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Research Papers: Structures and Safety Reliability

Effect of Partially Filled Spherical Cargo Tanks on the Roll Response of a Bargelike Vessel

[+] Author and Article Information
Wenhua Zhao

Faculty of Engineering,
Computing and Mathematics,
The University of Western Australia,
35 Stirling Highway,
Crawley, WA 6009, Australia
e-mail: wenhua.zhao@uwa.edu.au

Finlay McPhail

Shell Global Solutions BV (Shell),
Kessler Park 1,
Rijswijk 2280 AB, The Netherlands
e-mail: Finlay.McPhail@shell.com

Mike Efthymiou

Faculty of Engineering,
Computing and Mathematics,
The University of Western Australia,
35 Stirling Highway,
Crawley, WA 6009, Australia
e-mail: M.Efthymiou@shell.com

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 May 4, 2015; final manuscript received January 19, 2016; published online March 30, 2016. Assoc. Editor: Yi-Hsiang Yu.

J. Offshore Mech. Arct. Eng 138(3), 031601 (Mar 30, 2016) (9 pages) Paper No: OMAE-15-1035; doi: 10.1115/1.4032658 History: Received May 04, 2015; Revised January 19, 2016

Floating liquefied natural gas (FLNG) is an offshore structure which enables liquefaction, storage, and offloading of natural gas. It is a game changer in offshore hydrocarbon development. Side-by-side offloading is a promising way of transferring liquefied natural gas (LNG) from FLNG to an LNG carrier. The roll response of LNG carriers, which plays a critical role, has been observed to be influenced by the liquid cargo motion inside the tanks. Therefore, the operational window for side-by-side offloading may not be estimated robustly using a simplified method which ignores the liquid cargo and considers only the ballast condition. This necessitates a scientific understanding of the roll responses of an LNG carrier at different load conditions. In this study, a series of model tests are conducted on a bargelike vessel with two spherical tanks. The response amplitude operators (RAOs) and response spectra of the vessel in different load conditions and different headings are investigated. The effect of intermediate cargo volumes on global roll response is, for the first time, examined for spherical cargo tanks. It is suggested that intermediate loading conditions with explicit inclusion of the effects of cargo sloshing is utilized in side-by-side operability studies to robustly ascertain offloading availability.

Copyright © 2016 by ASME
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References

Figures

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Fig. 1

Lines plan of the vessel with two spherical tanks: (a) front view, (b) side view, and (c) top view

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Fig. 2

Adjustment of the inertia parameters

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Fig. 3

Configuration of the horizontally moored vessel in wave basin

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Fig. 4

White noise waves in beam seas: (a) response spectrum and (b) representative time series

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Fig. 5

White noise waves in quartering seas: (a) response spectrum and (b) representative time series

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Fig. 6

Relative contribution of roll damping components in different roll amplitudes [11]: Be represents the equivalent linear damping; BE, BF, BL, and BW refer to eddy-making, friction, lift, and wave-making damping, respectively; and BBKH, BBKN, and BBKW are the normal-force damping, hull-pressure damping, and wave-making damping induced by bilge keels

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Fig. 7

Time series of the roll decay curve in the 0% load condition

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Fig. 15

Roll response spectra for different load conditions in long beam swells

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Fig. 16

Roll response spectra for different load conditions in long quartering swells

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Fig. 14

Spectra of the swells: significant wave height is 0.9 m

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Fig. 13

A possible combination of metocean conditions

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Fig. 12

Roll RAOs against scaled period for different filling configurations in quartering seas

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Fig. 11

Roll RAOs against scaled period for different filling configurations in beam seas

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Fig. 10

Roll RAOs against periods for different loading conditions in quartering seas

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Fig. 9

Roll RAOs against periods for different loading conditions in beam seas

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Fig. 8

Comparison of RAOs obtained through split time series: the vessel is in the 50% load condition and in a beam sea

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Fig. 17

Roll response spectra for the 25% load condition in a beam swell with short period of 7.3 s

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