Turbulence measurements of compound open-channel flows were conducted with PIV and LDA. The horizontal vortices near the free surface have a big scale in condition that the ratio between the flow depth in the main channel and the height of the flood-plain is smaller than 1.5. In contrast, the vorticies, which have an axis in spanwise direction, are generated semi-periodically near the junction between the flood-plain and the main-channel in condition of the ratio is lager than 1.5. This generation mechanics of secondary currents and horizontal vorticies is quite different in both cases.

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The flow/particle interaction and the particle/particle interaction are the keys to investigate the sediment transport phenomena from the viewpoint of the computational mechanics of sediment transport. In this study, the flow/sediment interaction is described by introducing the interaction terms which reflects the effect of the contained sediment particles, into the governing equations of flow with k-ε turbulence model; on the other hand, the particle/particle interaction is modeled by the distinct element method. The characteristics of the mean velocity profile of the flow on a movable bed is well reproduced by the present model. Furthermore, the internal structure of the flow is discussed based on the results of the simulation, or the Reynolds stress distribution, the velocity profile of particle, the concentration profile of particles and so on.

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The mechanism of the long-time evolution of deep-water Stokes waves due to the sideband instability and the mode coupling is explained by the group-theoretic bifurcation theory. It has been found that random waves are created as a consequence of repeated bifurcations.

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In order to extend Green function method of constant depth to apply for variable depth, a systematic derivation of Green's function based on the mild-slope equation is proposed in this paper. A new method to determine density of wave source is also proposed. Because of wave refraction, wave sources on boundary are mutually related each other. Hence these densities satisfy an integral equation on the boundary. Result of wave analysis for a model harbor shows that the effect of the interaction between wave sources is quite significant. Moreover, it is shown that virtual topography outside wave field, which is necessary to assume for the calculation of the Green function, gives almost no influence on the wave field inside, provided the mild-slope condition is fulfilled in the harbor.

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In anaerobic layers of eutrophic lakes and reservoirs, various components of salinity are released from the bed, which produces heavy water mass right above the bed. When the bed is sloping, a plume motion is generated and the heavy water runs down to a deeper region of the lake. The plume transports high amount of dissolved materials to the lake's bottom, which might bring serious contamination of the bottom water with nutrients and ionic matters. The present study is to fundamentally investigate hydrodynamics of this type of plume. In an experimental model, measurements were made with respect to velocity and buoyancy profiles. Flow development along the streamwise direction is examined. Assuming the flow fields having self-similarity profiles of velocity and buoyancy, a theoretical model was developed to analyze the plume's dynamics. The present theory could be applied to estimate how much the plume-oriented transportation is responsible for lake's bottom water contamination.

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This paper discusses the applicability of a MacCormack finite difference scheme in a generalized coordinate system to flood flows in simplified basin models located in mountainous areas. The calculated results show that among three kinds of combinations of 1-D operators in the MacCormack finite difference scheme employing direction splitting method, the scheme with alternating difference directions is the best to eliminate truncation errors resulting from the fixed direction difference scheme. This scheme can produce almost similar results for different grid systems and can use small artificial viscosity to simulate experimental results stably. The scheme proves to predict well flood flow characteristics in basins with an incised channel or a tributary.

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