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  • 1
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    Numerical solutions for systems of `qualitative' nonlinear algebraic equations by fuzzy logic (2005)
    Elsevier
    Details
    Publication Date: 2005-03-01
    Print ISSN: 0165-0114
    Electronic ISSN: 1872-6801
    Topics: Mathematics
    Published by Elsevier
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  • 2
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    Synthesis of fixed-architecture, robustH2andH∞controllers (2000)
    Hindawi
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    Publication Date: 2000-01-01
    Description: This paper discusses and compares the synthesis of fixed-architecture controllers that guarantee either robustH2orH∞performance. The synthesis is accomplished by solving a Riccati equation feasibility problem resulting from mixed structured singular value theory with Popov multipliers. Whereas the algorithm for robustH2performance had been previously implemented, a major contribution described in this paper is the implementation of the much more complex algorithm for robustH∞performance. Both robustH2andH∞, controllers are designed for a benchmark problem and a comparison is made between the resulting controllers and control algorithms. It is found that the numerical algorithm for robustH∞performance is much more computationally intensive than that for robustH2performance. Both controllers are found to have smaller bandwidth, lower control authority and to be less conservative than controllers obtained using complex structured singular value synthesis.
    Print ISSN: 1024-123X
    Electronic ISSN: 1563-5147
    Topics: Mathematics , Technology
    Published by Hindawi
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  • 3
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    A homotopy algorithm for synthesizing robust controllers for flexible structures via the maximum entropy design equations (1990)
    In:  CASI
    Details
    Publication Date: 2004-12-04
    Description: One well known deficiency of LQG compensators is that they do not guarantee any measure of robustness. This deficiency is especially highlighted when considering control design for complex systems such as flexible structures. There has thus been a need to generalize LQG theory to incorporate robustness constraints. Here we describe the maximum entropy approach to robust control design for flexible structures, a generalization of LQG theory, pioneered by Hyland, which has proved useful in practice. The design equations consist of a set of coupled Riccati and Lyapunov equations. A homotopy algorithm that is used to solve these design equations is presented.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA. Langley Research Center, The Third Air Force(NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization; p 324-333
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  • 4
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    Regulation of the SCOLE configuration (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Studies were performed to determine location for proof mass actuators, if a significant reduction in the number of sensors would work, and to design a control law to meet requirements for line of sight error and actuators. Conclusions are drawn and briefly discussed.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Langley Research Center Proceedings of the 3rd Annual SCOLE Workshop; p 321-336
    Format: application/pdf
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  • 5
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    Design and implementation of robust decentralized control laws for the ACES structure at Marshall Space Flight Center (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An experiment was conducted to design controllers that would provide substantial reduction of line-of-sight control errors. The satisfaction of this objective required the controllers to attenuate the beam vibration significantly. Particular emphasis was placed on controller simplicity (i.e., reduced-order and decentralized controller architectures). Complexity reduction in control law implementation is of paramount interest due to stringent limitations on throughput of even state-of-the-art space qualified processors. The results of this experiment successfully demonstrate active vibrator control for a flexible structure. The testbed is the ACES structure at the NASA Marshall Space Flight Center. The ACES structure is dynamically traceable to future space systems and especially allows the study of line-of-sight control issues.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
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  • 6
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    Reliable design of H-2 optimal reduced-order controllers via a homotopy algorithm (1992)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Due to control processor limitations, the design of reduced-order controllers is an active area of research. Suboptimal methods based on truncating the order of the corresponding linear-quadratic-Gaussian (LQG) compensator tend to fail if the requested controller dimension is sufficiently small and/or the requested controller authority is sufficiently high. Also, traditional parameter optimization approaches have only local convergence properties. This paper discusses a homotopy algorithm for optimal reduced-order control that has global convergence properties. The exposition is for discrete-time systems. The algorithm has been implemented in MATLAB and is applied to a benchmark problem.
    Keywords: CYBERNETICS
    Type: In: Controls for optical systems; Proceedings of the Meeting, Orlando, FL, Apr. 21, 22, 1992 (A93-34276 13-74); p. 116-127.
    Format: text
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  • 7
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    Demonstrations of LSS active vibration control technology on representative ground-based testbeds (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: This paper describes two experiments which successfully demonstrate control of flexible structures. The first experiment involved control design and implementation for the ACES structure at NASA Marshall Space Flight Center, while the second experiment was conducted using the Multi-Hex Prototype structure. The paper concludes with some remarks on the lessons learned from conducting these experiments.
    Keywords: GROUND SUPPORT SYSTEMS AND FACILITIES (SPACE)
    Type: AAS PAPER 91-051 , In: Guidance and control 1991; Proceedings of the Annual Rocky Mountain Guidance and Control Conference, Keystone, CO, Feb. 2-6, 1991 (A93-15576 03-12); p. 217-230.
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  • 8
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    A homotopy algorithm for digital optimal projection control GASD-HADOC (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The linear-quadratic-gaussian (LQG) compensator was developed to facilitate the design of control laws for multi-input, multi-output (MIMO) systems. The compensator is computed by solving two algebraic equations for which standard closed-loop solutions exist. Unfortunately, the minimal dimension of an LQG compensator is almost always equal to the dimension of the plant and can thus often violate practical implementation constraints on controller order. This deficiency is especially highlighted when considering control-design for high-order systems such as flexible space structures. This deficiency motivated the development of techniques that enable the design of optimal controllers whose dimension is less than that of the design plant. A homotopy approach based on the optimal projection equations that characterize the necessary conditions for optimal reduced-order control. Homotopy algorithms have global convergence properties and hence do not require that the initializing reduced-order controller be close to the optimal reduced-order controller to guarantee convergence. However, the homotopy algorithm previously developed for solving the optimal projection equations has sublinear convergence properties and the convergence slows at higher authority levels and may fail. A new homotopy algorithm for synthesizing optimal reduced-order controllers for discrete-time systems is described. Unlike the previous homotopy approach, the new algorithm is a gradient-based, parameter optimization formulation and was implemented in MATLAB. The results reported may offer the foundation for a reliable approach to optimal, reduced-order controller design.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA-CR-193881 , NAS 1.26:193881
    Format: application/pdf
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  • 9
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    High performance, accelerometer-based control of the Mini-MAST structure at Langley Research Center (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Many large space system concepts will require active vibration control to satisfy critical performance requirements such as line of sight pointing accuracy and constraints on rms surface roughness. In order for these concepts to become operational, it is imperative that the benefits of active vibration control be shown to be practical in ground based experiments. The results of an experiment shows the successful application of the Maximum Entropy/Optimal Projection control design methodology to active vibration control for a flexible structure. The testbed is the Mini-Mast structure at NASA-Langley and has features dynamically traceable to future space systems. To maximize traceability to real flight systems, the controllers were designed and implemented using sensors (four accelerometers and one rate gyro) that are actually mounted to the structure. Ground mounted displacement sensors that could greatly ease the control design task were available but were used only for performance evaluation. The use of the accelerometers increased the potential of destabilizing the system due to spillover effects and motivated the use of precompensation strategy to achieve sufficient compensator roll-off.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-CR-4377 , NAS 1.26:4377
    Format: application/pdf
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  • 10
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    Robust Fault Detection (2003)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: This research used mixed structured singular value theory to develop new estimator (or observer) based approaches to fault detection for dynamic systems. The initial developments were based on minimizing the H-infinity, I-1 and H2 system norms. The resultant fault detection algorithms were each shown to be successful, but the fault detection algorithm based on the I-1 norm was best able to detect abrupt faults. This latter technique was further improved by using fuzzy logic for the fault evaluation. Based on an anomaly observed in this research and apparently ignored in the literature, current research focuses on the determination of a fault using a norm of the change in the residual (the difference between the output of the system and observer) and not simply a norm of the residual itself. This research may lead to a fundamental contribution to research in fault detection and isolation.
    Keywords: Numerical Analysis
    Type: HBCUs/OMUs Research Conference Agenda and Abstracts; 15; NASA/TM-2003-212207
    Format: text
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