The pressures on the slope of a dike that are caused by waves and wave impacts yield the forces that determine the stability of its revetment.
In previous years, studies were conducted to determine whether these wave forces could be computed using the free-surface Navier-Stokes model SKYLLA. For short time series of regular waves or irregular waves, this appears indeed to be possible. In all nine cases with irregular waves which were considered where both the geometry of the construction and the time signal were varied, good agreement was found between measured and computed wave forces. Some examples of measured and computed wave impact pressures at the slope are given below.
Part of this investigation involved coming up with recommendations as to how SKYLLA could be made more suitable and further improved for the computation of forces due to irregular waves. To this end, additional simulations were performed for the two cases with the highest and steepest waves. This confirmed the conclusion reached in previous years that the problem of air bubbles getting locked up in the water needs to be resolved. This problem is due to the absence of a buoyancy mechanism in the present version of SKYLLA. It is a shortcoming of the Volume-Of-Fluid method, which is also used in SKYLLA. When wave breaking occurs, pockets of air get trapped repeatedly, as a result of which the amount of air in the water slowly increases. The results obtained for short time series show that, as soon as this problem is solved, SKYLLA would also be suitable for the simulation of irregular waves over longer periods. |
