## 4 Numerical Modelling and Validation  
### Numerical Modelling  
In this paper, the dimensions of the two lifting barges amount to 140 m in length, 55.89 m in width, and 13.3 m in depth. Sixteen mooring cables, spanning 980 m, are arranged radially. The wave height is 1.6 m, and the wave period is 14.7 s. The mooring \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Category** & **Elements** & **Rule** & **Score (SA or ST)** & **Remark** \\ \hline \multirow{8}{*}{Stability} & & The assessment elements in P2 are lower than the average of the corresponding assessment elements in P1 and P3. & 1 & Stable \\  & & The assessment elements in P2 exceed the average value of the corresponding assessment elements in P1 and P3, but it is not the maximum value among P1, P2, and P3. & 2 & Medium \\ \cline{1-1} \cline{2-5}  & The CV of the 6 DOFs of the three vessels is selected as the assessment element. & & The assessment elements in P2 represent the maximum values among & 3 & Unstable \\ \cline{1-1} \cline{2-5}  & & The assessment elements in P2 represent the maximum values among & & \\ \cline{1-1} \cline{2-5}  & & corresponding assessment elements in P1, P2, and P3. & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: \(Cont.\)cables present a uniform and radial layout pattern, and the entire computational area necessitates comprehensive coverage of these mooring cables. Therefore, the calculation domain's length and width are set at 2100 m, while the water depth is 280 m. As per the recommendation of the International Towed Tank Conference (ITTC), it is optimal to maintain a scale range of 60-80 for conducting scaled-down studies of large offshore structures. For the numerical simulation in this study, the chosen scale is 70. Consequently, the numerical model in this paper assigns a value of 30 m for the length and width of the calculation domain, 4 m for the water depth (\(l_{12}\)), and 2.5 m for the upper height (\(l_{1}\)). A frequently employed approach for boundary condition selection [40] involves velocity inlets for the computational domain's front, upper, and back boundaries; pressure outlets for the back boundary; symmetry planes for the side boundaries; and a no-slip wall condition for the hull's surface boundary. The computational domain and boundary conditions are illustrated in Figure 2.  
Considering the length of this paper, Figure 3 presents an illustrative representation of the grid during the classical P2 stage. To optimize computational resources and achieve more precise wave simulations, meshes neighboring the interface exhibit augmented density compared to other regions. The grid size is suitably adjusted, with larger grids positioned farther from the vessels and smaller grids closer to them. The central overset mesh area models ships' motions. The present study employs a fully structured overset mesh, divisible into two components before overlapping: the background and overset mesh. Typically, the computational domain comprises a background grid and one or multiple minor overlapping grid regions [41; 42]. The overset mesh classifies mesh cells as active, inactive, or acceptor mesh cells. In active mesh cells, discrete governing equations are solved. In inactive mesh cells, no equations are solved; nevertheless, if regions of the overset mesh move, these mesh cells become active. The relative movement between subdomains does not necessitate mesh deformation or regeneration--the motion laws within the subdomain need to be defined. The primary advantage of this method lies in its capacity to handle intricate geometries and relative movements of objects in dynamic simulations. Owing to its convenience in mesh generation, the overset mesh is widely adopted and is efficacious in managing intricate mesh layouts [43]. Figure 2: The computational domain and boundary conditions. With the advancement of supercomputer technology, the entire computational process is executed on a platform with a full capacity of 1280 cores and a single node equipped with 64 cores.