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Numerical and experimental study of submerged supple nets: Applications to fish farms

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Abstract

Our aim is to investigate the behavior of submerged supple nets. This work generates many problems owing to the discontinuous and highly flexible nature of the nets. Only the action of external forces can bring an infinitely flexible structure like a net into a definite shape. When considering supple nets immersed in a fluid, these external forces themselves depend on the net geometry. A numerical method to solve this fluid-structure coupling problem is proposed, and is applied to fish farms. In order to validate the calculation model of the hydrodynamic forces on the mesh sides, we measured the hydrodynamic forces on a plane panel of netting spread across a transverse current. We thus proved that the Landweber model modified according to the Richtmeyer formula as regards friction gives good results. The calculated shape of the fixed net cage is qualitatively in accordance with flume tank observations. We have adapted the algorithm to the study of the dynamic behavior of floating fish farms.

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Abbreviations

ρ t :

specific mass of rigid elements

ρ:

specific mass of water

\(\vec g\) :

acceleration of gravity

D t :

cylindrical element diameter

ℓ:

cylindrical element length

E x :

solidity ratio

\(\overrightarrow {T_n }\) :

drag pressure force

\(\overrightarrow {F_t }\) :

tangential friction force

\(\overrightarrow {A_n }\) :

added mass force

C d :

pressure drag coefficient

C m :

added mass coefficient

f :

tangential friction coefficient

\(\overrightarrow {V_n }\) :

rigid element velocity projected on a plane perpendicular to the element (see Fig. 3)

\(\overrightarrow {\Gamma _n }\) :

rigid element acceleration projected on a plane perpendicular to the element (see Fig. 3)

\(\overrightarrow {V_t }\) :

tangential component of the relative rigid element velocity

C l :

lift coefficient

C D :

drag coefficient

ϕ:

angle of attack

β:

mesh opening

m i :

regular element mass affected to the knoti

m ik :

mass of the rigid bar “ik”

k :

adjacent knotk of the knoti

n i :

number of ajacent knots of knoti

\(\overrightarrow {\Gamma _i }\) :

acceleration of knoti

T ik :

tension of bar “ik”

ℓ ik :

length bar “ik”

\(\overrightarrow {F_{ik} }\) :

the whole external forces acting on the rigid bar “ik”

\(\overrightarrow {S_i }\) :

the whole external forces acting on knoti

M :

mass of the pontoon

J :

moment of inertia of the pontoon

\(\overrightarrow {V_G }\) :

velocity of the pontoon center of gravity (see Fig. 15)

Θ:

angle of rotation of the pontoon

Ω:

speed of rotation of the pontoon

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Authors and Affiliations

  1. Laboratoire de Mécanique des Fluides UMR CNRS 6598, Division Hydrodynamique Navale, Ecole Centrale de Nantes, BP 92101-44321, Nantes, Cedex 3, France

    Fabien Le Bris & Dominique Marichal

Authors
  1. Fabien Le Bris
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  2. Dominique Marichal
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Le Bris, F., Marichal, D. Numerical and experimental study of submerged supple nets: Applications to fish farms. J Mar Sci Technol 3, 161–170 (1998). https://doi.org/10.1007/BF02492931

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  • DOI: https://doi.org/10.1007/BF02492931

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