Research On Car Interior Noise Control And Structure Optimization

With the rapid development of social economy and the improvement of people’s living standards, car plays more and more important role in people’s life, lightweighting、dynamic performance、reliability、security and comfort have become the important criterions of measuring car quality. At present, the technologies of lightweighting、dynamic performance、reliability and security have been perfect for car manufacturers both at home and abroad, but car comfort has been a hot issue in automotive engineering. An important factor of car comfort is NVH performance, reducing vibration and noise can improve car comfort.This thesis was based on the NVH project of "YueSheng Program"—The high level of independent innovation of car manufacturing in China (referred to as "ZhongQi Project"), the finite element analysis method was applied to numerical simulation of "ZhongQi Project" car, the first-order whole torsion modal of body in white was studied and vibro-acoustic characteristics of car body acoustic-structure interaction system were analyzed, acoustic responses of interior car caused by unit excitations which were applied to the junctions of car body and rear subframe were calculated, through panel contribution analysis, the body panels which have greater influence on car interior noise were identified, the radiated noise caused by panel vibration can be reduced by modifying and optimizing the structural parameters of panel.The main research works are as follows:(1) The middle faces of component parts in "ZhongQi Project" car were extracted from the UG models, then they were put into HYPERMESH software to generate finite element mesh. The finite element models of body in white、trimmed body and interior acoustic cavity were established; the modals of these models were analyzed by using the finite element analysis software NASTRAN, the results shows that the first-order whole torsion modal frequency of body in white of "ZhongQi Project" car was low, it may cause resonance with the excitation frequency of engine idle speed.(2) Because the first-order whole torsion modal frequency of body in white in "ZhongQi Project" car was low, the modal sensitivity analysis method was used to calculate the sensitivity of the first-order whole torsion modal frequency to all plate thicknesses, considering the requirement of car lightweighting, the sensitivity of weight of body in white to that of single panel was also calculated, the ratio of the first-order whole torsion modal sensitivity and weight sensitivity was taken as the relative first-order whole torsion modal sensitivity value, then it was sort in accordance with the absolute size, structure optimization was carried out to the fifteen panels which have greater influence on the first-order whole torsion modal, the first-order whole torsion modal of body in white was improved to avoid resonance by optimizing the panel thicknesses, while the weight of body in white was added less, it meet the requirement of car lightweighting.(3) The acoustic responses of interior car caused by unit excitations at the junctions of car body and rear subframe were calculated through car body acoustic sensitivity analysis, several peak frequencies can be acquired from the frequency-acoustic pressure curves, then the panel contribution of the car compartment wallboards was calculated at these frequencies, it was known that acoustic pressure contribution of the middle floor was larger at the peak frequencies, from the coupled contour-mode of the middle floor at peak frequencies we can see that the forepart of the middle floor deformed larger in some local regions, then we can use partial reinforcement to control the vibration deformation and reduce the radiated noise to the interior. The results showed that the partial reinforcement procedure can availably reduce the acoustic pressure at the peak frequencies.(4) Adding mass is a procedure to control the noise radiated by a plate, it’s easier to achieve on the process. This thesis used an acoustic radiation power program written in MATLAB, took the acoustic radiation power at the former three orders of modal frequencies as optimization objective, combined with the optimization software ISIGHT to optimize the location and size of added mass on the finite element mesh of the plate. The results showed that the noise reduction effect was ideal and the effect was more obvious than that of added uniform mass, it laid the foundation for applying it to vibration and radiated noise control of car body panels in the future.