On the improvement of the solution accuracy for exterior acoustic problems with BEM and FMBEM

The boundary element formulations suffer from the non-uniqueness of the solution. Consequently, fictitious resonances degrade the exterior field prediction. This paper investigates the benefits of using different approaches to mitigate fictitious resonances to improve the solution accuracy in real industrial cases. For direct BEM simulations, over-determination points are added to the interior of the cavity as suggested by the CHIEF method. For indirect BEM and Fast Multipole BEM simulations, the impedance condition is put over the interior boundary and two different values of absorption are applied to observe the effects on the response. The different BEM methods are applied to simulate the exterior sound radiation of three different gearbox housings. The numerical results are compared with high quality measurements enabling the benefits and the improvements on the solution accuracy of each method to be evaluated.