Hydrodynamic Behaviors Of Deep-water Gravity Cage

To satisfy the global need for seafood, marine aquaculture is expected to play an increasing role as wild fish stocks decline due to environmental degradation and over-fishing. The deep-water sea cage industry developed fast in domestic. However, theoretical researches on the hydrodynamic behaviors of sea cages leg behind the applications. Safety and security of sea cages deployed in open ocean are lack of assurance. As a result, a national 863 high technology project has been initiated to develop basic researches on the hydrodynamic behaviors of open ocean sea cages and to establish an open ocean aquaculture industry. This dissertation is based on the National Natural Science Fund Project and the National 863 High Technology Development Plan Project of author's supervisor.The contents are mainly composed of five parts. In the first part, the author gives a general description on the development and prospects of open ocean aquaculture industry and relative researches. The second part is about basic researches including the similarity criterion of fishing net models and experimental technologies. Innovation achievements are obtained including the similarity criterion for fishing net and the CCD dynamic image technique. The third part is the main work about experimental researches on a gravity sea cage, in which the hydrodynamic behaviors of the plane fishing net and the floating system are discussed. Also, the influence of weight systems on the hydrodynamic behaviors of gravity cage are presented. Numerical researches are also developed to simulate the responses of the floating system under pure wave conditions. Values of drag coefficients are obtained, which will be useful to calculate the wave forces on small-sized floating structures, such as sea cages and floating oil pipes. This work is innovative in this field. In addition, the researches on weight system will give guidance to the design of weight style and weight size of gravity cage. In the following part, the author gives a comprehensive comparison on the hydrodynamic behaviors of three different styles of cages: gravity cage, Sea-station cage and Quasi-sea-station cage. Gravity cage is recommended in domestic based on the comparisons of hydrodynamic behaviors, prices, convenience of management, environment loads and our country's realities. In the last part, the author summarized the achievements and the limitations. Prospects of open ocean aquaculture are discussed at the end of the dissertation.