With the offshore wind industry aiming to deploy deeper water sites (> 30 m) while still utilizing monopiles, support structures with larger diameters are required. For the design and assessment of so-called XXL monopiles, wave-induced forces, which become more dominant with increasing diameter, have to be determined accurately. Thus, this study focuses on the identification of differences between state-of-the-art theories for wave load calculations with engineering models and the forces exerted on large monopiles from high-precision numerical reference methods. Within the framework of the research project TANDEM (Towards an Advanced Design of Large Monopiles) a 7 m diameter monopile is designed to support Fraunhofer’s IWT-7.5-164. This offshore wind turbine system is used as reference to determine wave-induced loads based on the MacCamy-Fuchs approach, implemented in models in Modelica. Different waves, defined in a simulation matrix, are investigated to elaborate the significance of diffraction effects, as well as the relevance of non-linear effects. The results are compared to CFD (Computational Fluid Dynamics) simulations. Deviations in the wave-induced forces are analyzed, taking into account the different capabilities of the applied tools, trends in the applicability of the engineering model are elaborated, and suggestions for improvement of the code based on state-of-the-art theories are given.

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