Study on the mechanism of flood inundation disasters involving sediment and driftwood and the development of an integrated numerical model

泥沙、浮木洪涝灾害机理研究及综合数值模型开发

• 批准号: 22H01596
• 负责人: 清水 義彦
• 金额: $ 10.73万
• 依托单位: Gunma University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2022
• 资助国家: 日本
• 起止时间: 2022-04-01 至 2025-03-31
• 项目状态: 未结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-22H01596/
• 关键词: 流木; 土砂輸送; 洪水氾濫; 数値解析モデル; 個別要素法; 流木災害; 河床変動; 流木集積; 堰上げ背水; 開水路流れの数値解析

本研究の目的は，河道及び氾濫原での流れ・土砂・流木の相互作用系を水理実験から捉え，その突合せから新たな解析手法を構築することである．具体的には，個々の流木追跡を個別要素法から行い，これをオイラー的な流れ・流砂の解析に組み込み，河道・氾濫原を一体的とした統合的な流木流動モデルを作成する． R4年度の研究実施計画は，① 橋脚を伴う河道区間の流れ・流木・流砂に関する水理現象の検討及び② 流木・土砂を伴う市街地氾濫の水理現象の検討の2項目であり，①の検討は，本研究の根幹となるもので，橋脚を伴う河道区間の流れ・流木・流砂の相互作用が，過去の被災事例から典型的な力学過程であると判断して，これを基礎的な水路実験より検討した．これより，橋脚での流木集積過程では流下流木量が多くなるほど水深方向の閉塞化が進み，3次元性の高い現象となること，その特徴から生じるバックウォーター効果等を水理実験から評価した．そして，流木が橋脚の水深方向に集積すると流れの遮蔽効果が卓越し，その結果，下降流が生じ局所洗堀が助長されることが予測された．以上の水理実験より得られた水理現象の再現性，すなわち，水位と流況特性，流木群の移動軌跡，集積状況（立体構造）等をレファレンスとして，数値解析モデルを構築した．また，実河道への適用から，一般化座標系のもと，平面2次元・3次元解析をモードスプリット法から構成したハイブリッドモデルに，流木群による水体積の変化を考慮してFAVOR法の組み込みも行っている．②の検討では，河道・市街地氾濫の水理現象を捉える基本的な実験を行い，その現象を再現できる数値解析モデルを構築した．すわわち，橋脚の流木集積より河道からの氾濫過程を再現し，氾濫原での流れ，流木の挙動を追跡する数値解析手法を，氾濫原では非構造格子系のもとに作成し，計算結果は流木の挙動を再現できることを確認した．

The purpose of this study is to construct a new analytical method for the interaction system between river channel and flood plain, soil, sand and driftwood. Specifically, the individual element method for tracing driftwood is used to create the flow pattern of driftwood. The flow pattern of driftwood is used to analyze the flow pattern of driftwood. The research and implementation plan of R4 year includes: (1) the analysis of hydrologic phenomena related to flow, drift-wood and drift-sand in the bridge foot and accompanying river channel section;(2) the analysis of hydrologic phenomena related to flow, drift-wood and drift-sand in the bridge foot and accompanying river channel section;(3) the analysis of hydrologic phenomena related to flow, drift-wood and drift-sand in the bridge foot and accompanying river channel section;(4) the analysis of the interaction of flow, drift-wood and drift-sand in the bridge foot and accompanying river channel section;(5) the typical mechanical process of the past disaster cases; and (6) the judgment of the typical mechanical process. The basic water route is open to discussion. In the process of accumulation of driftwood at the foot of the bridge, the amount of driftwood flowing down is increased, and the three-dimensional phenomenon of high water depth is increased. In addition, the results of the current accumulation in the water depth direction of the bridge foot are excellent, and the results of the downward current generation are good. The reproducibility of the above hydrologic phenomena, water level, flow characteristics, movement trajectory of the flow tree group, accumulation condition (three-dimensional structure), etc. are obtained. In this paper, the application of river channel theory, generalized coordinate system, plane 2-D 3-D analysis method, water volume variation of flow tree group, FAVOR method, and its application are discussed. (2) To discuss and analyze the basic phenomena of flood water in river channel, city street and ground, and to analyze and construct the numerical value of flood water. The flood process of the river course is reproduced by the accumulation of driftwood at the foot of the bridge. The numerical analysis method of the flow of the flood plain and the movement of the driftwood trace is established. The calculation result is confirmed by the reproduction of the movement of the driftwood.