Abstract
Floating offshore wind turbines are subjected to higher tower fatigue loads than their fixed-to-seabed counterparts, which could lead to reductions in turbine life. The worst increases are generally seen in the tower axial fatigue, associated with the tower fore-aft bending moment. For a spar type platform this has been shown to increase by up to x2.5 and, for a semi-submersible platform, by up to x1.8. Reducing these loads would be beneficial, as the alternative of strengthening the towers leads to increases in cost. Here, two offshore floating wind turbine systems, of the spar type, are analysed and selected responses and tower fatigue compared: one incorporates a variable speed, variable pitch-to-stall blade control system and a back twisted blade, and the other a conventional pitch-to-feather control. The results are then compared to those obtained in an earlier study, where the same turbine configurations were coupled to a semi-submersible platform. A weighted wind frequency analysis at three mean turbulent wind speeds highlights that the impact of the back twist angle magnitude and initiation point on tower axial fatigue life extension was the same for both platform types. Compared to their respective feather base models, an increase in the tower axial fatigue life of 18.8% was seen with a spar platform and 10.2% with a semi-submersible platform, when a back twist angle to the tip of −6° was imposed along with the variable speed, variable pitch-to-stall control.
Fatigue life extension of epoxy materials using ultrafast epoxy-SbF5 healing system introduced by manual infiltration
