Stress State Analysis Method For The High-speed Train Car-body With Considering Coupled Mechanical And Aerodynamic Loads

The car body of a high speed train(HST)is a bearing structure welded by large extruded aluminum profiles and frame-skin components.The car body has to face triple complexities from the structure,loads and initial state,which interact and influence each other.Stress state analysis is the fundamental for predicting potential damage,failure,and etc.Therefore,a coupling loads based method for stress state analysis is important for reliability evaluation and structural optimization of the car body.In this study,the dominant loads in practice including mechanical loads and aerodynamic loads are considered as coupling loads.The structural stress state of the car body is analyzed systematically by using simulation and experimental validation.The main research work includes following aspects: A coupling method for aerodynamic and mechanical loads acting on the car body of the HST is proposed.Firstly,a three train-sets with considering compressible ideal gas and sliding mesh method is modeled to accurately study behaviors of the flow field in the open track intersecting,passing through a tunnel and tunnel intersecting conditions.The simulation results show good agreement with the experimental results.Secondly,the boundary conditions are loaded through force system equivalent on the master nodes,with which aerodynamic loads computed in different conditions are introduced in the flexible-rigid coupling model of the car body.Compared with the conventional rigid model,the mechanical loads on the car body and the influence of the parameters are transferred more accurately by using this model.The results show that the aerodynamic loads on the car body work together with the mechanical loads as coupling loads,which means that one will influence the other one’s behavior.The flexible vibration of the car body and the influence of the aerodynamic loads on the mechanical loads can be considered simultaneously by using the rigid-flexible coupled model.A combined interpolation method is proposed by using elemental nodes and element center with a weight coefficient.Facing up to the data transfer problems of non-matching grids in the fluid-structure interaction(FSI),the relation between theoretical errors and actual errors using different interpolation points is derived by means of polynomial functions based pressure distribution in the fluid domain.Three dimensional plane and curved surface cases are designed to discuss the weight coefficient and shape parameters,and the method is used to perform data transfer in the unidirectional FSI of the car body.The results show that a constant value can be regarded as the weight coefficient in two dimensional cases by using the proposed combined interpolation method,the maximum error in the numerical cases is lower than that using the independent nodes or center interpolation algorithm.Global bearing analysis of the car body based on the coupling aerodynamic and mechanical loads.A full-scale FE model of the car body is conducted,and the loads coupling is implemented by coordinating the calculation step sizes of the mechanical loads and aerodynamic loads,respectively.The structural response is conducted by considering independent load and coupling loads to study the stress components and their contributions to the structural bearing in different conditions.The results show that the mechanical loads is the dominant load for the hydrostatic stress,and the aerodynamic loads have the main effect of the stress magnitude.The stress fluctuation from high to low in order are tunnel intersecting,passing through a tunnel and open track intersecting.A shell-solid boundary condition transfer method based on hypothetical nodes and the elemental volume constraint is proposed.For the local analysis using submodeling method,the reconstructed local model is carried out by extending the dimensions and nodal numbers at the cut boundary.It can be concluded that the proposed method show better results than the commercial software ANSYS in the in-plane tensile,bending,in-plane shear cases.Reconstructed analysis of the local stress state of the car body by using submodeling method.The local submodels are reconstructed with respect to loading characters,and the global model analysis under coupling loads are regarded as boundary conditions to study their influence on the local stress state.The influence of defects and initial stress on the bearing capacity are also discussed.The results show that the stress state varying with loads can be revealed more realistically by using the solid element reconstructed model,the global-local analysis makes it possible to introduce the welding defects and welding residual stress in the submodel.In conclusion,the global-local simulation technology performed in this study is sufficient to realize the analysis on complex structures like HST car body under coupling loads,which will provide a more scientific method and tools for the reliability evaluation and optimization design of the car body.