Trapped modes supported by submerged obstacles

In this paper, trapped modes are shown to exist for a pair of bodies that are submerged in deep water. An inverse procedure is used whereby a flow that represents a local oscillation is constructed and closed streamlines that surround the singularities of the flow are interpreted as body boundaries. The velocity potential for the flow is constructed from a symmetric combination of horizontal and vertical dipoles. This combination of singular solutions of Laplace's equation satisfies the free-surface boundary condition, and the spacing and relative amplitudes of the singularities are related in such a way that there is no radiation of waves to infinity. The existence of closed streamlines that surround the singularities is demonstrated by investigating how the structure of the streamlines varies as the parameters of the flow change.