EVALUATION OF THE BEHAVIOR OF MONOPILE FIXED OFFSHORE WIND TURBINES

Resumo

This work follows a worldwide trend of developing new wind farm projects on sea. Standard
models used by the academy of 5 and 10 MW wind turbines are introduced to the Brazilian environment
being supported by fixed foundations of the monopile type. The aim is to develop a sensitivity analysis
of the fatigue damage in a critical point of the foundation under the effect of important offshore cyclic
loads. The models employed in this paper were firstly validated through analyses of their natural
frequencies. The next step was to subject them to extreme loads caused by wind, wave and current to
determine the critical point in each turbine’s foundation. With these points in hand, the sensitivity
analysis was conducted assuming the wind with and without a dynamic component, while the sea waves
were represented by the Jonswap or Pierson-Moskowitz spectrum. Finally, fatigue was assessed through
the damage calculated by the Palmgren-Miner rule in association with the largely employed S-N curves
and the rainflow method for counting stress cycles in the time series generated by SIMA-RIFLEX. This
study showed the importance of the dynamic component of the wind in the structure’s lifespan, which
was reduced by at least one order of magnitude when considered. No significant change in fatigue
damage was observed with different wave spectra. Lastly, life results obtained for the 10 MW turbine
were better than the 5 MW due to its more robust geometric characteristics.