Application of nonlinear dynamics to hydro-geomorphology

点击翻译按钮获取中文摘要

A weakly nonlinear analysis considering the interference between alternate bar and double-row bar has been developed. Findings show that when the two modes are on the same order, the mode cross interference controls development process of each wave and they cannot grow simultaneously. The development process of bars is strongly influenced of the mode cross interference. Hydraulic experiments and the weakly nonlinear analysis, by setting several hydraulic conditions under which either alternate bars or double-row bars formed, have been conducted to clarify a changing process of bar shape formed during flood at usual time. It is found that the channel shape at usual time is strongly affected by the bar shape during flood.Effect of unsteady characteristics of flow and vegetation growth on number of braided streams and temporal stability of streams has been studied. The results show that the number of streams decreases and temporal change of streams is suppressed with vegetation under unsteady flow conditions. Furthermore, dynamic characteristics of bars on bed with non-uniform sediment have been studied. The results show that bar geometry on bed with non-uniform sediment has been changed with time and does not approach equilibrium state.A new model was proposed taking proper account of the functional relation between the Froude number and the Shields number by revisiting the existing weakly nonlinear stability analysis of the transition of dune and flat bed regimes. It is found that, from the analysis, the dune-flat bed transition is characterized by subcritical bifurcation in the range of relatively small average bed slopes, and large velocity coefficient. In addition, Izumi extended the existing model of the inception of channels to the more general cases in which the base state slope profile is arbitrary given. The analysis shows that the spacing of channels is approximately one thousand times the depth of surface flow on slopes.