## 4 Results
### Drift Area and Velocity of the Platform  
The incident wave and wind directions have an influence on the drift process (Figure 11). Most of the cases reached the new balance at a position around 800 m in the x-direction. By contrast, the surge drift distance was significantly reduced when the wind incidence angle was over 90\({}^{\circ}\) or when the incident wave and wind were both set at 180\({}^{\circ}\). During the drifting process, the obvious sway motion was mainly caused by incident wave angle cases such as LC6-9.  
To clarify the maximum drift area in X-Y plane, Table 8 presents the highest/lowest values in each load case for all three stages. The maximum range is given by the highest value minus the lowest value. Considering all load cases, the suggested alert area is a rectangle 830 m long and 192 m wide once mooring line#1 is broken.  
The platform takes less than 10 min to reach the new balance position after the mooring line failure occurs (Figure 12). In some extreme cases, it even immediately reaches stage three. The maximum velocity of the platform in the surge and sway directions is presented in Figure 12. The highest velocity occurred in LC1 in the surge direction; on the other hand, the highest sway velocity appeared with the lowest surge velocity in LC7.  
Figure 9: Motion trails in the numerical model: (**A**) Plan view and (**B**) side view.  
Figure 11: Floating platform drift trails during the entire simulation in the X–Y plane in ten load cases; the solid lines present the incident wind changing cases and the dotted lines are the incident wave changing cases.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Load Cases**} & **Wave** & **Wind** & \multicolumn{5}{c}{**X-Direction (m)**} & \multicolumn{5}{c}{**Y-Direction (m)**} \\ \cline{3-11}  & **(\({}^{\circ}\))** & **Wind** & \multicolumn{2}{c}{**All**} & \multicolumn{2}{c}{**Stage 1**} & \multicolumn{2}{c}{**Stage 2**} & \multicolumn{2}{c}{**Stage 3**} & \multicolumn{2}{c}{**All**} & \multicolumn{2}{c}{**Stage 1**} & \multicolumn{2}{c}{**Stage 2**} & \multicolumn{2}{c}{**Stage 3**} \\ \hline
1 & 0 & 0 & 814.23 & 8.88 & 814.23 & 10.43 & \(-\)6.25 & 0.16 & \(-\)6.25 & 0.10 \\
2 & 0 & 45 & 805.27 & 9.94 & 805.27 & 11.08 & 89.09 & 1.40 & 89.09 & 1.33 \\
3 & 0 & 90 & 161.23 & 10.54 & 161.23 & 12.46 & 67.39 & 2.84 & 67.39 & 3.10 \\
4 & 0 & 120 & 18.02 & 12.30 & 18.02 & 11.84 & 7.10 & 3.64 & 7.10 & 2.11 \\
5 & 0 & 180 & \(-\)13.02 & \(-\)13.02 & \(-\)11.26 & \(-\)10.71 & 0.02 & 0.02 & 0.02 & 0.02 \\
6 & 45 & 0 & 809.95 & 6.91 & 809.95 & 6.98 & \(-\)94.49 & 8.95 & \(-\)94.49 & 8.90 \\
7 & 90 & 0 & 804.22 & 0.82 & 804.22 & 1.81 & \(-\)45.08 & 10.61 & \(-\)45.08 & 10.83 \\
8 & 120 & 0 & 807.63 & 5.73 & 807.63 & 6.33 & 91.70 & 10.06 & 91.70 & 10.85 \\
9 & 180 & 0 & 809.49 & 11.19 & 809.49 & 10.66 & \(-\)99.49 & 0.20 & \(-\)99.49 & 3.71 \\
10 & 180 & 180 & 10.33 & 10.33 & 10.02 & 9.66 & 0.14 & 0.12 & 0.12 & 0.14 \\ \multicolumn{1}{c}{Maximum Range} & \multicolumn{5}{c}{827.25} & \multicolumn{1}{c}{25.32} & \multicolumn{1}{c}{825.50} & \multicolumn{1}{c}{23.17} & \multicolumn{1}{c}{191.19} & \multicolumn{1}{c}{10.59} & \multicolumn{1}{c}{191.19} & \multicolumn{1}{c}{10.83} \\ \multicolumn{1}{c}{(Highest–Lowest)} & \multicolumn{5}{c}{827.25} & \multicolumn{1}{c}{25.32} & \multicolumn{1}{c}{825.50} & \multicolumn{1}{c}{23.17} & \multicolumn{1}{c}{191.19} & \multicolumn{1}{c}{10.59} & \multicolumn{1}{c}{191.19} & \multicolumn{1}{c}{10.83} \\ \hline \hline \end{tabular}
\end{table}
Table 8: Maximum range for x-direction and y-direction.  
Figure 10: Description of the three stages.