Search Results (3)

Due to the limitations of farming space, fish cage aquaculture is gradually expanding into offshore deep-sea areas, where the environmental conditions surrounding deep-sea fish cages are more complex and harsher compared to those in shallower offshore locations. Conventional multi-point moored gravity flexible fish cages are prone to damage in the more hostile environments of the deep sea. In this paper, we present a design for a single-point mooring vessel-shaped fish cage that can quickly adjust its bow direction when subjected to waves from various angles. This design ensures that the floating frame consistently responds effectively to wave impacts, thereby reducing the wave forces experienced. The dynamic response of the floating frame and the mooring forces were simulated by coupling the Smoothed Particle Hydrodynamics method with the Moordyn numerical model for mooring analysis. The three degrees of freedom (heave, surge, and pitch) and the mooring forces of a scaled-down vessel-type ship cage model under wave conditions were investigated both numerically and experimentally. The results indicate that the error between the simulation data and the experimental results is maintained within 6%. Building on this foundation, the motion response and mooring force of a full-sized ship-shaped net box under wave conditions off the southeast coast of China were simulated. This study examined the effects of varying mooring lengths and buoy configurations on the motion response and mooring force of the fish cage. Finally, we constructed the fish cage and tested it under the influence of a typhoon. The results demonstrate that the fish cage could operate stably without structural damage, such as mooring failure or floating frame breakage, despite the significant deformation of the floating frame. Full article

The volume of a gravity cage is greatly reduced under a current due to the flexible structure, which affects the growth and health of the fish. Thus, an accurate assessment of cage volume is essential to determine the number of fishes in the cage. In this study, firstly, a numerical model was built to study the cage volume reduction of gravity cages due to the flexible net deformation when subjected to uniform flow. The remaining volume was calculated and compared with earlier experiments. Even though the flow velocity reductions were considered according to the data from previous experiments, the differences between the results from the numerical calculation and the towing tests are still significant. The physical model tests were treated as the reference value to investigate the uncertainty of the model results. Both the velocity-independent model error and velocity-dependent model error were calculated. With the help of the error models, the uncertainty of the remaining volume can be predicted. In addition, the velocity-dependent model error performs better in evaluating the uncertainty of the numerical calculation of the remaining culturing volume. Overall, the results show that the numerical model assisted by the model errors can calculate the cage volume accurately. Full article

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. Full article