Single (or mono) suction buckets were trialled as offshore wind turbine (OWT) foundations at Frederiksvan in 2002 and subsequently at Horn Rev 2, Dogger Bank, Dudgeon and Hornsea between 2009 and 2014. Supporting light and slender structures, and subject to high overturning moments due to wind and wave loads which act far above the level of the seabed, the mono-bucket foundation may need to resist net uplift on its windward side. The tension loads will comprise a combination of ‘static’ (e.g. continuous wind or current) loading and cyclic (e.g. wave or wind-gust generated) events, and could potentially lead to permanent tilting of an OWT due to progressive rotational movement.For a mono-bucket in dense sand, high undrained/ partially drained tension capacity and pore pressure dissipation between the short-duration peak (net tension) storm loads (Tjelta, 2015) may help to limit rotation. While this could be a crucial performance aspect for such foundation, it is typically not considered in design, and has not been studied systematically.This paper will present a series of centrifuge model tests conducted to investigate mono-bucket response under a range of load level and cyclic loading frequencies (i.e. drainage conditions) in dense sand. The results from the centrifuge tests suggest that mono-bucket rotational displacement and stiffness in dense sand is dependent on cyclic load frequency (or drainage conditions) as well as the contact condition between the bucket invert and the seabed.

Offshore Wind Turbine Mono-Bucket Foundations in Sand

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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