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Offshore and Structural Mechanics

Influence of Bilge Keel Width on the Roll Damping of FPSO

[+] Author and Article Information
Krish P. Thiagarajan1

School of Mechanical Engineering, University of Western Australia, Crawley, Western Australia 6009, Australiakrish.thiagarajan@uwa.edu.au

Ellen C. Braddock

School of Mechanical Engineering, University of Western Australia, Crawley, Western Australia 6009, Australia

1

Corresponding author.

J. Offshore Mech. Arct. Eng 132(1), 011303 (Dec 22, 2009) (7 pages) doi:10.1115/1.3160384 History: Received October 11, 2006; Revised August 28, 2007; Published December 22, 2009; Online December 22, 2009

Current industry practice to control roll motions in floating production storage and offloading (FPSO) vessels is based on using large-width bilge keels. This paper details an experimental study involving a range of bilge keel widths from 0% to 20% of half beam of a FPSO with rectangular geometry. Both free decay and forced oscillation tests were conducted on the range of geometries at different amplitudes and frequencies. The results show that, for given amplitude of roll motion, the damping coefficient increases with increasing bilge keel size up to a certain point and then declines. Numerical simulations using the free surface random vortex method were performed on rectangular cross sections with bilge keels, which show good agreement with the experimental results. Simulations extended up to even larger keel widths indicate that the same trend for damping coefficient as a function of keel size is found. An examination of the simulation results suggests a likely explanation for this behavior. A simplified formulation for damping coefficient is developed as a function of bilge keel width and roll amplitude.

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Figures

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Figure 1

Forced roll motion mechanism

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Figure 3

Experimental results for damping coefficient versus frequency (Hz) for various bilge keel widths. All results at roll amplitude of 12.5°

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Figure 4

FSRVM results for damping coefficient versus frequency (Hz) for various bilge keel widths. All results at roll amplitude of 12.5°.

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Figure 5

Experimental results for damping coefficient versus bilge keel widths at various frequencies. All results at roll amplitude of 12.5°.

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Figure 6

FSRVM results for damping coefficient versus bilge keel widths at various frequencies. All results at roll amplitude of 12.5°.

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Figure 7

Comparison of damping coefficients versus bilge keel widths at various roll amplitudes

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Figure 8

Vortex blob distribution for BK1 and BK5 for a typical amplitude and frequency of oscillation

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Figure 9

Experimental results for damping coefficient vs. roll amplitude for bilge keel widths

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Figure 10

FSRVM results for damping coefficient versus roll amplitude for bilge keel widths

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Figure 11

Slope of damping coefficient—roll amplitude curve versus bilge keel widths

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Figure 12

Comparison between simplified formulation (Eq. 27) and experiments for damping coefficient versus bilge keel width at various roll amplitudes

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Figure 2

FSRVM problem domain

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