Research Of Duct Noise Control Based On The Structural Acoustic Coupling

As one of the most important parts of environmental noise,duct noise brings a lot of negative effects into our life and work.Generally speaking,there are two categories of methods in the field of duct noise control:one is active noise control and another passive.For the former,issues that are related to the complexity of the system hinder its widespread use.Ultimately,the passive noise control approach is still seen to be the maturer engineering solution.Sound-absorbing material,as a kind of popularly used passive solutions,primarily works very well from middle to high frequencies,while the reactive elements,which based on the sudden change of the duct area or the resonance of chambers,are the most effective approach to block the propagation of the low-frequency noise.However,for the traditional reactive elements,the discontinuity of the duct cross section brings the increase of the pressure loss.Besides,the conflict between the noise attenuation level in low frequencies,the broadband performance and small space occupation remains and sometimes restricts their normal applications.Different from the traditional reactive elements relying on the change of the duct cross section,Huang introduced the idea of using flexible membranes or plate into the field of duct noise control.The structural acoustic coupling,as another form of impedance mismatch for silencing,is adopted to develop various kinds of membrane or plate silencers,which possess several potential,such as broadband,low-frequency and compact.Based on Huang's study,this paper established various analytical methods for membrane silencers with different configurations.Green's function and Kirchhoff-Helmholtz integral are used to solve the sound radiation field,and then the transmission loss of the silencers used in rectangular and circular ducts are obtained.Consequently,the two-dimensional analytical model with a single cavity is developed to those with two parallel or in-line cavities.After the optimization on the mass of the membrane and tension applied,the effects of parameters,which involve of the membrane position and the combination of multiple membranes,on the acoustic performance are studied.Study shows that the convergence of the particle velocity calculated by analytical method near the membrane is rather slow.Since the duct acoustics mode adopted here fails right on this surface,the wiggling of the particle velocity from the analytical solution is drastic.This failure is caused by the duct acoustics mode expansion of eigenfunctions of the cavity with rigid wall.As a result,with the aid of Chebyshev collocation method and the technique of domain decomposition,the current paper presented the corresponding numerical model with high accuracy to validate the analytical method.This problem of slow convergence is avoided by this numerical model and the two methods can verify each other.What is more,when the plate vibration velocity is expressed as the superposition of a Fourier series and auxiliary polynomials,the simply supported or clamped plate silencer model is extend to plates with various boundary conditions in the current paper.The present method can cover multiple boundary conditions with one analytical model.Further studies of the transmission loss with regard to the plate under several different classical boundaryconditions based on this model are conducted.Attempts to release the boundary restriction of the plate are also made to study its effect on the transmission loss of the plate silencer.Then,inspired by a cochlear analog device,this paper introduces a new mechanism named as locally reacting model into the field of duct noise control.The acoustic attenuation performance of this mechanism is analyzed with the help of lumped-parameter method and Fourier-Galerkin approach.The conclusions are as follows.In the absence of external fluid,it is the sudden slowdown over a short distance of incident wave that provides for excellent broadband noise reflection around the locally reacting design.It is also shown that the acoustic attenuation performance is broadband and the similar conclusion has arrived at for the plate or membrane silencer.However,for the former,both the frequencies of peaks and the level of transmission loss are easily controllable.Studies show that,if the cavity exists,the mass-like load from the fluid in the cavity suppresses the response of the structure.If helium,or some other gas with lower density than air in the duct,fills the cavity,the mass-like reactance of the cavity is reduced and the response of the structure is remarkably improved.The effects of the structural mass,stiffness and damping on the transmission loss of this design are also carried out.Finally,the schematic of the setup and the testing rig are designed.Then experimental study on the locally reacting model is implemented.The acoustic impedance of the membrane under different tension is measured by standing wave decomposition method,while the transmission losses of the expansion chamber and the locally reacting model silencer are obtained by the four-microphone and two-load method.The experimental performance of the LRM silencer is analyzed and the analytical predictions in the current paper are validated by the experimental results.