Acoustic Analysis And Optimization Of One-chamber Cross-flow Perforated Muffler

With the development of society and industry, more and more automobiles appear on the road. It brings us noise more and more seriously. In order to keep a quite environment and improve the quality of our life, people take more and more attention to how to low the noise. The muffler has a good performance of noise reduction and it maybe the first choice in reducing it in ordinary life. So it is the main purpose to design and produce a muffler which has a good attenuation performance and low pressure loss. Muffler design and manufacturing level also reflects the industry developed level from some aspect.There are three kinds of mufflers, they are active muffler, passive muffler and semi-active muffler. The reactive muffler is a kind of passive muffler which be widely used and it has a very good attenuation performance. We usually evaluate the attenuation performance from Insertion Loss (IL), Transmission Loss (TL) or Level Difference (LD). Based on the basic theory of acoustics and muffler in this thesis, we discussed the acoustic character of two kinds of one-chamber cross-flow perforated mufflers. And transmission matrices are derived by four-pole method. The four-pole method is based on one-dimensional plane wave theory which has low accuracy. It has enough accuracy in acoustic analyzing simple structure of muffler which has low frequence but not suit for high frequence. That’s why traditionary muffler research mainly rely on experiments and experience. So this essay used three-dimensional Finite Element Method. First, three-dimensional structure model was established. Then, finite element established use the Hypermesh software. Last, TL was calculated use the Virtual lab.Because mach number has a great effect in TL, and it will chang after the fluid velocity or enviroment chang though the muffler structure is fixed. So mach number is instable. After derived transmission matrices use the one-dimensional analysis method, uncertainty optimization method is used to optimize the muffler. And the result was taken into three-dimensional finite model and then TL was calculated again. The comparison show that the TL after optimization is much better than before.