Applying a Numerical Wave Flume to Predict Wave Overtopping

The hydraulic design of coastal structures like breakwaters and revetments is generally based on empirical formulations, physical model tests and a fair amount of expert judgement. Each of these techniques has his own accuracy and efficiency and the difference in these properties is quite large between the different methods. To provide an additional design tool, the Joint Industry Project (JIP) CoastalFOAM was started with the goal to further develop and apply a numerical wave flume to simulate the wave/structure interaction of permeable coastal structures.

The numerical wave flume is based on OpenFOAM in combination with a module for wave generation and a module to model the hydraulic conditions inside permeable coastal structures. This combination makes it possible to address the interaction between waves and permeable coastal structures in a numerical wave flume.

Over the past years, several applications of the numerical wave flume were investigated within the JIP CoastalFOAM framework. The modelling and design of open filters under wave loading was validated. Furthermore, the integrated wave loads on crest walls on top of rubble mound breakwaters were verified.

This study addresses another design criterion: wave overtopping. The wave overtopping is validated by comparing the modelled and measured overtopping for a permeable rubble mound breakwater. The overtopping is also calculated using standard design rules. Purposely, the numerical wave flume was not calibrated using the results of the physical scale tests to investigate the performance of the numerical wave flume in absence of such results.

The results revealed that the measured and modelled wave overtopping have a similar shape but still show differences in the average wave overtopping. The differences in average overtopping rate were too large to conclude that the numerical flume could fully replace a physical flume to determine the overtopping. On the other hand, the differences were small compared to the error made using a standard design rule. This study showed that a numerical wave flume could be useful in the design of hydraulic structures to determine the wave overtopping.