Spectral Modelling of Low-Frequency, High-Frequency, and Full Spectrum Atmospheric Turbulence, and Their Impact on Floating Offshore Wind Turbine Loads

Abstract

Floating Offshore Wind Turbines (FOWTs) have low natural frequencies of motion, typically around 0.01−0.001 Hz. If external wind fluctuations match these frequencies, they can excite the motion, leading to increased loads and higher fatigue at specific locations of the wind turbine. Until now, wind turbine design has only considered high-frequency, microscale turbulence, modelled using the Mann (1994) model, as recommended by the IEC. However, this model does not capture the full energy content of the wind fluctuations around the FOWT motions natural frequencies. Syed and Mann (2024) proposed a model for these low-frequency, mesoscale fluctuations. In this thesis, the two turbulence models were implemented, combined, and input in the Siemens Gamesa Renewable Energy (SGRE) in-house servo-hydro-aeroelastic wind turbine solver for a SGRE FOWT loads simulation. The goal was to assess whether adding low-frequency turbulence increases damage on the tower bottom and mooring lines compared to using high-frequency turbulence alone. It was found that indeed for the simplified load simulations done here, the lifetime of a FOWT could be impacted by mesoscale turbulence and thus could be considered in the FOWT design.