Modeling Theory And Experiment Research For Flexible Multibody System With Large Deformation

So far the theory for multi-rigid-body system dynamics is becoming mature. With the development of high-technology, many modern high-speed, light flexible multi-body systems such as flexible aircraft, flexible thin and long manipulator, train pantograph system, etc are used in many areas. In case that these mechanical systems undergo large overall motion, due to large deformation, the coupling effect of the deformation on the large overall motion is significant. Previous researches have indicated that the traditional modeling method based on the small deformation and small rotation assumptions can not lead to accurate results for these flexible multi-body systems. In this dissertation, based on the previous researches of multi-body dynamics and using the absolute nodal coordinate formulation, dynamic modeling theory of flexible multi-body system with large deformation is investigated. Experiment of rigid-flexible coupling system with large deformation is carried out to verify the correctness of dynamic theory. The research work is introduced as follows:In chapter 1, the engineering application background and the significance of the research work on flexible multi-body system dynamics are introduced. The research development of the theoretical analysis and experiment investigation for the flexible multi-body system dynamics is reviewed, and the objective of the research is proposed. In the chapter 2, dynamic modeling theory and experiment technique for flexible planar beam system are investigated. The rigid-flexible coupling dynamic equations for the multi-body system composed of air-bearing test bed and elastic beam are derived based on complete geometric nonlinear model for an elastic beam. Then simulation and experimental research on hub-beam system with large deformation are carried out for analysis of applicability of complete nonlinear model. Based on this, dynamics theory is extended to flexible multi-body system composed of a hub and several planar beams. Experiment of the rigid-flexible coupling system composed of an air-bearing test bed and two rectangular beams with large deformation is designed to verify the correctness of the complete nonlinear model of this dissertation by comparison of the theoretical and experiment results. Based on the nonlinear dynamic model of flexible planar beam, the arc coordinate is used in curved beam element. By using the absolute nodal coordinate method as well as nonlinear strain-displacement relationship, dynamic model for a curved beam with large deformation are established. Numerical simulation verifies the accuracy and effectiveness of dynamic model for curved beam element.In chapter 3, the precise geometric nonlinear dynamic model for a flexible spatial beam is established based on the absolute nodal coordinate method. In order to facilitate the calculation and to avoid the shear locking of the beam which may affect the convergence, it is assumed that the tangential direction of the beam element node coincides with the normal direction of the cross section. The number of generalized coordinates is reduced from 6 to 4 based on the assumption above, which can simplify dynamic model of flexible spatial beam as well as solving the long-standing problem of shear locking within a certain range. Through comparison of the simulation results of two methods under different physical parameters, the applicability in various circumstances of the simplified model is analyzed, and then the rigid-flexible coupling dynamic equations for the multi-body system with large deformation composed of air-bearing test bed and spatial beam are derived based on two models above, respectively.In chapter 4, experiment technique for flexible multi-body system composed of a hub and a spatial beam is investigated. Firstly, dynamic equations of hub-beam system are derived considering structural damping. In case of small deformation, comparison of the numerical simulation results with Ansys results verifies the correctness of the simplified model. In case of large deformation, experiment of the rigid-flexible coupling system composed of an air-bearing test bed and a spatial beam with large deformation is designed and carried out to verify the correctness and wide applicability of the complete nonlinear model of spatial beam with large deformation.In chapter 5, the investigations in this dissertation are summarized and the prospect of the research is proposed.