Ice Gouging over a Buried Pipeline: Superposition Error of Simple Beam-and-Spring Models
Publication: International Journal of Geomechanics
Volume 12, Issue 4
Abstract
Two types of models, coupled and uncoupled, are currently used to determine the extent to which it is necessary to bury subsea pipelines deeper than the maximum expected depth of ice gouges. In the uncoupled model, the soil is modeled by nonlinear Winkler springs attached to the pipe at one end, with the subgouge displacement imposed at the other end of the springs. In coupled models, the soil is modeled as a three-dimensional (3D) continuum, simultaneously capturing the processes of gouging (with associated very large deformations) and the pipeline resisting the soil displacements. This paper pinpoints the main reason for differences in predictions between the coupled and uncoupled model. It is not the coupling errors (attributable to directional coupling between Winkler springs in the axial, lateral, and vertical directions, and slice-to-slice coupling), but, rather, the superposition error, which arises in the uncoupled model by adding the soil displacements attributable to the load the pipe exerts on the soil to the subgouge deformations, despite the strongly nonlinear behavior of the soil.
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Acknowledgments
The writers would like to thank C-CORE, St. Johns, NL, Canada, for permission to reproduce Fig. 1, and in particular Ryan Phillips and Michael Paulin for their help in tracing the origins of this picture. It originates from Woodworth-Lynas (1992), drawing upon submarine observations of iceberg Bertha. However, the pipeline was added later, by Desireé King. For this purpose, the ice feature was used to represent a keel rather than a berg. Otherwise, a typical pipeline would appear smaller in Fig. 1, by about a factor of 10.
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Published In
International Journal of Geomechanics
Volume 12 • Issue 4 • August 2012
Pages: 508 - 516
Copyright
© 2012. American Society of Civil Engineers.
History
Received: Nov 18, 2010
Accepted: May 19, 2011
Published online: May 23, 2011
Published in print: Aug 1, 2012
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