Numerical Study of Scour beneath Sagging Cylinders and Spheres
Publication: Journal of Hydraulic Engineering
Volume 150, Issue 5
Abstract
Offshore structures are deployed extensively to harvest marine resources. Due to the harsh marine environments and heavy-duty working conditions, the risks associated with failure due to scour are high, and the need for accurate prediction of these risks is increasing. Often, pipelines and cables are critical elements of subsea energy transportation and telecommunication, and they are highly susceptible to scour-induced failure. The scour around spheres is relevant to the offshore industry as a simplified three-dimensional representation of subsea structures. This paper presents a numerical study, using FLOW-3D HYDRO, of the scour around on-bottom cylinders and spheres. Whereas most published research investigated scour around stationary solid objects, this paper presents numerical results of a more challenging case of scour around sagging cylinders and spheres. The model was validated against published experimental and numerical results. The scour depth was found to increase with the decrease of the sagging velocity of the solid object. For sagging horizontal cylinders, the scour depth reaches a plateau of 1.1 times the cylinder diameter when the dimensionless sagging velocity is smaller than 0.094. For sagging spheres, the maximum scour depth reaches 0.37 times the sphere diameter when the dimensionless sagging velocity is reduced to 0.0103. The findings provide guidelines for future research on more complicated interactions between flow, solid objects, and the seabed, accounting for the deformation of infrastructure over time.
Practical Applications
This paper concerns the flow, sediment transport, and scour around horizontal cylinders and spheres undergoing slow downward motion, which resembles the sagging of on-bottom infrastructure under the influence of gravity and bed erosion. Offshore structures are deployed extensively to harvest marine resources. Pipelines and cables are critical subsea infrastructures that are susceptible to scour-induced failure. Spherical objects are commonplace in the offshore industry, so a sphere can be deemed as an idealized three-dimensional body. This paper provides detailed FLOW-3D simulations and developed empirical relationships between the dimensionless scour depth and dimensionless sagging speed. Most previous research considered only the scour around fixed objects, so this paper provides a novel addition to the existing knowledge on the scour phenomenon. The computational methods established in this study are useful for simulating more-complicated scenarios. The findings provide guidelines for more-realistic predictions of scour and for the design of scour mitigation measures.
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Data Availability Statement
All data and models that support the findings of this study are available from the corresponding author upon reasonable request, including input files, model setup information, and data for producing the figures in the paper, but not proprietary software or third-party data.
Acknowledgments
The authors are grateful for the financial support from the Cambridge University Energy Interdisciplinary Research Centre (IRC), and Tsinghua–Cambridge Joint Research Initiative Fund. The authors are grateful to FLOW SCIENCE UK for an academic research license of FLOW-3D HYDRO.
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 150 • Issue 5 • September 2024
Copyright
© 2024 American Society of Civil Engineers.
History
Received: Jun 14, 2023
Accepted: May 1, 2024
Published online: Jul 9, 2024
Published in print: Sep 1, 2024
Discussion open until: Dec 9, 2024
ASCE Technical Topics:
- Analysis (by type)
- Cables
- Coasts, oceans, ports, and waterways engineering
- Cylinders
- Engineering fundamentals
- Equipment and machinery
- Geometry
- Hydraulic engineering
- Hydraulics
- Mathematics
- Methodology (by type)
- Numerical analysis
- Numerical methods
- Ocean engineering
- Offshore structures
- Scour
- Spheres
- Water and water resources
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