Boundary Element Analysis of Reactive Mufflers and Packed Silencers with Catalyst Converters

This paper reviews recent developments in the application of the boundary element method (BEM) to muffler and silencer analysis. Initial results of modeling built-in catalyst converters are also presented. A so-called “direct mixed-body boundary element method” has been developed for muffler and silencer analysis since 1996. The idea of the method is to integrate all kinds of different boundary and internal surfaces into a single integral equation set without using the conventional multi-domain approach, even though there may be different media in the domain. A key ingredient in this method is the hypersingular integral equation. The concept of the direct mixedbody BEM is not totally against the conventional multi-domain BEM, though. For very large structures or at high frequencies, a multi-domain or substructuring approach is still necessary in order to reduce the memory usage as well as the computation time. With the direct mixed-body BEM, each substructure does not need to be a well-defined and homogeneous subdomain. As such, substructuring can be done more naturally along the longitudinal direction. Catalyst converters may also be modeled as a modular in the general framework of substructuring. Several test cases are presented with experimental verification, including two cases with built-in converters.