Ultimate load design of jacket-type offshore wind turbines under tropical cyclones

Tropical cyclones are a high risk to offshore wind turbine (OWT) support structures, so the design conditions, including this risk, are necessary for tropical cyclone frequent occurrence zones. This study developed a computer program to carry out a critical ultimate load analysis and determine the optimum design for a Jacket-type OWT support structure. The total weight of the OWT support structure after the optimal steel design with the yaw operative condition is always considerably smaller than that without for the steel design results under the loads of the GL Tropical Cyclone Technical Note (GL TCTN). This paper studies OWTs under the tropical cyclone classes 1 to 3 and the terrain categories A, to C, where the 1-minute wind speed at 10-m height is gradually increased from classes 1 to 3, and the surface roughness decreases from A to C. When the yaw can operate, the total steel weight consumption due to the tropical cyclone 1C, 1B, and 2C loads is lower than that for the IEC 61400-3 loads. In the case of 1A, the overall steel consumption is only slightly higher than that of the IEC 61400-3. However, for other conditions, the design should include the GL TCTN loads. For the yaw inoperative condition, the GL TCTN results are always largely dominant in the steel design, so the use of only the IEC 61400-3 condition will result in extremely high risk to OWT support structures.