Dynamic Responses Of Floating Fish Cage System In Current And Waves

With the development of world economic and growth of world population, more fishresources are needed in the market. Thus, there will be a promising future of offshoreaquaculture engineering. Due to the limitations of near-shore spaces and increasedenvironment pollution, the fish farming industry has the tendency to move to offshore areaand the size of fish cage will be larger. Since the sea environment in deepwater is more harshcompared to near-shore area, the fish cage will suffer severe dynamic responses, which leadnew challenges to the safety and reliability of fish cage structure as well as the whole fishfarming platform. Thus, it is important to get an understanding of the dynamic responses ofthe fish cage in waves and current.Based on the demands above, dynamic responses of deepwater floating fish cage inwaves and current are investigated in the thesis. And the “Buoyancy Distribution” method isdeveloped to calculate the partly-immerged floating collar’s buoyancy. The main contents andcontributions of this thesis can be summarized as follows:1. A comprehensive review on main types of deepwater fish cage is carried out first.Then research progress of hydrodynamic responses of fish cages is summarized. And thegeneral problems involved in hydrodynamic research of fish cage are summed up.2. Derive and introduce the basic theory that relevant to the dynamic responses of fishcage in waves and current, including the theory to calculate hydrodynamic forces of the fishcage and the theory to calculate the structural dynamic responses. By the way, severalcalculation cases are made to verify the reliability of basic theory.3. Conduct numerical simulations of fish cages in regular waves and current. The singlefloating collar’s deformation, displacement and motion trail are studied. The volume reduce ofnet cage, cage deformation, interaction between the floating collar and net cage and theinfluence of net’s drag forces to the responses are also investigated.4. Conduct numerical simulations of fish cages in irregular waves. The floating collar’s displacement, the volume change of net cage and the time history of mooring lines are studied.Meanwhile, the hydro-elastic responses of the floating collar in irregular waves are furtherinvestigated with “Modal Analysis” method.5. Design and conduct the hydrodynamic experiment of fish cage structure based on the“Forced Oscillating” method. The current-induced forces of the floater and the net, the dragcoefficient of semi-immerged floater are studied. By the way, based on the “Least SquareMethod” and Morison equation, the mass coefficient and drag coefficient of semi-immergedfloater in waves and current are investigated. And these coefficient data base can be used innumerical simulations and load predictions for the fish cage structure.