Feasibility of the Application of a Spar-type Wind Turbine at a Moderate Water Depth

Abstract

The feasibility of the application of a spar-type wind turbine at a moderate water depth is studied in this paper. In the oil and gas industries, spar-type offshore platforms are widely applied in deep water. The same idea is used in offshore wind technology to present the Hywind concept based on a catenary moored spar in deep water. The draft of the spar limits the application of spar-type wind turbines in shallow water. However, it is possible to design spar-type wind turbines for moderate water depths. The present article studies the feasibility and performance of such a design. A spar-type wind turbine at a moderate water depth called “ShortSpar” is introduced in the present article. A catenary moored spar-type support structure is applied as a base for the 5-MW NREL land-based turbine. The power performance, structural integrity and dynamic responses of a 5-MW catenary moored spar-type wind turbine in deep water (DeepSpar) have previously been studied. In the present article, the responses of the spar-type wind turbines, ShortSpar and DeepSpar, are compared. The HAWC2 code is used to carry out the coupled aero-hydro-servo-elastic analyses. Different environmental conditions are used to compare the responses. A dynamic link library (DLL) is used to feed the mooring forces at each time step into the HAWC2 code. The force-displacement relationships are obtained from the Simo-Riflex code. The comparison of the responses of ShortSpar and DeepSpar in different load cases indicates the feasibility of implementation of spar-type wind turbine in moderate water depths. The results show that the spar-type wind turbine at a moderate water depth exhibits good performance, and its responses are reasonable compared with those associated with a spar-type wind turbine in deep water. The total mass (the structural mass plus the ballast) of ShortSpar is 35% less than the mass of DeepSpar, while the statistical characteristics of the generated power are almost the same for both spars. This mass reduction for ShortSpar helps to achieve a more cost-effective solution for floating wind turbines at a moderate water depth.