BOUNDARY-ELEMENT ANALYSIS OF MUFFLERS WITH AN IMPROVED METHOD FOR DERIVING THE 4-POLE PARAMETERS

When a muffler is modelled by the boundary element method (BEM), the t ransmission loss (TL) can be evaluated by either the conventional four -pole method or the recently developed three-point method. The three-p oint method produces only the transmission loss (TL), and nothing else . On the other hand, the four-pole method has the advantage of retaini ng the transfer matrix of the muffler, which contains important parame ters when the muffler is connected to another muffler or other compone nts in the exhaust system. However, the major drawback of the conventi onal four-pole method is that it requires two separate boundary elemen t runs due to the two different boundary conditions imposed on the out let boundary. Therefore, it can take twice as long to get the TL when compared to the more efficient three-point method. In this paper, an i mproved method to derive the four-pole parameters for use in the BEM i s introduced. Although two boundary element runs are still needed at e ach frequency, the improved method only solves the boundary element ma trix once at each frequency. Therefore, it is as efficient as the thre e-point method. More importantly, the improved method also produces th e four-pole parameters. The boundary element analysis is done by the d irect mixed-body BEM. Numerical predictions are compared to experiment al results for all test cases, including one with a mean flow effect. (C) 1998 Academic Press.