Comparative Study of Dynamics of Gravity Cages With Different Meshes in Waves and Current

Abstract

To investigate the dynamics of gravity cage, the finite element program Aqua-FE™, was applied to gravity cages with two different meshes, square-mesh net and diamond-mesh net. Two case studies are chosen to compare the dynamics of cages based on the numerical modeling techniques. The numerical models were developed in Aqua-FE™ to simulate the effects of waves and current. They were validated by comparison with water tank results. The comparison showed good agreement. In both case studies, we consider several loading conditions consisting of different uniform currents and monochromatic waves. Assuming that the system can be modeled as a linear system, we investigated the motion response (heave, surge and pitch) characteristics of the fish cages with square-mesh net and diamond-mesh net, their deformation and the resultant tension in mooring lines. For different wave conditions, we study the storm response of the two cages based on the response amplitude operators (RAOs). In particular, the length of the grid line has significantly effect on the motion of the cage and the tension in mooring lines in wave. In additional, the effect of the mesh shape on the motion of the cage and tension in mooring lines is also analyzed. The comparison results show that the surge motion of the fish cage with square-mesh net is significantly larger than that with diamond-mesh net.