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  • 1985-1989  (8)
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  • 1
    Publikationsdatum: 2011-08-19
    Beschreibung: Feedback control laws are derived for a class of optimal finite time tracking problems with terminal constraints. Analytical solutions are obtained for the feedback gain and the closed-loop response trajectory. Such formulations are expressed in recursive forms so that a real-time computer implementation becomes feasible. An example involving the feedback slewing of a flexible spacecraft is given to illustrate the validity and usefulness of the formulations.
    Schlagwort(e): CYBERNETICS
    Materialart: Journal of Optimization Theory and Applications (ISSN 0022-3239); 51; 307-320
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2013-08-31
    Beschreibung: The formulation of an Order (n) algorithm for DISCOS (Dynamics Interaction Simulation of Controls and Structures), which is an industry-standard software package for simulation and analysis of flexible multibody systems is presented. For systems involving many bodies, the new Order (n) version of DISCOS is much faster than the current version. Results of the experimental validation of the dynamics software are also presented. The experiment is carried out on a seven-joint robot arm at NASA's Goddard Space Flight Center. The algorithm used in the current version of DISCOS requires the inverse of a matrix whose dimension is equal to the number of constraints in the system. Generally, the number of constraints in a system is roughly proportional to the number of bodies in the system, and matrix inversion requires O(p exp 3) operations, where p is the dimension of the matrix. The current version of DISCOS is therefore considered an Order (n exp 3) algorithm. In contrast, the Order (n) algorithm requires inversion of matrices which are small, and the number of matrices to be inverted increases only linearly with the number of bodies. The newly-developed Order (n) DISCOS is currently capable of handling chain and tree topologies as well as multiple closed loops. Continuing development will extend the capability of the software to deal with typical robotics applications such as put-and-place, multi-arm hand-off and surface sliding.
    Schlagwort(e): COMPUTER PROGRAMMING AND SOFTWARE
    Materialart: JPL, Proceedings of the 3rd Annual Conference on Aerospace Computational Control, Volume 1; p 41
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2013-08-31
    Beschreibung: An optimal control solution process was developed for a general class of nonlinear dynamical systems. The method combines control theory, perturbation methods, and Van Loan's recent matrix exponential results. A variety of applications support the practical utility of this method. Nonlinear rigid body optimal maneuvers are routinely solved. Flexible body dynamical systems of an order greater than 40 were solved. The method fails occasionally due to poor convergence of the perturbation expansion or numerical difficulties associated with computing the matrix exponential. The method is attractive because it appears to be a good candidate for semi-automation; no initial guess is required, and it usually converges at 2nd or 3rd order in minutes of machine time.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: NASA. Marshall Space Flight Center Structural Dynamics and Control Interaction of Flexible Structures; p 759-774
    Format: application/pdf
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2011-08-19
    Beschreibung: In connection with the normal process of control system design, the determination of the state trajectories for the controlled system is frequently required. The procedure involved in the determination is straightforward. However, extensive computations may be needed, if either time-varying control gains are used, or if small integration step sizes are required by the presence of high-frequency system dynamics. The present investigation is concerned with an approach for overcoming the computational difficulties, taking into account a change of variables for the close-loop system dynamics equation. This procedure makes it possible to obtain a closed-form expression for the state trajectories.
    Schlagwort(e): CYBERNETICS
    Materialart: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 8; 147
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2011-08-19
    Schlagwort(e): CYBERNETICS
    Materialart: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 8; 39-43
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Publikationsdatum: 2014-09-25
    Beschreibung: A new approach is discussed for solving dual structural control optimization problems for high-order flexible space structures, where reduced-order structural models are employed and minimum mass designs are sought. For a given initial structural design, a quadratic control cost is minimized subject to a constant-mass constraint. The sensitivity of the optimal control cost with respect to the structural design variables is then determined and used to obtain successive structural redesigns, using a constrained gradient optimization algorithm. This process is repeated until the constrained control cost sensitivity becomes negligible. The minimum mass design is obtained by solving a sequence of neighboring optimal constant mass designs, where the sequence of optimal performance indices has a minimum at the optimal minimum mass design. A numerical example is presented which demonstrates that this new approach effectively addresses the problem of dual optimization for potentially very high-order structures.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: JPL Proc. of the Workshop on Identification and Control of Flexible Space Struct., Vol. 2; p 231-266
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2019-06-28
    Beschreibung: In this paper the problem of maneuvering a flexible spacecraft through a large angle is considered, where the disturbance-accommodating feedback control tracks a desired output state. The desired output state is provided from an open-loop solution for the linear system model. The components of the disturbance vector are assumed to be represented in terms of Fourier series. Closed-form solutions are provided for the Ricati, prefilter, state trajectory, and residual state trajectory equations which define the optimal control. Example maneuvers are presented where control-rate penalties have been included in the performance index for frequency-shaping, in order to smooth both the open- and closed-loop control commands.
    Schlagwort(e): SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Materialart: Journal of the Astronautical Sciences (ISSN 0021-9142); 33; 147-161
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2019-07-12
    Beschreibung: Commonly encountered 'passive' insulation has been improved in recent years using 'dynamic'insulation based on closed cycle cryocoolers attached to photon shields. The paper presents a novel insulation performance measure based on ideal thermodynamic limits. Each floating insulation package has a unique value. In contrast real vessels with vent tube and supports are characterized by an 'effectiveness' less than unity.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: AIChE Symposium Series (ISSN 0065-8812); 82; 101-103
    Format: text
    Standort Signatur Erwartet Verfügbarkeit
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