Reliability-Based Optimization Of Car Body’s Acoustic Performance Based On Response Surface Method

The vehicle NVH performance has become an important specification to measure the quality of automobile design and manufacturing, the vehicle interior noise has become one of the key factors that affect riding comfort. Therefore, how to reduce the vehicle interior noise, research the generation mechanism of automobile interior structural noise, improve the interior acoustic environment and riding comfort improve the design level on vehicle acoustics and market competitiveness, has important economic and social benefits.In the design stage, the topology optimization and coated with viscoelastic layer or absorption materials can effectively improve the acoustic performance of product structure, so as the product competitiveness. This thesis is based on the NVH project of "Yue Sheng Program"-the high level of independent innovation of car manufacturing in China (referred to as "Zhong Qi Project"), a reliability optimization method to improve the first-order whole torsion modal of body-in-white (BIW) is proposed by combining the response surface method and optimization technique, the vibration performance of car body is improved. This thesis has calculated the auto-body’s noise transfer function from the suspending point to driver’s right ear, through panel contribution analysis, the body panels which have greater influence on car interior noise are identified, a reliability optimization method to improve car body’s structure and acoustic performance is proposed by modifying the structural parameters of body panels or adding damping material.The main research works of this thesis are as follows:(1) After constructing the finite element models of the car body and acoustic-structure interaction models, the modal analysis is performed to research the vibration performance, the results shows that the first-order whole torsion modal frequency was close to the frequency of engine idling, it may cause resonance with the excitation frequency of engine idle speed. In order to get an intuitive understanding of the interior noise, based on the acoustic-structure coupling finite element model, the thesis calculated the auto-body’s noise transfer function from the left side spring of the front suspension to driver’s right ear by adding white noise excitation to car body. Then the vehicle interior noise is forecasted, the peak sound pressure and resonance frequency is determined, which provide guidance to control the car interior noise. (2) Because the first-order whole torsion modal frequency of the body in white of "Zhong Qi 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. Acoustic contribution of panel is applied to find out those car panel that have great effect on the peak sound pressure level, which can provid reference for noise reduction.(3) Aiming at the problem that the uncertainty of structure parameters of a vehicle body could lead to unreliable optimization results, a reliability optimization method to improve the first-order whole torsion modal of a body is proposed by combining the reliability analysis and optimization technology. The proposed method is based on an approximate structural model built through RSM (Response Surface Method), the body mass were taken as an optimization objective, the first order mode frequency as a design constraints of the reliability optimization. The reliability optimization on Structure vibration performance for a vehicle body is carried out, the results indicate that the proposed method can reduce the total mass, raise the first natural frequency, avoid idle resonance, reduce the vehicle interior noise and the goals of reliability optimization design are achieved.(4) In order to reduce the car interior noise and control the radiated noise caused by panel vibration, a reliability optimization method is proposed by modifying the structural parameters or adding damping material. In this method, the influence of various uncertain factors resulted from design functions and constraint conditions are considered. The first natural frequency and the total mass are taken as design constraints of the reliability optimization and the acoustic radiation power as optimization objective, the reliability-based optimization design for structure and acoustic performance based on response surface method is executed. The results verified the efficiency of proposed method.Based on the vibro-acoustic numerical simulation, response surface method, panel contribution analysis and optimization algorithm, the reliability theory was introduced into the optimization on vibro-acoustic performance; a reliability optimization method to improve the structural acoustic performance is proposed by optimizing the structural parameters of panels. The research findings have more engineering application foreground.