Boundary element analysis of packed silencers with a substructuring technique

It is well known that for certain large structures, substructuring can significantly reduce the matrix size and the total computational time. In this paper, a substructuring technique based on the impedance matrix synthesis is used along with the recently developed direct mixed-body boundary element method (BEM) to evaluate the transmission loss (TL) of packed silencers. Due to the single-domain nature of the direct mixed-body BEM, each substructure does not need to be a homogeneous domain. Complex internal components such as extended inlet/outlet tubes, perforated tubes, and thin baffles, as well as bulk-reacting linings, can all be in one single substructure. As such, dividing a large silencer into modular substructures can be done naturally in the longitudinal direction. This completely eliminates the traditional rule of having to construct well defined (no thin bodies) and homogeneous subdomains in the conventional multi-domain BEM. The substructuring technique presented in this paper also has the capability of modeling a catalytic converter in which a catalytic monolith containing a stack of capillary tubes is inserted between two connecting substructures. Several test cases including two parallel-baffle silencers are presented to demonstrate the technique. The BEM predictions for TL are verified by experimental data.