Abstract
Towers and rotor-nacelles are being enlarged to respond to the need for higher gross generation of the wind turbines. However, the accompanying enlargement of the substructure supporting these larger offshore wind turbines makes it strongly influenced by the effect of wave forces. In the present study, the hybrid substructure is suggested to reduce the wave forces by composing a multicylinder having different radii near free surface and a gravity substructure at the bottom of the multicylinder. In addition, the reaction forces acting on the substructure due to the very large dead load of the offshore wind turbine require very firm foundations. This implies that the dynamic pile-soil interaction has to be fully considered. Therefore, ENSOFT Group V7.0 is used to calculate the stiffness matrices on the pile-soil interaction conditions. These matrices are then used together with the loads at TP (Transition Piece) obtained from GH-Bladed for the structural analysis of the hybrid substructure by ANSYS ASAS. The structural strength and deformation are evaluated to derive an ultimate structural safety of the hybrid substructure for various soil conditions and show that the first few natural frequencies of the substructure are heavily influenced by the wind turbine. Therefore, modal analysis is carried out through GH-Bladed to examine the resonance between the wind turbine and the hybrid substructure.
Highlights
Offshore wind energy has gained attention in many countries as an alternative and reliable energy source since its potential has been recognized for long and mostly associated to the concept of nondestructive renewable energy
Many offshore wind farms are in the planning phase like in Europe, where wind farms will be established at greater water depths with larger turbines
Since the water particle velocity is the largest near free surface, the hybrid substructure is composed of a multicylinder having different radii near free surface to reduce the wave forces acting on the substructure and a gravity-based
Summary
Offshore wind energy has gained attention in many countries as an alternative and reliable energy source since its potential has been recognized for long and mostly associated to the concept of nondestructive renewable energy. Føreland et al [8] designed mono-pile, gravity-based structure, jacket, and three-pile fixed support structures for 2.5, 5, and 10 MW wind turbines for different water depths to quantify the economic differences provided by different wind turbine foundation systems for the environmental conditions of the North Sea. The southwestern coast of the Korean peninsula is one of the most suitable places for the construction of offshore wind turbines. It is difficult to determine a proper substructure type because of the water depth range between 20 and 30 m and the very soft clay layer constituting the seabed in this area This implies that a new substructure type suitable for the environmental characteristics of the southwestern coast of Korea must be developed.
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