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Research Papers: Ocean Engineering

Coupling Between Roll Motions of an FLNG Vessel and Internal Sloshing

[+] Author and Article Information
Wenhua Zhao

State Key Laboratory of Ocean Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 200240, China;
Faculty of Engineering,
Computing and Mathematics,
The University of Western Australia,
35 Stirling Highway,
WA 6009, Australia
e-mail: zwzldh@163.com

Jianmin Yang

State Key Laboratory of Ocean Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 200240, China
e-mail: jmyang@sjtu.edu.cn

Zhiqiang Hu

State Key Laboratory of Ocean Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 200240, China
e-mail: zhqhu@sjtu.edu.cn

Longbin Tao

State Key Laboratory of Ocean Engineering,
Shanghai Jiao Tong University,
800 Dongchuan Road,
Shanghai 200240, China;
School of Marine Science and Technology,
Newcastle University,
Newcastle Upon Tyne NE1 7RU, UK
e-mail: longbin.tao@newcastle.cu.uk

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received February 7, 2013; final manuscript received January 11, 2014; published online March 18, 2014. Assoc. Editor: Elzbieta Maria Bitner-Gregersen.

J. Offshore Mech. Arct. Eng 136(2), 021102 (Mar 18, 2014) (10 pages) Paper No: OMAE-13-1019; doi: 10.1115/1.4026586 History: Received February 07, 2013; Revised January 11, 2014

A series of two-dimensional model tests has been conducted to study the coupling between global roll motions of a floating liquefied natural gas (FLNG) vessel and internal sloshing. The model of the FLNG is allowed to move freely in roll under the excitations of an initial heel angle, band-limited waves, and regular waves. To clarify the coupling effects, the FLNG vessel in different filling conditions is ballasted in fresh water and equivalent steel ballast weights, respectively. Time series of both the internal sloshing and the global motions of the vessel are measured. Statistical and spectral analyses have been carried out on the measured data. Sloshing oscillations in different surface modes have been observed. Asymmetry of the internal wave profile relative to still-water surface is also observed. Attempts are made to clarify the influences of the internal sloshing on the global roll motions through the comparison of the experiment results between the liquid and steel ballasting cases. The coupling phenomenon is found to be sensitive to the period and height of excitation waves. Further discussion has been made on the experiment results, and some conclusions regarding the coupling mechanism between global motions and internal sloshing are drawn based on the present study.

Copyright © 2014 by ASME
Topics: Waves , Sloshing , Vessels , Water
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References

Figures

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Fig. 1

Model of the FLNG section containing a tank: (a) front view, (b) side view, and (c) top view. Two wave probes are fixed at each side of the tank for the measurement of the internal sloshing.

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Fig. 2

Snapshot of the FLNG section model: (a) the liquid ballasting condition, red color has been added to the water in the tank and (b) the equivalent solid weights ballasting condition

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Fig. 3

Schematic of experimental setups: (a) front view and (b) side view (physical are not to scale). The wave probe located at the head side of the tank is defined as “head side” and the wave probe at the following side of the tank is defined as “following side”.

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Fig. 4

Power spectrum density function of the band-limited white noise waves

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Fig. 5

Extinction curves for roll motions of the FLNG section in still water: (a) decay curves in filling condition 1, (b) decay curves in filling condition 2, and (c) decay curves in filling condition 3

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Fig. 6

Comparison of the response spectrums for the roll motions of the FLNG section

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Fig. 7

Comparison of the response spectrums for the internal sloshing oscillations at predefined locations

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Fig. 8

Comparison of the response amplitude operators for the roll motions of the FLNG section

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Fig. 9

Comparison of the response amplitude operators for the internal sloshing oscillations at predefined locations

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Fig. 10

Time histories in filling condition 2 (h = 12m, p1 = 8.85s) for wave case 1 (wave height = 3 m, wave period = 8.85 s): (a) excitation wave elevations, (b) roll motions, and (c) internal sloshing

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Fig. 11

Time histories in filling condition 2 (h = 12m, p1 = 8.85s) for wave case 2 (wave height = 6 m, wave period = 8.85 s): (a) excitation wave elevations, (b) roll motions, and (c) internal sloshing

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Fig. 12

Time histories in filling condition 2 (h = 12m, p1 = 8.85s) for wave case 3 (wave height = 9 m, wave period = 8.85 s): (a) excitation wave elevations, (b) roll motions, and (c) internal sloshing

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Fig. 13

Time series in filling condition 1 (h = 18m, p1 = 7.60s) for wave case 1 (wave height = 3 m, wave period = 8.85 s): (a) roll motions and (b) internal sloshing

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Fig. 14

Time series in filling condition 1 (h = 18m, p1 = 7.60s) and wave case 2 (wave height = 6 m, wave period = 8.85 s): (a) roll motions and (b) internal sloshing

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Fig. 15

Time series in filling condition 1 (h = 18m, p1 = 7.60s) and wave case 3 (wave height = 9 m, wave period = 8.85 s): (a) roll motions and (b) internal sloshing

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Fig. 16

Time series in filling condition 3 (h = 6m, p1 = 10.80s) and wave case 1 (wave height: 3 m, wave period: 8.85 s): (a) roll motions and (b) internal sloshing

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Fig. 17

Time series in filling condition 3 (h = 6m, p1 = 10.80s) and wave case 2 (wave height: 6 m, wave period: 8.85 s): (a) roll motions and (b) internal sloshing

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Fig. 18

Time series in filling condition 3 (h = 6m, p1 = 10.80s) and wave case 3 (wave height: 9 m, wave period: 8.85 s): (a) roll motions and (b) internal sloshing

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Fig. 19

Variations of the mean double amplitudes of the roll motions versus the excitation wave heights

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Fig. 20

Variations of the mean double amplitudes of the internal sloshing oscillations versus the excitation wave heights

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