Multi-objective Structure Optimization Of A SUV Body-in-white Based On Static Stiffness

The body is an important part of the automobile,the stiffness of the body is closely related to the safety and maneuverability of the vehicle.With the continuous development of science and technology,more and more components are added to the body of the car,which puts forward higher requirements for the stiffness of the body.The stiffness of the body is divided into dynamic and static stiffness,dynamic stiffness means modal stiffness,and static stiffness means bending and torsional stiffness.In this paper,the BIW(body in white)of an SUV is taken as the research object,and shape optimization and size optimization are used in combination.The bending and torsional stiffness of the body are improved without significant changes in the shape and quality of the body,which is of certain referen ce significance for the research and development of new cars and performance improvement.Firstly,the BIW static stiffness test is carried out.The test is conducted according to the enterprise’s static stiffness test standard,and the bending and torsional stiffness test values of the BIW are obtained.Secondly,the stiffness simulation analysis and verification of BIW finite element model.Carry out geometric cleaning of the body model,extract midplane,mesh division,establish solder joints and adhesive connections,and give each part thickness and material properties,establish a body-in-white finite element model and check the mesh quality,the results are in line with Simulation requirements.Refer to the actual vehicle test and set the bending and torsion conditions of the BIW.Considering the natural amount of sinking under the bending condition of the car body,a linear method is proposed to correct the displacement of the measuring point under the bending condition.The errors of the bending stiff ness and torsional stiffness obtained from the simulation and the actual vehicle test values are 6.1% and4.8%,respectively,and the established finite element model is considered reasonable.On this basis,the free mode analysis of the BIW is carried out,and the first six order elastic body modes are obtained.Finally,the multi-objective optimization design is carried out with the aim of improving the torsional rigidity of the BIW..Based on the simulation results of bending and torsional stiffness,the shape variables are set for the center longitudinal beam,and the dimensional design variables that have a significant influence on the bending stiffness and torsional stiffness are obtained through relative sensitivity analysis.Parameterize the finite element model and design variables of the set working conditions,write a custom function of bending and torsional stiffness,extract the mass,first-order modal frequency,bending and torsional stiffness of the body as the response,and set the upper and lower limits of the variables.Using the Hammersley sampling method to obtain 105 sample data,using moving least squares(MLSM)to establish a second-order approximate model of each response;using the Latin hypercube sampling method to obtain 60 sample data,verify that the established approximate model is reasonable.Taking bending amd torsional stiffness as the target and body mass and modal frequency as the constraints,the multi-objective genetic algorithm(MOGA)is used to calculate and solve,and the final optimization plan is determined through the comparative analysis of different programs and the lightweight index.The results show that the flexural stiffness is increased by 5.39% and the torsional stiffness is increased by 4.64% without increasing the mass by 0.65% and the first-order modal frequency.