This paper concerns the design of gravity base substructures for large offshore wind turbines, and in particular considers the possible advantages of the use of compliant towers. A specific substructure design is outlined, suitable for supporting a typical 90 m diameter teetered-rotor compliant-tower turbine such as the Boeing Mod-2. The required diameter at the wave impact zone is only 3.5 m compared with 10 m for a typical rigid design. As a consequence of this reduction in tower diameter, the forces caused by waves are considerably reduced. Because the wave forces dominate over wind forces, this allows a major reduction in the size of the lower substructure. This reduces the cost considerably, improves prospects for construction in existing facilities, and eases installation problems. Previous support structure designs for offshore turbines are compared, considering particularly the relationship between rotor diameter, tower diameter, and base diameter. This confirms that tower diameter is a major design and cost driver. Modern US land designs suggest that tower diameters may be reduced to 3 % of rotor diameter, well below even the thinnest of existing offshore designs. Systematic variations of tower diameter with rotor diameter are investigated, and it is concluded that their ratio can be expected to be roughly constant. Some possible further developments are suggested, including multiple-leg and very compliant towers.
Structure design for compliant-tower offshore wind turbines
Ausfuehrung von Offshore-Windturbinen fuer Montage auf nachgiebigem Turm
1982
8 Seiten, 3 Bilder, 3 Tabellen, 16 Quellen
Conference paper
English
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