Unconsolidated granular materials sound absorption model using sound propagation theories in porous media

The Sound Absorption Coefficient (SAC) of unconsolidated Granular Material (GM) is usually characterized by utilizing empirical models based on airflow resistivity correlations or more comprehensive models like Johnson–Champoux–Allard (JCA). These models rely on porous media geometrical parameters, which are obtained through inverse characterization methods using SAC experimental results. This presents challenges when GM’s SAC estimates are required in the absence of experimental results. Therefore, this paper reports a sound absorption model for GMs based on three porous media absorption models. Each model corresponds to GMs with a mean particle diameter (De) range, related to a specific SAC frequency profile that transitions through three stages, influenced by particle size changes, up to 2 kHz. Model parameters were determined based on granular frame geometrical properties as a function of airflow resistivity and porosity of packed polydisperse Discrete-Element spherical particles. SAC estimates for various GMs were validated against impedance tube measurements. JCA-based absorption model was found suitable for larger-particle GMs (De > 2 mm), exhibiting absorption peaks at frequencies above 1 kHz (Stage 1). Meanwhile, empirical-based absorption model characterized the frequency-independent SAC plateau observed in GMs with De < 2 mm (Stage 2). A newly developed coupled fluid-solid powders absorption model characterized SAC for 100-micron-sized particles (Stage 3).