In this study, the k-ω SST model is applied to analyze the vortex structure around the net cage in current. To validate the numerical simulation, a series of physical model tests were conducted. The results indicate the numerical model can accurately simulate the flow field around the net cage. The effect of net solidity on the flow pattern around the net cage is investigated by numerical simulation. The results indicate that the same net solidity may produce different vortex pattern around the net cage. A vortex first appears near to the net mesh and then a large-scale vortex appears in the wake region after the fish cage.
As the rapid improvement of people's living standard, the demand for the aquatic product is increased significantly. According to the report of the Food and Agriculture Organization of the United Nations, the demand for aquatic product can't be satisfied by marine fishing without causing the fish species to be endangered. In fact, the overfishing has led to a sharp decline in the wild fish stock, and the marine aquaculture industry is playing an important role for meeting the increasing demand of the aquatic product. The cage culture of marine fish has become one of the most important forms of aquatic product around the world. Numerous studies have shown that the force on the net cage is proportional to the square of the flow velocity. A small velocity differences may lead to a large force differences, therefore, it is necessary to analyze the velocity distribution around the net cage, especially the region close to the net mesh.
To our knowledge, the research on the interaction between the net cage and the environment has focused on the effects of currents and waves on the net cage. Tsukrov et.al (2003) proposed a numerical model to analyze the hydrodynamic response of net panels to environmental loading with the concept of consistent finite element. Lader and Fredheim (2006) investigated dynamic properties of a flexible net sheet exposed to waves and current by numerical simulation, in which the net was modeled by dividing it into super elements. Balash et.al (2009) measured the hydrodynamic loads on plane net of differing mesh geometry, and proposed an empirical formula for calculating the drag force and lift force. Kristiansen and Faltinsen (2012) proposed a screen type of force model for the viscous hydrodynamic load on nets, in which the net is divided into a number of flat net panels, or screens. Fredriksson et.al (2007) developed a finite-element modeling techniques to determine the structural capabilities of net pen, in which the critical loading conditions are predicted. In addition, the mechanical performance of net material used in the net cage structure was also analyzed. Moe et.al (2007) established a new method to investigate the tensile stiffness properties of knotless netting material.