This study presents a simplified analysis technique capable of predicting the dynamic behavior of a tripod suction pile subjected to a horizontal load. The first natural frequency of the system, horizontal displacement, and allowable rotation angle at the pile head were set as target physical quantities in accordance with substructure design requirements. In consideration of the physical characteristics of the tripod suction pile, the analysis was extended to the single pile-multi-pile-tripod-tower part to derive the influence factors. A possible displacement response function that could be applied to the intermediate pile range was also proposed. Thereafter, a detailed design was determined using an integrated load analysis, which included a turbine based on the basic design of simplified analysis method. Furthermore, the dynamic behavior of the offshore wind turbine at each installation stage was predicted using a numerical analysis and measured via field tests. The displacement at the pile head and the predicted value of the first natural frequency of the system were compared using the field-measured and numerical analysis values. The first natural frequency value produced by the simple analysis method showed an error range within 1%, and the displacement at the pile head also satisfied the structural design requirements. Therefore, this method provides a quick and accurate solution to the lateral response of tripod suction piles as foundations for offshore wind turbines.
In order to obtain more wind energy, offshore wind farms tend to be constructed in deeper water with larger wind turbines. Various kinds of support structures, including gravity base structures, are considered to reduce the CAPEX of wind farms. In this paper, feasibility of floated gravity base structures is investigated through floating stability analysis on lowering operations during the installation. In regard to the baseline model for 30 m water depth with the spherical base and the top diameter of 6 m, the floating stabilities are derived by varying the base diameter and the draft. As it is assumed that the structures are ballasted with sea water during the installation step, free surface effects are taken into account. The relevant structures satisfying the floating stability requirement are derived. It is shown that the structure should be equipped with the bulkheads to satisfy this requirement. Furthermore, the geometry of gravity base structure which minimize the weight of the structure is investigated.
As we are facing the shortage of oil energy, studies on renewable energy, wind energy research has been naturally getting attention. Among wind energies, ocean wind energy is relatively abundant compared to land wind energy and therefore, is getting much attention in terms of its efficiency. However, the problem is the cost. Generally, the cost ratio of the supporting structure is over 25% of the total installation cost of a offshore wind turbine system. Thus, it is very important to reduce the total installation cost of the offshore wind turbine and develop accurate analysis methodology for various offshore wind turbine foundations. In this study, nonlinear structure-soil interaction analyses have been proposed and conducted for the typical suction bucket model of an offshore wind turbine foundation, and the results were compared with experimental test data for numerical validations.
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