The fatigue resistance of floating offshore wind turbines is significantly affected by the wave forces to which their supporting platforms are exposed. Passive and active damper systems — preferably inexpensive — are thus being sought to mitigate these effects.
Existing solutions such as U-shaped column tubes, based on the principle of the dynamic transfer of water reserves (acting as moving masses), are passive and unsuited to the changing wave direction.
To overcome these difficulties, researchers at IFPEN have come up with a multi-directional, star-shaped damper system that was first modeled and for which an active control law has been proposed(1-3). This control is based on the continuous management of the size of the restrictions (fixed in the passive version) inside the pipes, making it possible to restrict natural water flow between the reservoirs.
The proposed system helps mitigate the effects of the wave irrespective of its direction. In the active version, the control law developed generates levels of performance that are much higher than those of the passive version (see figures).
There is still room for variations of this system to lead to further improvements, both in terms of platform design and control during operation. It would be possible, for example, to add and manage links between air columns or optimize the calibration for a given production site as a function of its wind and swell characteristics.
(1) O. Lepreux & C. Coudurier, Patent 3048409, 2017
(2) C. Coudurier, O. Lepreux, N. Petit, Proc. of 10th IFAC Conference on Manoeuvring and Control of Marine Craft, MCMC, 2015
(3) C. Coudurier, O. Lepreux, N. Petit, submitted to Journal of Ocean Engineering
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