J. Kor. Soc. Fish. Tech., 46 (1), 020 031, 2010 DOI:10.3796/KSFT.2010.46.1.020
Dynamic behavior of a submersible fish cage rigged with a circular floating and a sinking collar
Chun-Woo LEE*, Jihoon LEE1, Moo-Youl CHOE2and Gun-Ho LEE3
*Division of Marine Production System Management, Pukyong National University, Busan 608-737, Korea
1Institute of Low-Carbon Marine Production Technology, Pukyong National University, Busan 608-737, Korea
2Department of Fisheries Physics, Pukyong National University, Busan 608-737, Korea
3Fisheries Engineering Division, National Fisheries Research and Development Institute, Busan 619-705, Korea
In this research, the submersible fish cage was designed to avoid structural and biological damage during harsh sea conditions. The submersible cage system consists of netting, mooring ropes, a floating collar, floats, sinkers and anchors. Whole elements of the cage were modeled on the mass-spring model. The computer simulations were carried out to investigate the dynamic behavior of the cage and to calculate mooring line tension subjected to tidal currents and waves. As expected, the tension values in the mooring line of the submerged position are 36% less compared to that of the surface cage under the same loading conditions. As the wave was used in combination with the current velocity of 1m/s, the average tensile load for the submerged cage showed 85% of the value for the floating cage. The simulation results provide an improved understanding of the behaviors of the structure and valuable information on the optimized design of the cage system exposed to open ocean environmental factors.
Key words: Submersible fish cage, Underwater flexible structures, Dynamic simulation, Sinking collar, Floating collar
*Corresponding author: [email protected], Tel: 82-51-629-5891, Fax: 82-51-629-5886
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Fig. 1. Modeling of the fish cage net, the mooring line and the floating collar.
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Table 1. Physical characteristics of calculation parameters of the cage system
Items Specifications
Floating collar Material
Diameter of tube (mm) Thickness of tube (mm) Total buoyancy (N) Diameter of collar (m) Sinking collar
Material
Diameter of tube (mm) Thickness of tube (mm) Total sinking force (N) Diameter of collar (m) Netting
Material Density (g/cm3) Twine diameter (mm) Mesh size (mm) Total mass (kg) Mooring lines
Material Diameter (mm) Buoys
Material Size (m) Buoyancy (N) Number of pieces
PE 370 20 71,712 28
PE 370 20 20,781 25
DYNEEMA 0.96 1.8 22.5 576.9
PES 50
Plastic 1.7262 1.15 19,600 4
Fig. 2. The top view (a) and the side views of the fish cage in still water (b) at the surface position and (c) at the submerged position. A: referenced point for the tension values.
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Table 2. Simulation conditions of the fish cage
Case 1 Case 2 Case 3
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Floating collar position Surface
Submerged (20m below the surface)
Current (m/s) 0.5, 1 1 0.8
Height (m) 6 6
Wave Period (sec) 20 10
Length (m) 156 156
Breaking strength of the
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Fig. 3. The side views of the floating fish cage in surface position when the uniform tidal currents of (a) 0.5m/s and (b) 1.0m/s are applied.
Fig. 4. The side views of the floating fish cage in sub- merged position when the uniform tidal currents of (a) 0.5m/s and (b) 1.0m/s are applied.
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Fig. 5. Variations in tension acting on the upper side mooring line at the point A in fig. 2 for the cage at the surface and submerged positions under different environmental loading conditions.
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Fig. 6. Successive side shapes of the cage at surface position when current of 1.0m/s and waves (height: 6m, period: 20sec and length: 156m) are applied simultaneously.
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Fig. 7. Successive side shapes of the cage at submerged position when current of 1.0m/s combined with waves (height: 6m, period: 20sec and length: 156m) are applied.
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Fig. 8. Simulation of fatal damage by breaking the mooring lines of the cage due to strong current (0.8m/s) and waves (height:6m), (a): start to breaking the mooring line, (b) (d): increased loads transferred to the remaining lines and breaks one by one, (c): whole system swept away.
(a)
(c)
(e)
(d) (b)
.
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(PS-2006-027) .
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