Finite Element Analysis of Shared Suction Anchor Capacity Including Effects of Trenching 

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4. Finite Element Analysis of Shared Suction Anchor Capacity Including Effects of Trenching 

ABSTRACT:  This article presents results from a feasibility study investigating trenching effects for the anchors of a floating offshore wind farm located in the North Sea. A semi-taut mooring concept with suction anchors with 1, 2 and 3 mooring lines has been assessed. Soil conditions are representative of Norwegian Continental Shelf (NCS) conditions consisting of homogeneous very soft to medium clay in upper 20-30 m. Projects in comparable soil conditions have demonstrated significant trenching, especially for taut mooring floaters in the oil and gas industry. Since trenching might be a plausible scenario, there is a need in the industry to quantify its impact on the anchor design. A literature review on trench formation and trench susceptibility in soft clays has been performed to establish trenching geometries.  To quantify the impact of trenching on the anchor capacity, base case calculations with and without trench formations have been conducted. The loading effect of one or more mooring lines has also been quantified, and failure modes such as torsional loading in case mooring line failure have been analysed. This paper presents a practical engineering approach to account for a combination of the complex geometry of several mooring line trenches and different suction anchor geometries in 3D FEA to perform early-stage anchor design optimization. Structural considerations of the suction anchor layout are discussed on a high-level.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

11 - Suction installed foundations and anchors