| In recent years, with the continuous growth of the population and the standards of our living, the demand of aquatic products is increasing rapidly. Exploiting marine fishery resources is an important measure to solve the tension between supply and demand by the way of "Marine Ranching". In our country, the developing and utilizing marine resources have been promoted to a national strategy. The national Twelfth Five-year Plan specifically asks for giving great impetus to the continuous exploitation of marine fishery. In the past twenty or thirty years, the rapidly developing mariculture has become the essential source for human food and a new economic growth point. However, the influence of human activities results in poor water circulation and serious environmental pollution, which subsequently reduces the quality and production of sea product. Therefore, with the aim of sustainable development of the offshore resources, it is not suitable for the net cage to expand application scale in shallow water. On the contrary, the fish farm should be promoted to deep water. Nowadays, the deep-water sea cage, which is advantage in terms of simple structure, low installation cost and easy operations, has caused extensive attention and adoption from all over the world. But due to the effect of sea current, the rate of volume loss is high when the net drift a lot, which makes serious impact on aquaculture production and economic benefits.In this paper, rules of the influence on net deformation by weight system of Deep-water gravity cage are studied. Through physical model tests and numerical simulation, the general law is concluded which will provide reference for the reasonable selection of weight system. The content is summarized in the following:1. Introduce the research situation of deep-water cage and several main cage styles. Summarize the forward papers about Deep-water gravity cage and the technology for net deformation testing from both domestic and abroad field.2. Based on the characteristics of luminous plastic optical fiber, a testing system for net deformation is proposed to improve the shortcomings of the existing testing technologies. This method combined the technology of deformation display with the technology of image acquisition and processing, which can realize the volume measurement of the net with the use of software written for image recognition and pixel statistic. This test system can also be used for underwater deformation measurement of other flexible structures.3. According to the gravity similarity criterion, five weight schemes are designed for experiments. Through the contrast analysis of the cages against the interlayer spacing, the change of area and volume, the general rule of cage deformation under the influence of the water flow is obtained. Further analysis of the influence caused by the size and style of weight system on net deformation and the pros and cons of each idea provides scientific reference basis for the selection and optimization of weight system.4. Based on the structural bending stiffness and tensile stiffness, a method for equivalently replacing cable is discussed. This method is also employed to simulate the cage model by the finite element analysis software ANSYS. Through comparing with the test data, the method was validated to be reliable for the cable simulation. And it also provided a thinking pattern to study other types of cage and actual size cages for further study. |
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