Study On Multidisciplinary Optimization Of High Speed Train Carbody Structure

High speed train is a complex system engineering.And the design of the car body is not only required to meet the basic requirements of strength and stiffness,but also a variety of subject problem are involved,such as aerodynamics,multi-body dynamics,collision safety and lightweight structure design.During the actual operation of the train,the lightweight vehicle is subjected to different loads including the aerodynamic load,the random vibration load produced by the track excitation and the effective load produced by the equipment and the passenger.Therefore,to consider comprehensively the dynamic characteristics of car body under these loads,a multi-disciplinary structure optimization design method based on the specific structure is proposed under the support of the national natural fund project(51375405)and the free exploration project(2016TPL_T10)of the laboratory.High-speed train aerodynamic model,rigid-flexible coupled multi-body system dynamics model,car body structure finite element model and multi-objective optimization approximation model are used in this method.The multi-disciplinary performance of the carbody structure is calculated and analyzed.The multi-objective optimization design of the carbody structure is realized by using the multi-disciplinary optimization platform.Firstly,the aerodynamic load of the train under the action of different running speed and wind speed is calculated by the CFD software,and the distribution characteristics of the pressure distribution on the outer surface of the train and the distribution of the flow field are analyzed.Secondly,the aerodynamic load is added to the rigid flexible coupling multibody system,then the critical speed,safety and stability of the vehicle model are analyzed,and the dynamic stress data of the structure during the vehicle running process is used to calculate the body fatigue.Considering the aerodynamic load and the conventional static load of the rail vehicle as the boundary condition of the finite element calculation of the car body structure,the strength and stiffness performance of the structure are verified.In addition to considering the strength and stiffness requirements,the dynamic characteristics of the car body structure should also be considered,and the modal analysis of the car body finite element model should be carried out.Thirdly,26 thickNess parameters are taken as the design variables by using the Isight multi-disciplinary optimization design platform,where the maximum equivalent stress and the maximum vertical displacement of the car body structure under the integrated load are taken as the constraint conditions.And the vehicle body quality and the natural frequency of the first vertical bending vibration of the body structure are taken as the target.A multiobjective optimization is used to obtain a set of optimal parameter combinations for vehicle structure performance.Finally,the acceleration fatigue calculation of the body structure before and after the optimization is carried out,and the fatigue resistance of the body structure is coMpared and analyzed to ensure that the structure is satisfied the design requirements of the body strength,stiffness,fatigue resistance and dynamic characteristics,so that the lightweight design of the car body structure is realized.Under the premise of satisfying the static and dynamic performance of the structure,the quality of the carbody is reduced by 538 kg,and the lightweight efficiency is 6.68%.The natural frequency of the first order bending of the body structure is 18.65 Hz,which is 3.1% lower than the first order vertical bending frequency of the initial body structure,and it is higher than the proposed value 14 Hz of the first natural vertical bending frequency for the aluminum alloy car body structure.Accordingly,the dynamic design requirements of the EMU are achieved.The fatigue co Mparison of vehicle body structure before and after optimization is carried out under multiple load conditions.And it is found that the fatigue performance of the optimized car body structure is improved.This paper can provide useful information for relevant designers to weigh the multi performance targets of high-speed train body structure,and for the multi-objective optimization design of similar large-scale mechanical structures,it is also provided valuable reference for in-depth research and engineering application.