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  • 1
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    A least-squares parameter estimation algorithm for switched hammerstein systems with applications to the VOR (2005)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: A "Multimode" or "switched" system is one that switches between various modes of operation. When a switch occurs from one mode to another, a discontinuity may result followed by a smooth evolution under the new regime. Characterizing the switching behavior of these systems is not well understood and, therefore, identification of multimode systems typically requires a preprocessing step to classify the observed data according to a mode of operation. A further consequence of the switched nature of these systems is that data available for parameter estimation of any subsystem may be inadequate. As such, identification and parameter estimation of multimode systems remains an unresolved problem. In this paper, we 1) show that the NARMAX model structure can be used to describe the impulsive-smooth behavior of switched systems, 2) propose a modified extended least squares (MELS) algorithm to estimate the coefficients of such models, and 3) demonstrate its applicability to simulated and real data from the Vestibulo-Ocular Reflex (VOR). The approach will also allow the identification of other nonlinear bio-systems, suspected of containing "hard" nonlinearities.
    Keywords: Life Sciences (General)
    Type: IEEE transactions on bio-medical engineering (ISSN 0018-9294); Volume 52; 3; 431-44
    Format: text
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  • 2
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    A Sparse Matrix Approach for Simultaneous Quantification of Nystagmus and Saccade (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The vestibulo-ocular reflex (VOR) consists of two intermingled non-linear subsystems; namely, nystagmus and saccade. Typically, nystagmus is analysed using a single sufficiently long signal or a concatenation of them. Saccade information is not analysed and discarded due to insufficient data length to provide consistent and minimum variance estimates. This paper presents a novel sparse matrix approach to system identification of the VOR. It allows for the simultaneous estimation of both nystagmus and saccade signals. We show via simulation of the VOR that our technique provides consistent and unbiased estimates in the presence of output additive noise.
    Keywords: Aerospace Medicine
    Type: DFRC-E-DAA-TN5348 , 34th Annual International Conference of the Engineering in Medicine and Biology; Jun 08, 2012; San Diego, CA; United States
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  • 3
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    Data Driven Model Development for the Supersonic Semispan Transport (S(sup 4)T) (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: We investigate two common approaches to model development for robust control synthesis in the aerospace community; namely, reduced order aeroservoelastic modelling based on structural finite-element and computational fluid dynamics based aerodynamic models and a data-driven system identification procedure. It is shown via analysis of experimental Super- Sonic SemiSpan Transport (S4T) wind-tunnel data using a system identification approach it is possible to estimate a model at a fixed Mach, which is parsimonious and robust across varying dynamic pressures.
    Keywords: Air Transportation and Safety
    Type: DFRC-E-DAA-TN3206 , DFRC-E-DAA-TN3784 , International Forum on Aeroelasticity and Structural; Jun 26, 2011 - Jun 30, 2011; Paris; France
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  • 4
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    Data Driven Model Development for the SuperSonic SemiSpan Transport (S(sup 4)T) (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: In this report, we will investigate two common approaches to model development for robust control synthesis in the aerospace community; namely, reduced order aeroservoelastic modelling based on structural finite-element and computational fluid dynamics based aerodynamic models, and a data-driven system identification procedure. It is shown via analysis of experimental SuperSonic SemiSpan Transport (S4T) wind-tunnel data that by using a system identification approach it is possible to estimate a model at a fixed Mach, which is parsimonious and robust across varying dynamic pressures.
    Keywords: Aerodynamics
    Type: NASA/TM-2011-215966 , DFRC-E-DAA-TN2767 , H-3076
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  • 5
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    An Indirect System Identification Technique for Stable Estimation of Continuous-Time Parameters of the Vestibulo-Ocular Reflex (VOR) (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The vestibulo-ocular reflex (VOR) is a well-known dual mode bifurcating system that consists of slow and fast modes associated with nystagmus and saccade, respectively. Estimation of continuous-time parameters of nystagmus and saccade models are known to be sensitive to estimation methodology, noise and sampling rate. The stable and accurate estimation of these parameters are critical for accurate disease modelling, clinical diagnosis, robotic control strategies, mission planning for space exploration and pilot safety, etc. This paper presents a novel indirect system identification method for the estimation of continuous-time parameters of VOR employing standardised least-squares with dual sampling rates in a sparse structure. This approach permits the stable and simultaneous estimation of both nystagmus and saccade data. The efficacy of this approach is demonstrated via simulation of a continuous-time model of VOR with typical parameters found in clinical studies and in the presence of output additive noise.
    Keywords: Life Sciences (General)
    Type: DFRC-E-DAA-TN8887 , NASA/TM-2013-216528
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  • 6
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    Sensor-Only System Identification for Structural Health Monitoring of Advanced Aircraft (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Environmental conditions, cyclic loading, and aging contribute to structural wear and degradation, and thus potentially catastrophic events. The challenge of health monitoring technology is to determine incipient changes accurately and efficiently. This project addresses this challenge by developing health monitoring techniques that depend only on sensor measurements. Since actively controlled excitation is not needed, sensor-to-sensor identification (S2SID) provides an in-flight diagnostic tool that exploits ambient excitation to provide advance warning of significant changes. S2SID can subsequently be followed up by ground testing to localize and quantify structural changes. The conceptual foundation of S2SID is the notion of a pseudo-transfer function, where one sensor is viewed as the pseudo-input and another is viewed as the pseudo-output, is approach is less restrictive than transmissibility identification and operational modal analysis since no assumption is made about the locations of the sensors relative to the excitation.
    Keywords: Aerodynamics
    Type: NASA/TM-2012-216045 , DFRC-E-DAA-TN5924
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  • 7
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    Nonlinear System Identification for Aeroelastic Systems with Application to Experimental Data (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Representation and identification of a nonlinear aeroelastic pitch-plunge system as a model of the Nonlinear AutoRegressive, Moving Average eXogenous (NARMAX) class is considered. A nonlinear difference equation describing this aircraft model is derived theoretically and shown to be of the NARMAX form. Identification methods for NARMAX models are applied to aeroelastic dynamics and its properties demonstrated via continuous-time simulations of experimental conditions. Simulation results show that (1) the outputs of the NARMAX model closely match those generated using continuous-time methods, and (2) NARMAX identification methods applied to aeroelastic dynamics provide accurate discrete-time parameter estimates. Application of NARMAX identification to experimental pitch-plunge dynamics data gives a high percent fit for cross-validated data.
    Keywords: Engineering (General)
    Type: NASA/TM-2008-214641 , H-2887
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  • 8
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    F-15B Quiet Spike(TradeMark) Aeroservoelastic Flight-Test Data Analysis (2007)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: System identification is utilized in the aerospace community for development of simulation models for robust control law design. These models are often described as linear, time-invariant processes and assumed to be uniform throughout the flight envelope. Nevertheless, it is well known that the underlying process is inherently nonlinear. Over the past several decades the controls and biomedical communities have made great advances in developing tools for the identification of nonlin ear systems. In this report, we show the application of one such nonlinear system identification technique, structure detection, for the an alysis of Quiet Spike(TradeMark)(Gulfstream Aerospace Corporation, Savannah, Georgia) aeroservoelastic flight-test data. Structure detectio n is concerned with the selection of a subset of candidate terms that best describe the observed output. Structure computation as a tool fo r black-box modeling may be of critical importance for the development of robust, parsimonious models for the flight-test community. The ob jectives of this study are to demonstrate via analysis of Quiet Spike(TradeMark) aeroservoelastic flight-test data for several flight conditions that: linear models are inefficient for modelling aeroservoelast ic data, nonlinear identification provides a parsimonious model description whilst providing a high percent fit for cross-validated data an d the model structure and parameters vary as the flight condition is altered.
    Keywords: Aerodynamics
    Type: NASA/TM-2007-214618 , H-2713
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  • 9
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    A Cross-Validation Approach to Approximate Basis Function Selection of the Stall Flutter Response of a Rectangular Wing in a Wind Tunnel (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The stall flutter response of a rectangular wing in a low speed wind tunnel is modelled using a nonlinear difference equation description. Static and dynamic tests are used to select a suitable model structure and basis function. Bifurcation criteria such as the Hopf condition and vibration amplitude variation with airspeed were used to ensure the model was representative of experimentally measured stall flutter phenomena. Dynamic test data were used to estimate model parameters and estimate an approximate basis function.
    Keywords: Aerodynamics
    Type: DFRC-E-DAA-TN4875 , 53rd Structures, Structural Dynamics, and Materials; Apr 23, 2012 - Apr 26, 2012; Honolulu, HI; United States
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  • 10
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    A Computational Biology Approach to Modelling and Identification of Human Physiology (2010)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Conference presentation sharing aspects of a computational biology approach to modelling and identification of human physiology.
    Keywords: Aerospace Medicine
    Type: DFRC-E-DAA-TN1674 , ICNPAA 2010 World Congress: 8th International Conference on Mathematical Problems in Engineering, Aerospace and Sciences; Jun 30, 2010 - Jul 03, 2010; Sao Jose dos Campos; Brazil
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