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

The prediction model of the force exerted on a horizontal cylinder by an internal solitary wave based on
vortex-flow structure analysis
Shao-dong Wang, Hui Du*, Gang Wei, Pai Peng, Pu Xuan

College of Meteorology and Oceanography, National University of Defense Technology
Changsha, Hu Nan Province, China

ABSTRACT

calculating the wave force acting on piles (Morison J et al., 1950), theISW forces on the vertical piles were estimated by using the mode
separation method and the ISW theory (Cai et al., 2003). The forces
and torques of the ISW acting on the vertical piles were estimated by
the local observation data including temperature, salinity and amplitudeof the ISW (Cai et al., 2006; Cai et al., 2008). The continuous layered
nonlinear model and Morison formula were used to calculate the forces
and torques on the vertical piles, and the obtained results showed thatthe forces exerted by the ISW were much larger than that exerted by thesingle tidal current (Xie et al., 2011). Several studies of the ISW force
prediction model are mainly focused on the vertical piles presently.

An experiment on the interaction of an internal solitary wave (ISW)with a horizontal cylinder was conducted in a gravitationally stratified
fluid flume. The particle image velocimeter (PIV) and the force sensor
were used to study the flow structure and the forces on the cylinder
respectively. Based on the hydrodynamic coefficients with theexperimental corrections, the force prediction model of the cylinderinteracting with an ISW was established. The ISW forces on thecylinder are composed of the wave force and the disturbance force, inwhich the horizontal and vertical wave forces can be estimated by theMorison formula, additionally the disturbance force composed of the
reduced gravity and the vortex shedding lift are considered in thevertical direction. The quantitative relationship between the force
coefficients in the Morison formula and the KC Number is obtained
from the experimental measurements of ISW forces, and the force
prediction results are in well agreement with the experimental ones.
KEY WORDS: Stratified fluid; internal solitary wave; horizontal
cylinder; vortex-flow structure; force prediction model;

Different from the vertical pile mainly subjected to the ISW horizontal
flow, the horizontal pile is simultaneously subjected to both horizontal
and vertical flows, which make the interaction much more complex
than the former. Ermanyuk and Gavrilov (2005) carried out
experimental tests of the interaction between ISWs and horizontal
submerged cylinders in a two-layer fluid, this study suggested that thetwo-dimensional loads were substantially changed by the ratio of theupper fluid layer to the lower one and the submerged depth of cylinder.
Du et al. (2016) and Gu et al. (2017) pointed out that the changes in theISW structure caused by topographic effects could directly affect theforces acting on the slender body. As can be seen from the abovestudies, there are few studies related to the force prediction model ofthe ISW force on the horizontal cylinder. The Morison's formula is a
widely used semi-empirical method for calculating ISW forces on piles,of which the accuracy mainly depends on the inertia force and dragforce coefficients. The acquisition of coefficients requires a large
number of experimental data, but there is a scarcity of relevant data atpresent.

INTRODUCTION
Internal solitary wave (ISW) is a kind of internal fluctuation occurringin the stratified ocean. Different from the surface wind waves withsmall amplitude, short period and easy breaking, the ISWs arecharacterized by large amplitude, long period and far propagation. The
induced shear flows with gradient will inevitably can lead to kinds ofproblems concerned in Ocean Engineering, such as the threedimensional load, vortex-induced vibration (VIV) and multi-degree-offreedom (DOF) motion instability, etc. The facility safety is threatenedby the VIV response of marine riser under the shear flow (Duan etal.,2021). A semi-submersible platform in Liuhua Oilfield can bedrifted 120 m northward within 15 min due to an ISW (Yuan et al.,2013).

So the interaction of an ISW with a horizontal cylinder will be studied
experimentally in a stratified flume in this paper. Based on theexperimental measurements of flow structures, the prediction model ofthe ISW force on a horizontal cylinder is established by combining theISW theory model with the Morison formula.
The empiricalcoefficients in the Morison formula are solved with the force

Vertical and horizontal cylindrical structures are the fundamental formsof ocean engineering objects. Based on the Morison formula of2798