Abstract
Experiments in a laboratory tank have provided measurements of the normal and tangential drag forces exerted on flat nets for different flow conditions. From those forces, normal and tangential drag coefficients of the nets have been obtained as functions of the Reynolds number and the solidity index. The experiments used two types of nets employed in the operation of a cultivation center: the fish net and the sea lion net, for the clean situation and for real operating conditions, with fouling adhered to the nets. Polyethylene ropes were used to characterize the presence of fouling in the nets. The experiments were carried out to determine equations for the normal and tangential drag coefficients. For the normal drag coefficient, the equations are linear with the Reynolds number, and the coefficients of the equations are linear with the solidity index. The equations are not so accurate for the tangential drag coefficient. The Reynolds number is not a relevant parameter for this coefficient and neither is the solidity index for the fish net, but the coefficient grows slightly with it for single and double sea lion nets with fouling. The literature review on the drag forces of nets reports that the tangential drag force is around 30% of the normal drag force. This value is approximately an average value of the ratio for the sea lion net and is higher for the clean fish net in this article.
Highlights
Fish farming in the aquaculture industry is commonly done through cages
(i) empirically establish the ratio between CDn and CDt accounting for different types of nets with a wide range of solidity index; (ii) both coefficients are crucial for force predictions in numerical simulations on highly flexible nets subjected to uniform pressure; (iii) the damping matrix in a finite element formulation scheme of the dynamic response of a net depends on both coefficients; and (iv) account for the effects of currents on force predictions that are not normal to the surface under study
The experiments used two types of nets employed in the operation of a cultivation center: the fish net and the sea lion net, for the clean situation and real operating conditions, with fouling adhered to the nets
Summary
Fish farming in the aquaculture industry is commonly done through cages. These are structures constituted by a buoyant frame that, afloat in the sea, supports a cell formed by nets in whose interior the species to be cultivated is confined. Other studies use nets with three-dimensional arrangements, as is the case of the works of [2,11,12,13], which study the force that resists a cage of the cylindrical type Through experiments of this style, it is possible to perform more refined analyses that incorporate studies of the hydrodynamics of the flow around the nets [11,14] or to study the complete response presented by the physical model against a request for hydrodynamic drag [9,10]. The experiments carried out considered two cases: the determination of normal and tangential drag forces, which are two types of different forcing to which the cultivation centers are exposed; the results were translated to characteristic values of the drag coefficients for clean and fouling nets. This is another point in which the article is innovative
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