Analysis And Optimization Of Sound Absorption And Insulation Properties Of Acoustic Materials For Vehicle High Frequency Noise

The interior noise will not only affect the ride comfort but also harm the health of occupants.Reducing interior noise has become the focus of scholars and manufacturers.Vehicle acoustic material is one of the most important means to effectively isolate and absorb high frequency noise.For the high frequency NVH problem,the design of light acoustic materials with good robustness and excellent acoustic properties has important engineering application value.In this paper,an ABA structured layered acoustic material composed of felt,PE film,and felt is taken as the research object.Based on Biot theory and transfer matrix method,an acoustic model was established to analyze the acoustic properties of the layered acoustic material.The structure of sound package materials with gradient porosity is designed,and a method of robust optimization of acoustic materials was proposed based on global sensitivity analysis and Monte Carlo simulation.The specific research work is as follows:(1)To obtain the acoustic parameters of acoustic materials,the acoustic absorption coefficient and flow resistance of sound-absorbing cotton,polyurethane foam,soft layer felt and hard layer felt samples are measured.Based on the theoretical model of sound propagation of flexible and elastic porous materials,the differential evolution algorithm is used to conduct global optimization,and obtain other parameter values of the acoustic materials by an inverse method.Acoustic absorption coefficients are calculated by taking the inverse value of the material parameters into the acoustic propagation theory model.The validity of the acoustic parameter inverse method is verified by comparing the calculated values with the experimental values.(2)Four acoustic model of ABA structure acoustic materials is established,and the models are verified by comparing the theoretical values with the experimental values of sound absorption coefficient and transmission loss.Acoustic parameters of each layer of the acoustic materials are taken as the research object,the global sensitivity is analyzed based on Sobol’s method.The results show that the porosity,flow resistivity,tortuosity,and thickness of soft layer felt and the porosity,flow resistivity,and thickness of hard layer felt have a great influence on the sound absorption and insulation performance of sound package.(3)To analyze the effect of gradient porosity structure on acoustic properties,the effects of four gradient porosity structures and gradient difference on acoustic properties are analyzed.Low porosity and layer thickness are taken as design variables,and the sound absorption coefficient of the acoustic material is taken as the objective function.The results show that the reasonable design of porosity gradient difference and layer thickness can make the acoustic material have better broadband sound absorption performance and effectively improve the sound absorption coefficient in a specific frequency band.(4)Based on Sobol’s global sensitivity analysis of acoustic material parameters,the uncertain parameters of acoustic materials are selected and described.Acoustic material parameters are taken as design variables,and RMS value of transmission loss and total mass are taken as objective functions.Multi-objective deterministic optimization and robust optimization of acoustic materials are carried out by NSGA-Ⅱ method.The results show that after the robust optimization the RMS value of sound absorption coefficient is increased by35.4154%,the RMS value of transmission loss is increased by 8.9155%,and the total mass is decreased by 11.6619%.Compared with the deterministic optimization,the standard deviation of RMS value of the transmission loss is reduced by 11.4%,and the standard deviation of the total mass is reduced by 11.9%.The sound insulation performance and the robustness of the total mass of the acoustic material are significantly improved.On this basis,the low porosity and layer thickness are taken as design variables,and the sound absorption coefficient RMS value of the material is taken as the objective function.The deterministic optimization and robust optimization of the parameters of low to high gradient porosity structural are carried out by MIGA.The results show that after the robust optimization the RMS value of sound absorption coefficient is increased by 26.6602% compared with that before optimization.Based on the statistical energy method,the SEA model of firewall is established.The acoustic materials before and after material parameter optimization and gradient design are applied to the SEA model,and the noise reduction effects before and after optimization are compared.The results show that after optimization,the sound pressure level of the receiver chamber at 6300 Hz is reduced by 3.4585 d B,the mass of the firewall acoustic package is reduced by11.68%,and the NVH performance of the vehicle is improved.The optimization method can not only improve the acoustic performance and robustness of acoustic materials,but also reduce the total mass.