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  • 1990-1994  (9)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Computational mechanics 8 (1991), S. 1-18 
    ISSN: 1432-0924
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Conclusions An approach for combined control-structure optimization keyed to enhancing early design trade-offs has been outlined and illustrated by numerical examples. The approach employs a homotopic strategy and appears to be effective for generating families of designs that can be used in these early trade studies. Analytical results were obtained for classes of structure/control objectives with LQG and LQR costs. For these, we have demonstrated that global optima can be computed for small values of the homotopy parameter. Conditions for local optima along the homotopy path were also given. Details of three numerical examples employing the LQR control cost were given showing variations of the optimal design variables along the homotopy path. The results of the second example suggest that introducing a second homotopy parameter relating the two parts of the control index in the LQG/LQR formulation might serve to enlarge the family of Pareto optima, but its effect on modifying the optimal structural shapes may be analogous to the original parameter λ.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2011-08-19
    Description: System identification is studied for the explicit purpose of supporting modern H-infinity robust control design objectives. In the analysis, the true plant is not assumed to be in the identification model set. An integrated identification/robust control problem is posed in which the optimal solution guarantees the best robust performance relative to the system information contained in a given experimental data set. A numerical example demonstrating an approximate solution to the problem indicates the usefulness of the approach.
    Keywords: CYBERNETICS
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  • 3
    Publication Date: 2011-08-24
    Description: An approach to combined control-structural optimization aimed at enhancing early design trade-offs is outlined and illustrated by numerical examples. The approach employs a homotopic strategy and is capable of generating families of designs that can be used in early trade studies. Analytical results are obtained for classes of structure/control objectives with LQG and LQR costs. For these, it is demonstrated that global optima can be computed for small values of the homotopy parameter.
    Keywords: CYBERNETICS
    Type: Computational Mechanics (ISSN 0178-7675); 8; 1-18
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  • 4
    Publication Date: 2011-08-24
    Description: Recent experiences in the field of flexible structure control in space have indicated a need for on-orbit system identification to support robust control redesign to avoid in-flight instabilities and maintain high spacecraft performance. This paper highlights an automated frequency domain system identification methodology recently developed to fulfill this need. The methodology is focused to support (1) the estimation of system quantities useful for robust control analysis and design; (2) experiment design tailored to performing system identification in a typically constrained on-orbit environment; and (3) the automation of operations to reduce 'human in the loop' requirements.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Automatica (ISSN 0005-1098); 27; 931-946
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  • 5
    Publication Date: 2019-06-28
    Description: This paper outlines the development of methods for the combined control-structure optimization of physical systems encountered in the technology of large space structures. The objectives of the approach taken in this paper is not to produce the 'best' optimized design, but rather to efficiently produce a family of design options so as to assist in early trade studies, typically before hard design constraints are imposed. The philosophy is that these are candidate designs to be passed on for further considerations, and their function is more to guide the development of the system design rather than to represent the ultimate product. A homotopy approach involving multi-objective functions is developed for this purpose. Analytical and numerical examples are also presented.
    Keywords: CYBERNETICS
    Type: AIAA PAPER 90-0658
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  • 6
    Publication Date: 2019-07-13
    Description: A methodology is demonstrated for frequency domain identification of large space structures which systematically transforms experimental raw data into a form required for synthesizing H(infinity) controllers using modern robust control design software (e.g., Matlab Toolboxes). A unique feature of this approach is that the additive uncertainty is characterized to a specified statistic confidence rather than with hard bounds. In this study, the difference in robust performance is minimal between the two levels of confidence. In general cases, the present methodology provides a tool for performance/confidence level tradeoff studies. For simplicity, the additive uncertainty on a frequency grid is considered and the interpolation error in between grid points is neglected.
    Keywords: CYBERNETICS
    Type: 1991 American Control Conference; Jun 26, 1991 - Jun 28, 1991; Boston, MA; United States
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  • 7
    Publication Date: 2019-07-13
    Description: The intensity of dynamics in a flexible structure is characterized by its Hankel singular values. Low level dynamics may be caused by generic properties of a structure or by its actuator and sensor configurations. In the latter case, it is shown that the dynamics can significantly be amplified by small perturbations of actuator and/or sensor configurations. In the presented examples, the variations of sensor configuration of 0.05 or less caused an increase of Hankel singular values of order 1000. This approach is useful for model reduction and model order determination in the presence of noise.
    Keywords: CYBERNETICS
    Type: IEEE Conference on Decision and Control; Dec 05, 1990 - Dec 07, 1990; Honolulu, HI; United States
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  • 8
    Publication Date: 2019-07-13
    Description: The linear programming spectral overbounding and factorization (LPSOF) algorithm, an algorithm for finding a minimum phase transfer function of specified order whose magnitude tightly overbounds a specified nonparametric function of frequency, is introduced. This method has direct application to transforming nonparametric uncertainty bounds (available from system identification experiments) into parametric representations required for modern robust control design software (i.e., a minimum-phase transfer function multiplied by a norm-bounded perturbation).
    Keywords: CYBERNETICS
    Type: 1991 American Control Conference; Jun 26, 1991 - Jun 28, 1991; Boston, MA; United States
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  • 9
    Publication Date: 2019-07-12
    Description: Report discusses application of advanced techniques to maintain large wrap-rib, offset-feed spaceborne antenna reflector in precise shape required for high performance. Idea is to use integrated system of sensors, control processor, and actuators to measure and suppress both vibrations and static or slowly varying (e.g., thermal) deviations from desired shape. Technology applicable to other elastically deformable structures.
    Keywords: ELECTRONIC SYSTEMS
    Type: NPO-17598 , NASA Tech Briefs (ISSN 0145-319X); 14; 4; P. 43
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