54 JUNE 2015 • WORLD AQUACULTURE • WWW.WAS.ORG solution. Innovative designs and material study on supple structures used for netting that enable cage systems to tolerate oceanic forces are needed. Furthermore, a cage must be able to create a habitable environment for rearing species that is also economical. Physical and numerical studies have been carried out. The dynamic behavior of floating circular and square net cages was tested on a physical model and numerically with a spring mass model (Lee et al. 2008). Installing cages in a row is more advantageous due to a screening effect (Cheng et al. 2008). The influence of water depth on deformation of cages was evaluated by Huang et al. (2008). Cages installed in shallow waters had greater drag and increased volume deformation than those installed in deep water. The objective of this research was to analyze the hydrodynamic responses of two types of physical model of net cage, each with a different ballast weight system. The effect of currents and waves in two model cages with different ballast weight methods were studied in detail in a flume tank to evaluate the effect of current and in a towing tank to evaluate the effect of waves. Cage aquaculture in marine and freshwater plays an important role in seafood production. Strong environmental forces such as tidal waves and currents are major observable problems, especially offshore, and are accountable for substantial deformation net cages. The structural strength of a cage in the open ocean is predominantly governed by various environmental factors. Installation and use of offshore cage systems requires understanding of impacts caused by harsh environmental conditions to take into account their effect on design and construction. On one hand, water current is important for the dispersion of metabolic wastes and to maintain water quality. On the other hand, it has a negative influence on supple structural elements of the cage, and of course, on stocked fish. A cage should not be placed in areas where the current speed is greater than 1 m/s (Huang et al. 2006). Moreover, at a current speed of 1 m/s, a 30-50 percent volume reduction was observed. This situation requires skilled scientists, engineers, researchers and producers to collaborate and seek an environmentally friendly A Study on the Deformation and Response of Model Fish Cages in Currents and Waves Gebremeskel Eshetu Kebede, Chun Woo Lee, Jihoon Lee and Subong Park FIGURE 2. Flume tank (a) and towing tank (b). FIGURE 1. Model net cages with a sinking collar (a) and independent ballast weights (b). A. B. A. B.
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