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

近年来，浮动系统作为建设海上机场的一种有效措施被提出。今后，利用超大型浮式结构物开发海洋的计划将越来越多。虽然人们常说漂浮系统对海洋环境的影响要小于围垦系统，但这一说法还没有得到定量的证明。另一方面，有时有人指出，VLFS可能会对结构下方黑暗区域的生态系统造成不良影响，或者漂浮结构与制动水域之间的水质可能会因海水的停滞而恶化。本研究的目的是发展安装VLFS预测海洋环境影响的数值方法。重点研究了VLFS周围的水流和扩散问题以及浮体结构与防波堤之间的水流和波浪问题。首先，开发了二维分离区法（2D-SRM）和三维奇异分布法（3D-SDM）作为计算浮体浮壳周围波场和动力响应的工具。考虑到任意形状的多个浮体之间的相互作用，所开发的3D-SDM既适用于频域计算，也适用于时域计算。所建立的2D-SRM可用于计算浮体的水弹性响应以及结构与防波堤相互作用的影响。其次，对一个多层模型进行了修改，使其包含了VLFS对电流和扩散问题的影响。该模型可以计算密度变化，也可以评价海水交换率。为了研究VLFS对生态系统的影响，在垂直方向上建立了一个简单的一维模型，并应用于初步调查。

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.