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Design of a reference concrete semi-submersible floater and its cross-sections for a 10 MW wind turbine
  • Sho Oh
Sho Oh
DNV Energy Systems

Corresponding Author:[email protected]

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Abstract

Adequate design methods for concrete offshore wind turbines need to be determined through investigations on the characteristics of the dynamic responses and the concrete structural behavior. For these future studies, a reference concrete semi-submersible floater for a 10 MW wind turbine was designed in this study along with the associated cross-sections for the concrete members. A structural assessment was carried out for the ultimate, fatigue, and serviceability limit states. Six cases of combinations of the loading conditions and structural requirements were assumed for the assessment of watertightness, as the required criteria for floating wind turbines is not clarified in the presently available guidelines. The different assessment conditions for watertightness resulted in different design of prestressing tension, which also caused differences in the design margins for the ultimate limit states as well as the SN diagram used for the assessment of the fatigue limit states. The maximum stress acting on the member of the floating wind turbine differed by about 7.6 to 16.2 % for the 50-year and 1-year environmental conditions. The small difference between the stress for the two return periods can be attributed to the large component of the wind turbine thrust in the variable loads. When the partial load factor of 1.0 is used, the structural requirement in the prestressing design caused larger differences compared to the return period of the loading conditions in the watertightness assessment. The use of the partial load factor of 0.5 for the prestressing design also caused a large difference in the results of the structural assessment, indicating the importance of the careful choice of the partial load factor.