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Multibody dynamics Mechanical preliminary design Bending plate Model reduction a b s t r a c tThis article presents and validates a general framework to build a linear dynamic Finite Element-based model of large flexible structures for integrated Control/Structure design. An extension of the Two-Input Two-Output Port (TITOP) approach is here developed. The authors had already proposed such framework for simple beam-like structures: each beam was considered as a TITOP sub-system that could be interconnected to another beam thanks to the ports. The present work studies bodies with multiple attaching points by allowing complex interconnections among several sub-structures in tree-like assembly. The TITOP approach is extended to generate NINOP (N-Input N-Output Port) models. A Matlab toolbox is developed integrating beam and bending plate elements. In particular a NINOP formulation of bending plates is proposed to solve analytic two-dimensional problems. The computation of NINOP models using the outputs of a MSC/Nastran modal analysis is also investigated in order to directly use the results provided by a commercial finite element software. The main advantage of this tool is to provide a model of a multibody system under the form of a block diagram with a minimal number of states. This model is easy to operate for preliminary design and control. An illustrative example highlights the potential of the proposed approach: the synthesis of the dynamical model of a spacecraft with two deployable and flexible solar arrays.
Modern space observation missions demand stringent pointing requirements that motivated a significant amount of research on the topic of microvibration isolation and line-of-sight stabilization systems. While disturbances can be reduced by mounting some of the noisy equipment on various isolation platforms, residual vibrations can still propagate through and be amplified by the flexible structure of the spacecraft. In order to alleviate these issues, the line-of-sight must also be actively controlled at the payload level. However, such systems typically have to rely solely on low frequency sensors based on image processing algorithms. The goal of this paper is to present a model-based control methodology that can increase the bandwidth of such systems by making use of additional rate sensors mounted on the main disturbance elements impacting the optical path. Following a comprehensive model identification and uncertainty quantification part, the robust control strategy is designed to account for plant uncertainty and provide formal worst-case performance guarantees. Excellent agreement between theoretical prediction and experimental results are obtained on a test bench developed at the European Space Agency.
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