Gravity anchors astride subsea pipelines subject to oscillatory and combined steady and oscillatory flows
This writing presents results of simulating oscillatory and combined steady and oscillatory flows past gravity anchors astride subsea pipelines. It can be considered a companion to a previous numerical study on steady currents past gravity anchors. The gravity anchor system comprises large arch-shap...
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ftunivwestsyd:oai:researchdirect.westernsydney.edu.au:uws_14855 2023-05-15T14:23:08+02:00 Gravity anchors astride subsea pipelines subject to oscillatory and combined steady and oscillatory flows Zhao, Xu Cheng, Liang Zhao, Ming (R16667) An, Hongwei He, Wei School of Computing, Engineering and Mathematics (Host institution) International Conference on Ocean, Offshore and Arctic Engineering (Event place) 2012 print 8 http://handle.uws.edu.au:8081/1959.7/521584 https://www.asmeconferences.org/OMAE2012/ https://doi.org/10.1115/OMAE2012-83247 eng eng U.S., ASME Proceedings of the ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering: OMAE2012: July 1-6, 2012, Rio de Janeiro, Brazil--9780791844922 pp: 597-604 090599 - Civil Engineering not elsewhere classified 850203 - Oil and Gas Extraction pipelines oscillatory flows subsea gravity anchors steady flows hydrodynamic loads Petrov-Galerkin finite element method Navier-Stokes equations conference paper 2012 ftunivwestsyd https://doi.org/10.1115/OMAE2012-83247 2020-12-05T18:14:20Z This writing presents results of simulating oscillatory and combined steady and oscillatory flows past gravity anchors astride subsea pipelines. It can be considered a companion to a previous numerical study on steady currents past gravity anchors. The gravity anchor system comprises large arch-shaped concrete blocks positioned at intervals astride offshore pipelines, and it is engineered to provide innovative and cost-effective secondary stabilisation for high-capacity gas-transporting pipelines serving in severe metocean conditions, eg. cyclone-prone offshore areas. A free-settling marine object bottom-seated on the seabed, however, the gravity anchor may subside into scour pits around its base due to locally disturbed flow regimes, imposing integrity risks on the pipe. Also, the effect of gravity anchors on hydrodynamic loading on nearby pipeline lengths is of interest. The present study employed a Petrov-Galerkin finite element method to solve the three-dimensional Navier-Stokes equations in direct numerical simulation. Firstly sinusoidal flow oscillating perpendicularly to the pipe beneath gravity anchors on an immobile bed was simulated at a Keulegan-Carpenter number of 10 and a pipe Reynolds number of 1000. Then, a steady current co-directionally superimposed on the aforementioned oscillatory flow was modelled at a ratio of steady current velocity to oscillatory flow velocity amplitude of 1. With sediment transport capacity related to bed shear stresses, the time-averaged bed shear stress amplification around gravity anchors in oscillatory flow was revealed first, and found to be consistent with laboratory observations of scour patterns. The effect of superimposing steady flow onto oscillatory flow on bed shear stress amplification was then explored. Lastly, hydrodynamic forces on pipelines in the vicinity of gravity anchors were gauged. The present work intends to shed light on the initial seabed responses with regard to the scour process around gravity anchors immersed in the oceanic wave boundary layers, as well as the effect of gravity anchors on hydrodynamic loadings on pipelines. Conference Object Arctic University of Western Sydney (UWS): Research Direct Volume 5: Ocean Engineering; CFD and VIV 597 604 |
institution |
Open Polar |
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University of Western Sydney (UWS): Research Direct |
op_collection_id |
ftunivwestsyd |
language |
English |
topic |
090599 - Civil Engineering not elsewhere classified 850203 - Oil and Gas Extraction pipelines oscillatory flows subsea gravity anchors steady flows hydrodynamic loads Petrov-Galerkin finite element method Navier-Stokes equations |
spellingShingle |
090599 - Civil Engineering not elsewhere classified 850203 - Oil and Gas Extraction pipelines oscillatory flows subsea gravity anchors steady flows hydrodynamic loads Petrov-Galerkin finite element method Navier-Stokes equations Zhao, Xu Cheng, Liang Zhao, Ming (R16667) An, Hongwei He, Wei Gravity anchors astride subsea pipelines subject to oscillatory and combined steady and oscillatory flows |
topic_facet |
090599 - Civil Engineering not elsewhere classified 850203 - Oil and Gas Extraction pipelines oscillatory flows subsea gravity anchors steady flows hydrodynamic loads Petrov-Galerkin finite element method Navier-Stokes equations |
description |
This writing presents results of simulating oscillatory and combined steady and oscillatory flows past gravity anchors astride subsea pipelines. It can be considered a companion to a previous numerical study on steady currents past gravity anchors. The gravity anchor system comprises large arch-shaped concrete blocks positioned at intervals astride offshore pipelines, and it is engineered to provide innovative and cost-effective secondary stabilisation for high-capacity gas-transporting pipelines serving in severe metocean conditions, eg. cyclone-prone offshore areas. A free-settling marine object bottom-seated on the seabed, however, the gravity anchor may subside into scour pits around its base due to locally disturbed flow regimes, imposing integrity risks on the pipe. Also, the effect of gravity anchors on hydrodynamic loading on nearby pipeline lengths is of interest. The present study employed a Petrov-Galerkin finite element method to solve the three-dimensional Navier-Stokes equations in direct numerical simulation. Firstly sinusoidal flow oscillating perpendicularly to the pipe beneath gravity anchors on an immobile bed was simulated at a Keulegan-Carpenter number of 10 and a pipe Reynolds number of 1000. Then, a steady current co-directionally superimposed on the aforementioned oscillatory flow was modelled at a ratio of steady current velocity to oscillatory flow velocity amplitude of 1. With sediment transport capacity related to bed shear stresses, the time-averaged bed shear stress amplification around gravity anchors in oscillatory flow was revealed first, and found to be consistent with laboratory observations of scour patterns. The effect of superimposing steady flow onto oscillatory flow on bed shear stress amplification was then explored. Lastly, hydrodynamic forces on pipelines in the vicinity of gravity anchors were gauged. The present work intends to shed light on the initial seabed responses with regard to the scour process around gravity anchors immersed in the oceanic wave boundary layers, as well as the effect of gravity anchors on hydrodynamic loadings on pipelines. |
author2 |
School of Computing, Engineering and Mathematics (Host institution) International Conference on Ocean, Offshore and Arctic Engineering (Event place) |
format |
Conference Object |
author |
Zhao, Xu Cheng, Liang Zhao, Ming (R16667) An, Hongwei He, Wei |
author_facet |
Zhao, Xu Cheng, Liang Zhao, Ming (R16667) An, Hongwei He, Wei |
author_sort |
Zhao, Xu |
title |
Gravity anchors astride subsea pipelines subject to oscillatory and combined steady and oscillatory flows |
title_short |
Gravity anchors astride subsea pipelines subject to oscillatory and combined steady and oscillatory flows |
title_full |
Gravity anchors astride subsea pipelines subject to oscillatory and combined steady and oscillatory flows |
title_fullStr |
Gravity anchors astride subsea pipelines subject to oscillatory and combined steady and oscillatory flows |
title_full_unstemmed |
Gravity anchors astride subsea pipelines subject to oscillatory and combined steady and oscillatory flows |
title_sort |
gravity anchors astride subsea pipelines subject to oscillatory and combined steady and oscillatory flows |
publisher |
U.S., ASME |
publishDate |
2012 |
url |
http://handle.uws.edu.au:8081/1959.7/521584 https://www.asmeconferences.org/OMAE2012/ https://doi.org/10.1115/OMAE2012-83247 |
genre |
Arctic |
genre_facet |
Arctic |
op_relation |
Proceedings of the ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering: OMAE2012: July 1-6, 2012, Rio de Janeiro, Brazil--9780791844922 pp: 597-604 |
op_doi |
https://doi.org/10.1115/OMAE2012-83247 |
container_title |
Volume 5: Ocean Engineering; CFD and VIV |
container_start_page |
597 |
op_container_end_page |
604 |
_version_ |
1766295614194188288 |