Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Effects of Currents and Sediment Flushing on Marine Pipes
Pin-Tzu Su[1], Chen-Shan Kung[2]1. University of Oslo, Oslo, Norway
2.

ATE Energy International Co., Ltd., New Taipei City, Taiwan China

ABSTRACTINTRODUCTION

The stability and lives extension of marine pipes are important incoastal engineering and the factors that influence the pipelines arecorresponding to the coastal environment. To stabilize the pipes, blocks
are a good solution and they are widely utilized in the engineering field.
In this study, marine pipes are sited 0.5 meters higher than the sea bed
and attached with blocks. With 1 m/s currents and sea bed which size ofsand is 0.2 mm, we calculate the force load on marine pipes to analyze
the relation among currents, change of sea bed and the structure
including a marine pipe with blocks. A three-dimensional computational
fluid dynamics code, FLOW-3D, solves Navier-Stokes type equations
embedded with turbulence closure models is used. RNG model isutilized to solve turbulence calculation. Velocity, force load, andturbulent characteristics which are inconvenient to measure in the field
are simulated and investigated and the drag coefficients under various
situations are computed. Moreover, the interactions among current,
sediment flushing and marine pipes with blocks are also discussed. The
influences on the marine pipes caused by the distance between blocks
are concluded and regressed for appropriate design. With properprediction of impact on marine pipes and sediment flushing at sea bed,
the stability and lives extension of sea pipes are expected to beimproved in the future.

Pipelines are commonly used in the marine engineering, like taking
cooling water from the sea to cool down the facilities and thendischarging the effluent back to the environment. Since the pipelines
play such an important role, they have become one of the significant
concerns in application of engineering field, like Zhao et al. (2016)
study the influences of pore pressure accumulations around the buriedpipeline in the seabed and protected in trench layer with partial backfills. Chiew et al. (1990) and Sumer et al. (2002) also studied thesouring situation around the pipeline. Tom et al. (2018) concluded that
sediment transportation is related to the ratio of oscillation amplitude tocylinder diameter which is less than 12.
After the pipeline is settled on the seabed, it is affected by waves,periodic tides, currents and the change of the sea bed. However, in thearea of deep sea, the impacts of waves and tides upon the pipeline canbe ignored, and currents are the main impinge influencing pipelines andseabed. The influence of currents on the pipe is concerned as an issue ofpipes protection. Zhao et al. (2010) simulated the scour below avibrating pipeline under steady current by using a finite element
numerical model and Damroudi et al. (2021) experimentallyinvestigated the effect of pipe external geometry on local scour and selfburial time scales and flow pattern. Lee et al. (2018) predicted the scour
time scale beneath subsea pipelines with an elevation with respect to thefar-ﬁeld seabed under steady currents. Consequently, it is essential topredict the behavior of the currents and analyze its impacts on the pipes.
Some researchers discussed lift and drag coefficient of a circularcylinder, like Sumer et al. (1997) discussed about forces on a cylinder
under steady current. Besides, Roshko et al. (1975) and Goktun (1975)
both found that as the cylinder approaches the wall its drag decreases.
The drag exerted by an accelerating fluid on a stationary 2D circularcylinder is numerically investigated by Son et al. (2020). Mallick et al.
(2013) studied drag coefficient for the flow past a cylinder. From thepreceding researches, most researches are studied with the structure
which is circular cylinders only. In this study, we consider the effects ofblocks with different spaces as an important character affecting theforce on the pipeline. It is typical to use concrete ballast blocks for theKEY WORDS: Marine pipes; Spaces of the blocks; Currents;
Sediment scouring; Drag coefficients

1685