Research On Influence Mechanism Of Damping Characteristics On Acoustic Metamaterials

Acoustic metamaterial is a new kind of artificial microstructure materials,which has physical characteristics that are not existed in nature or difficult to realize,such as negative refraction,band gap characteristics and energy capture.Band gap characteristic means that the acoustic metamaterials have the capability of impeding the propagation of elastic waves in a certain frequency range,thereby achieving suppression of vibration and noise.Different structural designs and material choices will affect the band gap characteristics of acoustic metamaterials,and material damping is no exception.It is significative to research how to make acoustic metamaterials reduce more in vibration and noise via material damping.This thesis combines the damping theory,Bloch theory,and plane wave expansion method to derive a mathematical model for calculating the band structure of viscoelastic acoustic metamaterials.And the thesis analyzes the effects of damping parameters on the band gap characteristics,energy dissipation characteristics,and transmission characteristics.Based on this,topological optimization of viscoelastic acoustic metamaterials is performed by using genetic algorithms,and the vibration damping performance of the optimized structure is verified through finite element simulation and experiments.The main research contents of this article are as follows:Firstly,the structural,physical,mathematical,and damping models of the twodimensional viscoelastic acoustic metamaterial are established.And the energy band structure is calculated by?(k)plane wave expansion method and iterative algorithm.Based on the frequency dependence of viscoelastic damping,the influence of material damping on the number,position and width of band gap is analyzed to obtain viscoelastic acoustic metamaterials with low frequency and multi broadband.Secondly,the k(?)plane wave expansion method for solving the complex band structure of viscoelastic acoustic metamaterials is derived,and its attenuation coefficient is calculated.The effects of viscoelastic storage modulus and dissipation modulus on the complex band structure and attenuation coefficient are discussed,and the effects of viscoelasticity on the transmission characteristics of finite period structure are analyzed,so as to obtain viscoelastic damping which can bridge the band gap and increase the attenuation.Finally,based on genetic algorithm,two-dimensional circular holes in viscoelastic acoustic metamaterials have been topologically optimized.In the present study,design variables,the spatial distribution of the filling materials,have been optimized for the purpose of maximizing the relative band gap width of the first band gap.Consequently,the optimized structure with multiple scatterers is obtained.According to the optimized structure,the model for finite element analysis are performed and the corresponding transmission spectrum are calculated.Additionally,the prominent vibration attenuation ability have been confirmed by experiments.In this thesis,the effects of viscoelastic damping on the band gap,energy dissipation and transmission properties of acoustic metamaterials are studied.The relevant conclusions can be applied to the vibration and noise reduction in various engineering fields,which has certain theoretical value and practical significance.