Tension Characteristics Of Gravity Net Cage With The Mooring System

Along with the development of economy and the improvement of people’s living, the demand for seafood products which is the main source of animal protein in people’s diets is increasing larger. Marine aquaculture is expected to play a significant role as wild fish stocks decline due to environmental degradation and over-fishing. With the expansion of the inshore aquaculture industries, the number of suitable near-shore locations becomes limited, and inshore water pollution and dish disease become more severe. At present, Open Ocean Aquaculture has to be developed to settle those problems which occur in the inshore aquaculture. Compared with net cages used in sheltered area, the net cages in open sea will suffer more severe wave and current loading. In other words, the deep-water cage is required to withstand severe conditions such as strong waves, currents and storms. In order to ensure the safety of cages and minimize the loss of fishermen, the research on the mooring tension characteristic and hydrodynamic behaviors of cage under mooring system should be put into a significant place.The main contents of this dissertation can be summarized as follows:1. A comprehensive review on the background of Open Ocean Aquaculture, the research progress on deep-water net cage and the main types of cages are summarized. Besides, the basic theory that is relevant to the dynamic responses of net cage in waves and current is also introduced. And the parameters of numerical mode are summed up as well.2. The numerical simulations of net cage with four-point mooring system are conducted. The effects of wave incident angle, wave height and current velocity on mooring line tension are investigated. The tension curves changing with these factors are presented as well.3. The numerical simulations of net cage with frame mooring system are conducted. How the diameter of the buoy and the size of grid affect the mooring tension are studied. Results show that compared with the four-point mooring system, the frame mooring system can reduce the mooring line tension significantly.4. Design and manufacture a tension sensor which suits the in-situ measurement of mooring line tension of net cages. Besides that, the field measurement was carried out during the typhoon "Matmo" landing Fujian Province.