Analysis of the effect of a series of back twist blade configurations for an active pitch-to-stall floating offshore wind turbine

Dawn Ward, Maurizio Collu, Joy Sumner

Research output: Contribution to journalArticlepeer-review

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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.

Original languageEnglish
Article number062001
Number of pages9
JournalJournal of Offshore Mechanics and Arctic Engineering
Volume142
Issue number6
Early online date8 Apr 2020
DOIs
Publication statusPublished - 1 Dec 2020

Keywords

  • blade back twist
  • design of offshore structures
  • dynamics of structures
  • floating and moored production systems
  • floating offshore wind turbine (FOWT)
  • ocean energy technology
  • pitch-to-stall
  • structural mechanics and foundation
  • tower axial fatigue life

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