Deformation and stress distribution of floating collar of net cage in steady current

ABSTRACT A numerical model is developed to investigate the deformations and stress distribution of floating pipes of fish cage subjected to the flow. The modelling approach is based on the combination of the finite element method using the shell element to simulate the floating pipes and the hydrodynamic model improved from the Morison's equation and lumped-mass method. The hydrodynamic response of the fish cage and forces on the floating pipes can be obtained by the hydrodynamic model. The stress and deformation of the floating pipes can be calculated based on the finite element method. Employing an appropriate iterative scheme, the stress distribution and maximum stress of the floating pipes in high currents can be obtained using the proposed model. To validate the numerical model, the numerical results were compared with the data obtained from corresponding physical model tests. The comparisons show that the numerical results agree well with the experimental data. On that basis, the simulations of fish cage in currents were performed to investigate the maximum deformation and the stress distribution of the floating collars. Simulations of the fish cage in different flow velocity are performed to analyse the effect of the net and flow velocity on the deformations and stress of the floating pipes. The simulation results show that the stress and deformations drastically increase with the increase of flow velocity and the net has great influence on the stress distribution. Comparing results of floating pipes with different mooring line arrangements indicates that increasing mooring lines can efficiently lower the stress of the floating pipes. The simulations of the single-point mooring cage system with multiple net cages in current are performed and the results show that the middle cage is most dangerous for the tripartite-cage system.