The present work highlights differences between two soil models (the classical p-y curves and a FEM based super element model) and two hydrodynamic force models (the classical Morison approach and the more complex Rainey slender body force models). The paper highlights the differences between the models, focusing on the effect on the total fatigue experimented by the rotor on a reduced load matrix. A monopile for a 13.2 MW rotor was designed in the stiff-soft region and fully aeroservo-elastic simulations were run using the aero-servo-hydro-elastic tool 3DFloat. Results show conservative prediction of loads given by the PY curves, leading to a possible conservative design and increase of the overall amount of steel used. As for the hydrodynamic loads models, the Rainey and the Morison model gave identical results when provided with linear wave kinematics.


The wind industry is steadily growing in Europe. In 2017 nearly 3,148 MW of net additional capacity was installed, corresponding to 560 new Offshore Wind Turbines (OWTs) across 17 wind parks (WindEurope, 2018). At the same time, following the steady growth of the wind energy market, a steep decrease in Levelized Cost of Energy (LCoE) has been achieved through developments in wind turbine technology and in particular through the increase of the rotor size. Today's wind turbines have larger rotors, higher hub heights, longer blades and considerably increased rated power capacity. LM blades, a Danish company, has recently announced the world's longest blade: 88.4 m long and specifically designed for Adwen's AD 8–180 (Adwen, 2018) wind turbine model, with 8MW nominal capacity and a 180 meter rotor diameter. General Electric is planning a new 12 MW rotor Haliade-X (GE, 2018) which will stand 260 m tall and have 107 m long blades. Simultaneously, the research community has been putting consistent effort on large rotors (e.g., AVATAR (Schepers, 2017) INNWIND (Jensen et al., 2017) SANDIA (Griffith and Richards, 2014) with the Sandia 13.2 MW SNL-03 100 m blade developed by Griffith and Richards (2014) being the largest well documented concept currently present in the literature.

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