Finite element simulation of an embedded anchor chain

Research output: Chapter in Book/Conference paperConference 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 multilink 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.

Original languageEnglish
Title of host publicationProceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE
PublisherThe American Society of Mechanical Engineers (ASME)
Volume9
ISBN (Electronic)9780791851302
DOIs
Publication statusPublished - 1 Jan 2018
EventASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2018 - Madrid Marriott Auditorium Hotel & Conference Centre, Madrid, Spain
Duration: 17 Jun 201822 Jun 2018
https://www.asme.org/events/omae

Conference

ConferenceASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2018
Abbreviated titleOMAE 2018
CountrySpain
CityMadrid
Period17/06/1822/06/18
Internet address

Fingerprint

Anchors
Mooring
Soils
ABAQUS
Calibration
Economics
Computer simulation

Cite this

Sun, C., Feng, X., Gourvenec, S., Neubecker, S. R., & Randolph, M. F. (2018). Finite element simulation of an embedded anchor chain. In Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE (Vol. 9). The American Society of Mechanical Engineers (ASME). https://doi.org/10.1115/OMAE2018-77781
Sun, Chao ; Feng, Xiaowei ; Gourvenec, Susan ; Neubecker, Steven R. ; Randolph, Mark F. / Finite element simulation of an embedded anchor chain. Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE. Vol. 9 The American Society of Mechanical Engineers (ASME), 2018.
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Sun, C, Feng, X, Gourvenec, S, Neubecker, SR & Randolph, MF 2018, Finite element simulation of an embedded anchor chain. in Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE. vol. 9, The American Society of Mechanical Engineers (ASME), ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2018, Madrid, Spain, 17/06/18. https://doi.org/10.1115/OMAE2018-77781

Finite element simulation of an embedded anchor chain. / Sun, Chao; Feng, Xiaowei; Gourvenec, Susan; Neubecker, Steven R.; Randolph, Mark F.

Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE. Vol. 9 The American Society of Mechanical Engineers (ASME), 2018.

Research output: Chapter in Book/Conference paperConference paper

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N2 - 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 multilink 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.

AB - 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 multilink 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.

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Sun C, Feng X, Gourvenec S, Neubecker SR, Randolph MF. Finite element simulation of an embedded anchor chain. In Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE. Vol. 9. The American Society of Mechanical Engineers (ASME). 2018 https://doi.org/10.1115/OMAE2018-77781