Dynamic analysis of floating wind turbines during pitch actuator fault, grid loss, and shutdown

Coupled non-linear aero-hydro-servo-elastic simulations of three types of floating wind turbines (spar, semi- submersible, and tension leg platform) are carried out for several fault cases over a range of environmental conditions based on correlated wind and wave data from the North Sea. Three particular fault scenarios are considered: 1) blade seize, where the pitch actuator of one blade is blocked, 2) blade seize, recognized by the controller and followed by shutdown (grid disconnection and aerodynamic braking), and 3) grid loss followed by shutdown. The platform motions and structural loads caused by fault events are compared to loads encountered during normal operation and during selected extreme weather conditions. Although the global motions and mooring line loads tend to be largest during storm conditions, selected platforms experience large pitch or yaw motions due to blade seize and shutdown. Imbalance loads due to blade seize can lead to particularly large loads on the blades and tower, and the shutdown process can impose relatively large edgewise blade loads