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

Wind effects on wave overtopping over a fully impermeable vertical sea wall were studied numerically using the open-source computational fluid dynamics library OpenFoam. A pressure gradient correction term was incorporated in the momentum equations. In recent studies, it was found that, in the absence of wind, an increase in wave steepness results in a reduction of 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 0.285-0.443 from previous physical experiments for a regular wave interacting with a vertical structure. The existence of this regime was confirmed in the current study. It was also found that the stability of the standing wave determines the shape and volume of the overshooting jet, which has a strong effect on wave overtopping. When the wind is relatively weak (e.g. a wind speed of 10 m/s) it is unable to alter the overshooting jet very much, meaning a weak wind effect on wave overtopping. When the wind is strong (e.g. a wind speed of 30 m/s) it completely deforms the overshooting jet resulting in overtopping discharge almost three times that without wind.