Sound Speed and Attenuation in Multiphase Media

Abstract

Abstract : This report discusses an investigation of the sound speed and attenuation in multiphase media, sandy and muddy sediments, that has shown that a simplified-Biot theory adequately predicts the sound speed and attenuation in sandy sediments with porosities of less than 65%. In addition for muddy sediments with porosities of greater than 70% mixture theory can describe the sound speed. This report discusses the experimental and theoretical basis for these conclusions and related this investigation to other contemporary ONR sponsored research projects. A key finding is the conclusion that in waveguides with a sandy boundary that the effective attenuation obeys a power law with an exponent of 1.8 as proposed by Rosenfeld (2001) and Holmes (2007). Theory predicted a quadratic dependence, exponent of 2. This research has shown that energy removed by shear wave conversion explains this difference, that is the exponent of 1.8 compared to 2. Finally a card house theory was developed to explain the properties of high porosity muddy sediments and that a Mallock-Wood mixture equation describes the slow sound speed.