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Ocean Engineering

The Effects of Inner-Liquid Motion on LNG Vessel Responses

[+] Author and Article Information
S. J. Lee, M. H. Kim

Department of Civil Engineering, Ocean Engineering Program, Texas A&M University, College Station, TX 77843

J. Offshore Mech. Arct. Eng 132(2), 021101 (Mar 01, 2010) (8 pages) doi:10.1115/1.4000391 History: Received August 30, 2007; Revised September 08, 2008; Published March 01, 2010; Online March 01, 2010

The coupling and interactions between ship motion and inner-tank sloshing are investigated by a potential-viscous hybrid method in the time domain. For the time-domain simulation of vessel motion, the hydrodynamic coefficients and wave forces are obtained by a potential-theory-based 3D diffraction/radiation panel program in the frequency domain. Then, the corresponding simulations of motions in the time domain are carried out using the convolution-integral method. The liquid sloshing in a tank is simulated in the time domain by a Navier–Stokes solver. A finite difference method with SURF scheme assuming the single-valued free-surface profile is applied for the direct simulation of liquid sloshing. The computed sloshing forces and moments are then applied as external excitations to the ship motion. The calculated ship motion is in turn inputted as the excitation for liquid sloshing, which is repeated for the ensuing time steps. For comparison, we independently developed a 3D panel program for linear inner-fluid motions, and it is coupled with the vessel-motion program in the frequency domain. The developed computer programs are applied to a barge-type floating production storage and offloading (FPSO) hull equipped with two partially filled tanks. The time-domain simulation results show reasonably good agreement when compared with Maritime Research Institute Netherlands (MARIN’s) experimental results. The frequency-domain results qualitatively reproduce the trend of coupling effects, but the peaks are in general overpredicted. It is seen that the coupling effects on roll motions appreciably change with filling level. The most pronounced coupling effects on roll motions are the shift or split of peak frequencies. The pitch motions are much less influenced by the inner-fluid motion compared with roll motions.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Grid generation of hull for 3D panel method (number of panels=2300)

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Figure 2

Measured and predicted motion RAOs for 135 deg wave heading

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Figure 3

Grid generation for sloshing tanks (filling level: 37%)

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Figure 4

Roll added mass of sloshing fluid

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Figure 5

Coordinate system of sloshing analysis program

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Figure 6

Roll free-decay test of MARIN-FPSO

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Figure 7

Pitch free-decay test of MARIN-FPSO

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Figure 8

Roll free-decay test with regular wave amplitude 1.67 m

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Figure 10

Simulated and experimental results of 0% filling level

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Figure 12

Simulated and experimental results of 37% filling level

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Figure 13

Simulated time series of roll sloshing excitation moment of 37% filling level

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Figure 14

Simulated spectral density of roll sloshing excitation moment of 37% filling level

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Figure 15

Simulated time series of sway and roll: (a) 18% filling level and (b) 37% filling level

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Figure 16

Comparison of roll RAOs of experiments by MARIN, frequency domain, and time domain for 90 deg wave heading. (a) Without sloshing case, (b) 18% filling level, (c) 37% filling level, and (d) 56% filling level.

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Figure 17

Comparison of pitch RAOs of experiments by MARIN, frequency domain, and time domain 180 deg wave heading. (a) Without sloshing case, (b) 18% filling level, (c) 37% filling level, and (d) 56% filling level.

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Figure 18

Snapshot of motion-sloshing coupled animation (37% beam waves) in the time domain

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Figure 11

Simulated and experimental results of 18% filling level

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Figure 9

Wave spectral density (HS=5.0 m and γ=3.3).

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