COMPARATIVE STUDY ON NUMERICAL SIMULATION OF FLOW AROUND A VERY LARGE FLOATING STRUCTURE

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Needs for ocean space utilization will be increased more and more in future. Large part of coastal area shallower than 20m has been reclaimed to utilize for the industrial and residential purpose and the utilization of deeper area is necessary in future. A feasiblity research project on large-scale floating structures for ocean space utilization is now being conducted in Japan. Floating structures are superior to a reclaimed island in some aspects such as having less impact on the ocean environment. Because the scale is huge compared with those which now exist, however, environmental assessment of such a structure in a bay is necessary before construction. This cooperative study deals with the numerical methods used for the simulation of the flow and the diffusion of a bay with a large-scale floating structure. The validation and the accuracy of the methods are discussed by the comparative calculations. The studies covered during two years are summarized as follows :(1) Simulations of … More the flow and diffusion of a rectangular bay with a large-scale floating structure is compared by the finite difference methods (ADI method and Leap-Frog method) and the finite element method in two-dimensional plane.(2) A multi-level method is applied for the same problem and the result is compared with two-dimensional calculations.(3) Visualization of the flow around a model of the floating structure in a tidal tank is compared with the calculations. As an example of more practical case, two-and three-dimensional simulations are conducted for a large-scale floating structure in Tokyo bay.(4) Tidal currents and the residual currents by two-dimensional methods and a multi-level model are compared.(5) The diffusion patterns of COD (Chemical Oxygen Demand) from rivers inside the bay are compared by the methods.Results obtained from these studies are summarized as follows :(1) Two-dimensional results are equivalent to the vertical integration of the multi-level solution.(2) ADI-method is superior to Leap-Frog method in the numerical stability, it can take longer time-steps. Programming of Leap-Frog method, however, is much easier than ADI-method and the numerical accuracy is almost same between them.(3) A large-scale floating structure causes less effects on the flow and the diffusion in the bay than a reclaimed island.(4) A multi-level model is more effective to obtain the steady solution of COD in a short computational time than two-dimensional methods. Less