The mean velocity and turbulence intensity distributions were experimentally investigated for both water phase and air phase of air-water stratified two-phase flows. Mixing-length model in wind waves was expanded in the air flow of two-phase flows. It was clarified that the shear distribution was parabolic when there exist both the bed shear stress and the interface shear stress. In water layer, non-linearity increases as the ratio of friction velocities in both layers increases. In this way, it was found that the relative velocity between the air flow and the water flow is closely related to the turbulence structure near the free surface in two-phase flows.

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Although some direct numerical simulations (DNS) are recently conducted for low Reynolds number flows, it is still difficult to calculate high Froude (Reynolds) number flows. At that time, a Reynolds stress model is very effective for calculating the turubulence structure near the free surface in steep open-channel flow. In this study, a numerical simulation was conducted by using Reynolds stress model at a new boundary condition of free surface including the effect of Froude number. Furthermore, the turbulent redistributions were mostly reproduced by modifying the pressure-strain term in steep open-channel flows. It became clear that the pressure-strain term affects greatly the turbulent redistributions near the free surface.

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In this paper, FDS method is applied to numerical computation of open channel flow. First, three methods of “Roe's conservative linearization”, which satisfy the Rankine-Hugoniot relationship, are compared and the best applicable one is selected. Second, removal methods of non-physical solution (expansion shock in ideal gas) that arise near control section in open channel flow are studied and the most effective one is clarified. Third, the calculation techniques are made clear. Furthermore, numerical computation for dam break flow and open channel flow with transition are examined, and FDS method is verified to be effective for numerical computation of open channel flows.

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Numerical simulations are performed to examine the groundwater-flow fields in sandy-beaches. The model is based on Richards equation for saturated-unsaturated flow and advection-dispersion equation for salinity, incorporating tidal fluctuations into the seaward boundary conditions. The advantage of the present model is that it can accurately simulate unsteady behavior of groundwater in unconfined coastal aquifers considering the effects of water-level variations, density distributions and dynamics in the unsaturated zone. Computational results show that circulations are formed in the aquifer near the shoreline owing to the tidal oscillations, and accordingly saline seawater exists in this part. In addition, the structure of the circulation is greatly affected by amplitude of tidal fluctuations, density distribution, land-derived freshwater discharge, beach slope, and aquifer thickness.

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The 2D/3D hybrid tsunami numerical model is developed in which the conventional 2D model is adopted for the calculation in the wide region located far from the coastal structures although the 3D non-hydrostatic pressure numerical model is used in the limited region adjacent to the structures. Applicability of the domain connection technique is examined by comparing the numerical results obtained by the present hybrid model with those obtained by applying the 3D non-hydrostatic pressure numerical model for the whole domain. Further, the results of the model tests are compared with the numerical results obtained by both the present hybrid model and the 2D model, to examine the validity of the present model. It is shown that the present model reduces a calculation load significantly comparing to the case adopting the 3D model for the whole domain and reproduces the characteristics of three-dimensional complicated flow around the opening of breakwater which cannot be reproduced by the 2D model.

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Exchange flow of saline and fresh waters on the sloping bottom has been experimentally studied. Both undertow along the bottom and the compensating upper flow are treated. It has been found that the initial motion of inclined thermal is well described by bottom slope and scales of time, length and velocity determined by the initial volume and initial density exess of saline water. The growth rate of the maximum depth of underflow in this experiment is fairly smaller than that of the flow in which the influence of water surface is negligible. Densimetric Froude number of the front of underflow is almost constant, and the value increases as the bottom slope becomes steeper. Densimetiic Froude number of the compensating upper flow is about one, and the depth is 0.2-0.3 times the depth of gate position. The direction of circulation inside the density front is explained dynamically.

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As macrophytes have considerable structrual variation for prey communities by hindering predator foraging and affect the predator behavior, the swimming and feeding behavior of planktivore (Pseudorasbora parva) with their prey (Daphnia pulex) were studied in laboratory experiments with varying densities (350, 700, 1400, 2100 and 2800 stems·m^-2) of artificial submerged vegetation and with different prey densities (0.5, 1, 2, 5, 10 and 25 prey·1^-1). The swimming speed of the fist was found to be negatively related to the prey density; and a significant change in swimming speed was noted as being directly related to the level of satiation The maximum feeding rates was found to depend upon and snow a marked variation with average prey distance. As the stem density gradually increases, the predator's foraging efficiency decreases considerably relative to feeding in open water. Moreover, a good relation in the feeding rate and swimming speed exists with the average stem distance to fish body length ratio (D). Abrupt reduction in feeding and swimming was recorded when D was near 0.7, which is approximately equal to one stride length of a fish.

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