# Influencing Factors of Motion Responses for Large-Diameter Tripod Bucket Foundation
## 5 Results and Discussion
### Effect of Draft  
From the perspective of the structure's own performance, as shown in Tables 1-3, the bucket foundations used in laboratory tests have the same diameter and weight; no large difference is observed in the weights of connecting frames. Therefore, the masses of Model 1, Model 2, and Model 3 involved in the oscillating motions are basically identical under the same draught. However, the mass and moment of inertia increase with increasing draught in the case of the same model, and the moment of initial significantly increases with increasing spacing of bucket foundation under the same draught. Tables 4-6 show that the pressure heads in each bucket, provided by the difference of heads between external heads outside the bucket and interior heads inside the bucket, supported the weight of LDTBF. The relationship between pressure head and weight of structure is positive. From the perspectives of wave-induced loads on structure, the forces and motion responses of LDTBF are inevitably affected with the increase in draft, the increase in the distance between the structure and the seabed and the surface area of the wave action and the reduction of the gravity center. Figures 10-12 show the motion performances of Model 1, Model 2, and Model 3 with different drafts. Figure 11: Experimental RAOs for Model 2 with different drafts: (**a**) heave RAO and (**b**) pitch RAO. Figure 10: Experimental RAOs for Model 1 with different drafts: (**a**) heave RAO and (**b**) pitch RAO. The RAOs of heave acceleration for Model 1 with different drafts at a constant 12.5 m water depth are shown in Figure 10a. The maximum amplitudes of heave acceleration 0.59 m/s\({}^{2}\) at a 4.0 m draft, 0.54 m/s\({}^{2}\) at a 4.5 m draft, and 0.53 m/s\({}^{2}\) at a 5.0 m draft occurred near the period of 5 s, 6 s, and 7 s, respectively, i.e., the resonant periods of heaving motion increased with increasing draft, while the motion responses decreased with the increase in draft. When the period was longer than 7 s, the amplitudes of heave acceleration first decreased and then increased slightly with increasing draft. The larger the wave period, the more significant the trend. The heave acceleration at a 4.5 m draft is almost smaller in most periods. The RAOs of pitch angle for Model 1 with different drafts at a constant 12.5 m water depth are shown in Figure 10b. The maximum amplitudes of pitch angle appearing near the period of 6 s were 12.9\({}^{\circ}\) at a 4.0 m draft, 11.7\({}^{\circ}\) at a 4.5 m draft, and 10.0\({}^{\circ}\) at a 5.0 m draft. The pitch responses decreased with increasing draft and especially had a significant trend when the period was less than 9 s. When the period was longer than 9 s, the pitch angles varied from 4\({}^{\circ}\) to 5\({}^{\circ}\). The RAOs of heave acceleration for Model 2 with different drafts at a constant 12.5 m water depth are shown in Figure 11a. The maximum amplitudes of heave acceleration, 0.397 m/s\({}^{2}\) at a 4.0 m draft, 0.41 m/s\({}^{2}\) at a 4.5 m draft, and 0.36 m/s\({}^{2}\) at a 5.0 m draft, occurred near the period of 5 s, 6 s, and 6 s, respectively. The resonant periods of heaving motion increased with increasing draft, while the motion responses first increased and then decreased with the increase in draft. The amplitudes of heave acceleration decreased with increasing draft when the period was greater than 7 s. With a longer period, the heave RAOs were almost constant at 0.2 m/s\({}^{2}\). The RAOs of pitch angle for Model 2 with different drafts at a constant 12.5 m water depth are shown in Figure 11b. The maximum amplitudes of pitch angle appearing near the period of 6 s were 10.12\({}^{\circ}\) at a 4.0 m draft, 10.88\({}^{\circ}\) at a 4.5 m draft, and 9.66\({}^{\circ}\) at a 5.0 m draft, respectively. The pitch responses first increased and then decreased with the increase in draft.