Research On Simulation Of Vehicle Muffler Noise Attenuation Based On FEM

The paper researches on the acoustical performance of a kind of automotive silencer bythe method of acoustic FEM, and optimize the original prototype of the automotive silenceron theory. The simulation is mainly based on LMS Virtual Lab. The3D model of the silenceris discretized into hexahedron unstructured mesh elements. After that it is able to establishadmittance function to simulate the transmission relationship between outside surface andinside surface of perforated pipes with a large quantity of micro holes. It mainly studies onreactive acoustical performance of the muffler.The Numerical Computation Method of predicting the acoustical characteristic ofautomotive muffler includes transmission matrix, finite element method, boundary elementmethod and3D time domain CFD method. Presently transmission matrix has been a provenmethod. Mufflers with simple and axisymmetric structure and the frequency range lower to1000Hz is suitable in such a method. However, it is not accurate to predict the performanceabove1000Hz and the muffler with complicated inner chamber. Finite element methodoriginate from variation principle and weighted parameters method. The method is on the wayof dividing the fluid media into several blocks and having the blocks discretized into mesh.So that boundary value problem of mathematical equations is able to be converted to thesolution of a set of equivalent multi-variate linear equations. It is used to predict transmissionloss (TL) of muffler, especially with complicated inner chamber or non-axisymmetricstructure. But discretizing inner chamber of muffler will spend a large amount of workinghours, and the raw information is very much. Furthermore, its solution demands a greatnumber of computational resources. However, boundary element method just requiresdiscretization on the boundary of the fluid domain, which lessens the dimension of theequations and reduces Degree of Freedom of the system. Thus the problem has beensimplified. It is chiefly to analyze infinite field and half-infinite field problems such as theradiated sound power generated by exciting force, vector sound field, and etc.3D timedomain method is a kind of computational fluid dynamic method. By calculating the pressure oscillation at the respective positions of inlet and outlet and transform them into Fourierequation, frequency domain signal can be gained. It is almost used to predict transmission lossin flow field.The content of research includes cleaning and rebuilding of muffler geometrical model,meshing of rebuilt model, definition of boundary conditions, post-processing of experimentaldata, result analysis and optimization of the prototype. The first step is to predict thecharacteristics of the three prototypal silencers respectively. The second step is to attempt tosimulate the performance of modified models. After optimization attenuation at low andmiddle frequency range is enhanced to some extent significa ntly. The study shows that it ispotential to optimize the prototype of muffler assembly. The simulation provides a theorybasis to improve the acoustical performance of current products manufactured by thecompany.