Dynamics Of Flexible Multibody Dynamics With Elastohydrodynamic Lubricated Spherical Joints

Spherical joints for multibody systems have been widely used in various fields,such us vehicle transmission drive systems,parallel robots,space deployable mechanisms,ball bearings and human artificial hip joints.Previous studies indicated that Elasto Hydro Dynamic(EHD)lubrication with coupling effects between the joint outer bearing deformation and lubricant film pressure should be considered for the design of systems with high speed and heavy loads and artificial hip joints.However,most previous studies in the field of tribology only focused on an isolated EHD lubricated joint,which can't reveal the coupling dynamics behaviors of the flexible multibody system with EHD lubricated spherical joints.On the basis of previous studies,in the frame work of the multibody system dynamics theory,the dynamics of flexible multibody system with EHD lubricated spherical joints are studied in this thesis.The major work of the thesis is summarized as follows.1.A new spherical joint model for flexible multibody dynamics is proposed.The spherical joint model is described in a unified global coordinate system frame.That is,the flexible spherical socket is meshed by the finite element with global nodal position coordinates,and the rigid ball in the joint socket is described by the absolute nodal coordinate formulation reference node(ANCF-RN).This unified global coordinate description can lead to a constant mass matrix for the flexible multibody system dynamics equation,which helps to improve computation efficiency and simplify the constraint conditions.The Open MP based parallel computation scheme and the generalized-alpha method are used to solve the huge sets of flexible multibody system dynamic equations.The numerical results are also corroborated by using ADINA commercial software.2.The EHD lubricated spherical joint model and the algorithm to evaluate the lubricant pressure are proposed.The lubricant Reynolds' equation is discretized by the finite-difference method,and the lubricant pressures are obtained by solving the lubricant finite difference equations using the successive over relaxation(SOR)algorithm.To address the non-conformance problem between the finite-difference grid and the finite element grid,a novel rotation scheme of lubricant pressure field is also developed.3.The dynamics of flexible multibody system with a EHD lubricated spherical joint is studied.The solution algorithm for solving the dynamic equations of flexible multibody systems with an EHD lubricated spherical joint is established,and the influence of the EHD lubricated spherical joint on the system's dynamic responses is comparatively studied.To further study the dynamics of human gait mutlibody system with EHD lubricated spherical joints,a human gait multibody model with dry clearance spherical joints is established.The inverted pendulum model is used to plan the walking joint rotation angle,and the human gait dynamics behaviors are analyzed.