Acoustic Characteristics Analysis Of Automobile Exhaust Muffler

Most of the exhaust system design methods developed earlier have dealt primarily with one-dimension-plane wave theory. But the theory is hard to provide accurate analysis result because of the effect of the three dimensional wave. The three dimensional numerical method such as the finite element method can simulate the exhaust system's characteristic accurately and take the influence of several outside factors into account. So it is an effective method to an improved design.In this thesis, aiming at a muffler of some vehicle, an acoustic model of the muffler is built by Finite element method (FEM). The acoustics characteristic analysis of the muffler is carried out according this model, and some improvements are achieved as the demand of our factory. The optimization improvement is found after the acoustics characteristic analysis of each improvement.Based on Transfer matrix method (TMM) the basic muffler units' transfer matrix are figured out, meanwhile mathmatic models of the muffler transfer loss are carried out. Secondly, simple expansive chambers, expansive chambers with inserting cubes and helmholtz resonators are calculated by the 1D and 3D FEM, the comparison of the result concludes that 3D FEM is more exact and feasibility.Thirdly, the 3D model of the original muffler is carried out by UG and geometry clean-up and mesh job are finished to get the FE model for acoustic analysis,and by using SYSNOISE ,the sound field in the muffler are analyzed,including the pre-muffler and the rear-muffler. The comparison between the simulation result and the experimental result concludes that the 3D model is exact and improvements of the original muffler are carried out at the basis of understanding the purpose of the designer of the original muffler.At last, after caoustics analysis of these improvement mufflers to be finished, and through the comparison of the result with orignal caoustics characteristic, the optimization improvement about the pre-muffler and rear-muffler are gained, which shows that the optimization improvement can meet the requests basiclly.