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Strutures, Safety and Reliability

Extreme Response of Very Large Floating Structure Considering Second-Order Hydroelastic Effects in Multidirectional Irregular Waves

[+] Author and Article Information
Xujun Chen1

Engineering Institute of Engineering Corps, PLA University of Science and Technology, Nanjing 210007, China; Centre for Ships and Ocean Structures, Norwegian University of Science and Technology, N-7491 Trondheim, Norwayxjchen@sjtu.edu.cn

Torgeir Moan

Centre for Ships and Ocean Structures, Norwegian University of Science and Technology, N-7491 Trondheim, Norway

Shixiao Fu

Centre for Ships and Ocean Structures, Norwegian University of Science and Technology, N-7491, Trondheim, Norway; State Key Laboratory of Ocean Engineering, Shanghai Jiao Tong University, Shanghai 200030, China

1

Corresponding author.

J. Offshore Mech. Arct. Eng 132(4), 041601 (Sep 23, 2010) (11 pages) doi:10.1115/1.4001415 History: Received April 06, 2008; Revised February 14, 2009; Published September 23, 2010; Online September 23, 2010

Hydroelasticity theory, considering the second-order fluid forces induced by the coupling of first-order wave potentials, is introduced briefly in this paper. Based on the numerical results of second-order principal coordinates induced by the difference-frequency and sum-frequency fluid forces in multidirectional irregular waves, the bending moments, as well as the vertical displacements of a floating plate used as a numerical example are obtained in an efficient manner. As the phase angle components of the multidirectional waves are random variables, the principal coordinates, the vertical displacements, and the bending moments are all random variables. Extreme values of bending moments are predicted on the basis of the theory of stationary stochastic processes. The predicted linear and nonlinear results of bending moments show that the influences of nonlinear fluid forces are different not only for the different wave phase angles, but also for the different incident wave angles. In the example very large floating structure (VLFS) considered in this paper, the influence of nonlinear fluid force on the predicted extreme bending moment may be as large as 22% of the linear wave exciting forces. For an elastic body with large rigidity, the influence of nonlinear fluid force on the responses may be larger than the first-order exciting forces and should be considered in the hydroelastic analysis.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Wave energy spectrum of the irregular waves

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Figure 2

Definition of the wave directions and the grid of the plate (m)

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Figure 3

Time histories of the maximum envelope vertical displacements (EI=4.77×1011 N m2)

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Figure 4

Time histories of the maximum envelope vertical displacements (EI=4.77×1012 N m2)

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Figure 5

Distortion of the floating plate for Case 1 at t=0 s for EI=4.77×1011 N m2

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Figure 6

Distortion of the floating plate for Case 1 at t=0 s for EI=4.77×1012 N m2

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Figure 7

Predicted maximum extreme value of bending moment Mxe of the floating plate for two cases

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Figure 8

Predicted maximum extreme value of bending moment Mye of the floating plate for two cases

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Figure 9

Predicted maximum extreme value of bending moment Mxye of the floating plate for two cases

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Figure 10

Difference of predicted maximum extreme value induced by linear and nonlinear forces

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Figure 11

Predicted extreme value of bending moments of point 4 for two cases

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Figure 12

Predicted extreme value of bending moments of point 5 for two cases

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Figure 13

Predicted extreme value of bending moments of point 6 for two cases

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Figure 14

Predicted extreme value of bending moments of point 7 for two cases

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Figure 15

Predicted extreme value of bending moment of point 8 for two cases

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