Abstract
Over the last decades, the aquaculture sector increased significantly and constantly, moving fish-farm plants further from the coast, and exposing them to increasingly high forces due to currents and waves. The performances of cages in currents and waves have been widely studied in literature, by means of laboratory experiments and numerical models, but virtually all the research is focused on the global performances of the system, i.e., on the maximum displacement, the volume reduction or the mooring tension. In this work we propose a numerical model, derived from the net-truss model of Kristiansen and Faltinsen (2012), to study the dynamics of fish farm cages in current and waves. In this model the net is modeled with straight trusses connecting nodes, where the mass of the net is concentrated at the nodes. The deformation of the net is evaluated solving the equation of motion of the nodes, subjected to gravity, buoyancy, lift, and drag forces. With respect to the original model, the elasticity of the net is included. In this work the real size of the net is used for the computation mesh grid, this allowing the numerical model to reproduce the exact dynamics of the cage. The numerical model is used to simulate a cage with fixed rings, based on the concept of mooring the cage to the foundation of no longer functioning offshore structures. The deformations of the system subjected to currents and waves are studied.
Highlights
The aquaculture sector has been characterized by a significant increase in production and revenue over the last decades
We investigated the response of a fish farm new with respect to those treated so far in the sector, represented by a net cage fixed at the top and at the bottom, to two rigid rings)
Simulations show expected major displacements of the frontal and back points of the net in the sea current and wave direction, while unexpected displacements of the lateral points have been found in the crossflow direction, toward the center of the net
Summary
The aquaculture sector has been characterized by a significant increase in production and revenue over the last decades. Organization of the United Nations on fish consumption [1] showed that fish-farming provides more than 40% of the fish production in 2015. While fish capture amount remained constant in the period 2008–2015, fish farming was characterized by a constant rise. This trend required fish-farm plants to be larger and located in offshore sites, where they are exposed to stronger actions [2]. The performances of fish-farm cages have been analyzed both experimentally and numerically, with a large focus on the determination of the hydrodinamic coefficients of the net, forced by currents or waves. Numerical models (validated experimentally) have been applied to the study and design of real fish cages, including floating top rings, mooring elements, or coupling multiple cages
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