Local overshoot and wind effects on wave overtopping at vertical coastal structures

Wind effects on wave overtopping over a fully impermeable vertical sea wall are studied numerically using the open source CFD library OpenFOAM®. A pressure gradient correction term is incorporated in the momentum equations. In the range of wave conditions of the present studies, it is found that in the absence of wind, the increase of the wave steepness results in reduction of the wave overtopping. This is related to the instability of the standing wave formed at the front of a vertical structure. Such instability was noticed in the range of steepness between 0.285 and 0.443 from the previous physical experiments for a regular wave interacting with a vertical structure. In our numerical studies we confirm the existence of this regime. Our studies further show that the stability of the standing wave determines the shape and volume of the overshooting jet, which has a close effect on wave overtopping. When a wind is relatively weak, e.g. wind speed of 10m/s, it is unable to alter the shape and volume of the overshooting jet much, meaning a weak wind effect on wave overtopping. When a wind is strong, e.g. speed of 30m/s, it completely deforms the overshooting jet and volume, resulting in overtopping discharge almost 3 times of that without a wind.