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

Experimental investigation on the flow-induced vibration of a flexible catenary riser subjected to thecombination of internal liquid flow and external sheared flow
Yue Gao, Hongjun Zhu*, Jie Hu, Bing Xu, Wenli Liu

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University
Chengdu, Sichuan Province, P.R. China

practice of offshore oil and gas engineering, flexible risers are servicing
in a complex environment, where the external and internal flow interact
with the structure. When the internal flow travels inside the flexile
catenary riser, the centrifugal and Coriolis forces due to the curvature of
the riser are exerted on the flexible riser, affecting the dynamic response
and hence a more complicated behavior. As the numerical report in Guoet al. (2008), the oscillation was significantly enhanced due to the coexistence of internal flow. The flow-induced response of a 5486 m pipe
was predicted by Chung et al. (1994) using the finite element method(FEM). It was reported that the axial stress was reduced due to theupward internal slurry flow while the horizontal displacement wasaugmented. Li et al. (2020) even observed that extra high mode wasexcited with the introduction of internal flow. The similar phenomenonof such response amplification has been validated by Duan et al. (2021)
and Chen et al. (2021). As to experimental researches, Guo and Lou(2008) carried out an experimental study on the VIV response of a riser
model with different internal flow velocities. They observed that theresponse amplitude was magnified as the internal flow speed increased,
while the vibration frequency decreased. Zhu et al. (2019)
experimentally investigated the coupling response of a curved flexile
riser under the combination of internal gas-liquid mixture flow andexternal current. They observed that the contribution of internal slug flow
was greater than the external flow for the in-plane response at the upperpart, while the out-of-plane response was dominated by the externalcurrent.
Although the dynamic response of flexible risers considering thecombination of internal and external flows has been drawn muchattention recently, most of the work is mainly limited to the vibration
response of straight flexible pipes under external uniform currents. The
extant literature involving the catenary flexible riser subjected tononlinear external sheared flow is scanty. The associated experimental
researches are much few on the vibration response of curved flexible
risers under the combination of internal flow and external sheared current.
Therefore, this paper experimentally investigates the flow-induced
vibration of a free-hanging flexible riser with an aspect ratio of 125 underthe external nonlinear sheared current and the internal liquid flow,
aiming at identifying the coupled dynamic behavior of a free-hanging
flexible riser conveying flow.

ABSTRACTIn this work, a series of tests was conducted in a recirculating water
flume to investigate the dynamic behavior of a flexible catenary riser
under the combination of internal liquid flow and external shear current.
A non-intrusive high-speed imaging technique was employed to record
the vibration displacement varying along the riser span. The
experimental results illustrate that the response is enhanced withincreasing the internal flow velocity except for the mode transition cases.
When the internal fluid flows in the riser, the mode transition
accompanying with the amplitude reduction occurs compared to thepurely vortex-induced vibration response.

KEY WORDS: Flow-induced vibration; flexile riser; internal flow;mode transition

INTRODUCTION
Flow-induced vibration (FIV) of flexible structures is encounteredin a wide range of engineering applications, especially in the offshore
engineering. As oil and natural gas exploration extends to increasing
deep waters, the flexibility of riser is enhanced. It is easy for flexible riser
to experience an intricate vibration. The multi-mode vibration responseof flexible risers has been the main object of a number of researches, as
collected in Bourguet et al. (2011, 2013a, 2013b, 2020) and Fan et al.
(2019). Mono- and multi-frequency vibrations may occur in both the inline and cross-flow directions (Vandiver et al., 1996; Chaplin et al., 2005;
Lucor et al., 2006; Bourguet et al., 2013b). As reported in Bourguet et al.
(2013b), the profile of the normal component of oncoming flow is
identified to control the mono- or multi-frequency nature of the response.
In addition, the excitation region and the damping region correspond to
the lock-in region and non-lock-in region, respectively. Owing to themulti-mode participation, the mixture of standing and traveling wave
patterns often occurs in the flexible riser response (Bourguet et al., 2011;
Bourguet et al., 2013a; Lucor et al., 2006; Newman and Karniadakis,
1997; Gao et al., 2019). Gao et al. (2019) reported that the aspect ratio
can influence the wave patterns, which are dominated by standing waves
for small aspect ratio cases. When the oncoming flow is a sheared one,the travelling wave usually prefers to propagate from the high inflow
velocity to low inflow velocity (Bourguet et al. (2013a).
Although some work has been done for the VIV response of flexible
risers, the effect of internal flow has not been well documented. InEXPERIMENTAL DETAILSExperiments were conducted in a recirculating water flume with a test

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