On CFD Numerical Wave Tank Simulations: Static-Boundary Wave Absorption Enhancement Using a Geometrical Approach

The present study aims to extend the applicability of the static-boundary absorption method in phase-resolving CFD simulations outside the conventional shallow-water waves limit. Even though this method was originally formulated for shallow-water waves based on the conventional piston type wavemaker, extending its use to deeper water conditions provides a more practical and computationally cost efficient solution compared to other available numerical wave absorption alternatives. For this sake, absorption of unidirectional monochromatic waves in a semi-infinite flume by means of a static wall is investigated theoretically and numerically. Moreover, implementation to a practical wave-structure interaction application is investigated numerically and experimentally. A phase-resolving numerical model based on the Reynold-averaged Navier-Stokes (RANS) equations is implemented using the open source C++ toolbox OpenFOAM. The study presents the performance of the static-boundary method, in a dimensionless manner, by limiting the depth at which the active-absorption conventional-piston velocity profile is introduced; as a function of incident wave conditions. Moreover, it is shown that the performance of the static-boundary method can be significantly enhanced where wave reflection was reduced to about half of that of the conventional setup in deep-water conditions. Furthermore, the absorption depth is correlated to the incident wave conditions; providing an optimization framework for the selection of the proper dimensions of an absorbing wall. Finally, wave-structure interaction experimental tests were conducted to validate the numerical model performance; which shows an acceptable agreement between the model and the experimental observations. The proposed limiter is straight forward to be applied in pre-existing wave-structure interaction CFD solvers, without the need of code modifications.