Journal of The School of Marine Science and Technology,Vol.6 No.1
Natural Periods and Ductility of the Substructure consist
of Truss Tower
and Jacket Foundation for Offshore Wind Turbines
Kinji SEKITA and Hiroshi OHKUBO
Abstract
To construct offshore wind turbines (OWT)in such a country like Japan where typhoons attack every summer and earthquakes occur frequently, due considerations to them are indispensable. The support structure to mount a wind generator has enough flexural stiffness and strength,and has the shape such that isn’t liable to receive effects of the wind.Further,it is necessary that the first natural period of the OWT structural system avoids various periods such as a rotational period of a rotor,a 1/3 period that a blade intersects with the tower,wave periods,so as to reduce excessive vibrations and the fatigue damage.Most popular substructure is a combination of a monopile foundation and a cylinder tower with the large diameter and thick plate.A jacket foundation with a conventional tower was for the first time adopted for a 5MW-OWT which erected near Beatrice oilfield (depth of the water 45m) off 25km Scotland in 2006.As a candidate substructure to answer the above-mentioned request,the support structure that truss tower made by steel pipes and a jacket foundation may be appropriate. Therefore, we made a comparison of the influence of both truss and conventional towers onto wind loads and powers generated with excellent results. The paper presents structural and earthquake proofing performances about this new support structure obtained by the structure analysis considering pile and soil interaction, Eigen value analysis and push over analysis.