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Zhao HeSupervisor: Odd M. Faltinsen

The influence of fish on the mooring loads of a floating fish farm

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• Dead fish experiment

• Simulations related to the dead fish experiment

• Real fish experiment

• Simulations related to the real fish experiment

• Conclusions

ExperimentsAnd

Simulations

• Realistic background

• Theoretical assumptionsBackground

Outline

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Realistic background• 1. The total volume of the fish is 2.5% of the fish cage• 2. The fish keep static and against to the flow in strong current

Background

Theoretical background• Assumptions

– The wake flow is cancelled out by the jet flow– The fish body is rigid and each cross-section is circular– All the fish have the same dimension– The slender body theory in potential flow can be applied

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The dead fish experiment

The equipment setupDescription Parameter Model scale 

Floater diameter D 1.5m

Net depth H 1.3m

Cross‐sectional diameter of floater

Net solidity ratios                                 

Diameter of net twines 

Mass of bottom weights in air 

  

d

  Sn 

 dw 

   Mbw 

30mm

0.32 

0.6 0.8mm  

16 75g 

Experimental scale   1:25

 

9 fish with the total volume of 2.5% of the fish cage.

Net cage description

Fish model description

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Varification of the equipment setupThe dead fish experiment

Comparison with Trygve’s experiment(No fish inside)

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The influence of the 9 fish model

The dead fish experiment

For weight1(16*75g)

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The influence of the 9 fish model

The dead fish experiment

For weight2(16*75g+16*25g)

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The numerical model

Simulations related to the dead fish experiment

Figure1. Coupled model from net to fish Figure2. Coupled model from fish to net

Figure3. Strips for the fish model

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Simulations related to the dead fish experiment

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Experimental model

• The diameter of the top of the fish net D1=1.5m; • The depth of the cylinder part H1=0.77m; • The depth of the cone part H2=0.417m;• The diameter of the bottom circle D2=1.24m ;• The volume of the cage: ;• Solidity ratio: Sn=0.32;

Real fish experiment

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Fish1 Fish2

Real fish experiment

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Photo for the current case: U=0.16m/s

Real fish experiment

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Comparison of the three casesFor two minutes run

Real fish experiment

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Comparison of the three cases

For four minutes run

Real fish experiment

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Further discussion about the difference

The fish touched the bottom net

Real fish experiment

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Before the wave After the wave

The fish gather to the center of the net after the wave.

Real fish experiment

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Results for the experiments in wave and current

The fish gather to the center of the net in wave

Less touching in wave and current

Smaller effect in wave and current

Real fish experiment

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Underwater photos

with wave and current Current only

Real fish experiment

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Comparison with Pål Lader’s experiment(no fish in side)

Simulations related to the real fish experiment

Numerical simulation of closed bottom net

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Comparison with my experiment(No fish in side)

Numerical simulation of closed bottom net

Simulations related to the real fish experiment

10% overpredict

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Sensitivity study

Simulations related to the real fish experiment

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Displacement effect of the fish school

9 fish located as in the dead fish experiment

Simulations related to the real fish experiment

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Hydrodynamic influenc of the fish school in rigid net562 fish in paralleled distribution

814 fish in diamond-shape

Simulations related to the real fish experiment

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Further discussion about the difference

U=0.04m/s U=0.05m/s U=0.06m/s U=0.08m/s U=0.10m/s

Simulations related to the real fish experiment

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Simulations related to the real fish experimentFurther discussion about the difference

Results based on the simulation Results from the real fish experiment

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Conclusion

• The hydrodynamic influence of the fish school to the fish cage in strong current is small(around 3%).

Conclusion

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Reference1. Kristiansen, T. and Faltinsen, O. M., 2012. Modelling of current loads on aquaculture net cages. Journal of

Fluids and Structures.2. Kristiansen, T. and Faltinsen, O. M., 2012. Mooring loads of a circular net cage with elastic floater in waves

and current. 6th International conference on Hydroelasticity in Marine Technology.3. Lader, P., Moe, H., Jensen, Ø., Lien, E., 2009. Nøter med høy soliditet - modellforsøk. Technical Report.

SINTEF Fisheries and Aquaculture (In Norwegian).4. Newman, J. N. and Wu, T. Y., 1973. A generalized slender-body theory for fish-like forms. Journal of Fluid

Mechanics.5. Newman, J. N., 1973. The force on a slender fish-like body. Journal of Fluid Mechanics.6. Tuck, E.O. and Newman, J.N., 1974. Hydrodynamic interaction between ships. In Proceedings of the 10th

Symposium on Naval Hydrodynamics, Cambridge, MA, USA, pp. 35–70.7. Blevins, R. D., 2003. Applied fluid dynamics handbook. Krieger publishing company, Malabar, Florida.8. Ersdal, S., 2004. An experimental study of hydrodynamic forces on cylinders and cable in near axial flow. Ph.D

thesis in NTNU.

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Thanks!

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