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

 

FABIEN LE BRIS and DOMINIQUE MARICHAL

 

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

 

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.

 

Key words: supple net, fluid-structure coupling problem, fish farm, aquaculture, plane panel of netting

 

Address correspondence to: D. Marichal

Received for publication on July 27, 1998; accepted on Jan. 5, 1999

 

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Introduction

 

Aquaculture may allow us to solve a number of problems in connection with the difficulties inherent in fisheries or in an excessive exploitation of natural re-

sources. Extrapolation of trends1 suggests that at the end of the first quarter of the next century, farmed fish production will have outstripped capture fisheries production and will be the most important means of providing fish for food. From this developed the idea of developing aquaculture in net cages in the coastal zone. However, nets are both discontinuous and anisotropic structures which can be considered as infinitely flexible. The permeability of the meshes allows a variable flow of water through the net, but the obstacle presented by

 

 

 

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