A structural modification methodology adapted to a vibro-acoustic model to improve the interior noise

Abstract

The structural-borne noise inside the passenger cabin of automobiles, which is mainly caused by the vibrating panels enclosing the vehicle, dominates the low frequency noise inside the cabin. The sound pressure level (SPL) can be predicted using a vibro-acoustic model which includes the Finite Element Model (FEM) for the structural analysis and the Boundary Element Model (BEM) for the acoustic analysis. The structural design of the panels can be modified to improve the SPL. The modal analysis of the structural model must be repeated after every modification before the reanalysis of the vibro-acoustic model. However, such changes require considerable computational time especially when the structural models are very complex. In anticipation of these needs, we adapted a methodology that utilizes the frequency response functions (FRFs) of the original model for the reanalysis of the structure that is subjected to structural modification. We used a rectangular box with a flexible mid-panel to demonstrate the developed methodology. In the presented method, the receptances of the original structure are used together with the dynamic stiffness of the modifying components to perform the structural modification and to calculate the receptance matrices of the modified system. Then, the receptance matrices are used to calculate the velocities at the structural nodes under the effect of the excitation forces. The calculated velocities are used as boundary conditions for the acoustic analysis to calculate the nodal pressures at the predefined locations. Finally, the acoustic performance of the rectangular box is compared before and after the modification.