Equivalent Model Study And Performance Test Of Sound Absorption Calculation For Porous Materials

Porous foam material is a new sound absorbing material.Due to the complex sound absorption mechanism,there is no mature calculation method to analyze its sound absorption performance,which can't provide technical support for the selection,analysis and design of porous foam materials.Establishing a simple and reasonable equivalent model is the premise for the acoustic theory calculation of porous foam materials.The main research contents of this paper are as follows:(1)The resonance frequency and energy loss of a small-sized Helmholtz resonator considering the thermoviscosity of air are calculated by simulation.The Helmholtz resonator is equivalent to a mass-spring-damping system.The acoustic damping coefficient in the acoustic-force equivalent model is fitted,and an approximate solution formula for the damping natural frequency of the Helmholtz resonator is obtained.(2)Taking foamed nickel as an example,an industrial CT(Computed Tomography)scanning technique is used to perform image tomography on porous foam materials.A three-dimensional geometric model is reconstructed from porous materials using reverse engineering software.A numerical model representing a single hole is simplified and established from a porous foam material.The sound absorption of the single-hole acoustic cavity model is calculated by simulation,which is equivalent to the mass-spring-damped vibration system.(3)According to the actual spatial topology of porous materials,the formation of pores of porous foam materials is obtained.Based on the distribution law of foam nickel pores and the algorithm of Voronoi mathematical stochastic model,the space-random array mass-spring-damped vibration system equivalent model of porous materials is established.The mechanical energy loss of the equivalent model is calculated to analyze the sound absorbing properties of the porous material.(4)The sound absorption coefficients of foamed nickel specimens with different pore sizes are tested.The sound absorption coefficient curve of foamed nickel and the energy loss of the space random array equivalent model are analyzed.The approximate theoretical formula of the natural frequency of Helmholtz resonator damping is verified by a perforated plate combination test piece.An AC-type porous material flow resistance measuring device is designed and manufactured to test the flow resistance parameters of the sound absorbing cotton.The sound absorption coefficient of the sound absorbing cotton is measured by an impedance tube.The research method of this paper provides technical support for the study of acoustic theory model of porous materials,and its ideas can be extended to other applications such as vibration and impact of porous materials,which has important theoretical value and application prospects.