Key acoustical properties of a porous medium are the characteristic impedance and wave number defined as The equilibrium density of fluid, \rho_f.The other parameters in the above equations are standard and known: Often, the viscous and thermal flow resistivities are replaced with their static permeability counterparts, i.e., \kappa_0=\mu / \sigma and \kappa_0’=\mu / \sigma’, respectively. \alpha_\infty is a measure of the twistedness in the pore and complexity of the path that the sound wave takes while propagating through the porous layer. \Lambda’ is the pore scale where the thermal dissipation effects are particularly pronounced. \Lambda is a measure of the pore scale at which the viscous and inertia effects are particularly pronounced. In the above equations, the key nonacoustical parameters that control the acoustical properties of porous media are: The physical meaning of these equations is well explained in the COMSOL documentation and on the APMR portal run by Matelys. It requires 6 nonacoustical parameters to predict the complex, frequency-dependent dynamic density of the fluid trapped in the material poresįigure 1: Screenshot of the Settings window for the Poroacoustics interface, illustrating settings for the original six-parameter JCAL model. The basis for the JCAL model was originally proposed in 1991 ( Ref. Historically, the Johnson–Champoux–Allard–Lafarge (JCAL) model, included in the Poroacoustics feature (Figure 1) available in the Acoustics Module, has been used for this purpose and cited rather extensively (over 2000 Scopus citations as of November 15, 2020). In noise control applications, it is of interest to estimate the ability of a porous layer to absorb sound.Ħ-Parameter Johnson–Champoux–Allard–Lafarge ModelĬOMSOL Multiphysics includes a range of models that can predict the acoustical properties of porous media. In chemistry and chemical engineering applications, it is important to know the internal pore surface area of materials that are used to deliver catalysts to control the chemical reaction and convert noxious substances in chemically inert bonds. In pharmaceutical applications, it is often of interest to measure the mean particle size and compaction, particle size distribution, and amount of moisture absorbed by the particle mix. In applications related to filtration operations, similar characteristics are measured routinely to determine the permeability of the membrane in the presence of a flow of fluid. In applications related to energy storage, it is important to measure the porosity and tortuosity of ceramic separators, which control the electrolyte uptake by the porous separator and its ability to conduct an electrical current. Although for a majority of practical engineering problems, the acoustical properties of porous materials are not of direct interest, the relationship between the acoustical properties, porosity, and frame morphology are of significant interest. These effects are controlled by the material porosity and other parameters of the pore structure. Viscous friction, inertia, and thermal dissipation effects are responsible for the observed acoustical properties of rigid-frame porous media. The interest in the acoustical properties of porous media is mainly associated with the great ability of these media to absorb and modify the incident sound wave, which interacts with the fluid filling the material pores. Guest blogger Kirill Horoshenkov (FREng), professor of acoustics at the University of Sheffield in the UK, discusses how to model acoustical properties of porous media using the COMSOL Multiphysics® software and the Acoustics Module.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |