Research Papers: Piper and Riser Technology

Euler–Lagrange Two-Phase Model for Simulating Live-Bed Scour Beneath Marine Pipelines

[+] Author and Article Information
A. Yeganeh-Bakhtiary

Enviro-Hydroinformatics COE and School of Civil Engineering,
Iran University of Science & Technology (IUST),
Tehran 16846-13114, Iran;
Hydro-environmental Research Centre,
School of Engineering,
Cardiff University,
Queen's Buildings,
The Parade Cardiff,
CF24-3AA, Wales, UK
e-mail: yeganeh@iust.ac.ir & yeganeh@cf.ac.uk

E. Kazemi

School of Civil Engineering,
Tehran 16848-13114, Iran

L. Cheng

School of Civil and Resource Engineering,
The University of Western Australia,
Perth, WA 6009, Australia

A. K. Abd Wahab

Coastal & Offshore Engineering Institute,
Universiti Teknologi Malaysia (UTM),
International Campus,
Kuala Lumpur 54100, Malaysia

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received September 20, 2010; final manuscript received March 4, 2012; published online June 10, 2013. Assoc. Editor: Colin Leung.

J. Offshore Mech. Arct. Eng 135(3), 031705 (Jun 10, 2013) (10 pages) Paper No: OMAE-10-1095; doi: 10.1115/1.4023200 History: Received September 20, 2010; Revised March 04, 2012

In this study, an Euler–Lagrange coupling two-phase flow model, namely movable bed simulator (MBS)-two-dimensional (2D) model was employed to explore the current-induced live-bed scour beneath marine pipelines. The fluid phase characteristics, such as velocity and pressure, were obtained by the Reynolds-averaged Navier–Stokes (RANS) equations with a k-ε turbulence closure model in a two-dimensional Eulerian grid, whereas the seabed beneath pipelines was traced as an assembly of discrete sand grains from the Lagrangian point of view. The live-bed scour was evolved as the motion of a granular media based on distinct element method (DEM) formulation, in which the frequent interparticle collision was described with a spring and dashpot system. The fluid flow was coupled to the sediment phase, considering the acting drag forces between. Comparison between the numerical result and experimental measurement confirms that the numerical model successfully estimates the bed profile and flow velocity field. It is evident that the fluid shear stress decreases with the increasing of gap ratio e/D. The numerical model provides a useful approach to improve mechanistic understanding of hydrodynamic and sediment transport in live-bed scour beneath a marine pipeline.

Copyright © 2013 by ASME
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Fig. 1

Different stages of scouring beneath pipeline [23]

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Fig. 2

Schematic sketch of the computational flow domain

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Fig. 3

Comparison of the mean horizontal velocity of numerical result with Alper Oner et al. [8] experimental data at ReD = 9500: (a) e/D = 0.0 and (b) e/D = 0.3. The experimental data are presented by symbols and the model results denoted by solid line.

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Fig. 4

Time-averaged streamlines for ReD = 9500 and e/D = 0 at the top of the figure for the experimental result of Alper Oner et al. [8]

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Fig. 5

Snapshots of instantaneous streamlines for ReD = 9500 and e/D = 0.3 within t = 4.5 s; (a) t = 0.5 s, (b) t = 1.0 s, (c) t = 2.0 s, (d) t = 3.0 s, (e) t = 4.0 s, and (f) t = 4.5 s

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Fig. 6

Time variation of horizontal flow velocity at upper and downsides of pipe

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Fig. 7

Distribution of flow shear stress near the rigid bed at different gap ratios

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Fig. 8

PSD diagram for horizontal velocity upper around a pipe: (a) upper side of pipe and (b) lower side of pipe

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Fig. 9

Multiparticle collision and interaction system between each contacting grains in the DEM model [28]

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Fig. 10

Schematic sketch of computational domain of current-induced scour beneath a pipe

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Fig. 11

Snapshots of bed profile during scouring beneath a pipe. The shadow is the simulated profiles and the solid circle is the Mao [5] observation at: (a) t = 0 min; (b) t = 11 min; (c) t = 18 min; (d) t = 25 min; (e) t= 50 min; (f) t = 120 min.

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Fig. 12

Time-dependent scour depth and its comparison with Mao's [5] observation




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