MUFFLER PERFORMANCE STUDIES USING A DIRECT MIXED-BODY BOUNDARY-ELEMENT METHOD AND A 3-POINT METHOD FOR EVALUATING TRANSMISSION LOSS

In this paper, a single-domain boundary element method is presented fo r muffler analysis. This method is based on a direct mixed-body bounda ry integral formulation recently developed for acoustic radiation and scattering from a mix of regular and thin bodies. The main feature of the mixed-body integral formulation is that it can handle all kinds of complex internal geometries, such as thin baffles, extended inlet/out let tubes, and perforated tubes, without using the tedious multi-domai n approach. The variables used in the direct integral formulation are the velocity potential (or sound pressure) on the regular wall surface s, and the velocity potential jump (or pressure jump) on any thin-body or perforated surfaces. The linear impedance boundary condition propo sed by Sullivan and Crocker (1978) for perforated tubes is incorporate d into the mixed-body integral formulation. The transmission loss is e valuated by a new method called ''the three-point method.'' Unlike the conventional four-pole transfer-matrix approach that requires two sep arate computer runs for each frequency, the three-point method can dir ectly evaluate the transmission loss in one single boundary-element ru n. Numerical results are compared to existing experimental data for th ree different muffler configurations.