A single-domain boundary element method for packed silencers with multiple bulk-reacting sound absorbing materials

Traditionally, the boundary element method only applies to problems with one single homogenous material in the domain. For acoustic problems in air, the homogeneous material is simply the air. When a problem involves two or more different homogeneous materials, the most common choice has been the multi-domain boundary element method, which matches the continuity conditions or certain special interface conditions between any two homogeneous sub-domains in contact. Although the multi-domain concept is straightforward, defining each sub-domain and matching the interface conditions at all kinds of contacts could become an issue when the subdomains are intricately connected to one another in a complex design. In addition, several imaginary interfaces may also have to be created to have well-defined subdomain boundary surfaces. To alleviate these difficulties, this paper presents a single-domain boundary element method for the acoustic analysis of packed silencers with multiple bulk-reacting sound-absorbing materials inside. This single-domain boundary element method does not define any subdomains, nor does it use any imaginary interfaces. It can handle as many materials as one can have. Numerical examples are compared to the available experimental data and the local-reacting normal impedance approximation.