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Subsea cable stability on rocky seabeds - Comparison of field observations against conventional and novel design methods

Subsea cable stability on rocky seabeds - Comparison of field observations against conventional and novel design methods
Subsea cable stability on rocky seabeds - Comparison of field observations against conventional and novel design methods
As offshore renewable energy projects progress from concept demonstration to commercial-scale developments there is a need for improved approaches beyond conventional cable engineering design methods that have evolved from larger diameter pipelines for the oil and gas industry. New approaches are needed to capture the relevant physics for small diameter cables on rocky seabeds to reduce the costs and risks of power transmission and increase operational reliability. This paper reports on subsea cables that MeyGen installed for Phase 1a of the Pentland Firth Inner Sound tidal stream energy project. These cables are located on rocky seabeds in an area where severe metocean conditions occur. ROV field observation of these cables shows them to be stable on the seabed with little or no movement occurring over almost all of the cable routes, despite conventional engineering methods predicting significant dynamic movement. We cite recent research undertaken by the University of Western Australia (UWA) to more accurately assess the hydrodynamic forces and geotechnical interaction of cables on rocky seabeds. We quantify the conformity between the cables and the undulating rocky seabed, and the distributions of cable seabed contact and spanning via simulations of the centimetric scale seabed bathymetry. This analysis leads to calculated profiles of lift, drag and seabed friction along the cable, which show that all of these load and reaction components are modelled in an over-conservative way by conventional pipeline engineering techniques. Overall, our analysis highlights that current cable stability design can be unnecessarily conservative on rocky seabeds. Our work foreshadows a new design approach that offers more efficient cable design to reduce project capex and enhance through-life integrity management.
V005T04A043
American Society Of Mechanical Engineers (ASME)
Draper, Scott
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Tong, Feifei
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Fogliani, Antonino
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White, David
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Johnson, Fraser
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Coles, Daniel
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Ingham, Stephen
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Lourie, Caroline
c2a372e8-d12f-4354-b7fe-a153197341d7
Draper, Scott
efe46b7d-3989-403b-8b19-0b17dd54194f
Tong, Feifei
aa23589b-714f-47f5-8313-5511ca94e937
Fogliani, Antonino
10bd8e2f-fda7-4f3b-94af-93047361164f
White, David
a986033d-d26d-4419-a3f3-20dc54efce93
Johnson, Fraser
c8e46f16-c36f-493d-9ee4-7f2f3910946b
Coles, Daniel
58e46bef-2a32-4b6e-b78b-7efede2a93ab
Ingham, Stephen
3133b006-95c7-4160-907d-9679ec16f32b
Lourie, Caroline
c2a372e8-d12f-4354-b7fe-a153197341d7

Draper, Scott, Tong, Feifei, Fogliani, Antonino, White, David, Johnson, Fraser, Coles, Daniel, Ingham, Stephen and Lourie, Caroline (2018) Subsea cable stability on rocky seabeds - Comparison of field observations against conventional and novel design methods. In Proceedings of the ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering. vol. 5, American Society Of Mechanical Engineers (ASME). V005T04A043 . (doi:10.1115/OMAE2018-77130).

Record type: Conference or Workshop Item (Paper)

Abstract

As offshore renewable energy projects progress from concept demonstration to commercial-scale developments there is a need for improved approaches beyond conventional cable engineering design methods that have evolved from larger diameter pipelines for the oil and gas industry. New approaches are needed to capture the relevant physics for small diameter cables on rocky seabeds to reduce the costs and risks of power transmission and increase operational reliability. This paper reports on subsea cables that MeyGen installed for Phase 1a of the Pentland Firth Inner Sound tidal stream energy project. These cables are located on rocky seabeds in an area where severe metocean conditions occur. ROV field observation of these cables shows them to be stable on the seabed with little or no movement occurring over almost all of the cable routes, despite conventional engineering methods predicting significant dynamic movement. We cite recent research undertaken by the University of Western Australia (UWA) to more accurately assess the hydrodynamic forces and geotechnical interaction of cables on rocky seabeds. We quantify the conformity between the cables and the undulating rocky seabed, and the distributions of cable seabed contact and spanning via simulations of the centimetric scale seabed bathymetry. This analysis leads to calculated profiles of lift, drag and seabed friction along the cable, which show that all of these load and reaction components are modelled in an over-conservative way by conventional pipeline engineering techniques. Overall, our analysis highlights that current cable stability design can be unnecessarily conservative on rocky seabeds. Our work foreshadows a new design approach that offers more efficient cable design to reduce project capex and enhance through-life integrity management.

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Published date: 2018
Venue - Dates: ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2018, , Madrid, Spain, 2018-06-16 - 2018-06-21

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Local EPrints ID: 422785
URI: http://eprints.soton.ac.uk/id/eprint/422785
PURE UUID: f047715c-f635-48db-888a-077d21ccdb4d
ORCID for David White: ORCID iD orcid.org/0000-0002-2968-582X

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Date deposited: 06 Aug 2018 16:30
Last modified: 18 Feb 2021 17:33

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Contributors

Author: Scott Draper
Author: Feifei Tong
Author: Antonino Fogliani
Author: David White ORCID iD
Author: Fraser Johnson
Author: Daniel Coles
Author: Stephen Ingham
Author: Caroline Lourie

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