Analysis And Optimization Of Commercial Vehicle Cab Structure Noise Based On The Response Surface Method

NVH performance is an important factor of vehicles comfort and an important specification to measure the quality of automobile design and manufacturing. Commercial vehicles always run on poor road with complex and changing condition. Therefore the cab structure will produce strong vibration and noise, which can seriously affect the acoustic comfort of the driver, and can easily lead to fatigue and malaise. Furthermore, the strong vibration and noise in the cab structure may also result in errors of judgment and even cause accidents. Reducing the cab interior noise is an effective way to improve the interior acoustic environment and riding comfort, it also has important economic and social benefits.This thesis, funded by the project "The Key Technology of Vehicle Lightweight and Its Industrialization"(Project’s Serial Number:K1306007-11-1), chose a commercial vehicle as the research object. The FEM and acoustic CAE technology are used to analyze the structure dynamic performance and interior noise response characteristics of the cab of this commercial vehicle. The cab noise transfer function from the suspending point to the measured point (driver’s right ear) has been calculated. Through the panel contribution analysis, the body panels which have greater influence on the cab interior noise are identified. The thickness of those plates is set as the design variable in the follow-up optimization design. A structural optimization approximation model based on the RSM (Response Surface Method) with the objective of minimizing the maximum of SPL (Sound Pressure Level) at measure point was built up in this thesis. Then, the optimization model was optimized by the genetic algorithm and the cab interior noise was decreased by modifying the structural parameters of body panels.The main contents of this thesis are as follows(1) The middle faces of component parts in the cab were extracted from the UG models and imported into the Hypermesh software to generate the finite element mesh. The finite element model of the cab and interior acoustic cavity were established; the modals of these models were analyzed by the software Nastran. The natural frequencies of the cab and interior acoustic cavity as well as the distribution of interior sound levels were obtained from those analyses.(2) The white noise excitation was added to the cab body and the SPL at the measuring point (Driver’s right ear) was calculated. Based on those results, the cab interior structure noise was predicted and the peak sound pressures and resonance frequencies were determined, which can provide the guidance for noise control.(3) Through the panel contribution analysis, the cab panels which have greater influence on the cab interior noise are identified. The thickness of those plates is chosen as the design variables in the follow-up optimization design. The cab interior noise can be reduced by changing the body structure.(4) In order to reduce the cab interior noise and control the radiated noise caused by panel vibration, the minimizing of the maximum of SPL (Sound Pressure Level) at the measuring point was taken as the optimization objective, the weight of the cab body was taken as the constraint condition, the thickness of plates were taken as the design variables. The approximation model based on the response surface method was built up and optimized by the genetic algorithm. At last, a new set of thickness of the cab panels after the optimization was got. The SPL results at the driver’s right ear before and after optimization were compared, which show that the peak sound level is decreased by the optimization, and the goal of interior structure noise reduction is achieved.This thesis investigates the problem of modal analysis, interior structure noise predicting and panel contribution analysis of a commercial vehicle cab. Based on the RSM approximation model, a method to reduce the sound pressure level at the driver’s right ear by modifying the structural parameters of cab panels was proposed in this thesis. The numerical analysis results of a commercial vehicle cab show that the proposed method is feasible and effective.