# Influencing Factors of Motion Responses for Large-Diameter Tripod Bucket Foundation
## 5 Results and Discussion
### Effect of Spacing between Bucket Foundations  
As shown in Tables 1-3, the moment of inertia of LDTBF, one of the key factors affecting the pitch motion, increases with increasing spacing between bucket foundations. In Table 4, the ratio of wavelength to spacing of structures is inversely proportional to the spacing and the motion responses for LDTBF are inevitably changed in waves with the coupled variations of wave exciting forces caused  
Figure 15: Experimental RAOs for Model 1 with different water depths: (**a**) heave RAO and (**b**) pitch RAO.  
The RAOs of heave motion and pitch motion with different bucket spacings at a 4.0 m draft at water depth of 12.5 m are shown in Figure 16. In Figure 16a, the maximum amplitudes of heave acceleration 0.461 m/s\({}^{2}\) for S = 1.5 D, 0.415 m/s\({}^{2}\) for S = 2.0 D, and 0.457 m/s\({}^{2}\) for S = 2.0 D occurred near the period of 5 s, 5 s, and 6 s, respectively. Other amplitudes of heave acceleration for S = 1.5 D and S = 2.5 D are 0.386 m/s\({}^{2}\) at a period of 14 s and 0.406 m/s\({}^{2}\) at a period of 15 s, respectively, while the responses of heave acceleration for S = 2.0 D are almost the smallest in all the periods than those of S = 1.5 D and S = 2.5 D. As shown in Figure 16b, the pitch RAOs decreased with the increase in S. This can be attributed to a larger moment of inertia with wider spacing. However, the maximum values of the pitch angle are 12.87\({}^{\circ}\), 10.12\({}^{\circ}\), and 9.82\({}^{\circ}\), respectively. With increasing S from 1.5 D to 2.0 D, the maximum amplitude decreased by 2.75\({}^{\circ}\), while this amplitude only decreased by 0.3\({}^{\circ}\) when S increased from 2.0 D to 2.5 D. This indicates that simply improving the pitch RAOs by increasing the spacing between bucket foundations is limited. This cannot satisfy the requirements of low cost and high efficiency development for offshore wind power, while a larger spacing results in increasing material consumption of connecting members and the cost.  
The RAOs of heave motion and pitch motion with different bucket spacings at 4.5 m draft in a water depth of 12.5 m are shown in Figure 17. The maximum amplitudes of heave acceleration for S = 2.0 D are less than those of S = 1.5 D and S = 2.5 D around the resonant period. The heave RAOs with a wider spacing were slightly larger than those with a narrower spacing with the period longer than 7 s. Figure 17b shows that the pitch RAOs have a similar decreasing trend as the 4.0 m draft with the increase in s. The maximum amplitudes of pitch angle, smaller than the amplitudes at 4.0 m draft, are 11.67\({}^{\circ}\) for S = 1.5 D, 10.88\({}^{\circ}\) for S = 2.0 D, and 9.17\({}^{\circ}\) for S = 2.5 D.  
The RAOs of heave motion and pitch motion with different bucket spacings at 5.0 m draft at the water depth of 12.5 m are shown in Figure 18. Figure 18a shows that the maximum amplitudes of heave acceleration 0.532 m/s\({}^{2}\) for S = 1.5 D, 0.367 m/s\({}^{2}\) for S = 2.0 D, and 0.475 m/s\({}^{2}\) for S = 2.0 D occurred near the period of 7 s, 6 s, and 6 s, respectively. The heave RAOs with a wider spacing were larger than those with a narrower spacing when the periods were longer than 7s. As shown in Figure 18b, the maximum amplitudes of pitch angle, smaller than the amplitudes at 4.0 m and 4.5 m draft, are 10.03\({}^{\circ}\) for S = 1.5D, 9.66\({}^{\circ}\) for S = 2.0 D, and 9.19\({}^{\circ}\) for S = 2.5 D. However, the pitch RAOs increase with the increase in spacing between bucket foundations, and the variation trend is contrary to the trend at a 4.0 m draft and a 4.5 m draft. The heave RAOs for S = 2.5D were much larger than those for S = 1.5D and S = 2.0 D in almost each period, i.e., the wider the spacing between bucket foundations, the larger the heave RAOs. Therefore, simply improving the pitch RAOs by increasing the spacing between bucket foundations is limited and negatively affects the motion performance during the transportation of LDTBF.