Wave loads on monopiles, Maasvlakte-2

The Challenge

In the transformation from fossil fuels towards renewable energy sources the Dutch government (Rijkswaterstaat) planned to build an onshore wind park on Maasvlakte-2, the seaward extension of the Rotterdam Harbour. The energy company Eneco has been awarded the building concession. Royal HaskoningDHV has assisted Eneco in this multidisciplinary project.

Part of the wind park is located on the soft sea barrier of Maasvlakte-2, where the monopile was selected as preferred solution for the wind turbine foundation. Additional to wind loads, these monopiles will be exposed to breaking waves, especially during storm conditions. As part of the multidisciplinary project, RHDHV was contracted to determine the wave loads on the monopiles.

Our Solution

To determine the wave-induced forces on the monopile first the nearshore wave conditions were determined. Because the monopiles are located on the beach, the wave timeseries were transformed to this location. This transformation was performed using a simplicity digital wave flume. Based on the timeseries on the beach, a timeseries of the forces on the monopiles was calculated.

Because wind turbines have never been built on a beach, no design guidelines exist. With approval of DNV-GL, nearshore design rules were determined, using the offshore design guidelines and the timeseries of the forces on the monopiles.

The Outcome

The transformation of offshore wave conditions to onshore forces was used to determine the design conditions for the monopile. Additionally, the timeseries of the wave forces have been incorporated in the metal fatigue analysis of the monopile. Finally, the different timeseries have been utilized by the contractor to access different construction methods.