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

Numerical Investigation on Coupling Dynamic Performance of FLNG and LNG Carriers
Jideofor Collins Nwafor

Marine, Offshore and Subsea Technology group, School of Engineering, Newcastle University.
Newcastle Upon Tyne, Tyne and Wear, United Kingdom.

ABSTRACTeven in moderate seas. It is important to study the multibody vessel
motion behavior relative to the connecting systems, offloading arms
and mooring lines for different filling conditions in order to manage
any potential collision of the vessels or damage to the loading arms andimprove safety.

In this paper the nonlinear coupling of the gap resonance and thehydrodynamics of a floating liquefied natural gas (FLNG) facility andliquefied natural gas (LNG) carrier in proximity for the offloading
operation in side-by-side configuration is investigated numericallyusing potential flow solver SIMA running on state-of-the-art software
code SIMO. A damping lid technique is used to circumvent theunrealistic high wave elevation in the narrow gap region using
calibrated damping factors and compared against experimental data.
The time domain analysis is carried out by importing the frequency
domain results. A number of simulation cases with different loading
condition are being evaluated under a combination of environmental
factors of wind, current and waves. The relative motion of the FLNG
and LNGC’s side by side system in the horizontal plane are comparedfor different loading conditions, the mechanical loads on the hawser,
fender and mooring systems are also calculated. The results provide
insights into the hydrodynamic characteristics and loads on theconnecting system of the side-by-side operation vessels for different
vessel loading conditions and environmental factors to boost therobustness and safety for future operations.

Literature Review
The multibody hydrodynamic interaction between FLNG and LNGC
vessels can bring about a considerable risk to the connecting system
which maintains the gap distance between the side-by-side vessels
during offloading operation.
Lee (1995) stated that the radiation potential, which is separated into
different components, that are corresponding to the modes of the rigid
body motion, can be applied to multi-body interaction. This was doneby defining the velocity potential which matches a particular mode ofone vessel while the second vessel is stationary. With this approach, thetotal radiation potential will be made up of “6N” components, with N,
the number of bodies. Tajali and Shafieefar (2011) studied the dynamic
interactions between floating piers subjected to various wave
frequencies and wave directions in the frequency domain. To estimate
the influence of hydrodynamics on arrays of hinged floating offshore
structures, a numerical simulation method was used for that function.
Whereas, analysis done in the frequency domain generate useful data of
the hydrodynamic interaction of multibody systems, it is restricted inits capacity to analyse the nonlinear coupling effects of multibodysystems. Harichandan and Roy (2012) did research on characteristics offlow past single and multi-bodies. From various studies it was observedthat the flow in the gap region of the vessels in side-by-side
configuration shows complex vorticities which is affected by the gap
size. The research focus has now been on studies using time domain
method, to analyse the nonlinear effects such as the mooring forces andthe viscous flow, where retardation functions are used to transform theresults from the frequency domain. Buchner et al. (2001) analysed thehydrodynamic interactions of two vessels moored in side-by-sideconfiguration, taking into cognisance the effects of coupling between
the motions of the vessels. Moreover, to decrease the unrealistic
resonance wave oscillation in the gap region, a free surface lid wasapplied in-between the multi-body diffraction. This is an advancementfrom earlier approaches.

KEY WORDS: FLNG; side-by-side; offloading; Connecting system;
Multi-body systems; numerical simulation.
INTRODUCTION
BackgroundThe demand for clean energy is increasing globally and that of natural
gas is expected to also increase because it is the cleanest burning fossil
fuel. Floating liquified natural gas (FLNG) facility is a relatively newtechnology that exploits gas reserves that are in deep waters andinaccessible from available offshore pipelines. To overcome thesechallenges of transporting the product onshore, the side-by-side loading
configuration has been widely adopted to offload LNG from the FLNG
to an LNG carrier. This is partly due to the cryogenic state the LNG isstored and transferred, by using offloading arms. The operating window
is for a limited duration and is performed in calm sea state. There is theoccurrence of increased vessel motions at certain wave frequencies

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