The Study On Several Key Problems Of Derect-inverse Mixed Dynamics Of Multibody System

With the development of space science and technology, the application of multibody dynamics in space science is extending. The calculation of direct problems can no longer supply the demands of engineering. The direct-inverse mixed dynamics has become the hot topic. Thus, this paper studies on several key problems about the mixed dynamics to expand the application of multibody dynamics in engineering.Nowadays, the design of flexible parts of spacecraft has new directions of complex geometry, high flexibility, large deflection and nonlinear material, which claimed new requirements in simulation. The main targets of this paper are the data transformation from finite element method(FEM) to multibody dynamics, the handle of nonlinear model and order reduction of models with dense modal.In the first chapter, the target and significance of this paper are discussed. Research status of multibody dynamics and developing situation of simulation software is given. The research extent and contents of this dissertation are put forward.In the second chapter, the forward recursive formulation of flexible multibody system is introduced. First of all, the dynamics equation of single flexible body is given by speed variational principles. Then the kinematics recursive relations between objects is given by the motion of the hinge and the hinge effect point. At last, the dynamics equation taking hinge coordinate and modal coordinate of the flexibility body of the systems is given by changing the absolute kinematics amounts into the relative kinematics amounts.In the third chapter, the multibody dynamic software named CADAMB is expanded. After the introduction of CADAMB, the idea and method of expanding is described. The data interface program written in Matlab language can transform FEM information from MSC. Patran to CADAMB. The program is divided into four parts, each of which handles different data of modal, frequency, node positions and node mass. The interface has generality that independent on the solution of FEM software. The expanded CADAMB can build any type of dynamic model through FEM software, which applying scope is thus expanded.In the forth chapter, nonlinearity of spacecraft system is discussed. After checking the correction of CADAMB, a space station system is chosen as an example to found the dynamics model. The simulation of several conditions of the system is calculated by both linear and nonlinear data. The comparison of the two method shows that the application of nonlinear modal in mixed dynamics problems is necessary. It is also suggested that expanded CADAMB is able to handle nonlinear modal while ADAMS cannot. In the fifth chapter, the problem of order reduction is studied. Modal contribution analysis(MCA) is introduced to reduce the mechanics model of spacecraft systems with dense modal. The response of driving mechanism of both reduced and original model are simulated to compare with each other. It is found that MCA is suitable for dense modal system and efficiency of computation is improved, which provides ideas for similar problems in future.The topic of dynamics of flexible multibody system is challenging both in mechanics and in control engineering, where many aspects need further study and more efforts. At conclusion, a summary of work done in this dissertation is given and some problems of interest are also brought forward for future research.