## 3 Test Results
### Wave Forces According to Wave Heights of Regular Waves  
Table 4 summarizes the maximum amplitudes of the wave forces to significant wave heights for the real-scale models and Figure 11 plots the maximum amplitude of wave forces obtained under a regular wave for the real-scale models of the three types of support structure. The wave force according to the wave height exhibits a different tendency for the three sea levels. According to the change of wave height at HSWL and MSL, all the models undergo an almost linear increase in the wave force with a higher wave height increasing from wave R-#3 (3.435 m) to wave R-#5 (12.78 m) [23; 24; 25], which is consistent with the linear wave theory with wave height. At HSWL, the wave force increases by about 1.85-2.08 times when the wave height doubles (2.00 times) from wave R-#3 (3.435 m) to wave  
Figure 10: Wave force patterns to P\({}_{\mathrm{w}}\) under regular waves: (**a**) monopile; (**b**) GBS; (**c**) hybrid. R-#4 (6.87 m). When the wave height increases by 3.72 times from wave R-#3 (3.435 m) to wave R-#5 (12.78 m), the wave forces increase by about 3.27-3.47 times at HSWL and 3.11-3.79 times at MSL. However, according to the change of wave height at LSWL, most of the models undergo a nonlinear increase of the wave force with a higher wave height increasing from wave R-#3 (3.435 m) to wave R-#5 (9.5 m). When the wave height at LSWL doubles (2.00 times) from wave R-#3 (3.435 m) to wave R-#4 (6.87 m), the wave forces increase by about 2.04-2.21 times, which is consistent with the linear wave theory with wave height. However, when the wave height increases by 2.77 times from wave R-#3 (3.435 m) to wave R-#5 (9.5 m), the wave forces increase by about 3.24-3.86 times. It is considered that the increased rate of the wave force (about 3.24-3.86 times) is higher than the increased rate of the wave height (about 2.77 times) because the wave height increases nonlinearly due to the occurrence of shoaling at the higher wave height (R-#5) in shallow water (LSWL), and the wave force also increases with increasing wave height [26]. Judging from the test results with respect to the support structure type, the increasing effect of the wave force is about 3.86 times for the monopile, and 3.54-3.61 times for the hybrid, and 3.24 times for the GBS, respectively. That is, the larger the diameter of the support structure, the less the effect of the nonlinear increase of the wave force. This is because the increase in wave force due to shoaling decreases as the diameter of the support structure increases. In other words, the larger the diameter of the support structure within the range of this study, the larger the diffraction effect is, and the increase in wave force due to shoaling is suppressed. According to the study of [PERSON] [19], it was found to get lower wave slamming forces on truss structure members than on a monopile. In addition, according to other theoretical studies [3], it has been reported that the impact wave force was somewhat reduced when the diameter of the support structure increased within a certain range, as presented in Figure 12. In GBS and hybrid, the wave force at LSWL is somewhat higher than that at HSWL and MSL over wave height 6.87 m. As described in Section 3.2, it is considered that, as the water depth is lowered, the larger projected area of these two types affects the increase of the wave force, and the increase of the wave force at the higher wave height is larger.