Stress factors in helical components of a 66 kV dynamic inter-array power cable for floating offshore wind turbines under tension dominant conditions

초록

This study investigates stress factors of helical components in a 66 kV dynamic inter-array power cable used for floating offshore wind turbines and examines their influence on fatigue damage evaluation. A detailed threedimensional finite element analysis (FEA) was conducted to derive the stress-strain relationships of copper conductors and steel wire armors within the cable. The stress factor was defined as the ratio between the von Mises stress acting on individual components and the nominal stress calculated from the overall cable cross section. To obtain realistic loading conditions, fully coupled load analysis (FCLA) was performed for a 15 MW floating offshore wind turbine operating in offshore environmental conditions. The global load time histories obtained from the FCLA were used to derive nominal stresses and strains of the cable cross section. By combining these results with the stress-strain relationships derived from the FEA, the actual stress histories of the helical components were determined using the stress factors. The results show that even under pure tensile loading, helical components experience combined axial, bending, and torsional shear stresses due to their geometric configuration, leading to von Mises stresses greater than the nominal stress of the overall cross section. In addition, the stress factor exhibited nonlinear behavior depending on the axial strain. When the stress factors were applied in the fatigue assessment, the accumulated fatigue damage increased by approximately three times for the armors and six times for the conductors. The proposed approach enables efficient estimation of the actual stress histories of internal cable components without performing repeated dynamic three-dimensional FEA, thereby improving the reliability of fatigue life assessment for dynamic power cables used in floating offshore wind applications.

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