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Safety and Reliability

The Equivalent Depth of Wave-Induced Scour Around Offshore Pipelines

[+] Author and Article Information
Mir Emad Mousavi, Abbas Yeganeh Bakhtiary

Iran University of Science and Technology

Nastaran Enshaei

Tarbiat Modares University

J. Offshore Mech. Arct. Eng 131(2), 021601 (Jan 27, 2009) (5 pages) doi:10.1115/1.3058681 History: Received August 28, 2006; Revised September 26, 2008; Published January 27, 2009

Physical experiments have been conducted to study the scouring around a pipe over an erodible bed under wave motion. The results show that the depth of the wave-induced scour is reduced when the pipe is installed in a primary depth. It is also indicated that when the primary installation depth of the pipe, |e|, exceeds a specified depth, no scouring occurs underneath the pipe. This specific depth is called the equivalent depth of wave-induced scour, Se. The equivalent depth of wave-induced scour is estimated as a function of pipe diameter and the Keulegan–Carpenter number. With respect to the primary installation depth of the pipe, a new equation is suggested to predict the scour depth before installation of the pipe. And the scour width is predicted in two other new equations. The proposed equations are then simplified in the form of diagrams. The experiments cover small KC numbers (KC<6) that represent deep water conditions.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic view of the model

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Figure 2

The development of the wave-induced scour profile leading to equilibrium stage in test W1

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Figure 3

Comparison between the present experimental data and the results from Eq. 3 in tests W1–W11

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Figure 4

Comparison between present experimental data and the results from Eq. 4 in tests W1–W11

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Figure 5

Equivalent scour depth

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Figure 6

Test W12. (a): start of the test; (b): end of the test.

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Figure 7

Relation between the scour upstream width and total width with scour depth at equilibrium stage

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Figure 8

Estimating scour profile triangle in test W6

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Figure 9

Prediction of ESD for the case of D=1 m based on wave height and relative water depth

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Figure 10

Modification factor of predicted ESD for different pipe diameters based on Eq. 13

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