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Offshore and Structural Mechanics

Numerical Analysis of the Flotation Ring of a Gravity-Type Fish Cage

[+] Author and Article Information
Guo-hai Dong

State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning 116024, Chinaghdong@dlut.edu.cn

Shuang-hu Hao1

 China Offshore Oil Engineering Co. Ltd., No. 1078, DanJiang Road, Tanggu, P.O. Box 616, Tianjin 300451, Chinaerhu10@yahoo.com.cn

Yun-peng Zhao1

State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian, Liaoning 116024, China

Zhi Zong

School of Naval Architecture, Dalian University of Technology, Dalian, Liaoning116024, China

Fu-kun Gui

Marine Science and Technology School, Zhejiang Ocean University, Zhoushan 316000, China

1

Corresponding authors.

J. Offshore Mech. Arct. Eng 132(3), 031304 (Jul 19, 2010) (7 pages) doi:10.1115/1.4001416 History: Received August 22, 2008; Revised December 17, 2009; Published July 19, 2010; Online July 19, 2010

The gravity-type fish cage is extensively applied with the increasing demand for fishery products. The flotation ring is its main load-bearing component and supports the whole cage. So it is essential to study the hydroelasticity of the flotation ring for the safety of a fish cage. An analytical method is proposed to study the elastic deformation of a simplified flotation ring subjected to water waves. The equations governing in-plane deformations are obtained according to curved beam theory, in which the modal superposition method is used to represent the in-plane deformation of an element of the ring. Then, the motion equations of the ring are built up coupled with deformation equations. The correlation between the predicted results and the experimental data is acceptable to validate the numerical modeling. Then the effect of Young’s module, radius of the ring, and wave conditions on elastic responses is discussed in terms of the prototype scale of a flotation ring. It is concluded that the deformations over the ring in the direction of waves’ propagation are the largest, and that the mooring point in the head-on direction of the waves is critical for reliability of the ring. Large deformations of the flotation ring may induce the failure of the fish cage when the storm covers it. So more attention to the hydroelasticity of the flotation ring should be paid in the design for a fish cage.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Configuration of the ring

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Figure 2

Coordinate system of the ring

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Figure 3

Element of the ring

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Figure 4

Cross section of the ring

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Figure 5

Comparison of the numerical results with the experimental data with different coefficients in the model (the top is about xg, and the bottom is about zg)

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Figure 6

History of ξ2 with wave height 0.34 m and wave period 2.0 s in model

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Figure 7

Histories of u at point 1 and ξ2 with H 2.0 m and T 5.37 s in prototype

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Figure 8

Histories of u at point 1 with variable modulus of elasticity with H 2.0 m and T 5.37 s in prototype

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Figure 9

Histories of u at point 1 with variable radii with H 2.0 m and T 5.37 s in prototype

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Figure 10

Period responses of radial deformations with H 2.0 m

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Figure 11

Histories of u at points 1, 2, 3, 4, and 5 with H 7.0 m and T 8.94 s in prototype

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Figure 12

History of the maximum tensile stress at points 1, 2, 3, 4, and 5 with H 7.0 m and T 8.94 s in prototype

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