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Title: | Numerical study of a flow over and through spherical fish cage | Authors: | Cuong Mai Bui | Keywords: | Seafood demand;Offshore aquaculture;Mooring system;Submersible type | Issue Date: | 2018 | Abstract: | There has been a dramatic growth in seafood demand in recent years, leading to a development of offshore aquaculture. Offshore aquaculture is seen to possess various superiorities over traditional inland one; these include for example being away from contaminant sources, ensuring a healthy environment for fish and less harmful to the aquatic ecosystem. However, in order for an offshore fish cage to operate under violent conditions such as strong currents high waves and storms, its mechanical frame and mooring system must be able to sustain the mechanical load on it. It is therefore necessary to investigate the interaction between the current and the cage, typically the characteristics of and the factors affecting the flow over and through it. In this thesis, a numerical approach is employed; and the flow over and through a single cage and several cages arranged in different patterns is investigated in detail. The cage’s design is of a spherical and submersible type, however, here it is assumed to be totally submerged in the water. The spherical cage is modeled as a hollow sphere with its wall being a thin and porous layer, which represents the net and the mechanical frame. The porosity of this layer is estimated based on practical design of this type. Other characteristic parameters of the porous medium are determined by fitting with results of the flow field available in the literature. For the purpose of verification of the numerical approach, simulation of a flow over a solid sphere is conducted. It is noted that when the porosity approaches zero, a situation when complete bio-fouling happens, the cage resembles the solid sphere. Special focus is on the flow inside the cage/cages, where the low is observed to weaken, reducing the exchange of well-oxygenated water and nutrients. Effect of the bio-fouling phenomena is also investigated by associating them with a porosity; drag force acting on the cage is computed accordingly. Moreover, it is found that there exists a velocity reduction zone behind a single cage; it is narrow but long. Other cages that happen to be within this zone can experience a severe velocity reduction. Several patterns of cages’ arrangement are additionally analyzed, and among them, the staggered pattern is recommended. |
URI(1): | http://epub.vgu.edu.vn/handle/dlibvgu/744 |
Appears in Collections: | Computational Engineering (CompEng) |
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