Modelling Method Research For Coupling Dynamics Of Multibody Systems Based On Bond Graph Theory

To complicated multibody systems, different kinds of computer aided modeling and simulation procedure based on analytic mechanics have been proposed. As a result, some representative system dynamic analysis softwares with powerful function are developed. But these procedures and softwares are only suitable for the partial dynamic analysis of systems with single energy domain such as mechanical system. For the system with the coupling of multi-energy domains, such as the systems with the coupling of machine, electricity, hydraulics, pneumatics, rigidity and flexibility, they can not be used for deriving the forward and inverse system dynamic equations and constraint force equations in a unified manner automatically on a computer. So that the global dynamic analysis of systems can not be carried out. These result in larger error in dynamic analysis. In addition to these, the simulation efficiency of system should be increased further. The above problems have become the ultimate obstacle of analysis, study, development and application for the multibody mechanical systems with the integration of multi-energy domains, and made bond graph theory become very important to the global dynamics of systems with multi-energy domains.By the research work in this dissertation,a series of important problems of global dynamic modelling and simulation for multibody systems with the coupling of multi-enegy domains based on bond graph theory are solved. As a result, the dynamic analysis software with more powerful function are supported theoretically, and the automatic and reliable level of this kind of work can be raised greatly. The research work in this dissertation can be widely used in the fields such as vehicle system, numerical control machine, engineering machine, robot, general machine,and space machine, etc.In this dissertation, the modeling and simulation procedure based on bond graph theory for the coupling dynamics of multibody systems is described systematically. From the viewpoint of enegy conservation, the properties of bond graph multiport element MTF are discussed. Thus knowledge of the flow vector relationship across the MTF dictates the effort vector relationship through a simple matrix transposition, and vice versa. Based on this, the generic procedures of modeling planar rigid multibody system, planar rigid multibody system in non-inertial coordinate system, planar flexible multibody system, planar flexible multibody system in non-inertial coordinate system and spatial multibody system by bond graphs and their dynamic principles are described.The kinematic and geometric constraints between bodies of multibody system result in differential causality loop, and the nonlinear velocity relationship between the mass center and an arbitrary point on a body leads to the nonlinear junction strcture. These bring very difficult algebraic problem for automatic modeling and simulation on a computer by traditional standard bond graph method. To solve this problem, two strategies with different characteristic are proposed in this dissertation. First, in the frame of standard bond graph theory, the constraint forces at joints can be considered as unknown effort sources and added to the corresponding 0-junctions of system bond graph model. Second, by means of the equivalent transformation between basic elements of bond graph, the standard bond graph can be transformed into gyrobondgraph. By means of the two above strategies, the decoupling to differential causality loop and nonlinear junction structure can be realized. As a result, the algebraic difficulty brought by them for computer aided modelling and simulation of system global coupling dynamics can be solved.For inverse dynamic problem of multibody system, the different form of unified formulae of system state-space equations and constraint force equations at joints are derived in the frame of bond graph and gyrobondgraph theory respectively, they are very suitable for the automatic modeling and simulation on a computer for complex multibody systems with multi-energy domains. For forward dynamic problem, the different form of unified formulae of balancing moments and constraint forces at joints are derived in the frame of bond graph and gyrobondgraph theory respectively, they are very suitable for computer aided static analysis for dynamic of complex multibody systems with multi-energy domains. By these procedure, the acceleration analysis of system is not needed, so that the efficiency and reliability of static analysis for dynamic of complex multibody systems is increased.In addition to above work, the corresponding system dynamic analysis software is developed based on MATLAB. As a result, the automatic dynamic modeling and simulation on a computer are realized. The validity of the procedures are illustrated by a lot of typical examples of application.