Research On Rigid-flexible Coupling Dynamic Modeling And Attitude Control Technology For Flexible Spacecreaft

The flexible spacecraft is investigated in this thesis. The continuous dynamic modeland the finite dimensional dynamic model of the flexible spacecraft are both established.Based on the simplified rigid flexible coupling state space model, the trajectory of theattitude maneuver of the flexible spacecraft is optimized, and the corresponding controlleris designed to track the standard trajectory. The main content and the innovation of thethesis can be summarized as following:Aiming at the rigid flexible coupling dynamic characteristics of the flexible spacecraftof which the attitude maneuver is in the plane, a typical kind of rigid flexible couplingphysical models is proposed for dynamic modeling. The models can be sorted into threebasic classes on the basis of the modeling methods: central rigid body-flexible beamsystem (Hub-beam), central rigid body-flexible beam-tip additional payload(Hub-beam-tip payload), central rigid body-flexible beam-non-tip additional payload(Hub-beam-payload). On the basis of the structural characteristics of the flexibleappendages, the models can be sorted into two basic classes: the uniformed section systemand the variable section system. The physical structures of these models can besuperimposed together, and the modeling methods of them can be combined for applicationeither. Thus, a complete series of methods for rigid flexible coupling modeling and analysisof the models (whose structure is like central rigid body-flexible beam-additional payloadsystem) could be established.A comprehensive description of the flexible appendage is provided in two aspects:behaviors and inherent attributes. First, based on the assumption of the nonlinearstress-strain relationship of the material, the expressions of the geometry-stress relationshipof the transverse vibration of the beam are established. Then, based on the expressionsobtained and the virtual displacement principle of the deformation solid, the descriptionequation of the dynamic deflection of the transverse vibration of the beam is derived. Thus,the transverse vibration of the flexible beam could be successfully described via thedynamic deflection. The equivalent bending stiffness of the transverse vibration of the linear elastic deformation beam is studied as the prime inherent attribute. Based on twobasic models of the beam, the complete calculating methods of the equivalent bendingstiffness are obtained.According to the theory of mechanics problem in a non-inertial coordinate system, twokind of inertial forces are introduced. By using the subsystem modeling method, thecorresponding continuous dynamic model of the rigid flexible coupling system isestablished with the assumption of the liner elastic deformation. The continuous dynamicequation of the flexible beam of the system is analyzed, and the terms of the external actingload in the equation are sorted into three types according to the mechanics effect: theoscillation starting term, the dynamic stiffening term and the coriolis inertial coupling term.Then, the mechanisms of the three are analyzed comprehensively. In this thesis, Thetheoretical explanation for dynamic stiffening is provided in the form of continuousdynamics for the first time.Based on the orthogonalization conclusions of the normal constrained modes of theflexible beam, the finite dimensional dynamic model of the flexible spacecraft isestablished. First, for the uniform section system, a series of conclusions about thefrequency equation and the orthogonalization of the constrained modes are obtained byanalyzing the boundary conditions of the free vibration of the flexible beam. Then, basedon the conclusions above, the continuous dynamic equations of the subsystems arediscretized to establish the finite dimensional dynamic model and the rigid flexiblecoupling state space model. Finally, the dynamic modeling of the central rigidbody-variable section beam system is simply investigated. It is pointed out that, the keypoint of the finite dimensional modeling of the system with variable section beam is to offerthe exact expression of the constrained mode.Based on the finite dimensional dynamic model of the flexible spacecraft, thenumerical simulations are carried on in two aspects: the natural frequency of the transversevibration of the flexible beam and the dynamic responses of the rigid flexible couplingsystem. The dynamic stiffening phenomenon of the first-order model is validated, thedynamic softening effect of the coriolis inertial coupling term is clearly provided, and therigid flexible coupling dynamic response characteristics of the first-order model are studied. Meanwhile, the effect of the additional payload on the transverse vibration of the beam iscomprehensively discussed, and the final conclusion is provided: the additional payload hasa dynamic softening effect.Aiming at the optimization of the attitude maneuver trajectory, based on the globalpseudo spectral method, an adaptive Radau pseudo spectral method is put forward. In thepractical examples, the simulations are carried on by using the simplified state space modelof the flexible spacecraft. The simulation results show that, via the adaptive Radau pseudospectral method, the optimized attitude maneuver trajectory of the flexible spacecraft notonly can meet the optimal objective function, but also can satisfy the terminal constraint.To solve the robustness problem of the classic control method when there existsdisturbance in the process of the attitude maneuver of a flexible spacecraft, a controlalgorithm based on the second-order quasi-continuous sliding control theory is presentedto track the nominal attitude-time profile. The simulation results show that, the adjustmentof the coefficient of this method is very simple, and it can deal with the influence of theinitial state bias and the external disturbance torque, and has a good robustness.