On Wave-Absorbing Boundaries for Numerical Wave Flumes: Geometrical Optimization of the Static-Boundary Method for Deep-Water Conditions

The present study is concerned with enhancing numerical CFD wave tanks by extending the range of applicability of the static-boundary absorption technique to include deep-water conditions; which was limited to the use in shallow-water conditions only. This is done by proposing a limited absorption depth αh, which corresponds to incident wave conditions, to better match the wave kinematics in deep-water regime compared to the conventional shallow-water formulation. For this sake, the classical problem of wave absorption by a wall is revisited and investigated theoretically and numerically from a hydrodynamical perspective. First, the problem is mathematically modelled using the classical wavemaker theory to physically evaluate the hydrodynamic performance of the proposed geometrical modification. After that, fully non-linear phase-resolving CFD numerical simulations are conducted, using OpenFOAM, to investigate the effectiveness of the proposed limiter on wave progression. Moreover, an optimization framework is proposed to tune the wave absorber in correspondence to the simulated wave conditions; saving users the drudgery of conducting preliminary parametric simulations to determine the proper absorption parameters. Furthermore, a grid dependency study is conducted to report numerical uncertainty of the outcomes; following the Grid Convergence Index (GCI) method.

Despite the pre-existence of other wave absorption techniques, none seems to have the relatively lower computational cost of implementing the static-boundary absorption method. Moreover, the proposed geometrical modification is relatively easy and straight-forward to be implemented to existing numerical packages; without code modifications. Finally, it directly improves the computational cost which is one of the major bottle-necks in novel numerical CFD simulations of industrial marine and ocean engineering applications.