Comparison Analysis About Ultimate Loads And Fatigue Loads For Floating Offshore Wind Turbine

Floating Offshore Wind Turbines(FOWTs) have been developed tremendously, and this thesis covered a comprehensive load analysis of FOWTs based on the design regulations- IEC61400-3. According to the IEC61400-3, and by using FAST software, the ultimate loads and fatigue loads of wind turbines with TLP, Semi-submersible, Spar and Barge platform have been simulated, respectively. Comparisons among the four platforms have also been analyzed.In IEC, it is recommended to use the statistical extrapolation to calculate ultimate loads of FOWTs, and this thesis has applied the POT method to analyze the simulation results from FAST, and then use the Gumbel distribution of extrapolation to calculate FOWTs’ ultimate loads. To keep the accuracy of the results, the extrapolation calculation needs to be taken with massive of simulations under the IEC61400-3 design conditions. By analyzing the simulation of shallow water fixed wind turbines, and calculating their ultimate loads to conclude the effect of main wind speeds which can affect the ultimate loads for FOWTs can save the computational expense. The research results show that for shallow water fixed wind turbines, it can reach the maximum value for each parameter of the out of plane loads when the wind speed is at the rated speed, while the loads in plane reached the maximum value when at high wind speeds.Thus, when calculating the ultimate loads and fatigue loads of FOWTs, only rated wind speed and high wind speeds have been taken into consideration for simulations in this thesis. Considering the randomness of marine environment and the natural frequencies for the four types of the FOWTs, the calculation of ultimate load for FOWTs is undertaken with group of wind speeds and each of them along with three different wave loads. For the result analysis, mainly the 1): the comparisons of the four types of FOWTs under rated wind speeds; 2): the semi-submersible FOWT under different marine environment conditions and the analysis of the ultimate load and fatigue load are presented.