Study On Sound Absorption Properties Of Porous Materials

Noise pollution,one of the four major pollutions in the world,is becoming more and more harmful to human society.With the rapid economic development,traffic noise has become the main source of urban noise pollution.To enhance the comfort of human life,sound absorption and noise reduction has become an essential part.As a new kind of material,porous material has been widely used in the field of sound absorption.Therefore,it is significant to study the sound absorption performance of porous sound-absorbing materials.In this thesis,the acoustic model of porous sound-absorbing material has been established,the acoustic characteristic parameters and their influence on the sound absorption performance have been introduced,and the influence of material on the noise elimination performance of conventional muffler has been studied.The main contents are as follows:Firstly,the research status of porous sound-absorbing materials at home and abroad is summarized.The basic characteristics and classification of porous sound-absorbing materials are introduced.This thesis introduces the sound absorption principle and coefficient of porous sound absorption material,and deduces and summarizes its sound absorption characteristic curve.In addition to the characteristic parameters studied in this thesis,the influence rules of other parameters on the sound absorption properties of porous sound-absorbing materials are introduced.The acoustic model of porous sound-absorbing material is established.Secondly,the definition and measurement method of five main acoustic characteristic parameters of porous sound-absorbing materials are introduced.The porosity of porous material is measured by density method,the flow resistance of porous materials is measured by direct current method,and the sound absorption coefficient is measured by impedance tube transfer function method.The structure shape factor and two characteristic lengths are calculated according to empirical formula.Then,based on Johnson-Champoux-Allard model,the finite element simulation analysis of the porous materials is carried out by using acoustic analysis software with five acoustic characteristic parameters and two physical parameters as a single variable,and the law of influence on the sound absorption performance of porous materials is obtained.Then,the formula for calculating the sound absorption coefficient of multi-layer composite porous material is derived by using the transfer matrix method,and the influence of several important parameters on the sound absorption performance of multi-layer composite porous material is simulated and analyzed.Finally,the acoustic transmission loss curve of Sullivan&Crocker muffler before and after adding porous materials is calculated by acoustic finite element analysis software,and the law of influence of porous sound absorbing material on the muffler in the whole frequency domain is obtained.It is found that adding glass fiber into the muffler can greatly improve the performance of muffler.