Research On Sound Absorption Performance Of Automobile Multilayer Fiber Material

Automobile noise affects passengers' comfort and makes noise pollution,the market has more and more demand for automobiles with better noise-reducing effect.Therefore,it is one of the difficult problems for the automobile manufacturers to control the automobile noise effectively.Automobile sound package is an effective means to control the airborne sound of automobiles,and the sound absorbing material is an important part of automobile sound package.In addition to absorbing noise,fiber material has advantages such as low cost,good thermal insulation and so on,so it is widely utilized as automobile sound absorbing material.Sound absorption performance of different fiber materials are different,parameters of material also affects the sound absorption performance.Accordingly,it will play a certain role in guiding for the choice of sound package materials to analyze the impact of different materials and their parameters on the sound absorption performance.In this paper,the sound absorbing materials of jute and sisal fiber were prepared,and the fiber diameter,porosity and flow resistance were measured by experiments.Based on these physical parameters,Delany-Bazley model and Voronina model were used to calculate the sound absorption coefficient of fiber material.It was found that the calculation results of the Voronina model in the middle and high frequency range are closer to the measurement results when comparing the calculated results of the two models with the experimental results.Hence,Voronina model was selected to calculate the sound absorption properties of the fiber materials.The influence on the Noise Reduction Coefficient(NRC)of input parameters which are fiber diameter,porosity and thickness of materials,were studied through the method of sensitivity analysis.The computing method was from the instrument proposed by Saltelli,which based on the original approach provided by Sobol'.Results of the sensitivity analysis indicated that the variation of porosity influences NRC the most prominently,thickness is in the second place and fiber diameter makes the least influences.A multilayer fiber sound absorbing material composed of different fiber materials was prepared.The sound absorbing property of multilayer fiber material is better than that of single-layer fiber material in the case of the same thickness.It was found from the sound absorption coefficient curve that the sound absorbing property of multilayer fiber material could synthesize the advantage frequency band of each monolayer material.By using the transfer matrix method,the sound absorption coefficient of multilayer fiber material can be calculated based on the Voronina model.Comparing with the experimental results,it can be seen that the calculation results of the middle and high frequencies are close.Genetic algorithm was used to optimize multilayer fiber material,taking NRC as the objective function,the porosity and thickness of each layer as the design variable.The sound absorbing property of the optimized material is obviously higher than that before the optimization when the total thicknesses of the materials are 30 mm.Pareto solution set and the Pareto front were derived by using the total thickness of material and the noise reduction coefficient as the objective functions.The optimized materials and the ones before optimization were used as part of sound package of automobile firewall,two kinds of sound package were applied to the statistical energy model of automobile firewall.The results showed that the noise reduction effect of the optimized material is better than that before optimization while the total thickness is 10 mm lower.