Numerical Analysis Of Car Interior Noise For Acoustic-Structure Coupled System

When we designs a new car, it will be great significant to predict and improve the interior noise of the cavity. As the quick development of the computer technology and numerical analysis method, Finite Element Method(FEM) and Boundary Element(BEM) method have been widely applied on the simulation of noise. This paper uses a developing car as an object, studying on how to apply FEM and BEM to predict the low frequency(200-200Hz) noise character, then optimizing the car body to reduce interior noise. The series of method about predicting and reducing low frequency noise studied in this paper is significance to the car design. The main research contents and consequent conclusions as follow:1. The body in white FEM model is built ,so as the whole car and cavity sound field, then the body FEM is justified by comparation the structure modal results to analysis and experiment. The modal results show that the body floor, front window and roof vibrate strongly; it also shows that the first two acoustic modal shapes are profit passengers.2. The sound pressure response character excitated by force of engine mount and spring system is analyzed. We can find out that the pressure distribution is closely related to the panels'vibration velocity and acoustic modal shapes, there are three pressure peaks near 100Hz, 130Hz and 157Hz at front chairs and also to 58Hz, 66Hz and 157Hz at back chairs. It also shows that the pressure below 120Hz is mainly excitated by spring load and the pressure above 140Hz is almost cased by engine mount load.3. From the results of panel acoustic contribution, we can conclude that the primary positive panels are dash, floor and back roof. The pressure peak near 157Hz is mainly contribute by front floor and dash, the lower frequency pressure peaks is mainly cased by back floor, middle floor and roof.4. The acoustic sensitivity analysis revealed that it will decrease little pressure by increase the Sabine absorption coefficient because of its small value in low frequency.5. In order to reduce the sound radiation, we apply topology technology to optimize the shape and location of beads on the panels which are the main positive contribution ones. After that, we optimize the thick of those panels. At last, all the pressure peaks decrease 2dB(A) at least, and the peaks near 58Hz and 66Hz totally disappear.