# Numerical Study on Hydrodynamic Performance of a New Semi-Submersible Aquaculture Platform
## 4 Results and Discussion
### Dynamic Response in Waves, Winds, and Currents
#### 4.3.2 Six-Degree-of-Freedom Motion
It is found that the amplitude of roll motion increases as the incident angle gradually changes from 180\({}^{\circ}\) (LC1) to 90\({}^{\circ}\) (LC5), with the largest amplitude of 8.96\({}^{\circ}\) occurring at the condition LC5. When one of the mooring lines is damaged, the change in roll motion is not noticeable compared with the intact survival condition. Similar to the variation observed in surge motion amplitude, the maximum amplitude of pitch motion is observed at the condition LC4, rather than the condition LC1. The maximum value of pitch motion is 3.41\({}^{\circ}\). Under the conditions LC1 and LC5, the motion of the yaw is quite small. However, the amplitude of yaw motion increases obviously under the condition LC3 for both the intact survival and damaged survival conditions. The typical loading case of LC3 is further considered to analyze the effects of nets on the six-degree-of-freedom motion of the platform. Table 12 presents the statistics of the motion of six-degree-of-freedom under the condition LC3. It is found that the range of roll motion without nets increases significantly compared with the case with nets. The amplitude varies from 4.55\({}^{\circ}\) to 6.59\({}^{\circ}\), with an increase of 45%. Compared with the case with nets, the range of pitch motion without nets increases slightly, and the amplitude changes from 5.45\({}^{\circ}\) to 5.83\({}^{\circ}\), with an increase of 7%. Compared with the case with nets, the range of yaw motion without nets also increases slightly by 7%. The range of heave motion without nets significantly increased from 1.66 m to 2.27 m compared with the case with nets, with an increase of 36%. [PERSON] et al. [48] investigated the effects of nets on the motion of a floating offshore wind turbine with a steel fish farming cage (FOWT-SFFC) and found that the presence of nets can also alleviate the motion of FOWT-SFFC under certain conditions. Figure 23 shows the partial results of the whole-time histories of the heave of the platform under the condition LC3. Figure 24 shows the planar motion of the platform in the whole-time histories under the condition LC3. From Figure 23, it is observed that \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Mean** & **Std. Dev.** & **Max** & **Min** \\ \hline Surge with nets (m) & \(-\)4.25 & 0.23 & \(-\)3.48 & \(-\)5.32 \\ Surge without nets (m) & \(-\)2.90 & 0.73 & 0.01 & \(-\)4.87 \\ Sway with nets (m) & 5.13 & 0.16 & 5.99 & 4.53 \\ Sway without nets (m) & 4.84 & 0.50 & 6.13 & 2.88 \\ Heave with nets (m) & \(-\)6.09 & 0.09 & \(-\)5.56 & \(-\)6.49 \\ Heave without nets (m) & \(-\)6.02 & 0.12 & \(-\)5.40 & \(-\)6.53 \\ Roll with nets (\({}^{\circ}\)) & \(-\)0.32 & 0.28 & 0.78 & \(-\)1.87 \\ Roll without nets (\({}^{\circ}\)) & \(-\)0.11 & 0.33 & 1.35 & \(-\)1.67 \\ Pitch with nets (\({}^{\circ}\)) & 0.17 & 0.32 & 1.62 & \(-\)1.32 \\ Pitch without nets (\({}^{\circ}\)) & 0.11 & 0.38 & 2.08 & \(-\)1.63 \\ Yaw with nets (\({}^{\circ}\)) & \(-\)7.00 & 0.50 & \(-\)4.68 & \(-\)9.17 \\ Yaw without nets (\({}^{\circ}\)) & \(-\)4.62 & 1.49 & 1.45 & \(-\)8.65 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Statistics of the six-degree-of-freedom motion under the condition LC3. the variation range of heave motion with nets is apparently smaller than that without nets. From Figure 24, it is observed that the range of the whole plane motion becomes larger significantly without nets, and both the amplitude ranges of the sway and the surge obviously increase, compared with those with nets. These findings imply that the presence of nets alleviates the motion response of the platform.