Fully nonlinear simulation of wave interaction with fixed and floating flared structures

Abstract

The interaction between fully nonlinear water waves in a wave tank and fixed or floating structures with vertical and flared side surfaces is investigated. The higher-order boundary element method is used to solve the mixed boundary value problem in an Eulerian formulation at each time step. The time stepping scheme updates the boundary conditions on the free water surface and body surface, based on a Lagrangian description. In order to increase the efficiency of the calculation, the domain decomposition technique is implemented, with continuity conditions enforced on the interface between adjacent subdomains by an iterative procedure. For the calculation of wave forces acting on structures, some auxiliary functions are used, instead of predicting the time derivative of the potential directly. By means of these auxiliary functions, the coupled fluid–structure interaction can be decoupled easily, so that the calculation of body motions becomes independent of the hydrodynamic force. In addition, mesh regridding using the Laplace smoothing technique and interpolation are applied on the free surface to avoid possible numerical instabilities. Numerical results are obtained for the wave interactions with vertical cylinders and flared structures at different wave numbers, in which the bodies are fixed, freely floating in one direction and totally freely floating, respectively. The effect of different flared shapes on the forces, wave run-up and body motions is also studied.