水路頭部の分岐過程 The bifurcation process of channel heads

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Abstract

水路頭部では周辺の流れが集まるため更に活発な侵食が生じ,水路は上流側へと発達していく.上流側へ発達する際,水路頭部は時折二つあるいはそれ以上の水路へ分岐することがある.このような分岐を幾度となく繰り返すことによって,最初単純だった水路群は複雑な水路網へと変化していく.本研究は,このような分岐が生じる原因が水路頭部周辺に生じる2次不安定現象であるとの観点から,水路頭部前縁部に円周方向の擾乱を与えることによって分岐の物理機構を理論的に説明したものである.解析の結果から,限界水深/抵抗係数と水路頭部半径の比が小さくなると,水路頭部は擾乱に対して不安定となり,分岐が生じ始めることが明らかとなった.

Channels tend to develop upslope due to the concentration of flow around their channel heads. In the developing process, a channel head sometimes splits into two or more than two branches. By repeating such a bifurcation process, simple patterns of channels evolves into complex patterns of channel networks. In this study, a mathematical model of channel bifurcation is presented in terms of secondary instability of channel heads. Linear stability analysis is performed around a channel head modeled by a hole on a flat plane. It is found that a channel head becomes unstable for perturbation and channel bifurcation is initiated when the critical depth divided by the friction coefficient decreases compared with the channel head radius.

Journal

  • NCTAM papers, National Congress of Theoretical and Applied Mechanics, Japan

    NCTAM papers, National Congress of Theoretical and Applied Mechanics, Japan 54(0), 299-299, 2005

    National Committee for IUTAM

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