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Typical automotive muffler designs contain complex internal components such as extended inlet/outlet tubes, thin baffles with eccentric holes, internal connecting tubes, perforated tubes, perforated baffles, flow plugs and sound-absorbing materials. An accurate performance prediction for highly complicated muffler designs would greatly reduce the effort in fabricating and testing of multiple design iterations for engineers. This paper discusses the use of a component-based computer simulation tool for design and analysis of exhaust mufflers. A comprehensive computer program based on the Direct Mixed-Body Boundary Element Method was developed to predict the transmission loss characteristics of muffler systems. The transmission loss is calculated by an improved four-pole method that does not require solving the boundary element matrix twice at each frequency, and hence, it is a significantly faster approach when compared to the conventional four-pole method.

In this paper the application of the Boundary Element Method (BEM) to problems in acoustics and noise control will be reviewed. The BEM is a computational method for solving the acoustic wave equation when the acoustic domain has an irregular or arbitrary shape. Examples of such problems in the automotive industry include the radiation of sound from engines and other vibrating structures, the scattering (diffraction) of sound from irregular surfaces and obstacles, the acoustical response of passenger compartments of vehicles and the attenuation of mufflers and other exhaust or intake system components. The BEM is distinguished from other numerical methods such as the finite element method in that with the BEM only the surface or boundary of the acoustic domain must be discretized. This is an important feature in solving radiation problems, where the domain is infinite or semi-infinite, but is also beneficial for cavity and muffler problems as well.