Acoustic wave scattering from random porous media
Date of Award
Doctor of Philosophy (Ph.D.)
Applied Marine Physics/Ocean Engineering
First Committee Member
Tokuo Yamamoto, Committee Chair
Acoustic wave scattering from random porous media is formulated from the Biot theory, which describes the acoustic interaction between a porous solid matrix and pore fluid. Equations of motion valid for heterogeneous, non-uniform porous materials are derived fast. The equations are simplified in the absence of the shear-wave. By applying a modal decoupling method to the simplified Biot's equations of motion, coupled Helmholtz equations for compressional waves in inhomogeneous porous medium are derived. A first-order perturbation and the Born approximation are applied to the coupled Helmholtz equations in random porous media. Pressure reflection and transmission coefficients necessary for the model are derived as well. The state-of-the-art model applying the Biot theory to volume-scattering enables us to evaluate the effects of volume-scattering from Biot's slow compressional wave. Numerical evaluations show that effects of the slow wave in the volume-scattering from the air-saturated sand are detectable.The model-data comparison of the back-scattering at a frequency of 5.5 kHz is made. The interface roughness-scattering model is extended to the poro-elastic medium. Unknown parameters are estimated using a non-linear optimization procedure based on the matched field processing and the adaptive simulated annealing. The model-data comparison shows that the interface roughness-scattering is dominant at lower grazing angles, while the volume-scattering is dominant at higher grazing angles at the sandy site. The frequency dependence of sound speeds is also discussed.
Ohkawa, Keiichi, "Acoustic wave scattering from random porous media" (2004). Dissertations from ProQuest. 2086.