TRANSIENT ACOUSTIC DIFFRACTION IN A FLUID LAYER

Acoustic and elastodynamic waves serve as diagnostic tools in the non- destructive search for cracks and holes in material structures, in thi s article, the diffraction of acoustic waves caused by a semi-infinite screen in a fluid layer is investigated. A homogeneous half-space mod els the substructure of the object under investigation. The transient wave problem is then solved by means of an iterative scheme in which s uccessively the Wiener-Hopf technique and the Cagniard-De Hoop method are applied [Kooij and Quak, ''Three-dimensional scattering of impulsi ve acoustic waves by a semi-infinite crack in the plane interface of a half-space and a layer'', J. Math, Phys. 29, 1712-1721 (1988)]. From the numerical results it turns out that in case of deep embedded semi- infinite screens only the first order diffracted wavefield gives a sig nificant contribution to the geometrical wavefield. Application of the se results in the iterative solution procedure yields a very effective solution scheme in which the exact transient wave field in the config uration at hand can be calculated within any finite time window.