Finite element predictive method and analysis for the acoustic attenuation performance of hybrid mufflers

A high-efficient acoustic finite element approach is established to predict and analyze the acoustic attenuation performance of combined reactive and dissipative（hybrid） mufflers with complicated structures in wide frequency range.The treatment details for the boundary integrals at different boundary conditions are presented,the finite element global coefficient matrix formula is obtained,and then a computational program is built to implement the algorithms,which has advantages in the scale of evaluation model and the speed of computation over commercial software.In order to predict the transmission loss of hybrid mufflers,the empirical expressions for acoustic properties of the long fiber glass wool are presented through the impedance tube measurement and curve fitting.The transmission loss is measured and predicted by using the present finite element program for a two-pass perforated hybrid muffler,and good agreements between them validated the present approach and program.The study demonstrates that the extended length affects the acoustic attenuation performance in middle to higher frequency range,perforations on the right bulkhead may eliminate the resonance,and the acoustic attenuation performance in middle to higher frequency range is improved with increase of the porosity of outlet tube.