Current forces on, and water flow through and around, floating fish farms (original) (raw)
Abstract
The wake generated by a screen or a net is analysed by the linear free-wake equations in conjunction with an eddy viscosity formulation. The behaviour of the near and far-field wake is investigated, and a relationship between the drag coefficient and the wake velocity is derived. A method for calculating the current forces experienced by the net structure and the resulting deformation is derived and compared with model tests. The effects of the wake behaviour and the deformation of the net cages, on the design and operation of floating fish farms are discussed and some recommendations are given.
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Abbreviations
A :
Area of a net panel
d_A_:
Area of a portion of a net panel
A N :
Area of the net panel normal to the flow direction
A P :
Area of the net panel parallel to the flow direction
CD,i :
Drag coefficient of the_i_ th cylinder
CD(α):
Drag coefficient as function of the angle between the normal to the net and flow direction
CL(α):
Lift coefficient as function of the angle between the normal to the net and flow direction
D :
Diameter
D i :
Diameter of the_i_ th cylinder
DO :
Dissolved oxygen concentration
F D :
Drag force
F L :
Lift force
H:
Heaviside function
L :
Width of net panel
l i :
Length of the_i_ th cylinder
N :
Number of cylinders
N i :
Number of cylinders in y-direction
N j :
Number of cylinders in z-direction
N N :
Number of cages in direction normal to the flow
N C :
Number of cages in direction of the flow
r=u/U :
Velocity reduction factor
Rn=U*D/v:
Reynolds number
Sn:
Solidity ratio, defined as the ratio between the area covered by the threads and the total area of the net panel
t :
Time
U :
Current or free flow velocity
u 1=U−u:
Velocity defect
u=U−u 1 :
Wake velocity
x,y,z:
Cartesian coordinate system or field point for calculation of velocity
x i ,y i ,z i :
Source point on screen element
α:
Angle between the flow direction and the normal vector to the net, in the direction of the flow
ɛτ:
Eddy viscosity
λ:
Mesh size
ν:
Kinematic viscosity
ρ:
Density of water
Φ:
Error function
∂:
Partial differential operator
∞:
Infinity
References
- Aarsnes, J.V., Rudi, H. and Løland, G. (1990) Current forces on cage, net deflection. In:Engineering for Offshore Fish Farming (ed. The Institution of Civil Engineers) Thomas Telford, London. pp. 137–152.
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Authors and Affiliations
- Norwegian Marine Technology Research Institute (MARINTEK), Valentinlyst, P.O.B. 4125, 7002, Trondheim, Norway
Geir Løland
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Løland, G. Current forces on, and water flow through and around, floating fish farms.Aquacult Int 1, 72–89 (1993). https://doi.org/10.1007/BF00692665
- Issue date: September 1993
- DOI: https://doi.org/10.1007/BF00692665