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Gravity-type fish cages are playing an increasingly important role in fishery aquaculture. As the main load-bearing component of gravity-type fish cages, the floating collar supports the whole cage and undergoes large deformations. In this paper, a numerical method is developed to study the motions and elastic deformations of an HDPE floating collar in waves. The governing equations of motions are established by Newton׳s second law, and those governing the deformations are obtained according to the curved beam theory and the modal superposition method. Damping of the elastic deformations is introduced and analysed in detail to improve the numerical model. To validate the numerical model, a series of physical model tests are conducted. Good agreement between the numerical and experimental data is obtained. The numerical results indicate that the in-plane and out-of-plane deformations calculated using the first four modes yield satisfactory precision. The positions of the maximum deformations in different wave propagation directions and the effect of the forms of the mooring line arrangement have also been investigated. The numerical results show that the four-point-mooring cage is more reliable than the single-point-mooring cage. The endpoints of the diameters that are parallel or perpendicular to the wave direction have the largest deformation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Interaction between the flow and net cages is simulated using an iterative scheme. [•] Flow through a net cage is studied considering the fluid–structure interaction. [•] Application of the present numerical approach to multiple net cages is presented. [Copyright &y& Elsevier]

Abstract: A numerical approach is proposed to simulate the interaction between flow and flexible nets in steady current. The numerical approach is based on the joint use of the porous-media model and the lumped-mass model. The configuration of flexible nets can be simulated using the lumped-mass model and the flow field around fishing nets can be simulated using the porous-media model. Using an appropriate iterative scheme, the fluid–structure interaction problem can be solved and the steady flow field around flexible nets can be obtained. In order to validate the numerical models, the numerical results were compared with the data obtained from corresponding physical model tests. The comparisons show that the numerical results are in good agreement with the experimental data. Using the proposed numerical approach, this paper presents the flow field around a single flexible net and two flexible nets with a spacing distance. Both the configuration of the flexible nets and the flow velocity results are in accordance with those of the corresponding physical model tests. [Copyright &y& Elsevier]

Abstract: Numerical simulation is performed to analyze the hydrodynamic response of a net cage and submerged mooring grid system exposed to waves and current. A series of experiments are conducted to validate the numerical model of net cage and grid mooring system. The numerical results of this model correspond with those obtained from experimental observations. Then, the numerical simulation of a multi-cage and mooring system under the action of waves combined with current is conducted. The influence of waves and current directions and the length of grid lines on the cage responses are discussed. The twin mooring system and the orthogonal mooring system are compared. Results show that for the orthogonal mooring system, the maximum tension force on the anchor line of the four-cage system is less than four times of that of the single-cage system, when both waves and current travel along the x-axis. The minimum net cage volume holding coefficient of the single-cage system is smaller than that of the four-cage system. The amplitude of the mooring line tension force for the twin mooring system is larger than the orthogonal mooring system. [Copyright &y& Elsevier]

Abstract: A three-dimensional (3D) numerical model is established to simulate the flow field around fishing plane nets in a current. The realizable k–ε turbulence model was chosen to describe the flow, and the governing equations are solved by using the finite volume method. In this model, the net is modeled using the porous media model. The unknown porous coefficients are determined from the hydrodynamic forces on the net and from the flow velocities and the attack angles using the least squares method. In order to validate the numerical model, the numerical results were compared with the data obtained from two physical model tests. The comparisons show that the numerical results are in good agreement with the experimental data. This numerical model is applicable for the simulation of the flow field around a fishing net. Using the proposed method, this paper presents the flow field around a plane net with different plane net inclination angles, plane net heights, spacing distances between two plane nets and plane net numbers. This study provides information about the flow field around the fishing net cage. [Copyright &y& Elsevier]

Abstract: A numerical model of box-shaped net cage is built based on the lumped mass method and the principle of rigid body kinematics. To validate the numerical model, a series of physical model tests are conducted in the wave flume. The numerical results agree well with the data obtained from physical model test. The mooring line force and motion of a box-shaped net are simulated in pure waves and steady current by numerical model and physical experiments. In order to analyze the effect of cage shape on dynamic responses, net cages with a box and column shape are simulated and compared in pure waves and current. The results indicate that the net cage with column shape is more stable and reserve more breeding volume than that with box shape in waves and current action. [Copyright &y& Elsevier]