The dragged surge motion of tension-leg type fish cage system subjected to multi-interactions among wave and structures

In this paper, a typical tension-leg type net cage system is analyzed, and a set of motion equations for the cage system in the simplified two-dimensional case is derived. Subsequently, a close form analytical solution is obtained when all of the multi-interactions between the top platform structure, the incident wave, and the motion of both the tether and net are considered. The parameter of solidity as a ratio of the twine diameter to the mesh size of the cage is also taken into account in the analysis. The purpose of this paper is to investigate the dragged surge motion of the tension-leg type cage system when subjected to incident waves and flow drags on the net-cages. Furthermore, the dynamic behavior of the platform is compared to the case when the net-cage drag is not considered. Numerical examples are carried out in a range of periods of waves, and the results are discussed focusing on the motion of both the platform and cage. It was found that there is a significant influence of the net-cage drag on the surge motion of the entire structural system. Various parameters such as the material property, twine diameter, mesh size and the dimension of the net-cages were considered. It was found that the vibration of the net-cage system might be significantly overestimated if the drag effect of the net and tethers is neglected.