Acoustic-modeling of random fibrous materials

We present a microstructure-based model for determining the sound absorption behavior and transport parameters of random fibrous materials and exploring the physical mechanisms underlying acoustic energy dissipation. In order to increase the generalizability of the model, a three-dimensional random fiber structure is employed for simulation. The propagation of sound waves is associated with four transport parameters, including viscous permeability, tortuosity, as well as viscous and thermal characteristic lengths. These parameters are determined by the porosity and diameter of the fibrous material. By using the method of multi-scale asymptotic simulation, the theoretical model for transport parameters includes unknown coefficients that are adjusted based on the simulated results. The sound absorption coefficients are then obtained by integrating the transport parameters into the widely-used Johnson-Champoux-Allard (JCA) model for porous materials. The theoretical predictions match well with existing experimental measurements on sintered fiber metals and fibrous copper wires. Our model systematically examines the impact of fiber diameter, porosity, and material thickness on sound absorption performance. Optimal results are achieved by carefully selecting fiber diameter and porosity to enhance the acoustic dissipation of sound waves, while thicker fibrous materials increase sound absorption in the low frequency range. The model provides a theoretical framework for designing and fabricating fibrous materials to reduce noise.