# Numerical Study on Hydrodynamic Performance of a New Semi-Submersible Aquaculture Platform
## 4 Results and Discussion
### Dynamic Response in Waves, Winds, and Currents
#### 4.3.1 Mooring Line Tension  
Table 9 presents the statistics of the mooring line tension (the average value of the results obtained from five different seed numbers) under various loading cases for survival conditions. The statistics of mooring line tension for operation conditions are omitted to reduce the length of this paper. For intact survival conditions, the maximum tension occurs in Line 1, which is 2460 kN when the wave, wind, and current approach simultaneously from 90\({}^{\circ}\) (LC5). For damaged survival conditions, the maximum tension occurs in Line 2, which is 3337 kN. It also occurs when the wave, wind, and current come from 90\({}^{\circ}\) simultaneously (LC10). The minimum safety factor of all mooring lines for all intact survival conditions is 1.81 in LC5, which exceeds the CCS requirement of 1.67. Similarly, the minimum safety factor of all mooring lines for all damaged survival conditions is 1.33 in LC10, exceeding the CCS requirement of 1.25. For all the loading cases, the safety factors of the mooring lines meet the design rule requirements. Consequently, the mooring system designed for this semi-submersible aquaculture platform can be deemed reliable. For both the intact survival conditions and the damaged survival conditions, the most critical loading case occurs when the wave, wind, and current have an incident angle of 90\({}^{\circ}\). The reason is that the platform has a larger lateral area. When the incident wave, wind, and current are transverse, the platform is subject to greater forces. When one of the two mooring lines in the same group is damaged, the tension of the remaining mooring line increases significantly. For example, when comparing the conditions LC5 and LC10,  
Figure 19: Pitch RAOs for the moored platform with/without nets.  
the maximum line tension of Line 2 increases from 1262 kN to 3337 kN, representing a significant increase of 164%. Additionally, the average line tension of Line 2 increases from 285 kN to 937 kN, which corresponds to a substantial increase of 228%.  
Three typical loading cases (LC1, LC3, and LC5), were considered to analyze the net effects on the mooring line tension. Table 10 presents the statistics of the tension of the weakest mooring line under these conditions. It is evident that for all these loading cases, there are significant differences among the maximum, minimum and mean mooring line tensions, which is also verified by the standard deviation. For instance, the minimum and mean tensions of Line 1 for LC5 without nets are 2 kN and 420 kN, respectively. However, the maximum tension of Line 1 is 2471 kN, representing an increase of 488% compared with the mean tension. Moreover, it can be observed that the average and minimum mooring line tensions with nets are larger than those without nets, while the maximum mooring line tension with nets is smaller than that without nets. This suggests that the presence of nets enhances the safety of the entire mooring system, as it is determined by the maximum value of the mooring line. [PERSON] et al. (2014) also investigated the net effects on the mooring line tension and found that the presence of nets can alleviate the maximum mooring line tension in pure wave conditions. However, when the current coming from the same direction as the wave is included, the different solidity ratio of nets can either increase or decrease the maximum mooring line tension compared with the case without nets. This implies that, for the platform in this study, changes in the solidity ratio of nets and current may also increase the maximum mooring line tension, contrary to the results shown in Table 10.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \multicolumn{2}{c}{**Extreme Response**} & **LC1** & **LC2** & **LC3** & **LC4** & **LC5** & **LC6** & **LC7** & **LC8** & **LC9** & **LC10** \\ \hline \multirow{3}{*}{Line 1} & Mean (kN) & 205 & 330 & 425 & 572 & 652 & 546 & 772 & — & — & — \\  & Max (kN) & 523 & 895 & 948 & 1729 & 2460 & 1381 & 1817 & — & — & —