Lightweight Design Of Body Structure Based On NVH Performance

Vibration and Noise(Noise Vibration and Harshness,NVH)performance,as the main index for evaluating car comfort,will directly affect consumers’ purchase intention.Noise Transfer Function(NTF)is an important parameter for the NVH performance of the vehicle body,which is defined as the sound pressure value obtained by applying a unit-sized excitation force at the main attachment point of the vehicle body to the chassis somewhere in the cab.NTF reflects the acoustic characteristics between the body and the passenger compartment,and can be analyzed and predicted by the sound-solid coupling theory in the early stage of body design.The lightweight research of automobiles also has important significance for energy consumption and environmental development.Therefore,the mastery of NVH performance and lightweight technology is an effective way for major car companies to improve their competitiveness.In this paper,a new domestic unlisted SUV is taken as the research object,the finite element simulation and test method are used,the purpose of this paper is to optimize the vehicle body NTF function and reduce body weight.The main research work is as follows:(1)Finite element models of the interior trim body(Trim Body,TB)and the acoustic cavity of the car are developed based on the Body In White(BIP),the free mode of the body in white is calculated,and a preliminary understanding of dynamic characteristics of the body structure and the acoustic characteristics in the passenger compartment is improved;test the typical modes of the BIP and TB body structures using tests,and compare with the finite element calculation results to verify the reliability of the simulation model;and then perform NTF test tests on the TB body.Put the experimental and simulation NTF curves in the same graph for comparison to verify that the trends and key peaks of the two are consistent.Based on the results of simulation and experimental analysis,the frequency of the NTF problem is determined,and the goal is to reduce the peak NTF of the problem,and the multi-objective optimization analysis and calculation are performed in conjunction with the body weight reduction requirements.(2)The total body mass is proportional to the body panel thickness,however,the relationship between body noise transfer function and body panel thickness are nonlinear.According to the body structure,the thickness of 16 panels is selected as the optimization variable.In order to reduce unnecessary calculations,the sensitivity analysis is used 10 optimization variables that are sensitive to the target response are selected to perform the final multi-objective optimization analysis.(3)A multi-objective optimization design method to reduce the sound pressure at the driver’s right ear and the weight of the body structure is provided in this paper.The plate thickness of the selected 10 body structures is used as the design variables,and the Latin hypercube method was used to generate sample points.The target is the root mean square value of sound pressure at the driver’s right ear and the total mass of the components where the optimization variables are located.The first-order bending modal frequency and the first-order torsional frequency of the Trim Body are used as constraint conditions.Then multi-objective optimization software Isight is used to build three commonly used approximate models based on experimental design.After error analysis and accuracy verification,Kriging is finally used.The finite element model is replaced by the model based on Kriging function for multiobjective optimization.The results show that the noise value at the right ear of the driver is reduced by 1.6d B which achieves the target value,and the body mass is also reduced by 8kg.