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TECHNICAL PAPERS

Second Order Wave Diffraction Around a Fixed Ship-Shaped Body in Unidirectional Steep Waves

[+] Author and Article Information
J. Zang1

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UKjun.zang@eng.ox.ac.uk

R. Gibson

Department of Civil and Environmental Engineering, Imperial College, London SW7 2BU, UK

P. H. Taylor, R. Eatock Taylor

Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, U.K.

C. Swan

Department of Civil and Environmental Engineering, Imperial College, London SW7 2BU, U.K.

1

Corresponding author.

J. Offshore Mech. Arct. Eng 128(2), 89-99 (Jan 12, 2006) (11 pages) doi:10.1115/1.2185130 History: Received April 24, 2005; Revised January 12, 2006

The objective of this research, part of the EU FP5 REBASDO Program, is to examine the effects of second order wave diffraction in wave run-up around the bow of a vessel (FPSO) in random seas. In this work, the nonlinear wave scattering problem is solved by employing a quadratic boundary element method. A computer program, DIFFRACT, has been developed and recently extended to deal with unidirectional and directional bichromatic input wave systems, calculating second order wave diffraction loads and free surface elevation under regular waves and focused wave groups. The second order wave interaction with a vessel in a unidirectional focused wave group is presented in this paper. Comparison of numerical results and experimental measurements conducted at Imperial College shows excellent agreement. The second order free surface components at the bow of the ship are very significant, and cannot be neglected if one requires accurate prediction of the wave-structure interaction; otherwise a major underestimation of the wave impact on the structure could occur.

Copyright © 2006 by American Society of Mechanical Engineers
Topics: Diffraction , Waves , Ships
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Figures

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Figure 1

Experimental FPSO model

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Figure 3

Measured free surface time histories (without ship) and linearized incoming wave

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Figure 4

Amplitude spectrum for linearized experimental incoming wave

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Figure 5

Comparison of symmetric experimental linearized free surface time history and simulated results

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Figure 6

Amplitude spectrum for the ship not in place

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Figure 7

Amplitude spectrum for ship in place

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Figure 8

Amplitude spectrum for linear and odd terms with and without ship in place

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Figure 9

Amplitude spectrum for higher order even terms with and without ship in place

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Figure 10

Experimental nonlinear difference component of free surface time history around bow (derived from (C+T)∕2)

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Figure 11

Nonlinear free surface around bow

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Figure 12

Incoming wave, first order diffracted wave, and complete first plus second order diffracted wave time history around the bow

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Figure 13

Second order sum frequency term of free surface at gauge 4 (510mm upstream)

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Figure 14

Second order difference frequency term of free surface at bow

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Figure 15

Spatial profiles for second order difference frequency component of the free surface

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