Research On Low Frequency Broadband Pipeline Noise Suppression On Acoustic Metamaterials

Among the means of pipeline noise suppression,passive noise suppression technology has wider application requirements and more economical maintenance and repair costs.However,the passive resistive muffler is suitable for middle and high frequency noise,and it is difficult to suppress low frequency noise.The volume and frequency band of general resistant mufflers are mutually restricted,and the frequency selectivity is high,it is difficult to meet the demand of low frequency broadband muffler.The acoustic metamaterials show excellent manipulation ability in the low frequency sound wave and are expected to be applied in the low frequency noise suppression of pipelines.Therefore,aiming at the suppression of low frequency broadband noise in the pipeline,this paper proposes a new low frequency noise suppression structure for the pipeline combined with acoustic metamaterials.After the incident sound wave is passed through the noise suppression structure,the noise suppression effect can be more than 90% in the working frequency band,and the thickness of the structure is thin,which is more suitable for practical application.The main contents of this paper are as follows:Firstly,the acoustic wave propagation characteristics in the pipe are analyzed,the acoustic wave equation in the rigid boundary circular waveguide is solved,and the plane wave approximation conditions in the circular tube are obtained.The acoustic propagation characteristics of the side branches with single and multiple Helmholtz resonators are analyzed,and the corresponding sound pressure transfer matrix is calculated for the pipes under different conditions.Secondly,on the basis of theoretical analysis,a new design method of pipe muffler structure unit is proposed.The structure is designed in the form of thin layer cavity embedded in the neck,which avoids the local expansion of the side branch of Helmholtz resonant cavity and greatly reduces the thickness of the muffler.The impedance analytical formula and transmission loss calculation formula of helical silencing structure are derived by using equivalent model.The finite element simulation model is established by COMSOL software,and the TL of transmission loss calculated by simulation is consistent with the theoretical results.According to the freedom of impedance adjustment of the helical silencer unit,the silencer frequency tuning ability of different parameters of the helical silencer unit was analyzed.Finally,the low frequency wideband muffler structure is designed by coupling several micro-detuning muffler units.In the frequency range of interest(100Hz-500Hz),two coupling modes of series and parallel were adopted respectively to explore the silencing ability of different number of coupling units.The silencing ability of coupling structures with different numbers is analyzed,and the mechanism of acoustic wave dissipation is explored.Finally,an experimental scheme was designed,the model was printed and the experiment was carried out.The four-sensor method was used to measure the sound insulation quantity.The experimental results are in good agreement with the simulation results.