Abstract:

The boundary-element method has gained wide acceptance as an acoustic analysis tool in the automobile industry. The methodology for extracting eigenvalues of acoustic cavities of complex shapes by the boundary element method is not yet well established. The finite-element method is widely used for eigenvalue analysis, but it is very expensive and time consuming to build a finite-element mesh solely for this purpose. Two ways for estimating the natural frequencies of a cab cavity from its boundary element model are discussed in this paper. One approach is derived from the experimental technique for determining cavity modes. An acoustic (point) source(s) placed inside the cab is used to excite the various cavity modes by doing a frequency sweep in the range of interest. The response is measured at suitable locations and the identified peaks in the frequency response function give an estimate of the cavity modes. By examining the sound pressure level plots on the boundary, the type of mode is identified. The second approach makes use of an automatic mesh generator which automatically meshes the interior cavity by tetra elements from a boundary element model. Then, a finite-element eigenvalue analysis is carried out to determine the cavity modes. Both of the above approaches require significantly less time than constructing a finite-element model. Numerical examples of a rectangular box and a simple car model are considered, and results obtained from a regular finite-element model, tetra finite-element model, and a boundary-element model are compared. [See NOISE-CON Proceedings for full paper.]