Study Group report 2005: acoustic scattering (Thales)
This is the final report on acoustic scattering from a strained region, brought to ESGI53 by Thales Underwater Systems. Click on the link at the bottom to download the full report as a pdf document.

Report authors
David Allwright (Smith Institute)
Gareth Jones (University of Oxford)
William Parnell (University of Manchester)

Introduction
A composite material consists of a rubber filled with gas-filled microspheres. In underwater applications it is compressed hydrostatically by a pressure that may be not insignificant compared with the shear modulus of the rubber. Thus large strains are produced around each spherical inclusion. When these spherical inclusions scatter an incident acoustic wave, the strained region around an inclusion has had its elastic properties altered by the large static strain. The quesion addressed by the Study Group report is 'How does this strained region affect the elastic scattering?'.

For the purposes of this Study Group problem, the homogenization problem (obtaining the macroscopic behaviour of the bulk material from the behaviour of a single microsphere) is to be assumed solvable. So the Study Group was asked to focus on scattering by a single microsphere and the strained region around it. The particular concern that the Study Group was asked to address is that the material dynamic moduli are different from the static moduli, and we wish to allow properly for this in the analysis.

In the problem report, the work is divided up into various sections. First, there are obviously some material modelling issues: a mathematical model is needed for small strain dynamic viscoelasticity superimposed on a large static strain. Some of the existing models for this are reviewed. Then, in order to formulate the scattering problem for compressive waves correctly, calculation of the static state allowing for a finite compressibility is carried out. Eventually, in the final section of the report, the scattering problem itself is addressed.

Download 'Thales-report.pdf' (147 Kb).