Substructuring has been a classical technique in structural FEM analysis to reduce the matrix size and the computation time. In this paper, a substracturing technique based on the impedance matrix synthesis is used along with the recently developed direct mixed-body 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. The substracturing 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. A parallel-baffle silencer is presented to demonstrate the technique.
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