Prediction of flow properties of granular porous materials for acoustic applications

Abstract

Johnson-Champoux-Allard, Johnson-Champoux-Allard-Lafarge, and Johnson-Champoux-Allard-Pride-Lafarge are commonly used acoustic models for cellular, fibrous, and granular materials. These models treat the material as homogenous and require non-acoustic fluid flow properties through the porous media. These flow properties can either be directly measured or calculated by inverse techniques. A simple inverse method based on a pore size distribution model developed by Horoshenkov et al, is used. All these acoustic models are programmed in MATELYS AlphaCell code, and once the flow properties are estimated, MATELYS code could be used to predict the acoustic response of a porous material. A new method of fabricating a shaped micro-porous material was developed, prepared several specimens, impedance tested, and test results were used to validate the predictions from MATELYS. The calculated results from the flow properties reported in the literature agree well with the experiment. Results also showed that the ratio of minimum specimen dimension to particle diameter of about 10 or more will provide specimen independent flow properties. This study was conducted for solid spherical beads; for lightweight and multifunctional applications we must use lightweight hollow microbubbles.