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

Terry Griffiths, Scott Draper, Liang Cheng, Feifei Tong, Antonino Fogliani, David White, Fraser Johnson, Daniel Coles, Stephen Ingham, Caroline Lourie

Research output: Chapter in Book/Conference paperConference paper

4 Citations (Scopus)

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.

Original languageEnglish
Title of host publicationPipelines, Risers, and Subsea Systems
Place of PublicationSpain
PublisherThe American Society of Mechanical Engineers (ASME)
Volume5
ISBN (Electronic)9780791851241
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

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Cite this

Griffiths, T., Draper, S., Cheng, L., Tong, F., Fogliani, A., White, D., ... Lourie, C. (2018). Subsea cable stability on rocky seabeds - Comparison of field observations against conventional and novel design methods. In Pipelines, Risers, and Subsea Systems (Vol. 5). Spain: The American Society of Mechanical Engineers (ASME). https://doi.org/10.1115/OMAE2018-77130