Abstract
Abstract For a turbine mounted on a floating platform, extreme induced loads can be increased by up to 1.6 times those experienced by a turbine situated on a fixed base. If these loads cannot be reduced, towers must be strengthened which will result in increased costs and weight. These tower loads would be additionally exasperated for a pitch-to-feather controlled turbine by a phenomenon generally referred to as “negative damping,” if it were not avoided. Preventing negative damping from occurring on a pitch-to-feather controlled floating platform negatively affects rotor speed control and regulated power performance. However, minimizing the blade bending moment response can result in a reduction in the tower fore-aft moment response, which can increase the tower life. A variable-speed, variable pitch-to-stall (VSVP-S) floating semi-submersible wind turbine, which does not suffer from the negative damping and hence provides a more regulated power output, is presented. This incorporates a back twist blade profile such that the blade twist, starting at the root, initially twists toward stall and, at some pre-determined “initiation” point, changes direction to twist back toward feather until the tip. Wind frequency weighting was applied to the tower axial fatigue life trends of different blade profiles and a preferred blade back twist profile was identified. This had a back twist angle of −3 deg and started at 87.5% along the blade length and achieved a 5.1% increase in the tower fatigue life.
Highlights
Increasing the proportion of our energy that comes from renewable sources is imperative
To enable the analysis of the effects of back twist magnitude (BTM) and back twist initiation point (BTIP) on tower axial fatigue life, an initial study on the effects on the constant pitch angle setting below rated was performed at mean turbulent winds of 8 and 13 mps
From the analysis of the effects on the tower axial fatigue life of varying the constant pitch angle setting, it was clearly highlighted that reductions in the variance of both blade flapwise bending moment and blade deflection created a corresponding reduction in the range of the rotor thrust (Fig 2)
Summary
Increasing the proportion of our energy that comes from renewable sources is imperative. Extreme environmental events are increasing driven by indisputable anthropogenic contributions to climate change [1]. This disproportionately effects the world’s poorest people, which has likely contributed to the lack of adequate speedy action on the part of the world’s economic leaders. If greenhouse gas emissions continue to rise, it is predicted that the planet will experience a 1.5 °C human-orchestrated global warming impact by 2030 [2]. This will cause wide spread issues with food, water security, flooding, droughts and storm conditions, which will shadow the devastating impact from global warming, that has already been seen in recent years. Worldwide predictions are for a 5% contribution of the global offshore wind energy market by 2030 [4]
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