Research On Low-frequency Noise Control Of Acoustic Metasurface

Duct low-frequency noise is one of the important factors affecting the quietness of the ship.Acoustic metasurface has become the research hotspot in the field of ship duct noise control with its unique regulation performance on sound waves.In this paper,membrane-type acoustic metasurface and acoustic cavity-type acoustic metasurface are designed.The theoretical analysis,simulation calculation and experimental verification method are combined to verify the two acoustic metasurfaces for duct low-frequency noise control.The main research contents are as follows:Firstly,based on the analysis of the wave equation of sound,the generation mechanism of metasurface band gap and the calculation of the energy band structure are studied by using phononic crystal theory,which provides the theoretical basis for the design of acoustic metasurface.Secondly,the membrane-type acoustic metasurface is designed.According to the theory of acoustic wave transmission,the vibration equation and natural frequency of the elastic membrane under the action of sound pressure are studied.The simulation analysis of the elastic membrane mode was carried out.The acoustic performance of the membrane-type acoustic metasurface shows that the membrane has the best sound elimination effect at the resonance frequency,and the frequency is adjusted by changing the parameters of the elastic membrane.With the pre-stress and thickness applied to the membrane are changed,respectively,the transmission loss peak frequency shift is 120 Hz and 110Hz;by changing the size of the attached mass,noise reduction of 100 Hz and below is realized.Then,the acoustic cavity-type metasurface is designed.From the single-domain resonance acoustic metasurface,the noise control mechanism of Helmholtz resonator is studied by band theory.The simulation results show that the local resonance band gap and Bragg band gap of the acoustic cavity-type metasurface hinder the acoustic wave propagation,the Bragg band gap and the local band gap are respectively shifted by changing the length of the duct cell and the cavity size.Based on this,a double local resonance acoustic metasurface is proposed,which can generate two local resonance band gaps and two Bragg band gaps simultaneously.The local resonance band gap is shifted by 100 Hz by changing the state of the elastic membrane.Finally,an acoustic test system is designed,and acoustic metasurface samples were processed for acoustic testing.The experimental results are consistent with the theoretical and simulation results.The designed acoustic metasurface has good control performance for low-frequency noise,and the frequency shift can be realized by changing the parameter.