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

Transcription

1 The influence of fish on the mooring loads of a floating fish farm Zhao He Supervisor: Odd M. Faltinsen 1

2 Outline Realistic background Background Theoretical assumptions Dead fish experiment Simulations related to the dead fish experiment Experiments And Simulations Real fish experiment Simulations related to the real fish experiment Conclusions 2

3 Background 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 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 3

4 The dead fish experiment The equipment setup Net cage description Description 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 mm 16 75g Experimental scale 1:25 Fish model description 9 fish with the total volume of 2.5% of the fish cage. 4

5 The dead fish experiment Varification of the equipment setup Comparison with Trygve s experiment(no fish inside) 5

6 The dead fish experiment The influence of the 9 fish model For weight1(16*75g) 6

7 The dead fish experiment The influence of the 9 fish model For weight2(16*75g+16*25g) 7

8 Simulations related to the dead fish experiment The numerical model Figure1. Coupled model from net to fish Figure2. Coupled model from fish to net Figure3. Strips for the fish model 8

9 Simulations related to the dead fish experiment 9

10 Real fish experiment 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; 10

11 Real fish experiment 11 Fish1 Fish2

12 Real fish experiment Photo for the current case: U=0.16m/s 12

13 Real fish experiment Comparison of the three cases For two minutes run 13

14 Real fish experiment Comparison of the three cases For four minutes run 14

15 Real fish experiment Further discussion about the difference The fish touched the bottom net 15

16 Real fish experiment Before the wave After the wave 16 The fish gather to the center of the net after the wave.

17 Real fish experiment 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 17

18 Real fish experiment Underwater photos with wave and current Current only 18

19 Simulations related to the real fish experiment Comparison with Pål Lader s experiment(no fish in side) Numerical simulation of closed bottom net 19

20 Simulations related to the real fish experiment Comparison with my experiment(no fish in side) 10% overpredict Numerical simulation of closed bottom net 20

21 Simulations related to the real fish experiment Sensitivity study 21

22 Simulations related to the real fish experiment Displacement effect of the fish school 9 fish located as in the dead fish experiment 22

23 Simulations related to the real fish experiment Hydrodynamic influenc of the fish school in rigid net 562 fish in paralleled distribution 814 fish in diamond-shape 23

24 Simulations related to the real fish experiment 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 24

25 Simulations related to the real fish experiment Further discussion about the difference Results based on the simulation Results from the real fish experiment 25

26 Conclusion Conclusion The hydrodynamic influence of the fish school to the fish cage in strong current is small(around 3%). 26

27 Reference 1. Kristiansen, T. and Faltinsen, O. M., Modelling of current loads on aquaculture net cages. Journal of Fluids and Structures. 2. Kristiansen, T. and Faltinsen, O. M., 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., Nøter med høy soliditet - modellforsøk. Technical Report. SINTEF Fisheries and Aquaculture (In Norwegian). 4. Newman, J. N. and Wu, T. Y., A generalized slender-body theory for fish-like forms. Journal of Fluid Mechanics. 5. Newman, J. N., The force on a slender fish-like body. Journal of Fluid Mechanics. 6. Tuck, E.O. and Newman, J.N., Hydrodynamic interaction between ships. In Proceedings of the 10 th Symposium on Naval Hydrodynamics, Cambridge, MA, USA, pp Blevins, R. D., Applied fluid dynamics handbook. Krieger publishing company, Malabar, Florida. 8. Ersdal, S., An experimental study of hydrodynamic forces on cylinders and cable in near axial flow. Ph.D thesis in NTNU. 27

28 Thanks! 28