DEVELOPMENT OF PREDICTION METHOD FOR ENVIRONMENTAL IMPACTS BY VERY LARGE FLOATING STRUCTURES

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In recent years, the floating system is proposed as an effective measure in constructing ocean airports. The plans of ocean utilization by means of very large floating structures (VLFS) will be increased in the future. Although it is often said that the floating system less affected ocean environment than the reclamation system, it has not been quantitatively proved. On the other hand, it is sometimes pointed out that VLFS may cause bad influence over the eosystem in the dark area below the structure or that the water quality between the floating structure and brakwater may become worse because of the stagnation of sea water. The purpose of this study is to develop numerical methods for the prediction of marine environmental impacts by installing VLFS.Especially, currents and diffusion problems around VLFS and currents and waves between the floating sturcture and breakwater were carefully investigated.At first, 2-dimensional separate region method (2D-SRM) and 3-dimensional singularity distribution method (3D-SDM) were developed as the tools to calculate wave field around the VLFS and dynamic response of the floating body. The developed 3D-SDM is applicable to the calculations of both frequency and time domain, considering the mutual interaction between multiple floating bodies with arbitrary shape. The developed 2D-SRM is applicable to the calculations including the effects of hydroelastic response of the floating body and interaction between the structure and breakwater. Next, a multilevel model has been modified to include the effects of VLFS for currents and diffusion problem. This model can calculate the density variation and can also evaluate the exchange ratio of sea water. For investigating the influences on ecosystem by VLFS,a simple 1-dimensional model in the vertical direction was deeloped and applied to the preliminary investigation.