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Ocean Engineering

Simulation of Sloshing in LNG-Tanks

[+] Author and Article Information
Milovan Peric

 CD-adapco, Dürrenhofstrasse 4, 90402 Nürnberg, Germanymilovan.peric@de.cd-adapco.com

Tobias Zorn

 Germanischer Lloyd AG, Vorsetzen 35, Hamburg, 20459 Germanytobias.zorn@gl-group.com

Ould el Moctar

 Germanischer Lloyd AG, Vorsetzen 35, Hamburg, 20459 Germanyould.el-moctar@gl-group.com

Thomas E. Schellin1

 Germanischer Lloyd AG, Vorsetzen 35, Hamburg, 20459 Germanythomas.schellin@gl-group.com

Yong-Soo Kim

 Daewoo Shipbuilding & Marine Engineering, 1 Aju-dong, Geoje City, 656-714 Gyungnam, Korea (Republic)youngsu@dsme.co.kr

1

Corresponding author.

J. Offshore Mech. Arct. Eng 131(3), 031101 (May 28, 2009) (11 pages) doi:10.1115/1.3058688 History: Received July 02, 2007; Revised October 22, 2008; Published May 28, 2009

The purpose of this paper was to demonstrate the application of a procedure to predict internal sloshing loads on partially filled tank walls of liquefied natural gas (LNG) tankers that are subject to the action of sea waves. The method is numerical. We used a moving grid approach and a finite-volume solution method designed to allow for arbitrary ship motions. An interface-capturing scheme that accounts for overturning and breaking waves computed the motion of liquid inside the tanks. The method suppressed numerical mixing. Mixing effects close to the interface were buried in the numerical treatment of the interface. This interface, which was at least one cell wide, amounted to about 20–50 cm at full scale. Droplets and bubbles smaller than mesh size were not resolved. Tank walls were considered rigid. The results are first presented for an LNG tank whose motion was prescribed in accordance with planned laboratory experiments. Both two-dimensional and three-dimensional simulations were performed. The aim was to demonstrate that (1) realistic loads can be predicted using grids of moderate fineness, (2) the numerical method accurately resolves the free surface even when severe fragmentation occurs, and (3) long-term simulations over many oscillation periods are possible without numerical mixing of liquid and gas. The coupled simulation of a sea-going full-sized LNG tanker with partially filled tanks demonstrated the plausibility of this approach. Comparative experimental data were unavailable for validation; however, results were plausible and encouraged further validation.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Geometry of the investigated tank and the associated hexahedral grid

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Figure 2

Free-surface shapes after 99.5 (top) and 100 (bottom) oscillation periods; two-dimensional computations on coarse grid

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Figure 3

Free-surface shapes after 14, 12, 34, and full period (from top to bottom, respectively) for the 21st oscillation pitch period; two-dimensional computations on refined grid

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Figure 4

Pressure time histories at points A, B, C, and D in Fig. 3 (from top to bottom, respectively); two-dimensional computations on coarse and refined grid

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Figure 7

Pressure distribution at the front tank wall for three time instants that are 20 time steps apart, near time when tank reached its lowest position (34 of a period)

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Figure 8

Velocity vectors in the longitudinal symmetry plane

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Figure 9

Volume fraction (top) and pressure distribution (center) shortly after a cylindrical blob of water hits a wall and the associated pressure trace at the center of the impact area (bottom)

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Figure 11

Time histories of pressure at corner points 1 and 2 (top) and 3 and 4 (bottom) in Fig. 7; three-dimensional simulation

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Figure 12

Free-surface shapes at 14, 12, 34, and full period (from top to bottom, respectively) during the 101st oscillation roll period; two-dimensional computations on coarse grid

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Figure 13

Time histories of pressures at points A, B, C, and D in Fig. 1 (from top to bottom, respectively)

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Figure 14

Geometry of LNG ship and grids on free surface, hull, and tank walls

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Figure 15

The LNG tanker on a wave crest (top) and in a wave trough (bottom)

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Figure 5

Pressure time histories at points A, B, C, and D in Fig. 3 (from top to bottom, respectively) over 100 periods; two-dimensional computations on a coarse grid

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Figure 6

Free-surface shapes after 34 of the eighth oscillation period and after full, 14, and 12 of the ninth oscillation period (from top to bottom, respectively)

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Figure 10

Time histories of pressure at wall locations A (top), B (center), and C (bottom) in the longitudinal symmetry plane, corresponding to locations A, B, and C in Fig. 3; two- and three-dimensional simulations

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Figure 16

Representative sample of ship position in waves and free-surface shape in tanks at four instants of time over one regular wave period

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