ИСТИНА

Acoustic spectroscopy is known to be an important tool for studying various media. In the presented work, specific features of acoustic dissipation in two--phase porous media are theoretically studied and the propagation of a finite--amplitude attenuating sound beam described by the KZK--type equation is analysed numerically for the case of a marine sediment. The KZK--type equation has been derived from the classical Biot equations, and it contains a dissipative operator corresponding to the frequency correction function $F(\kappa)$ in the Biot equations. In the present work, the properties of the correction function are studied and its well applicable representations are obtained. It is shown that the expansion of the correction function over $\kappa^2$ converges at $\kappa<5$. An asymptotic expansion of this function is obtained at large $\kappa$ values. For high frequencies simple dependence of viscous attenuation and phase velocity on parameters of a medium, useful for diagnostics for these parameters, has been found. The propagation of a finite--amplitude acoustic beam in a dissipative marine sediment has been numerically analyzed which showed that intense acoustic beam propagation can been accompanied by considerable nonlinear phenomena while diffraction only weakly affects the process.