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Structural aspects of offshore wind turbines in extreme loading events are under scrutiny in the Wave impacts on Fixed turbines (WiFi) JIP.


WiFi JIP helps offshore wind industry take the next step in foundation design


Marcus Schiere & Erik-Jan de Ridder m.schiere@marin.nl


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As offshore wind farms go further offshore in harsher environments, the WiFi JIP is aiming to reach a better understanding of the influence of steep and breaking waves on the foundation and secondary structures of offshore fixed wind turbines and to avoid damage. This will lead to improved design methods and standards for the turbine foundations. Fixed offshore wind turbines are long and slender bodies with heavy turbines placed on top. The slender frame, in combination with the weight distribution, results in a relatively flexible structure that causes a significant structural response when the turbine is subjected to a wave impact. Therefore, the flexibility of the total structure with the foundations had to be modelled for the JIP. A monopile foundation and a jacket type foundation were tested. In the first model test phase, the monopile structure was modelled twice: a flexible model with the scaled natural frequencies and mode shapes of the structure and one


rigid model that was stiff. The two models were placed side by side in the model test basin. Accelerations and loads on the two structures could be compared directly. During the second phase, the structural properties of the wind turbine with a jacket type foundation were scaled. Following the tests, there is now a better understanding of the loading and response of real wind turbines in extreme wave events. The model tests also provide a valuable basis of validation material for simulation techniques, and will be the basis for the improved design method. The WiFi JIP project is a very strong group, which includes around 20 participants from research institutes, classification societies, contractors, engineering and utility companies. By involving such a broad range of partici- pants a considerable amount of knowledge is available for and distributed within the group, making it much easier to take the next step in foundation design and classification.


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