## 2 Floating Offshore Wind Turbine Model
### OC4 and OC5 Projects  
Previous studies mostly used test data from the study by [PERSON] et al. [17], which was led by the University of Maine at the maritime research institute Netherlands (MARIN) offshore wave basin in 2011; however, the geometrically scaled model did not perform as expected under the low-Reynolds number wind conditions. In addition, only semi-submersible properties (center of mass, inertia force, etc.) were considered in the OC4 project, while the OC5 project considered the properties of the full system, and the mooring line properties could be adjusted. Hence, a new model was built that resulted in better-scaled thrust and torque loads. However, this turbine was retested in 2013, and this turbine was examined in Phase II of the OC5 project [18]. The different physical properties of the semi-submersible platforms in the two projects are summarized in Table 4.  
The turbine is a 1/50 th scale horizontal-axis model of the NREL 5-MW reference wind turbine with a flexible tower affixed atop a semi-submersible platform. The DeepCwind semisubmersible platform is composed of the main column and three offset columns linked to the main column via several pontoons and braces, as mentioned in the OC5 report [18]; the 1/50 th scale and full-scale models are shown in Figure 2. A 5-MW baseline wind turbine is vertically mounted on the main column so that the hub height from the sea surface is 90 m. In addition, the platform is moored with three catenary mooring lines, with fairleads located at the base columns. The anchors are located 200 m below the sea surface, on the seabed. One mooring line is aligned in the wave direction, which is also the platform surge direction; the other two mooring lines are distributed around the platform uniformly and the attachment angle between each mooring line is 120\({}^{\circ}\).  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Semisubmersible Platform** & **OC5 Phase II** & **OC4 Phase II** \\ \hline Mass & 12,919,000 kg & 13,444,000 kg \\ \cline{2-3} Draft & 20 m & 20 m \\ \cline{2-3} CM below SWL & 14.09 m & 14.4 m \\ \cline{2-3} Roll inertia & 7.5534 \(\times\) 10\({}^{9}\) kg/m\({}^{2}\) & \(8.011\times 10^{9}\) kg/m\({}^{2}\) \\ \cline{2-3} Pitch inertia & 8.2236 \(\times\) 10\({}^{9}\) kg/m\({}^{2}\) & \(8.011\times 10^{9}\) kg/m\({}^{2}\) \\ \cline{2-3} Yaw inertia & 1.3612 \(\times\) 10\({}^{10}\) kg/m\({}^{2}\) & 1.391 \(\times\) 10\({}^{10}\) kg/m\({}^{2}\) \\ \cline{2-3} Buoyancy center below SWL & 13.15 m & - \\ \cline{2-3} Mooringline anchors from center & 837.6 m & 837.6 m \\ \cline{2-3} Mooringline fairlead from center & 40.868 m & 40.868 m \\ \cline{2-3} Unstretched mooringline length & 835.5 m & 835.5 m \\ \hline \multirow{3}{*}{Mooringline mass density} & Line 1: 125.6 kg/m \\ \cline{2-3} Mooringline mass density & Line 2: 125.8 kg/m \\ \cline{2-3}  & Line 3: 125.4 kg/m \\ \hline \multirow{3}{*}{Mooringline extensional stiffness} & Line 1: 7.520 E8 N \\ \cline{2-3}  & Line 2: 7.461 E8 N \\ \cline{2-3}  & Line 3: 7.478 E8 N \\ \hline \multirow{3}{*}{6 degrees of freedom (DOF)} & Surge: 107 s \\ \cline{2-3}  & Sway: 112 s & Sway: 113 s \\ \cline{2-3}  & Heave: 17.5 s & Heave: 17.5 s \\ \cline{2-3} Natural Periods & Roll: 32.8 s & Roll: 26.9 s \\ \cline{2-3}  & Pitch: 32.5 s & Pitch: 26.8 s \\ \cline{2-3}  & Yaw: 80.8 s & Yaw: 82.3 s \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison of OC4 and OC5 project.