## 4 Parametric Study
### Buoyancy-Weight Ratio (BWR)  
In floating structures, BWR, the buoyancy-weight ratio, is a key factor. The buoyancy and weight can determine the initial tension of tethers, and the possibility of the rapid motion of structures implies that it depends on the BWR. In this section, the behavior of the proposed SFT was analyzed, considering the BWR. The common variables of the analytical model included a wave condition of 6 m (8 s), a main cable angle of 12 degrees, a tube external diameter of 23 m, and an installation depth of 70 m.  
Figure 13 shows the motion, the acceleration, the reaction force, the section force, and the section moment in the SFT, according to BWR. Figure 13a displays the absolute maximum motion of the SFT, according to the BWR. It can be seen that the motion in Type 1 and Type 2 was significantly different. For Type 1, with open shapes, it was found that the heave motion grew as the BWR was increased. The deformation of the heave was increased by the buoyancy, as shown in Figure 13b. Maximum and minimum values at each point in the SFT were maintained at regular intervals. Figure 13c shows the heave motion in Type 2, according to the BWR. Comparing Figure 13b,c, the maximum heave value with a BWR of 1.3 was 6.3 m for Type 1. In contrast, the motion in Type 2 was decreased as the BWR was increased, as shown in Figure 13c. In addition, at a BWR of 1.1, it was found that the heave value was about 2 m, then above a BWR of 1.2, the motions were almost the same, at approximately 1.3 m. Moreover, at a BWR of 1.1, the SFT underwent a sudden slack and generated a negative heave motion of \(-\)1.7 m. This mainly occurred when the buoyancy is weak.  
Figure 13: _Cont._  
Figure 13: Cont.  
Figure 13: Behavior of the SFT, according to the buoyancy-weight ratio: (**a**) maximum motion of the SFT; (**b**) heave motion of the SFT Type 1; (**c**) heave motion of the SFT Type 2; (**d**) maximum acceleration of the SFT; (**e**) maximum reaction force on the foundation of the SFT; (**f**) maximum section force of the SFT; (**g**) maximum section moment of the SFT.  
Next, Figure 13d shows the absolute maximum acceleration of the SFT model, according to the BWR. Again, the open shape represents Type 1, and the closed shape represents Type 2. For Type 1, the acceleration value was less than 0.25 m/s\({}^{2}\) and was steady. For Type 2, however, it can be seen that the acceleration value in the z-axis direction, with a BWR of 1.1, had a large value, at 3.75 m/s\({}^{2}\), and the value in the wave acting direction (y-axis) was 0.75 m/s\({}^{2}\), which was much larger than that of Type 1. These figures are shown in Figure 13a-c. For Type 2, since the motion was stabilized with the rising initial tension, which was due to increasing the BWR, the acceleration was decreased.  
Next, Figure 13e indicates the absolute maximum reaction force on the foundation of the SFT model, according to the BWR, and indicates the largest value of each point. In the case of Type 1, the reaction force was increased proportionally as the BWR was increased. In contrast to Type 2, the greatest motion occurred at a BWR of 1.1, declined at a BWR of 1.2, and was rebounded at a BWR of 1.3.  
Next, Figure 13f,g plot the maximum section force and section moment of the SFT model, according to the BWR. For Type 1, the section force rose as the BWR was increased. Moreover, the shear force in the y-axis direction (SFy), which is the wave load acting direction, was the largest, followed by the axial force and, finally, the SFx. Here, the axial force is the sum of all tensile forces, as shown in Table 2.  
Finally, Figure 13g illustrates the absolute maximum section moment of the SFT model, according to the BWR. The shear moment is also affected by motion. Type 1 and Type 2 were both under a great amount of torsion. It can be seen that this was proportional to the heave motion, and the section moment in the other directions was small (below 2000 MN-m).