Refined Fatigue Analysis for Tripod Support Structure of Offshore Wind Turbine (OWT)

Fatigue design and certification of OWT is a special challenge. As the turbine manufacturers are reluctant to share detailed turbines information and the offshore contractors have not full knowledge of integrated OWT design, integrated and non-linear time domain simulations are too cumbersome. A simplified approach is proposed, that requires complete separation between turbine and support structure, the only interaction between turbine and support structure is the aerodynamic damping, which is calculated separately and incorporated in the model of the support structure as additional viscous damping. Then, refined fatigue spectral analysis and damage assessment of critical joints for tripod support structure are carried out based on S-N curve method. This enables the use of standard design tools from the wind energy and offshore technology communities by superposition of separate analyses of hydrodynamic fatigue and aerodynamic fatigue. Simultaneously, for tripod constructions, they ofen include extra ordinarily large and complex tubular joints. In this work, a 3d-shlell model building in ANSYS approach, allowing for detailed modeling of local joint flexibility, is presented.The approach is to arrive at an efficient reference for the support structure design.