Research On Vehicle Interior Noise Reduction Method Based On Nonuniform Phononic Crystal

With the rapid development of modern industry and transportation,noise pollution in cities has become increasingly prominent.As a commonly used means of transportation,vehicle brings convenience and has become one of the important sources of noise pollution.As a new acoustic composite material,the phononic crystal provides a new alternate for reduction of vehicle interior noise.In this thesis,the sound insulation characteristic s of a non-uniform phononic crystal are adopted to reduce vehicle interior noise.The rationality of this method is verified through theoretical analysis and tests.Firstly,based on elastic wave and its theoretical basis,the characteristic function of periodic wave equation is deduced.The characteristic function is the product of a plane wave and a periodic function of a crystal lattice.It is verified that the elastic wave belongs to the Bloch wave.A local resonance unit structure is established and its characteristics of sound insulation and band gap are calculated.The influences of structure parameters,such as array configuration pattern,filling rate,the thickness of scatterer,etc.,and the material of non-uniform phononic crystal on sound insulation characteristics is analyzed.The conclusions can be used in the design of a chiral non-uniform phononic crystal.Secondly,a non-uniform phononic crystal model,which includes a Greek cross chiral structure,is established.Aiming at sound insulation characteristics,a procedure of the model structure optimization is performed.The key structure parameters of the phononic crystal,such as the length and width of hole,are analyzed for studying their influences on the sound insulation characteristics.According to the sound insulation index within a target frequency band,the results of the 1st Opt intelligent fitting and polynomial fitting are compared,and therefore the fitting equation of sound insulation optimization is determined.Furthermore,an optimal solution of structure parameter within the frequency band is obtained by using the genetic algorithm.Finally,according to the optimal solution,a finite element model of the non-uniform phononic crystal is established to predict the sound insulation characteristics.The sample piece is manufactured and a test bed is set up for verification.The simulation results are in good agreement with the tested ones,which verified the feasibility of the newly designed structure in reduction of vehicle interior noise within certain frequency band.This thesis aims at studying the method of reducing the vehicle interior noise based on the non-uniform phononic crystal.The conclusions obtained may apply to the fields that need noise reduction such as highway,railway and aviation,which have certain theoretical value and practical guiding significance.