Deltares performed tens of simulations with stream function waves and individual, extreme irregular waves to resolve the impulsive impact. Désirée Plenker (Deltares) explains: “Our study has shown how important it is to investigate the impact of individual, extreme irregular waves, since the largest loads are found here and not due to stream function waves, which are otherwise widely applied as a design wave in the offshore wind industry”. As part of this study, Deltares refined the selection procedure for which irregular waves to include in the modelling: First, 50,000 individual irregular waves belonging to the 50-year condition were modelled with a simpler and faster wave model. Second, tens of representative individual extreme waves were selected from the total set of 50,000 waves. This procedure gives confidence that realistic load scenarios are covered in the analysis.
Vattenfall will now use the results for their secondary steel design, where “the CFD results are important for the last design iteration, because they allow us to adjust initial load assumptions, while ensuring platform integrity over the lifetime of the wind farm”, says Achim Schmidt (Vattenfall).
An artistic impression of a wave impact due to a stream function wave.