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Finite element simulation of an embedded anchor chain

Finite element simulation of an embedded anchor chain
Finite element simulation of an embedded anchor chain

The embedded portion of a mooring line plays an important role for efficient and economic design of an overall mooring system. This paper presents a methodology for numerical simulation of the behaviour of an embedded anchor chain as it cuts through the soil, focusing on the tensioning of a catenary mooring. The Coupled Eulerian–Lagrangian (CEL) approach within ABAQUS is used to capture the interaction between the embedded chain (Lagrangian structure) and the soil (Eulerian material). The anchor chain is simulated by a series of rigid cylindrical segments connected together by LINK connectors.

Before analysing the global behaviour of an embedded chain, a calibration exercise is undertaken where a straight multi-link portion of the chain is displaced normally and axially in soil. The resulting normal and frictional resistances (per unit length) are compared with those adopted in general practice, in order to calibrate the relationship between the diameter of the cylindrical segments and the bar diameter of the chain. After that, the tensioning process of an anchor chain is simulated, starting from an initial configuration with a 9 m length embedded vertically (attached to a fixed padeye), with the remaining length lying on the seabed. Horizontal tensioning of the chain causes it to cut through the soil until it forms an inverse catenary with an angle of just under 35 degrees to the horizontal at the padeye (and zero degrees at the mudline).

The loading curve, and also the inverse catenary profile of the chain for different angles at the padeye, are shown to agree well with the Neubecker-Randolph closed-form analytical solution. However, the ratio of the tensions at the padeye and the mudline from the CEL results differs significantly from the analytical solution. Insights from the CEL results indicate that this is because the frictional soil resistance is not fully mobilised, particularly for the portion of the chain in the stronger soil at depth, near the padeye, where the axial displacements are small. This result has significant implications for the geotechnical design of anchoring systems that involve a (nominally) fixed padeye. The simulation methodology also has considerable potential for exploring the creation of an open trench adjacent to a fixed anchor due to monotonic and cyclic perturbations of the anchor chain.

V009T10A001
American Society Of Mechanical Engineers (ASME)
Sun, Chao
16c59dfc-f89f-47dd-96ec-b4734295f1f8
Feng, Xiaowei
33d164d1-5589-41f6-995a-9b17374bdd0c
Gourvenec, Susan
6ff91ad8-1a91-42fe-a3f4-1b5d6f5ce0b8
Neubecker, Steven R.
1b5a0163-c410-4db0-a353-22bbd4bad3c2
Randolph, Mark F.
75caa33a-e630-4ae8-84cd-758797bf9633
Sun, Chao
16c59dfc-f89f-47dd-96ec-b4734295f1f8
Feng, Xiaowei
33d164d1-5589-41f6-995a-9b17374bdd0c
Gourvenec, Susan
6ff91ad8-1a91-42fe-a3f4-1b5d6f5ce0b8
Neubecker, Steven R.
1b5a0163-c410-4db0-a353-22bbd4bad3c2
Randolph, Mark F.
75caa33a-e630-4ae8-84cd-758797bf9633

Sun, Chao, Feng, Xiaowei, Gourvenec, Susan, Neubecker, Steven R. and Randolph, Mark F. (2018) Finite element simulation of an embedded anchor chain. In ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics. vol. 9, American Society Of Mechanical Engineers (ASME). V009T10A001 . (doi:10.1115/OMAE2018-77781).

Record type: Conference or Workshop Item (Paper)

Abstract

The embedded portion of a mooring line plays an important role for efficient and economic design of an overall mooring system. This paper presents a methodology for numerical simulation of the behaviour of an embedded anchor chain as it cuts through the soil, focusing on the tensioning of a catenary mooring. The Coupled Eulerian–Lagrangian (CEL) approach within ABAQUS is used to capture the interaction between the embedded chain (Lagrangian structure) and the soil (Eulerian material). The anchor chain is simulated by a series of rigid cylindrical segments connected together by LINK connectors.

Before analysing the global behaviour of an embedded chain, a calibration exercise is undertaken where a straight multi-link portion of the chain is displaced normally and axially in soil. The resulting normal and frictional resistances (per unit length) are compared with those adopted in general practice, in order to calibrate the relationship between the diameter of the cylindrical segments and the bar diameter of the chain. After that, the tensioning process of an anchor chain is simulated, starting from an initial configuration with a 9 m length embedded vertically (attached to a fixed padeye), with the remaining length lying on the seabed. Horizontal tensioning of the chain causes it to cut through the soil until it forms an inverse catenary with an angle of just under 35 degrees to the horizontal at the padeye (and zero degrees at the mudline).

The loading curve, and also the inverse catenary profile of the chain for different angles at the padeye, are shown to agree well with the Neubecker-Randolph closed-form analytical solution. However, the ratio of the tensions at the padeye and the mudline from the CEL results differs significantly from the analytical solution. Insights from the CEL results indicate that this is because the frictional soil resistance is not fully mobilised, particularly for the portion of the chain in the stronger soil at depth, near the padeye, where the axial displacements are small. This result has significant implications for the geotechnical design of anchoring systems that involve a (nominally) fixed padeye. The simulation methodology also has considerable potential for exploring the creation of an open trench adjacent to a fixed anchor due to monotonic and cyclic perturbations of the anchor chain.

Full text not available from this repository.

More information

Published date: 2018
Venue - Dates: ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2018, Madrid, Spain, 2018-06-17 - 2018-06-22

Identifiers

Local EPrints ID: 426111
URI: http://eprints.soton.ac.uk/id/eprint/426111
PURE UUID: abfab720-cc4b-4637-8c93-5f86a460aeb0
ORCID for Susan Gourvenec: ORCID iD orcid.org/0000-0002-2628-7914

Catalogue record

Date deposited: 14 Nov 2018 17:30
Last modified: 20 Jul 2019 00:25

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Contributors

Author: Chao Sun
Author: Xiaowei Feng
Author: Susan Gourvenec ORCID iD
Author: Steven R. Neubecker
Author: Mark F. Randolph

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