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Abstract
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A piggyback pipeline consists of two pipes such that the secondary line rides on the main pipe with a fixed distance
between two pipes in length. The novel strategy is utilized in offshore areas instead of a single flow line. In this
regard, there are only a handful of experimental and numerical studies investigating the effect of scour below a
piggyback pipeline under steady current. Hence, this study focuses on examining the influential factors on scouring
due to steady current including the pipe diameter and the gap between pipes through numerical simulations and
experimental tests. Accordingly, at the first phase of the research, a single pipe was established and tested in
laboratory to compare the results with those of an empirical equation. After finishing experimental verifications,
piggyback pipelines were also assembled to study the scouring under steady current conditions. It was concluded that
by increasing the gap distance between the pipes, the maximum scour depth decreases; however, an increase in the
small pipe’s diameter results in a larger maximum scour depth. Secondly, numerical simulations were carried out
using the FLOW-3D software which was found to be a suitable tool for the numerical investigation of this study.
Finally, the numerical results have been compared with the corresponding experimental data and a relatively good
agreement was achieved between them.
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