# Parallel Analysis of Offshore Wind Turbine Structures under Ultimate Loads
## 4 Study of 10 MW OWT under IEC 61400-3 Loads with Earthquake and Typhoon
An earthquake with a PGA of 0.32 g and Ts of 1 s is similar to the designed seismic load of buildings and bridges in Taiwan, where a strong seismic zone is located, and the 20 m soil liquefaction is also a conservative assumption. Tables 4 and 5 indicate that the required steel weight increases about 5%, compared to the IEC 61400-3 loads, due to this. The major controlled parts are pile and brace members, while the column and tower members are still dominated by the IEC 61400-3 loads. 5. Class-3 tropical cyclones may occur near the Pacific and Atlantic regions. Table 6 indicates that, due to this, required steel weight increases about 19%, compared to the IEC 61400-3 loads. Almost all steel design is controlled by IEC 61400-3 DLC I.2, in which the yaw misalignment is an important factor; this condition is similar to the results discussed by [PERSON] et al. [19], according to GL Tropical Cyclone Technical Note [36]. 6. If one needs to include the class-3 tropical cyclone load and the seismic load, with the PGA of 0.32 g and 20 m soil liquefaction, the required steel weight increases about 21% compared to the IEC 61400-3 loads, as shown in Table 6. The structure is still dominated by the tropical cyclone load of DLC I.2, but some of the bracings and piles are controlled by seismic loads. The reason for this is that the 20 m soil liquefaction causes the piles and bracings to weaken. \end{table}
Table 3: Computer time for the structural analysis and design changes, with the number of Intel I7-6700K computers used in a parallel computation (there are five analysis and design cycles with \(N_{\text{load}}\) = 10 and \(N_{\text{total}}\) = 213 in each computer, while Turbsim and Fast programs are only required to execute the first cycle). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Element** & **Control Cases** & \begin{tabular}{c} **Wind Speed** \\ **(m/s)** \\ \end{tabular} & \begin{tabular}{c} **\(H_{\text{s}}\) or \(H\)** \\ **(m)** \\ \end{tabular} & \
\begin{tabular}{c} **Direction** \\ **Wind/Wave/Yaw** \\ \end{tabular} &
\begin{tabular}{c} **Weight** \\ **Ratio (\%)** \\ \end{tabular} \\ \hline \multirow{3}{*}{Column} & DLC 12 & 72 & 14 & 120\({}^{\circ}\)/30\({}^{\circ}\)/30\({}^{\circ}\) & 76 \\  & DLC 12 & 72 & 14 & 90\({}^{\circ}\)/30\({}^{\circ}\)/60\({}^{\circ}\) & 24 \\ \hline \multirow{3}{*}{Brace} & DLC 12 & 72 & 14 & 0\({}^{\circ}\)/0\({}^{\circ}\)/30\({}^{\circ}\) & 97 \\  & DLC 12 & 72 & 14 & 30\({}^{\circ}\)/0\({}^{\circ}\)/30\({}^{\circ}\) & 3 \\ \hline \multirow{3}{*}{Tower} & DLC 12 & 72 & 14 & 90\({}^{\circ}\)/60\({}^{\circ}\)/60\({}^{\circ}\) & 52 \\  & DLC 12 & 72 & 14 & 30\({}^{\circ}\)/0\({}^{\circ}\)/60\({}^{\circ}\) & 28 \\ \cline{1-1}  & DLC 12 & 72 & 14 & 90\({}^{\circ}\)/30\({}^{\circ}\)/60\({}^{\circ}\) & 14 \\ \cline{1-1}  & DLC 12 & 72 & 14 & 30\({}^{\circ}\)/30\({}^{\circ}\)/90\({}^{\circ}\) & 5 \\ \cline{1-1}  & DLC 7.1 & 45.6 & 9 & 30\({}^{\circ}\)/0\({}^{\circ}\)/0\({}^{\circ}\) & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: The control loads of the analyzed structure at the last design cycle for IEC 61400-3 and typhoon loads (total required steel weight of the design = 2582 t).