PSI - Issue 57

Baran Yeter et al. / Procedia Structural Integrity 57 (2024) 133–143 Baran Yeter & Feargal Brennan / Structural Integrity Procedia 00 (2023) 000 – 000

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3.2. Structural Response of the FOWT using Fully Coupled Dynamic Analysis The global load analysis is performed based on DLC 1.2 as prescribed by IEC 61400-3 (2009) for the fatigue limit state. To this end, firstly, the data analysis of the relevant met ocean data related to the “NE8” offshore wind farm site results in the relevant sea states for which fully coupled AHSE simulations should be carried out. Then, the sea states are selected considering the representative expected significant wave height and peak period. For each sea state, a one-hour simulation of the coupled dynamic behaviour of the FOWT is carried out using OpenFAST (2023). Table 2 shows the details of the selected sea states with their characteristics, and Fig. 3 illustrates the mean values and standard deviations of the overturning moment for each sea state in a boxplot.

Table 2. Design Load Case (DLC 1.2) – NTM, Unidirectional

Sea State No

Mean Wind Speed (m/s) Significant Wave Height (m)

Peak Period (s)

Probability of occurrence (%)

1 2 3 4 5 6 7 8 9

3 – 4 4 – 5 5 – 6 6 – 7 7 – 8 8 – 9

1.294 1.342 1.397 1.484 1.546 1.655 1.774 1.932 2.093 2.280 2.510 2.727 2.982 3.222 3.544 3.827

9.669 9.190 9.023 8.963 8.932 8.670 8.355 8.222 7.823 7.973 7.918 7.877 8.093 8.065 8.385 8.608

4.885% 5.791% 6.327% 7.181% 7.507% 7.890% 8.215% 7.860% 7.407% 6.965% 6.440% 5.385% 4.579% 3.708% 2.939% 2.212%

9 – 10 10 – 11 11 – 12 12 – 13 13 – 14 14 – 15 15 – 16 16 – 17 17 – 18 18 – 19

10 11 12 13 14 15 16

Fig. 3. Overturning bending moment for all the sea states for fatigue limit state