On representativeness of the representative cells for the microstructure-based predictions of sound absorption in fibrous and porous media

Realistic microstructure-based calculations have recently become an important tool for a performance prediction of sound absorbing porous media, seemingly suitable also for a design and optimization of novel acoustic materials. However, the accuracy of such calculations strongly depends on a correct choice of the representative microstructural geometry of porous media, and that choice is constrained by some requirements, like, the periodicity, a relative simplicity, and the size small enough to allow for the so-called separation of scales. This paper discusses some issues concerning this important matter of the representativeness of representative geometries (two-dimensional cells or three-dimensional volume elements) for sound absorbing porous and fibrous media with rigid frame. To this end, the accuracy of twoand three-dimensional cells for fibrous materials is compared, and the microstructurebased predictions of sound absorption are validated experimentally in case of a fibrous material made up of a copper wire. Similarly, the numerical predictions of sound absorption obtained from some regular Representative Volume Elements proposed for porous media made up of loosely-packed identical rigid spheres are confronted with the corresponding analytical estimations and experimental results. Finally, a method for controlled random generation of representative microstructural geometries for sound absorbing open foams with spherical pores is briefly presented.