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, to face the appetite for green energy sources. 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 tension capacity while their installation generates far less noise and vibrations than impact pile driving. Most of recent studies on screw anchors have focused on separated geotechnical problems such as their uplift capacity or installation requirements. This paper incorporates within a single procedure geotechnical and structural constraints 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 case study, representative of offshore conditions. Results show that single screw anchors are more efficient (e.g. shorter and lighter) than driven piles to sustain tension loading. The results presented in this study support the applicability of screw anchors to be used as part of the mooring system for wave energy converters. However, tension requirements for tension-leg platform wind turbines would probably require the use of group of anchors.

Control of screw pile installation to optimise performance for offshore energy applications

“…The embedment depth corresponded to a shallow mechanism in uplift, but was close to the limit for shallow to deep mechanism formation (in the range 5Dh-8Dh (Cerfontaine et al, 2019)). The geometry and embedment depths are considered representative of anchors for floating wave or tidal offshore energy devices, whilst groups of them should be used for floating wind turbines (Cerfontaine et al, 2020a).…”

“…The design of offshore screw piles or anchors is based on the maximisation of their capacity (depending on embedment depth or helix and shaft diameters), whilst minimising the installation torque and force requirements. To achieve these objectives, offshore piles/anchors will typically have larger shaft and helix diameters than their onshore counterparts (Cerfontaine et al, 2020a). They will also be installed at a lower relative embedment depth.…”

Uplift resistance capacity of anchor piles used in marine aquaculture

“…The study of the uplift resistance of anchors is well established in another field of engineering 8 – 11 . However, the most of the anchors mentioned are used in offshore structures such as offshore drilling platforms, and the designed water depth is not less than 100 m. The mainly designed water depth of marine aquaculture engineering equipment is generally within 50 m 12 , and the above research results cannot be directly applied to marine aquaculture engineering equipment.…”

Uplift Resistance Capacity of Anchor Piles used in Marine Aquaculture

“…Yi et al 10 used finite element analysis to study the uplift resistance capacity and failure envelopes of torpedo anchors embedded off-verticality. However, the most of the anchors mentioned are used in offshore structures such as offshore drilling platforms, and the designed water depth is not less than 100 m. The current design water depth of marine aquaculture engineering equipment is generally within 50 m 11 , and the above research results cannot be directly applied to marine aquaculture engineering equipment.…”