To predict the penetration depth of the offshore jack-up drilling platform during the preloading process, the fluid-solid coupling theory was introduced to establish the finite element model of the soil-spudcan system in saturated clay. With this model, the spudcan bearing capacity factor was numerically calculated when spudcans penetrated into homogeneous and heterogeneous clay. The results show that, the spudcan bearing capacity factor is mainly decided by soil strength and spudcan penetration depth: for soil with lower strength heterogeneous coefficient, the spudcan bearing factor has a positive correlation with the spudcan penetration depth, while for soil with higher strength heterogeneous coefficients, the correlation is negative. When the spudcan penetration depth is about 20 m, the maximum bearing capacity factor of spudcan is 10.30 (not consider soil backflow) and 12.25 (consider soil backflow), respectively. The calculation method for spudcan bearing capacity during the preloading process was given. With this method, the penetration depth of spudcan under certain soil condition for the Bohai No. 5 platform was calculated. Because the proposed calculation method considers the influences of reaction between soil and spudcan, the nonlinear property of soil, end resistance at the bottom of spudcan, and lateral resistance of spudcan during the whole preloading process, the predicted spudcan penetration depth is more reasonable and has a difference of about 20% from the result of traditional calculation methods.
In connection with the design of floating wind turbines, stochastic dynamic analysis is a critical task considering nonlinear wind and wave forces. To study the random structural responses of a newly designed submerged tension leg platform (STLP) wind turbine, a set of dynamic simulations and comparison analysis with the MIT/NREL TLP wind turbine are carried out. The signal filter method is used to evaluate the mean and standard deviations of the structural response. Furthermore, the extreme responses are estimated by using the mean upcrossing rate method. The fatigue damages for blade root, tower, and mooring line are also studied according to the simulated time-series. The results and comparison analysis show that the STLP gives small surge and pitch motions and mooring line tensions in operational sea states due to the small water-plane area. Additionally, in severe sea states, the STLP gives lower extreme values of platform pitch, slightly larger surge and heave motions and better towerbase and mooring line fatigue performances than those of the MIT/NREL TLP. It is found that the STLP wind turbine has good performances in structural responses and could be a potential type for exploiting the wind resources located in deep waters.
The composite bucket foundation (CBF) consists of a concrete curved transition section, a concrete beam-slab system, and a suction caisson and is increasingly used as the foundation for offshore wind turbines. The curved transition section transmits the upper load from the tower to the foundation, and its force and transmission characteristics are related to the safety of the entire wind turbine structure. The arced transition section has the characteristics of complex geometry, load conditions, and large curvature. It is difficult to determine its bearing characteristics and force transmission system. In this paper, the boundary conditions and loading device of the CBF model test are designed, and three 1:20 arced transition section model specimens are made. The mechanical characteristic experiments of CBF are used to analyze the failure process, failure characteristics, and seismic performance of the structure. Results show that the cracking effect of the arced transition section after prestressing is obviously better than that of a reinforced concrete arced transition section structure. The arced transition section specimens equipped with prestressed tendons can increase the structural cracking load ratio by about 35% for reinforced concrete members. The energy dissipation capacity of the specimens has been significantly improved, and the material properties can be fully utilized. The failure mode of the arced transition section structure under horizontal reciprocating load shows the characteristics of bending and shear failure.
In this study, the Jinzhou 9-3 CEPD float-over installation project was investigated. During the undocking condition, the water depth of the motion path of the working barge gradually changed from 10.31 m to 9.41 m. The undocking clearance of the HYSY 228 is smaller than 1 m; therefore, the barge shows highly nonlinear hydrodynamic characteristics, and it is difficult to be accurately simulated by numerical analysis. Thus, it is necessary to obtain the hydrodynamic characteristics and laws of the float-over barge at different water depths by using tank model test, to provide some reference and guidance for float-over operations in shallow water.
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