Discrepancies between element tests and large-scale LDFE simulations: A case study on anchor kinematics during installation in clay

Harsh offshore conditions impose significant challenges to the design of floating offshore wind turbines (FOWTs). In particular anchoring systems face many uncertainties due to the unknown soil response and post-installation soil state. This study investigates the drag embedment anchor (DEA) installation in fine-grained soil through numerical simulations, employing large-deformation finite element (LDFE) analyses using the CEL method and visco-hypoplastic constitutive equations. Three parameter sets for kaolin clay were determined, which show excellent agreement to experimental data (MPE <6%). The study analyses the variation of the viscosity index Iv, determined by three acknowledged methods (oedometer test, triaxial test, and liquid limit). Despite element tests revealing minimal differences, large-scale LDFE simulations of DEA installation with varying Iv values significantly diverge. However, the viscosity index does not impact the relationship between anchor rotation and penetration. These findings emphasise the necessity for a comprehensive understanding of anchor-soil interaction and the limitations of numerical simulations lacking physical validation. This study contributes to the reliable design and installation of FOWTs by spreading awareness on the complex DEA kinematics in fine-grained soils and showcasing the importance of careful parameter calibration for numerical frameworks.

Subjects

Anchor installation

CEL

Clay

Drag embedment anchor (DEA)

Floating offshore wind (FOW)

Visco-hypoplasticity

Viscosity index

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Discrepancies between element tests and large-scale LDFE simulations: A case study on anchor kinematics during installation in clay