Nonlinear interaction between surface waves and a submerged slender body is investigated. In the simulation, the incident waves are generated by a paddle type wavemaker. The fully-nonlinear, viscous, wave-body interaction problem is solved using a boundary-fitted coordinates based finite-difference method. Results are obtained for a range of parameters, with particular emphasis on that of small body-submergence and large-amplitude incident waves. In such highly-nonlinear cases, generation of breaking waves and strong free-surface vorticity layers are observed. Time-averaged hydrodynamic force reveal a negative drift force when the body is close to the free surface. Effect of wave motion on the transport of vortical structures is found to be significant in the presence of long incident waves.
Prediction and control of motion response to ocean waves is crucial to efficient operation of autonomous underwater vehicles (AUV) in shallow-water environments. Existing controller algorithms were however developed based on somewhat crude hydrodynamics models. These models approximate the hydrodynamic forces using hydrodynamic coefficients that do not properly take into account the free-surface and sea-bottom effects on the dynamics of the vehicle. With the current interest in AUV applications focussed on littoral shallow-water regions, there is a good reason for fully understanding AUV-wave interactions. Even when in deep water, an AUV has to continually approach the surface to seek satellite GPS fixes for the purpose of navigation. Such AUV applications, besides prediction of ship motion in high seas and identification of submerged objects based on free-surface signature and far-field flow structures, are the motivating factors for the present research. In traditional naval hydrodynamics, the linearized problem of wave-body interactions is decomposed into wave incidence, diffraction and radiation problems for analysis in the frequency domain (see, e.g., Newman, 1977). The diffraction and radiation problems have similar mathematical structure, in that both have to satisfy the Sommerfeld radiation condition at infinity.
