Different regimes of nonlinear pulse propagation in porous medium.

Abstract

High-amplitude pulse propagation in rigid porous media has been investigated numerically and experimentally. At high-sound levels, strong interactions between different spectral components of the pulse make any frequency domain models difficult to use, therefore a time domain approach has been applied for the present research. The effect of Forchheimer nonlinearity (i.e., flow resistivity growth with particle velocity amplitude) in porous media is well studied. However, much less is known about the influence of memory effects on high-amplitude pulse propagation. The aim of this work is to study their relevance for high-amplitude pulses of different durations. A numerical finite difference time domain scheme has been developed which accounts for second order convection nonlinearity, Forchheimer correction, and memory effect simultaneously. It is shown that Forchheimer nonlinearity dominates for longer duration high-amplitude pulses, while convection terms and memory effect contribution become noticeable for shorter pulses of moderate amplitude. The numerical results are confirmed in a series of experiments with different duration pulses in the amplitude range from 120 Pa to 40 kPa.