Analysis of Static, Dynamic, Global, and Local Load Effects for Ultimate Limit State Assessment of Semi-Submersible Hulls of Floating Wind Turbines

Very limited research has been conducted on structural load effect analysis and design checks of large semi-submersible floating wind turbines (FWTs). Determining the combined static, dynamic, global, and local load effects in FWT is essential for the ultimate limit state (ULS) assessment of the floaters. This paper deals with the complex structural load effects for ULS analysis of column structures of a 10-MW semi-submersible FWT. First, a multi-body numerical modeling approach is employed to develop the floater model in a fully coupled FWT system to capture the time domain internal loads of column cross-sections under wind and wave conditions. Then, a high-fidelity approach and a simplified approach are developed to estimate lateral pressures on columns. With the obtained global cross-sectional loads and the corresponding lateral pressure, the ULS design check considering buckling for hull panels are performed for representative load cases. Detailed analysis results are presented and discussed, including perspectives of permanent and environmental load effects, as well as global and local lateral pressure load effects for buckling analysis of column structures. Moreover, comparisons of lateral pressures estimated by the high-fidelity and simplified approaches for buckling assessment of the outer column are made. Finally, the main conclusions are summarized. This study shed light on the importance of different structural load effects on ULS design checks. In addition, the simplified approach for lateral pressure estimate can be well used in the preliminary design stage of floaters to save large computational costs while obtaining acceptable results.