(1)Development of current-induced scour beneath elevated subsea pipelines
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Jun Y. Leea,∗, Alexander L. Forresta,b,Fauzi A. Hardjantoa, Shuhong Chaia, Remo Cossuc, Zhi Q. Leonga
a National Centre for Maritime Engineering and Hydrodynamics, Australian Maritime College, University of Tasmania, Locked Bag 1395, Launceston Tasmania 7250, Australia
b Department of Civil and Environmental Engineering, University of California – Davis, Davis, CA 95616, United States
c School of Civil Engineering, University of Queensland, St Lucia Queensland 4072, Australia
Received 15 May 2018; received in revised form 9 August 2018; accepted 15 September 2018
Available online 21 September 2018
Abstract
When scour occurs beneath a subsea pipeline and develops to a certain extent, the pipeline may experience vortex-induced vibrations, through which there can be a potential accumulation of fatigue damage. However, when a pipeline is laid on an uneven seabed, certain sections may have an elevation with respect to the far-field seabed, eo , at which the development of scour would vary. This work focused on predicting the development of the scour depth beneath subsea pipelines with an elevation under steady flow conditions. A range of pipe elevation-to-diameter ratios (i.e. 0 ≤ eo / D ≤ 0.5) have been considered for laboratory experiments conducted in a sediment flume. The corresponding equilibrium scour depths and scour time scales were obtained; experimental data from published literature have been collected and added to the present study to produce a more complete analysis database. The correlation between existing empirical equations for predicting the time scale and the experimental data was assessed, resulting in a new set of constants. A new manner of converting the scour time scale into a non-dimensional form was found to aid the empirical equations in attaining a better correlation to the experimental data. Subsequently, a new empirical equation has also been proposed in this work, which accounts for the influence of eo / D on the non-dimensional scour time scale. It was found to have the best overall correlation with the experimental data. Finally, full-scale predictions of the seabed gaps and time scales were made for the Tasmanian Gas Pipeline (TGP).
© 2018 Shanghai Jiaotong University. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Keywords: Scour time scale; Equilibrium scour depth; Subsea pipelines; Pipe elevation; Steady currents.