Finite element models for the solution of underwater acoustics problems

Acoustic waves are used in SONAR systems for the detection and classification of objects which may be swimming in the water column, proud on the seafloor, or buried below the sediment. In some applications, such as low frequency detection and classification of structurally complex objects immersed in a fluid, signal processing techniques must be aided by a-priori model based knowledge of the target echo. Because objects of interest in practical applications have a complex geometry and a detailed internal structure, consisting of elastic materials and fluid partitions, mathematical techniques capable of dealing with generic 3-D geometries, and capable of coupling different physical domains (i.e. the solid and the fluid domains) must be used. For these reasons, the Finite Element (FE) Method is the technique of choice for many researchers in the field. A FEMlab application for computing the scattering from undersea targets is presented, and guidelines for the discretization of the computational domain in the presence of structureborne guided elastic waves are given. It is found that the guided elastic waves impose strict requirements on the meshing of the elastic structure and of the surrounding water volume. The presented results are relevant also to other areas of acoustics, where one is interested in modeling scattering or radiation from elastic structures and within elastic structures. Such areas include non destructive testing, vehicle noise prediction and control, acoustic transducer design, MEMS, architectural acoustics, and medical acoustics.