Numerical simulation of fully nonlinear wave interaction with submerged structures: Fixed or subjected to constrained motion

The interaction between fully nonlinear water waves and fully submerged fixed or moving structures is investigated. A three-dimensional numerical wave tank model, based on potential theory is extended to include a submerged horizontal or vertical cylinder of arbitrary cross section. The vertical cylinder is allowed to have a constrained motion while attached to a rigid cable, which could represent the submerged payload of an offshore crane vessel subjected to wave actions. In this fully nonlinear time-domain approach, the higher-order boundary element method is used to solve the mixed boundary value problem based on an Eulerian description at each time step. The 4th-order Runge-Kutta scheme is adopted to update the free water surface boundary conditions expressed in a Lagrangian formulation. Interaction between waves and a submerged fixed horizontal cylinder is then computed by the model and compared with experimental and other numerical results. After that, a parametric study is performed to obtain numerical results for the vertical cylinder undergoing forced pitch motions. More simulations are carried out to investigate the hydrodynamic features of the submerged vertical cylinder in water waves attached to a cable for constrained motion and moving towards the sea bed at a constant velocity.