Dynamic response of a single point mooring submersible fish cages in waves and current

Abstract

Submersible fish cages are designed for installing in the open sea sites that are subjected to violent sea conditions to reduce the hydrodynamic forces acting on the fish cages. To assess the dynamic responses of a single point mooring submersible fish cage under the rough sea conditions, a numerical model including hydrodynamic and structural methods is proposed. The waves and current are modelled using the airy wave theory. For the floating collars and sinker tube, the Morison model is adopted to calculate the hydrodynamic force and the modal superposition method is proposed to calculate the structural responses. For the aquaculture net, the screen model is adopted to calculate the hydrodynamic force and the extended position-based dynamics (XPBD) method is proposed to obtain the structural deformations. The hydrodynamic dynamic forces and the deformations of the fish cages are compared between the fish cages on water surface and in deep water. Results show that when the fish cage is submerged 20m from the water surface, the average horizontal force is reduced by 30% and the variation of the horizontal force is reduced by 81%. Significant reductions in the deformation of the floating collars are observed. Therefore, using submersible fish cage can help reduce physical stress and avoid structural damage for the fish cage system. In addition, the coupling of XPBD and MS can provide a quick solution for the structural modelling of the fish farm system, which can be utilized at the initial stage of fish farm design.