Acoustical Analysis And Design Of Reactive Silencers Based On Acoustic Mode

Noise pollution is one of the world's three major sources of pollution, A silencer is often used to reduce kinds of noise. Silencers are conventionally classified as dissipative and reflective and hybrid silencer. This paper studies the reflective silencers.Transmission loss is the most important parameter which frequently used to evaluate acoustic performance of a silencer. That is because TL is able to visually reflect the attenuation performance of a silencer. Besides TL is the inherent characteristic of a silencer, it is able to be predicted very conveniently from the known physical parameters of silencer and are not be influenced by source impedance and the radiation impedance, there is only relationship with configure of silencer.Main contents of this article is the impact of expansion ratio, location of inlet/outlet, extended inlet/outlet, perforated panels, shape of expansion chamber on transmission loss of a simple expansion chamber in the reflective silencer. Utilize the FEM software Sysnoise to obtain the relationships between each parameters and transmission loss. Acoustic mode as an important acoustical parameter of expansion chamber. This thesis utilize the geometric size variables of the expansion chambers to explain the internal relations between transmission loss and acoustic mode. After that derive a method which is able to achieve a satisfied value of transmission loss in a target frequence.This thesis adopts the way which combines the finite element method and three-points method. The model is generated in Catia first ofall. After that utilize the preprocess software Hypermesh for meshing. Then import the model to the Sysnoise proceeds finite element analysis. Finally data processing is done in the Matlab. Because of the FEM is very time consuming, so this thesis presents replace three-dimensional model by two-dimensional model. First utilize analysis of the two-dimensional model to obtain the relationships between parameters and transmission loss then proved it by analysis of three-dimensional model. Compare the results form two kinds of model and derive the differences between them.