The acoustic pressure distribution of the reactive muffler and the variation of transfer loss with frequency are obtained from a series of procedure, such as loading, solving and postprocessing.

The calculating model of sound field distribution along the urban elevated railway.;

According to the theory of wave acoustics and ray acoustics,train is regarded as a moving limited line sound source and the mathematics model of sound field distribution is set up around the elevated railway.

Through monitoring with sound arrester and without sound arrester, analyses the sound field distribution on the side of high way, discover the sound field distribution character for the purpose of advising the scientific methods of sound degrading design and checking.

The interior sound pressure distribution, which is on the condition of with air current and no air current, and velocity distribution in Helmholtz resonance muffler are gained in the computer simulation.

This article,based on the finite element theory,simulatively analyses the non-air current existence sound pressure distribution characteristic and the velocity distribution characteristic of expansion type silencer interior using acoustics analysis software Sysnoise.