Numerical Investigation On Hydrodynamic Behavior Of Deep-water Gravity Cage

In China, inshore aquaculture, mainly located on protected coastal zones, has grownconsiderably in the past 20 years to meet the increased demand for seafood products. With theexpansion of the inshore aquaculture industries, the number of suitable near-shore locationsbecomes limited, and inshore water pollution and fish disease become more severe. At present,Open Ocean Aquaculture has to be developed to settle the problems which occur in theinshore aquaculture. Growing fish offshore in exposed waters, however, brings a newchallenge to the industry. The cages, mooring systems and auxiliary equipment need towithstand a high energy environment with a full range of loading conditions such as strong,winds, currents and storms. The study of the hydrodynamic characters of deep-water net cageshould be carried out to settle the technical bottleneck of the development of offshoreaquaculture.In the dissertation, a numerical model of gravity cage is developed, based on lumped massmethod and rigid body kinematics. Based on the numerical model, an easy-to-usecomputer-simulation system for designing gravity cage is set up to reduce costs, save time,and avoid the labor of flume tank tests. The doctoral dissertation is financially supported bythe National 863 High Technology Project and National Natural Science Foundation Project.The contents of the dissertation are mainly composed of seven parts. In the first part, theauthor gives a general introduction of the development and prospects of open oceanaquaculture industry and relative researches. The second part is about the description of basicnumerical method and theory, which will be applied in the following chapters. In the thirdpart, the numerical simulations of the plane net are carried out in waves and current, andmodel test data are used to verify the validity of the simulated results. In the fourth part, basedon the research of the plane net, a three-dimensional (3D) net model is established andvalidated by other people's model tests. At the same time, the 3D net model is applied toinvestigate the effects of structure size ratio (RDH), mesh type and weight system on the 3Dnet deformation of the gravity cage in current. In the fifth part, the dynamic properties ofgravity cage exposed to waves are investigated by numerical model, and a special discussionis carried out to analyze the wave theory selection in the simulation of gravity cage. In thesixth part, the dynamic response of gravity cage in waves combined with currents aresimulated and verified by the experimental data. In the seventh part, the numerical model is developed to simulate the hydrodynamic behavior of net cage which is fully submerged underwater. Physical model tests were carried out to examine the validity of the numerical model.Then under different submergence depth, the mooring line force of gravity cage in waves arecalculated and compared. At the end of the dissertation, the achievements and the limitationsof my study are summarized, and prospects of open ocean aquaculture are given in personalopinion.