Kazuhiro Ezaki

Three-dimensional turbulent structure in straight open channel flows

Secondary currents are generated and modified as a result of the anisotropy of turbulence, which is caused by the boundary conditions of the bed, the side-wall and the free surface, as well as the aspect ratio of the channel and the channel geometry. Secondary currents affect the primary mean flow, producing threedimensional structures. Such a generation mechanism for secondary currents in closed and open channel flows can be explained well by using the longitudinal vorticity equation. The secondary motions in open channel flows are quite different from those in closed channel flows.

Experimental Study on Characteristics of Flood Wave Propagation in a Vegetated Channel

A knowledge of the nature of flood wave propagation in vegetated rivers is very important for predicting the flood routing. Vegetation in rivers often make sudden-contractions and cause high flow resistance at a flood stage. The high water stage and the channel storage of flood appear, due to the backwater effect of vegetation roughness. In this paper, the characteristics of flood wave propagation in a vegetated channel are studied through fundamental experiments with changing the rate of vegetation-covered area which is defined as the ratio of the vegetation-covered area to the non-covered area. Especially, the relationships between the rate of vegetation-covered area and the increasing rate of the maximum water stage, the decreasing rate of the maximum food discharge are investigated.

Turbulent Structure in the Junction Region of Compound Open Channels

An investigation on three-dimensional turbulent structure including secondary currents in compound open-channel flow is very important in basic hydraulics as well as practical engineering to verify the friction law of flow and sediment transport. In this study, secondary currents and three-dimensional turbulent structures in compound open channels were revealed experimentally by making use of a fiber-optic laser Doppler anemometer. Strong inclined upflow which is associated with a pair of longitudinal vortices is generated in a junction region between a main channel and a flood plain. Primary mean-flow field and turbulent structure are affected by the secondary currents.

ESTIMATION OF SCALE OF SLOPE FAILURE TAKING ACCOUNT OF DISTRIBUTION OF SUB-SURFACE FLOW DEPTH

Stability analysis of slope, based on the assumption of uniform field, cannot estimate two-dimensional scale of failure. On the other side, the depth of sub-surface flow which is highly related to slope failure is never considered uniform at natural slope. Paticularly, at a V-shaped micro configuration of the ground, the rise of sub-surface flow depth must be rapid and the failure will occur first at there. This paper proposes a model which estimates two-dimensional scale of failure occurred at such a not uniform field. The model consists of two parts, one is configuration model as shown in Fig. 1-Fig. 3 and one is stability analysis model. The stability analysis model is based on circular arc method, which introduces cohesion on the side of circular arc in addition to the bottom of the arc.