A hybrid model for the three-dimensional scattering from objects in underwater waveguides

Abstract

The scattering from objects in underwater waveguides is a multi-scale problem, involving both near-field effects in the vicinity of the scatterer as well as long-range propagation through the waveguide. To solve this problem, 3-D Finite-Element STructural Acoustics software developed at SACLANTCEN (FESTA) and an underwater waveguide propagation model based on wavenumber integration developed at MIT (3-D OASES), are coupled into a hybrid model. In a three-step method, the propagation model is used to compute the incident acoustic field in the vicinity of the target, which may be floating, proud, partially buried or buried in the sediment. The incident field data is subsequently passed as an input to the finite-element tool to compute the target-scattered acoustic nearfield. In the final step, the scattered field is propagated through the waveguide by OASES. A second method of coupling between the two models is based on the characterization of the target scattering via spherical harmonic basis responses. The advantage of the second method is that the finite-element computations need to be performed only once for each frequency, regardless of the incident field. Results for different targets with multistatic source–receiver configurations and with focused acoustic incident fields are presented.