Offshore Wind Farms under Freak Wave Loading

Freak waves are extreme wave events that currently cannot be predicted by statistically analyzing wave measurements from the past. They are often significantly larger than the waves that statistically occur only once every 100 years. Considering the ambitious targets for the expansion of offshore wind energy worldwide, the probability of freak waves occurring within wind farms will increase in the future. This work presents, to the best of our knowledge, the first steps for considering freak wave action on monopile foundations for offshore wind farms in geotechnical design using a hydromechanically coupled formulation realized in the FE-code numgeo. The results highlight that explicit consideration of water pressure variations at the seabed, leading to seepage flow in the soil, significantly affects pile behavior under freak wave loading. Considering a documented freak wave event, the stability of current offshore wind farms is shown to be compromised, underscoring the need for improved design strategies to account for such extreme scenarios. Self-healing of the foundation during regular wave conditions with a large number of load cycles following a freak wave event is unlikely to occur, which is analyzed using the high-cycle accumulation model. It is concluded that incorporating water pressure variations at seabed level during large wave events is crucial for the accurate analysis of offshore foundations, and further research in this direction is strongly recommended.