Presentazioni e Articoli Tecnici

Sound absorption in porous materials with rigid frame and open porosity can be very effectively estimated by applying the Johnson-Allard model in order to substitute a porous medium with an equivalent effective fluid and then utilise the Helmholtz equation for time-harmonic acoustics. The model uses several parameters which characterize the micro-geometry of porous material from the macroscopic perspective; they are: the total porosity, the viscous permeability and its thermal analogue, the tortuosity, and two characteristic lengths -- one specific for viscous forces, the other for thermal effects. The acoustic absorption for a layer of freely packed assemblies of small rigid spheres was measured and compared with the result calculated from the microsctructural analyses using COMSOL Multiphysics®.