Transient Scattering from Submerged Objects. Theoretical Predictions and211 Experimental Results (Transient Spridning fran Foeremal under Vatten och Inuti 211 Sjoebotten: Teorestiska Prediktioner och Experimentella Resultat)

摘要

Computational predictions of mono-and bistatic acoustic scattering by two211u001edifferent underwater objects are compared with results from a sea trial conducted 211u001ein the Stockholm archipelago in September 1997 as part of the ISACS project for 211u001eseafloor characterization and detection of buried underwater objects. The first 211u001eobject is a water-filled spherical steel shell lying on the seafloor, the second 211u001eis a concrete-filled tractor tyre buried in the sediment. The objects are 211u001einsonified by a vertically downward moving Ricker-like transient with center 211u001efrequency 5 KHz, modeling the pulse emitted by a bottom-penetrating parametric 211u001esonar used in the trials. A frequency domain boundary-integral-equation method, 211u001edeveloped recently as part of the ISACS project, is used. The method can handle 211u001escattering from smooth 3D bodies and shells in a layered fluid-solid medium. The 211u001escatterer may be either rigid, vacuous or a penetrable fluid volume enclosed in a 211u001ethin elastic shell. Transient scattering is treated by Fourier synthesis with 211u001eadaptive choice of the frequency grid. Parallel execution on a network of 211u001eworkstations under the MPICH message passing interface is used, to enable 211u001ecomputationally demanding broad-band excitations of the presented type to be 211u001ehandled within manageable time.