## 7 Conclusions  
This investigation performed a CFD numerical analysis for a semi-submersible-type FOWT used in Phase II of the OC5 project, by advanced DFEI method and overlap mesh techno lede. The full-configuration FOWT in a wind-wave excitation condition has been successfully performed,  
Figure 16: Comparison between onshore and offshore. \begin{table}
\begin{tabular}{c c c} \hline  & **Parameters** & **Value** \\ \hline \multirow{2}{*}{Power output} & Range (kW) & 3446–4689 \\  & Mean value (kW) & 4181 \\ \hline \multirow{2}{*}{Thrust force} & Range (kN) & 759–838 \\  & Mean value (kN) & 801 \\ \hline \multirow{2}{*}{Pitch angle} & Range (deg) & 4.5–5.3 \\  & Mean value (deg) & 4.9 \\ \hline \multirow{2}{*}{Surge motion} & Range (m) & 7.9–9.8 \\  & Mean value (m) & 9.1 \\ \hline \multirow{2}{*}{Heave motion} & Range (m) & \(-\)0.7–0.7 \\  & Mean value (m) & 0.1 \\ \hline \end{tabular}
\end{table} 
Table 8: Dynamic response of floating offshore wind turbines (FOWT) in the wind–wave condition. with simultaneous consideration of the wind turbine movement due to 6-DOF platform dynamics. The RAOs of the surge, heave, and pitch were compared to MARIN test data and data reported in previous studies when only the wave condition was considered. A slight discrepancy was observed between the CFD studies with regard to the pitch, possibly because of the different physical properties of the platform and mooring lines in the OC4 and OC5 projects. There was a relatively large discrepancy in the hydrodynamic response, which can induce large deviations in the prediction procedure. Particularly, pitch natural period showed a 21% discrepancy between OC4 and OC5 projects, as indicated by the results of the free decay test of the pitch and the numerical discrepancy in the RAOs in the regular wave test. Besides, unsteady blade-tip vortices and strong flow interactions with the turbulent wakes of the tower due to the surge motion of the platform were successfully simulated and visualized using the advanced DFBI and VOF methods. The power and thrust force of the FOWT increased when the floating platform moved in the upwind direction, while the aerodynamic loads decreased as the pitch motion reversed direction. This can be explained by the variation in the angle of attack for each blade section when the FOWT system experiences pitch motion. All the 3-DOFs, including heave, surge, and pitch had smaller amplitudes compared with the results in the regular wave test without wind conditions. Incoming wind from the x-direction obviously has a large effect on the restoring force in the mooring line, and, as a result, the whole FOWT system cannot be restored back to the equilibrium position as in the regular wave test. In addition, a relatively heavy load on the hub and blades was observed for the FOWT compared with the onshore wind turbine. This is because of the thrust force acting on the top of the tower, due to which the platform moves in the upwind direction to offset the capsizing moment induced by the thrust force. With regard to the power curve, a 10% decrease was observed for the floating offshore wind turbine, which is likely due to the smaller project area and relative income wind speed when the platform experiences pitch motion. Overall, there is a greater variation in the power than in the thrust force, that is, the power output is more sensitive than the thrust force to platform motions. Until now, all published papers based on an OC4 project which was carried out in 2013 (this was code-to-code comparison project 5 years ago), which found a large discrepancy from the experimental test data of the OC5 project. This study could be a good insight for future studies, as there has not been any specific CFD research based on OC5 test data until now. Examination of the OC5 Phase II project, with a computational fluid dynamics code (which has a higher-fidelity model of the underlying physics), could help determine if there are some deficiencies in the hydrodynamic models being employed by participants in an OC5 code-to-test project [18].