Numerical Simulation And Characteristics Analysis For Sound-Structure Coupling Of Silencers

Intake and exhaust noise is the main source of internal combustion engine noise.The simplest measure to control the intake and exhaust noise of an internal combustion engine is using a silencer.Usually,the transmission loss(TL)is obtained without consideration of the shell noise,and the rigid wall is assumed for a silencer structure.In fact,when the size of the silencer is large enough and the shell is thin enough,the shell noise could be higher than the pipe termination radiated noise,the shell noise should not be ignored.Therefore,it is necessary to establish the computational strategy with consideration of the sound-structure coupling to investigate the effects of structure on the acoustic characteristics of silencers.In this thesis,two typical silencers: a marine double expansion chamber silencer and an automotive three-pass perforated tube muffler are considered.Firstly,the finite element model of silencer's acoustic cavity is established,and the transmission loss and acoustic modes of the silencer are calculated by using the finite element method,and the sound pressure distribution inside the silencer is obtained.Secondly,the structural model of silencer is established,and then the structural modes of silencers are calculated and analyzed by using the structural finite element method.Finally,the finite element-infinite element computational model for the internal acoustic cavity-shell-external sound field of the silencer is established.The TL of silencer is obtained through the sound-structure coupling calculation.The effect of sound-structure coupling on the acoustic characteristics of silencer is analyzed by comparing TL predictions for the rigid wall model and the sound-structure coupling model.The effect of wall thicknesses on the TL of silencer is investigated in detail,and the guidance was provided for the necessity of considering the sound-structure coupling effect when calculating the acoustic performance of silencer.Through the calculation of the sound-structure coupling,the noise levels radiated from the silencer shell and the pipe termination can be obtained,and then the contribution of the both can be compared.For the thin-shell silencers,by setting the external observation points and using the Green's function analysis,the contribution of different shell elements to the sound power level(SPL)at the observation points may be obtained.The radiated noise from silencer shell may be lowered by increasing approximately the thickness of structure,which is a main contributor to the overall noise level or by painting the damping material,thereby the overall acoustic performance of the silencer may be improved.