Numerical investigation of multidirectional response of shared anchor piles for offshore wind

Abstract

Shared anchor systems, where multiple FOWTs are connected to a single anchor, can reduce the number of anchors across a windfarm by up to 60%, hence reduce the overall cost of energy and demands on the supply chain. During a single storm episode, the resultant anchor load acts predominantly in the direction of prevailing wind, wave, and currents, but over a design lifetime, loads may act in different principal directions. Multidirectional cyclic loading may accelerate vertical ratcheting and degrade the holding resistance of an anchor. However, this behaviour is currently poorly understood. This paper presents results of a numerical study investigating the drained cyclic response of shared pile anchors under multidirectional one-way cyclic loads. Finite element simulations of a wished-in-place pile in sand are modelled using the hypoplastic constitutive model. Inclined loading relative to the seabed, representative of a taut configuration, is considered, in conjunction with the impact of load directionality from two consecutive storms, covering a range of load path directions. The results of the multidirectional tests reveal an increase of cyclic displacement accumulation compared to the unidirectional case. A factor to describe this amplification from multidirectionality is proposed based on the findings, to quantify pile uplift ratcheting as a function of the multidirectional load attributes.

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Identifiers

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

ORCID for S. Gourvenec: orcid.org/0000-0002-2628-7914

ORCID for D.J. White: orcid.org/0000-0002-2968-582X

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