farms are located such as the North Sea. Particular attention was paid to the probability of the occurrence of breaking and steep waves and the associated slamming load. During these tests both waves and current were simulated and two seabed bathymetries, including the effect of a local sand wave were modelled. During the test campaign more than 250,000 wave events were simulated, of which more than 500 gave a slamming impact. The outcome of the tests were summarised in a wave catalogue, ensuring that the results can easily be accessed by the participants.

Furthermore, full-scale measurements were done for a Vestas V90 3MW wind turbine in the Belwind wind farm, which is located 46 km off the coast of Zeebrugge on Bligh Bank. The full-scale measurements provided analyses of the response of a turbine in a real environment.

enabled the next step in foundation design and classification to be taken.

The overall project budget was 2 million euro, which included contributions from the industry and the Dutch Ministry of Economic Affairs through its ‘Top consortium for Knowledge and Innovation Offshore Wind’ (TKI Wind op Zee).

The objectives of the WiFi JIP were to improve the way the effects of steep (and breaking) waves are taken into account in the design methodology of fixed offshore wind turbines, so the turbines can be better optimised. Knowledge was signifi- cantly improved during the project by a combination of experimental verification by model testing, numerical calculations, full-scale measurements and industry experience.

The project started by reviewing the latest design methods and guidelines. These methods were then used for the design of a base case monopile and jacket design by Ramboll. In the next phase the designed foundations were tested in MARIN’s shallow water model basin. The foundation for the monopile was modelled as a rigid and flexible foundation and they were tested in regular waves, irregular sea states and so-called focused waves. During the model tests the wave heights, wave run-up, dynamic response, impact pressures and loads on the foundation and boat landing were measured.

Furthermore, an extensive five-week experi- mental programme was performed in the wide wave-current flume at Deltares (Atlantic Basin). The goal of these tests was to gain more understanding of realistic design conditions for areas where offshore wind

Both the model tests and full-scale measure- ment results were then used for the validation of detailed CFD calculations. The outcome of the study showed that the CFD calculated loads and responses were consistent with the full-scale and model-scale measurements.

As a last step, an improved design methodol- ogy and guideline was developed based on the outcome of the WiFi JIP results to model the (breaking) wave impact on offshore wind turbines.

The new WiFi JIP guideline approach for calculating a representative slamming wave load on a monopile foundation (1 out of 1000) is presented in the figure. The formula gives the maximum loads on a fixed monopile for a certain sea state.

From the CFD simulations it followed that the wave impact can be accurately predicted if the correct wave kinematic is known. For this, 2D CFD simulations were performed, and the impact load was determined by using Morrison coefficients. Based on this finding a non-linear wave model was validated in the WIFI II JIP and delivered to the JIP participants as an improved design method.

New WiFi JIP Flow chart for the calculation of the impact of a breaking wave

A new JIP has now been initiated by Deltares and MARIN. The SCALE JIP focuses on wave loads on secondary structures and wave run-up. And this JIP is open for new participants so you are more than welcome to join.

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