## 3 Global Performance of SFTs with Suspension Cables
Moreover, the behavior of the tube was evaluated at installation depths of 40, 70, and 100 m, which was assumed to be a certain top clearance from the sea level for installing the SFT. The main cable and hangers were applied as wires, while the tether supporting both sides of the SFT was made of APLX70 steel tube. The cross section of the tower, which primarily supports the system, had an A shape form, was 10 m wide, 5 m high and 1 m thick, and was made of reinforced concrete. With these specifications, listed in Table 1, a preliminary analysis was performed by selecting one case with a diameter of 23 m, BWR 1.2, an installation depth of 70 m, a wave height of 6.0 m, a wave period of 8 s, and an inclination angle for the main cable of 12 degrees. Since the wave load in Figure 7 is applied, time series data for each point can be obtained. In addition, a repetitive motion occurs, because the wave load acts irregularly. These results were graphed in Figures 8-11, with the maximum and minimum values for each point. For investigation of this model, the ABAQUS AQUA FE Program was used. When this FE program was applied to the new type structure, such as SFTs, verification of analysis model was very important. This analysis model was verified through comparison with hydraulic experimental study by [PERSON] et al [(16)]. [PERSON] et al [(17)] investigated hydraulic experimental study of SFT under a regular wave condition. The dimension of the SFT was 98 m of length and 23m of diameter. Through this experimental study, wave pressure, motion, and tension force of tether on SFT were evaluated. [PERSON] et al [(16)] verified a comparison between hydraulic experimental study results and analyzed the results. Element SFTs  
Figure 8: Motion of SFT: (**a**) motion at each point of Type 1; (**b**) motion at each point of Type 2.  
and tethers for FE analysis were beam elements (b31) and truss elements (T3D2), respectively. Each tether and SFT were connected by multi-point constraint (MPC) option. Further, they proposed mesh size for FE analysis through parametric analysis. For boundary conditions, tethers were constrained by three directions and both ends of the SFT were only by way of constrained torsional rotation direction. As a result of sway motion of SFT, analysis results had very similar tendency with experimental results according to wave height and period. In addition, maximum and minimum tension force of tethers had similar results. Therefore, a verified analysis model of SFT was applied in this study. Figure 10: _Cont._  
Figure 9: Acceleration at each point of Type 1 and Type 2: (a) acceleration at each point of Type 1; (b) acceleration at each point of Type 2. First, Figure 8 shows the translation motion at each point of the SFT model. Here, the heave is for the linear vertical motion, the sway is for the linear transverse, and the surge is for the linear longitudinal motion. Moreover, they were expressed as a triangle, rectangle and circle, respectively. Additionally, the maximum value was plotted as a closed shape, and the open shape represents the minimum value in Figure 8. Figure 8a shows Type 1, and Figure 8b shows Type 2. It can be seen that the heave for Type 1 and Type 2 was the most responsive motion, because both have a BWR of 1.2. In Figure 8a, the maximum heave motion value was 5 m, and there was a fluctuation of approximately 1 m. Additionally, the sway motion value had a maximum of 0.5 m and minimum of 0.5 m and also fluctuated by approximately 0.5 m. Moreover, little surge motion occurred in the model, which was fixed with towers at both ends. On the other hand, in Figure 8b, showing Type 2, which is installed in the middle, as shown in Figure 6c, all motions were lower than those for Type 1. The maximum heave motion was 1.2 m due to the buoyancy of the model, and the sway motion, which acts in waves, was deformed by a maximum of 0.2 m and minimum of 0.3 m.  
Next, Figure 9 illustrates the acceleration at each point of the SFT model.