Analysis And Optimization Of Sound Absorption Performance Of Porous Material Used In Automobile

Noise,as one of the four major pollution sources in today's society,not only causes great distress to people's life and work,but also affects people's health.Automobile is one of the main sources of noise.With the rigid requirements of national regulations and passengers,the automobile manufacturers and scientific research units are working to reduce the noise of vehicle.Acoustic package is one of the methods for noise reduction inside the vehicle.It can effectively reduce the interior noise and improve the sound quality of automobile.And the porous material is widely used in acoustic package.Therefore,the analysis of the factors influencing the absorption performance of porous material is essential.In this paper,the influence factors of sound absorption performance of porous material are analyzed by inversing the acoustic parameters of porous material.And the double-layer composite porous material with excellent sound absorption performance is obtained by multi-objective optimization method.The main work of the paper is shown as follows:Firstly,the measuring equipment of porosity and flow resistivity are developed,and the porosity and flow resistivity of porous materials are measured.At the same time,the sound absorption coefficient of porous material is measured using an impedance tube.Based on the Johnson-Champoux-Allard model,porosity,flow resistivity and sound absorption coefficient,the viscous characteristic length,thermal characteristic length and tortuosity of the porous material are inversed by using tabu search algorithm and multi-island genetic algorithm respectively.The sound absorption coefficient of the porous material is calculated by the inversed parameters.The accuracy of the inverse method is verified by comparing the calculated sound absorption coefficient with the measured sound absorption coefficient.Secondly,the polyurethane foam is selected.The single-layer absorptive model of the polyurethane foam is established by utilizing the Johnson-Champoux-Allard model and acoustic parameters(porosity,flow resistivity,tortuosity,viscous characteristic length,thermal characteristic length).The accuracy of the model is verified by experiment.The model is utilized to analyze the effects of acoustic parameters,density,thickness and air layer on sound absorption properties of porous materials.Based on acoustic parameters,transfer matrix method and Johnson-Champoux-Allard model,the formula for calculating the sound absorption coefficient of multi-layer porous materials is proposed.The double-layer polyurethane foam is taken as an example to verify the accuracy of the formula.The acoustic parameters with the greatest influence on the sound absorption performance of single-layer polyurethane foam are selected.The effect of these parameters on the sound absorption performance of double-layer porous materials is analyzed by utilizing the double-layer polyurethane foam.Finally,the statistical energy model of automobile firewall is established,and the double-layer composite polyurethane foam is applied to the sound-absorbing layer of the acoustic package of the firewall.Based on the optimal Latin hypercube method and Kriging model,the approximate model of the total sound pressure level of the statistical energy model of the firewall,the mass of the double-layer composite polyurethane foam and the noise reduction coefficient are established.And the optimal value of the parameters of the double-layer polyurethane foam is obtained by using the multi-objective optimization method.The total sound pressure level of the statistical energy model of the firewall,the mass of double-layer polyurethane foam and the noise reduction coefficient are compared before and after the optimization.The results show that with the improvement of the noise reduction coefficient,the mass of the double-layer polyurethane foam and the total sound pressure level of the statistical energy of the firewall are effectively reduced.