Analytical and BEM solutions of sound attenuation in bar silencers

Bar silencers, usually with large dimensions, consist of an array of rectangular or round bars made of sound absorbing materials packed in a rectangular lattice arrangement. Each bar is covered by a perforated facing sheet to protect the material from being blown away by the exhaust gas. Due to the large dimensions of the full cross section, a small representative cell is isolated from the entire array for analysis purposes. To predict the acoustical performance of the isolated cell for different geometric configurations, a numerical method based on the direct mixed-body boundary element method (BEM) was used. An analytical solution for a simplified circular geometry was also derived to serve as a comparison tool for the BEM. Both the numerical and analytical solutions used the bulk-reacting material approach instead of the local-reacting normal impedance approach. For rectangular bars, the BEM solution is compared to an existing finite element method (FEM) solution available in literature.