DISCUSSION An Improved Formulation for Acoustic Eigenmode Ex traction from Boundary Element Models

Table 3 lists the first five modes of the car bodies. Figures 3 and 4 show the nodal contour lines of the first and third modes of these bodies. These results are in good agreement with the general trends observed by Nefske (1985) in his study of car cavity acoustic properties. As expected, the resonant frequencies fall with increasing cavity length and the nodal lines shift towards the rear of the car. It must be pointed out that computation times are greater for the BE models than for the FE models. This result is mainly due to the fact that BE models, while dimensionally smaller than FE models, generate full unsymmetric matrices, thus the BE formulation does not have a computational advantage over FE formulation proportional to the size reduction of the model. For pre-design evaluation, the BE model is however very attractive because it enables fast model generation and allows to easily assess effects of geometry modifications.