Research On Exact Geometry Based Quasi-conforming Analysis For Load-bearing Body Frame Structure

The load-bearing body frame structure is a major part in the auto body structure,and bears most of the vehicle's self weight and external loads,so its structural quality determines to a large extent the overall performance and service life of the vehicle.At the same time,load-bearing skeleton body also accounts for a large proportion of vehicle weight,which has great research value for vehicle body lightweight design.Therefore,in order to study the static and dynamic performances of load-bearing body frame structure,this paper establishes a simplified model of car body and beam element for racing car and passenger car.In this paper,the exact geometry based analysis method is applied.The beam structure is described by multi-patch non-uniform rational B-spline functions.The geometry is exactly described and the geometrical error introduced with finite element mesh can be avoided.In this paper,the following works are done for exact geometry based quasi-conforming analysis of the load-bearing body frame structure.(1)In order to improve the precision and efficiency of static simulation of the load-bearing body frame structure,the technique of multiple sets of approximation functions which originated from quasi-conforming finite element method is first applied in analysis of three-dimensional beam structure to solve the locking problem.Order-reduced approximation functions are applied to simulate the strains of beam.Global formulation of strains of beam is applied and the stiffness matrices of beam elements and patches can be combined without transformation between local and global coordinate systems.Numerical experiments prove that the proposed algorithm effectively avoids the locking problem in Timoshenko beam formulation,and is suitable for analysis of complex three-dimensional beam structures.(2)The dynamic simulation of the load-bearing body frame structure is investigated,and the mass matrix is derived by the Hamilton principle,and applied to the dynamic analysis of the three-dimensional frame beam structure.Numerical results show that the algorithm can effectively deal with the modal analysis of three-dimensional complex beam structures.(3)The simplified model of the beam element of the car and bus frame body is established,and the bending,torsional and modal analysis of the simplified model of the car and bus frame body are verified.The numerical results show that the method can effectively deal with the static and dynamic problems of the bearing frame body,which lays thetheoretical foundation for the further study of the exact geometric quasi coordination algorithm of the bearing frame body.