Scattering by two very close immersed shells. Numerical results

The aim of this work is to analyse the scattering by two very close elastic shells immersed in water when they receive an acoustic wave in the eclipsed configuration. The behaviour of the external circumferential A wave is investigated. In order to get an interpretation of previous experimental results about the scattering from two identical close shells, a numerical study is achieved : one shell has a fixed value of its ratio between the inner radius b and the outer one a, the other shell has a variable b/a value. This study is performed for different values of P (where βa is the distance between the axis of the shells). Two cases must be enlightened: if β is superior to a critical value the resonance spectrum of the composite structure is the superposition of those of the two shells. In the opposite case a coupling between the shells exists. It is clearly shown on the spectrum.