinite plate, or any structure identified by a finite element stiffness matrix. In all cases, the mass, stiffness, and damping matrices of the engine-mount system are constructed and the frequency response to the rotating unbalance is determined. For the infinite and clamped circular plate cases, analytical methods are used to determine the real and imaginary parts of the flexibility matrix at different frequencies in responses to the harmonic forces transmitted to the plate through the rubber mounts. It is shown here that the foundation elasticity may have a significant effect on the engine vibration and the mounting forces transmitted from the engine to the structure. It is also shown that only the dynamic model of the foundation is able to capture the correct response of the system at frequencies close to the foundation's natural frequencies.
BibTeX: 
@article{Ashrafiuon1992j,
  author = {Ashrafiuon, H. and Nataraj, C.},
  title = {Dynamic analysis of engine-mount systems},
  journal = {Journal of Vibration, Acoustics, Stress, and Reliability in Design},
  year = {1992},
  volume = { 114},
  number = { 1},
  pages = {79-83},
  doi = {http://dx.doi.org/10.1115/1.2930238}
}
Nataraj, C., Arakere, N.K. & Ashrafiuon, H. (1992), "Effect of Fluid Inertia on Journal Bearing Parameters", In STLE Annual Tribology Meeting. Philadelphia, PA

[BibTeX]
BibTeX: 
@inproceedings{Nataraj1992,
  author = {C. Nataraj and N. K. Arakere and H. Ashrafiuon},
  title = {Effect of Fluid Inertia on Journal Bearing Parameters},
  booktitle = {STLE Annual Tribology Meeting},
  year = {1992}
}
Nataraj, C. & Raju, P.K. (1992), "The Vibrational Response of Coupled Composite Beams", In Proceedings of the Second International Congress on Recent Developments in Air and Structure Borne Sound and Vibration. Auburn, AL

[BibTeX]
BibTeX: 
@inproceedings{Nataraj1992a,
  author = {C. Nataraj and P. K. Raju},
  title = {The Vibrational Response of Coupled Composite Beams},
  booktitle = {Proceedings of the Second International Congress on Recent Developments in Air and Structure Borne Sound and Vibration},
  year = {1992}
}
Ashrafiuon, H. & Nataraj, C. (1991), "Dynamic analysis of engine-mount systems", American Society of Mechanical Engineers, Design Engineering Division (Publication) DE., In Proceedings of the ASME International Design Engineering Technical Conference. New York, NY, USA Vol. 34, pp. 191 - 196.

[Abstract] [BibTeX]
Abstract: This paper examines the forced response of an airplane engine supported by an elastic foundation. It is assumed that the vibrations of the engine and the foundation are small enough such that the equations of motion are linear. The engine is modeled as a rigid body connected to the foundation by standard industrial rubber mounts which act as three dimensional springs with a significant amount of hysteresis damping. Three fundamental models of the foundation are considered: rigid, statically flexible, and dynamically flexible. In the flexible cases, the foundation is modeled as a clamped circular plate, infinite plate, or any structure identified by a finite element stiffness matrix. In all cases, the mass, stiffness, and damping matrices of the engine-mount system are constructed and the frequency response to the rotating unbalance is determined. For the infinite and clamped circular plate cases, analytical methods are used to determine the real and imaginary parts of the flexibility matrix at different frequencies in response to the harmonic forces transmitted to the plate through the rubber mounts. It is shown here that the foundation elasticity may have a significant effect on the engine vibration and the mounting forces transmitted from the engine to the structure. It is also shown that only the dynamic model of the foundation is able to capture the correct response of the system at frequencies close to the foundation's natural frequencies.
BibTeX: 
@inproceedings{Ashrafiuon1991,
  author = {Ashrafiuon, Hashem and Nataraj, C.},
  title = {Dynamic analysis of engine-mount systems},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference},
  journal = {American Society of Mechanical Engineers, Design Engineering Division (Publication) DE},
  year = {1991},
  volume = { 34},
  pages = {191 - 196}
}
Ashrafiuon, H. & Nataraj, C. (1991), "Effect on flexibility on manipulator dynamics", Proceedings of the International Conference on CAD/CAM, Robotics, and Factories of the Future., In Proceedings of the ASME International Design Engineering Technical Conference. Secaucus, NJ, US , pp. 565 - .

[BibTeX]
BibTeX: 
@inproceedings{Ashrafiuon1991a,
  author = {Ashrafiuon, H. and Nataraj, C.},
  title = {Effect on flexibility on manipulator dynamics},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference},
  journal = {Proceedings of the International Conference on CAD/CAM, Robotics, and Factories of the Future},
  year = {1991},
  pages = {565 - }
}
Ashrafiuon, H. & Nataraj, C. (1991), "Dynamic Analysis of Serial Rotary Manipulators With Flexible Links", In Proceedings of the Second National Applied Mechanisms and Robotics Conference. Cincinnati, OH (91 AMR-IIB-2)

[BibTeX]
BibTeX: 
@inproceedings{Ashrafiuon1991b,
  author = {H. Ashrafiuon and C. Nataraj},
  title = {Dynamic Analysis of Serial Rotary Manipulators With Flexible Links},
  booktitle = {Proceedings of the Second National Applied Mechanisms and Robotics Conference},
  year = {1991},
  number = {91 AMR-IIB-2}
}
Nataraj, C. & Wallace, C.E. (1990), "Analysis of transverse vibration of coupled beams using SEA", In Proceedings of the International Congress on Recent Developments in Air and Structure Borne Sound and Vibration. Auburn, AL

[BibTeX]
BibTeX: 
@inproceedings{Nataraj1990,
  author = {C. Nataraj and C. E. Wallace},
  title = {Analysis of transverse vibration of coupled beams using SEA},
  booktitle = {Proceedings of the International Congress on Recent Developments in Air and Structure Borne Sound and Vibration},
  year = {1990}
}
Nataraj, C. & Nelson, H. (1989), "Collocation method for the investigation of periodic solutions in nonlinear systems", American Society of Mechanical Engineers, Design Engineering Division (Publication) DE., In Proceedings of the ASME International Design Engineering Technical Conference. New York, NY, USA Vol. 18( pt 5), pp. 325 - 330.

[Abstract] [BibTeX]
Abstract: The problem of periodic solution of non-autonomous and autonomous ordinary differential equations is considered. A trigonometric collocation method (TCM), recently developed by Ronto (Samoilenko and Ronto, 1979), is extended and implemented for the analysis of engineering systems. The procedure developed is applied to the problem of forced response of a journal on a hydrodynamic bearing. The self-excited galloping vibration of a single degree-of-freedom oscillator is also discussed and the results by the present method are compared to previously published works. A typical nonlinear control system with an on-off relay is analyzed and the results obtained by the Describing Function method and the TCM are compared. The TCM is thus shown to be a viable procedure for engineering analysis and design.
BibTeX: 
@inproceedings{Nataraj1989,
  author = {Nataraj, C. and Nelson, H.D.},
  title = {Collocation method for the investigation of periodic solutions in nonlinear systems},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference},
  journal = {American Society of Mechanical Engineers, Design Engineering Division (Publication) DE},
  year = {1989},
  volume = { 18},
  number = { pt 5},
  pages = {325 - 330}
}
Nataraj, C. & Nelson, H. (1989), "Periodic solutions in rotor dynamic systems with nonlinear supports: A general approach", Journal of Vibration, Acoustics, Stress, and Reliability in Design. Vol. 111(2), pp. 187-193.

[Abstract] [BibTeX] [DOI]
Abstract: A new quantitative method of estimating steady state periodic behavior in nonlinear systems, based on the trigonometric collocation method, is outlined. A procedure is developed to analyze large rotor dynamic systems with nonlinear supports by the use of the above method in conjunction with Component Mode Synthesis. The algorithm discussed is seen to reduce the original problem to solving nonlinear algebraic equations in terms of only the coordinates associated with the nonlinear supports and is a big improvement over commonly used integration methods. The feasibility and advantages of the procedure so developed are illustrated with the help of an example of a typical rotor dynamic system with an uncentered squeeze film damper. Future work on the investigation of the stability of the periodic response so obtained is outlined.
BibTeX: 
@article{Nataraj1989aj,
  author = {Nataraj, C. and Nelson, H.D.},
  title = {Periodic solutions in rotor dynamic systems with nonlinear supports: A general approach},
  journal = {Journal of Vibration, Acoustics, Stress, and Reliability in Design},
  year = {1989},
  volume = { 111},
  number = {2},
  pages = {187-193},
  doi = {http://dx.doi.org/10.1115/1.3269840}
}
Nataraj, C. & Nelson, H.D. (1987), "Periodic solutions in rotor dynamic systems with nonlinear supports: a general approach", American Society of Mechanical Engineers, Design Engineering Division (Publication) DE., In Proceedings of the ASME International Design Engineering Technical Conference. New York, NY, USA Vol. 3, pp. 51 - 58.

[Abstract] [BibTeX]
Abstract: A new quantitative method of estimating steady state periodic behavior in nonlinear systems, based on the trigonometric collocation method, is outlined. A procedure is developed to analyze large rotor dynamic systems with nonlinear supports by the use of the above method in conjunction with Component Mode Synthesis. The algorithm discussed is seen to reduce the original problem to solving nonlinear algebraic equations in terms of only the coordinates associated with nonlinear supports and is a big improvement over commonly used integration methods. The feasibility and advantages of the procedure so developed are illustrated with the help of an example of a typical rotor dynamic system with an uncentered squeeze film damper. Future work on the investigation of the stability of the periodic response so obtained is outlined.
BibTeX: 
@inproceedings{Nataraj1987,
  author = {Nataraj, C. and Nelson, H. D.},
  title = {Periodic solutions in rotor dynamic systems with nonlinear supports: a general approach},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference},
  journal = {American Society of Mechanical Engineers, Design Engineering Division (Publication) DE},
  year = {1987},
  volume = { 3},
  pages = {51 - 58}
}
Nelson, H.D. & Nataraj, C. (1986), "Dynamics of a rotor system with a cracked shaft", Journal of Vibration, Acoustics, Stress, and Reliability in Design. Vol. 108(2), pp. 189-196.

[Abstract] [BibTeX] [DOI]
Abstract: A theoretical analysis of the dynamics of a rotor-bearing system with a transversely cracked rotor is presented. The rotating assembly is modeled using finite rotating shaft elements and the presence of a crack is taken into account by a rotating stiffness variation. This stiffness variation is a function of the rotor's bending curvature at the crack location and is represented by a Fourier series expansion. The resulting parametrically excited system is nonlinear and is analyzed using a perturbation method coupled with an iteration procedure. The system equations are written in terms of complex variables and an associated computer code has been developed for simulation studies. Results obtained by this analysis procedure are compared with previous analytical and experimental work presented by Grabowski.
BibTeX: 
@article{Nelson1986j,
  author = {Nelson, H. D. and Nataraj, C.},
  title = {Dynamics of a rotor system with a cracked shaft},
  journal = {Journal of Vibration, Acoustics, Stress, and Reliability in Design},
  year = {1986},
  volume = {108},
  number = {2},
  pages = {189-196},
  doi = {http://dx.doi.org/10.1115/1.3269321}
}
Nataraj, C., Nelson, H.D. & Arakere, N. (1985), "Effect of coulomb spline on rotor dynamic response", NASA Conference Publication. Washington, DC, USA , pp. 225 - 233.

[Abstract] [BibTeX]
Abstract: A rigid rotor system coupled by a coulomb spline is modelled and analyzed by approximate analytical and numerical-analytical methods. Expressions are derived for the variables of the resulting limit cycle and are shown to be quite accurate for a small departure from isotropy.
BibTeX: 
@inproceedings{Nataraj1985,
  author = {Nataraj, C. and Nelson, H. D. and Arakere, N.},
  title = {Effect of coulomb spline on rotor dynamic response},
  journal = {NASA Conference Publication},
  year = {1985},
  pages = {225 - 233}
}
Nelson, H.D. & Nataraj, C. (1985), "Dynamics of a rotor system with a cracked shaft", American Society of Mechanical Engineers (Paper)., In Proceedings of the ASME International Design Engineering Technical Conference. New York, NY, USA , pp. 8 - .

[Abstract] [BibTeX]
Abstract: A theoretical analysis of the dynamics of a rotor-bearing system with a transversely cracked rotor is presented. The rotating assembly is modeled using finite rotating shaft elements and the presence of a crack is taken into account by a rotating stiffness variation. This stiffness variation is a function of the rotor's bending curvature at the crack location and is represented by a Fourier series expansion. The resulting parametrically excited system is nonlinear and is analyzed using a perturbation method coupled with an iteration procedure. The system equations are written in terms of complex variables and an associated computer code has been developed for simulation studies. Results obtained by this analysis procedure are compared with previous analytical and experimental work presented by Grabowski.
BibTeX: 
@inproceedings{Nelson1985,
  author = {Nelson, H. D. and Nataraj, C.},
  title = {Dynamics of a rotor system with a cracked shaft},
  booktitle = {Proceedings of the ASME International Design Engineering Technical Conference},
  journal = {American Society of Mechanical Engineers (Paper)},
  year = {1985},
  pages = {8 - }
}
Kamath, M., Narasimhan, R., Nataraj, C. & Ramamurti, V. (1982), "Dynamic response of multicylinder engines with a viscous or hysteretic crankshaft damper", Journal of Sound and Vibration., April, 1982. Vol. 81(3), pp. 448-452.

[BibTeX] [DOI]
BibTeX: 
@article{Kamath1982j,
  author = {M. Kamath and R. Narasimhan and C. Nataraj and V. Ramamurti},
  title = {Dynamic response of multicylinder engines with a viscous or hysteretic crankshaft damper},
  journal = {Journal of Sound and Vibration},
  year = {1982},
  volume = {81},
  number = {3},
  pages = {448-452},
  doi = {http://dx.doi.org/10.1016/0022-460X(82)90255-3}
}

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