| dc.description.abstract | The dynamic behaviors of fish cages are numerically studied to explore the safety issue of the aquaculture system. The hydrodynamic forces acting on the net panels are simplified into Morison forces acting on the net ropes. The structural responses of the fish cages and the mooring system are calculated using an extended position-based dynamics (XPBD) algorithm, where correction forces are added to improve the accuracy of the original XPBD. Two typical cases are involved in the present study: lifting operations of a fish cage during the de-lice or harvest operations and ultimate state analysis of multiple fish cages with a mooring system. In the case of lifting operations, the environmental loads are neglected due to the operational condition. The structural model of modified XPBD is validated against experimental results obtained from a flexible horizontal net. A time-step sensitivity study is conducted for the lifting operation of the fish cage. The results of the lifting operations reveal a rapid increase in lifting force due to the weight of the sinkers positioned at the bottom of the side net. Furthermore, it is observed that the maximum tension in the net occurs at the net ropes connected to the center point of the bottom net. The damaged fish cages with broken net ropes at the bottom net exhibit no significant changes in lifting force and net tension. However, structural reinforcements are recommended for the bottom net to ensure safe lifting operations. In the case of the ultimate state analysis of multiple fish cages with a mooring system, the environmental loads due to waves and currents are included to conduct the ultimate state analysis. The present modified XPBD is coupled with the Morison model, and the method is validated against the experimental results of a vertical net panel and a cage net. Grid and time-step sensitivity studies are conducted for the single fish cage with a mooring system. Results show that the maximum pitch angle of the floating collar and sinker tube, the horizontal displacement, and the vertical displacement are reached when the flow angle is 0 degrees. However, the maximum horizontal force is observed when the flow angle is 30 degrees and the maximum roll angle is observed when the flow angle is 45 degrees. The effect of regular and irregular waves on a single fish cage with a mooring system shows minimal changes in the maximum calculated values. However, when subjected to regular waves, the fish cage exhibits an increased pitch angle. Summarised from the two cases, the safety of the fish cage system can be enhanced by numerically exploring the operational activities and the ultimate state. | |
