Experimental and Numerical Analysis of Hydrodynamic Forces on Non-Traditional Net Types Used in Salmon Farming

Abstract On order to minimize their environmental impact and make use of more exposed sites, innovative types of nets, complementary to the traditional polyester nets, have been investigated. One of them are metallic nets made of a copper alloy that not only allow for the use of a single net, leaving behind the need of a predator netting system, but also reduce the presence of biofouling while better controlling the production volume due to its higher wet weight and axial stiffness compared to commonly used nets used in aquaculture operations. Another innovative type of net are low-porosity membranes, which are used to contain organic residues on the bottom of the cage or to constrain the exchange of water between the inside of the cage and the external flow, limiting the effects of diseases or sudden environmental changes on the biomass. Currently, there is a gap in the determination of hydrodynamic response on these innovative netting systems, considering typical operational and extreme conditions on aquaculture sites. Thus, the present work numerically simulates drag and lift forces on single nets considering a wide range of current speeds and angles of attack using the open-source CFD code REEF3D. The nets are implemented according to the Screen Force Model, where the hydrodynamical forces are estimated with an experimental data basis of drag and lift coefficients fitted into a truncated Fourier series, obtained from experiments at the Wave/Towing tank at Universidad Austral de Chile. The results emphasize the need to carry out experiments to describe drag and lift forces for each netting types before more complex scenarios are modeled while, since the initial results, using a generic formulation for drag and lift coefficients, lead to large errors on the numerical results, discrepancies that are reduced when the Fourier series specifically determined for the net are implemented on the numerical scheme.