Optimised design of screw anchors in tension in sand for renewable energy applications

Abstract

The offshore deployment of floating offshore structures such as wind turbines or wave energy converters is expected to strongly increase during the next decade. The growing size of these structures' dimensions inducing very large mooring forces, makes the anchoring solution adopted a critical issue for the commercial success of floating marine energy farms.The upscaling of the screw anchor technology from onshore to the offshore environment has been recently proposed as an efficient way of providing a large uplift capacity while their installation generates far less noise and vibrations than pile driving. This paper incorporates within a single procedure geotechnical and structural constraints related to the installation and operation of screw anchors to calculate the optimal anchor geometry able to maximise the uplift capacity available.Performance envelopes for screw anchors have been derived in a parametric study, covering a broad range of soil conditions as well as in a representative case study. Results show that single screw anchors are more efficient (e.g. shorter and lighter) than driven piles to sustain tension loading. A sufficient capacity could be developed to address the needs of wave energy converters. However, tension requirements for tension-leg platform wind turbines would probably require groups of anchors.

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ORCID for Benjamin Cerfontaine: orcid.org/0000-0002-4833-9412

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