Study of the influence of met-ocean data in fatigue loads calculations of a floating offshore wind turbine

The design of a floating offshore wind turbine (FOWT) requires the computation of loads with time domain simulations that depend heavily on the metocean conditions of the site. Guidelines, such as IEC 61400-3, recommend the use of scatter tables with the combined probability of the significant wave height (Hs) and peak period (Tp) as a function of the mean wind speed. Nevertheless, at early engineering phases it may be difficult to obtain the adequate environmental wind-wave data where both parameters are correlated for the site of interest. The main objective of this work is to assess the influence of neglecting or not the correlation between wind speed and wave data in the resulting fatigue Damage Equivalent Load (DEL) for different FOWT components. The analysis is performed through the comparison of the fatigue loads obtained for correlated and non correlated wind-wave data. Results show that fatigue loads are very similar for both data sets at the rotor loads, and present slight differences, at mooring tensions and tower base. The use of a simpler metocean data, where wave height and period occurrences are given independently of the wind speed, might be a sufficient solution for initial fatigue load estimations.