## 4 Numerical Modelling and Validation
### Basin Test and Validation
Overall, the numerical simulation values exhibit conformity with the experimental values, which reflects the ship's motion characteristics. Notably, their fluctuation trends remain generally consistent as the wave direction varies. However, it is noteworthy that, overall, the experimental values of the ship's 6 DOFs slightly surpass those in the numerical simulations. This divergence can be attributed to the arrangement of the lifting cables. Although the numerical simulation involves ideally setting 30 lifting cables with identical initial states, experimental salvage operations present a far more intricate scenario. Lifting cables do not exhibit complete uniformity in their initial states. Some cables possess larger initial stretches, resulting in a larger pulling force, while others exhibit smaller initial stretches, yielding less pulling force. Such disparate pulling force responses impact the ship's motion, resulting in larger experimental values of the ship's 6 DOFs. The ship's motion notably demonstrates enhanced stability when confronted with waves propagating in the 180\({}^{\circ}\) direction, as observed in both experimental and numerically simulated values. Specifically, the RAO values of the roll response and heave response, which warrant heightened attention in salvage operations, diminish under the influence of waves propagating in the 180\({}^{\circ}\) direction. Moreover, in general, the RAO value of the P3 stage tends to be higher than those of the P1 and P2 stages. Concerning the heave response at the P3 stage, the force exerted by waves counters some of the downward force, thus reducing the vertical motion of the ship. Other DOFs are comparatively less influenced by this phenomenon, leading to larger experimental and numerical simulation values at P3. In summary, as the direction of the waves changes, the values obtained by the experiment and numerical simulation are close, and the changing trend of the values is similar, contributing to a more comprehensive understanding of its behavior. Figure 5: _Cont._  
In [PERSON]'s research [34], certain intuitive conclusions can be deduced by investigating the increase in the maximum tension of the lifting cables. Hence, Figure 6 illustrates the augmentation of the lifting cables' maximum tension in numerical simulations and experiments under the influence of waves in the 90\({}^{\circ}\) direction. The selected tension values stem from the maximum value during P1-P3 stages. These values are comparable to the maximum tension of the hoisting cable under the impact of waves in the 180\({}^{\circ}\) direction. The figure reveals that, as the wave direction shifts from 180\({}^{\circ}\) to 90\({}^{\circ}\), the numerical simulation and experimental values increase at the bow and stern and exhibit close agreement. However, disparities arise for the cables situated in the middle of the ship, namely, cables 7-9 and 22-24. In the experiment, the tension values of these cables slightly exceed the numerical simulation values. This phenomenon stems from the fact that when the ship encounters waves in the 90\({}^{\circ}\) direction, the middle cables bear the brunt of the impact. The cables in the experiment hardly maintain the same initial state as their numerical simulation counterparts. Some experimental cables undergo larger initial stretching, leading to relatively high tension generation, while others experience less stretching and, correspondingly, generate less pull. This inconsistency engenders tension fluctuations, which become more pronounced for the middle cables under the influence of waves in the 90\({}^{\circ}\) direction. The conclusions drawn from the experiment and numerical simulation are consistent. Specifically, under the influence of waves in the 90\({}^{\circ}\) direction, the tension response of the cable is lower than that under waves in the 180\({}^{\circ}\) direction. If the aim is to enhance the safety  
Figure 5: RAOs of 6 DOFs: (**a**) Roll; (**b**) Pitch; (**c**) Yaw; (**d**) Surge; (**e**) Sway; (**f**) Heave.