Flow fields of open channel flows with adverse pressure gradients were measured with a laser Doppler anemometer (LDA) and digital-type point gauge. Mean velocity profiles of the inner- and outer-layer in equilibrium region can be expressed by the log-wake law. The von Karman constant is, then, universal one (=0.41) irrespective of the pressure gradients. In contrast, the integration constant in the log-law decreases with an increase of the pressure gradient. The turbulent energy is transported from the upstream region by the mean flow.

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Turbulence measurements in open-channel flows with a horizontally dead zone were conducted with a two-component LDA system. The aspect ratio(=streamwise length/spanwise length) is changed to 3, 5 and 10. In the case of the aspect ratio of 3, the strength of the rotation of the vortices is large in compared with other cases. In the case of the aspect ratio of 5, the mass exchange is small, however, the momentum exchange is larger than the other case. In the case of the aspect ratio is 10, the reattachment can be seen. The reattachment length is about 5 times of the spanwise length of the dead zone. A new eddy model in open-channel flows with a horizontally dead zone is suggested.

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This paper presents a numerical model to simulate local scour around a spur dike. Governing equations of flow are formulated in a moving boundary fitted coordinate system in order to calculate open channel flows with temporal changes in bed and water surfaces. In calculating Reynolds stress tensors, the nonlinear k-ε model is adopted. A model for bed deformation is developed by using a stochastic model for bed-load transport because a nonequilibrium situation of sediment transport dominates around the spur dike due to rapid changes in the near-bed flow and local bed slopes. For the sake of verification, the model is applied to two laboratory experiments. Comparisons between the numerical results and the observed ones demonstrate the ability of the present model in reproducing the flow and bed scour around the spur dike.

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In this research, horizontal bed-topography due to dam-construction or large-scale river improvement was studied as simplified processes of bed degradation with side-bank erosion, through flume experiments and numerical analysis. Firstly, we investigated the interaction between widening of gravel channel and degradation of channel bed with hydraulic model experiment. As a result, it was understood that the conventional diffusion model of the degradation with a modified diffusion coefficient could be applied even if the channel widening accompanies. Secondary, we constructed the 2-D numerical simulation model taking account of the widening process with bank erosion in a gravel channel, and examined the application of the numerical model by using the experimental data. The numerical analysis could explain the flume experiments well.

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A method to identify the source area of tsunamis is presented assuming that the source area is elliptical in shape. The traveling time of the first arriving wave of a tsunami is solved as the shortest mute problem in which the submarine topography is given. Some numerical experiments have been carried out to discuss the validity of the proposed method. Sequently, it has been applied to identify the source area of the tunamis accompanied by some historical earthquakes, compared with the results by the inverse refraction diagram.

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A numerical model, based on an energy balance equation with wave breaking and diffraction effects, is proposed to predict the transformation of multi-directional random waves over a varying bathymetry. In the numerical model, a high-order difference scheme called QUICK is employed to suppress numerical diffusions. The numerical predictions were compared with the theoretical predictions of wave heights behind breakwaters and with experimental results of wave transformations due to a circular shoal conducted by Chawla et al. (1998). The comparison showed that the numerical model performs well as a whole, except a poor reproduction of abrupt decrease in the wave height due to breaking and subsequent increase near the top of the shoal.

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To solve the global warming problem, one of the environmental ones presented all over the world. we need to evaluate accurately the quantitative and qualitative characteristics in the global circulation process of the issued gas, such as CO₂. However, there is little basic information about hydrodynamic relationships between air and water at the water sphere in the earth. As we reveal the gas transport phenomenon across the air-water interface, we find it very important to investigate the mutual turbulent structures in air/water phase of the wavy interface. Therefore in this study, we examined the instantaneous vortex motions in the air/water interface instantaneously, by making use of Particle-Image Velocimetry (PIV) which enables us to measure the simultaneous velocity components at all points in laser-light sheet (LLS), and analyzed turbulent structures using phase-averaged method. This study inspired us the idea that the effect of both water disturbance and air entrainment will be superior to the one of turbulence in terms of gas transfer mechanism on the flow with breaking wave.

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A numerical analysis for distribution of hydrodynamic pressure on arbitrary shaped offshore structure vibrating in water at constant depth is developed. The source distribution method is used in the analysis after deriving Green's function for pressure waves in water satisfying boundary conditions on the water surface and bottom. On the bottom, partial reflection of the pressure waves is considered, and the reflection ratio is estimated from physical constants of the bottom material. Pressure distributions and resultant forces on vertical walls and circular cylinders are analyzed. The partial reflection of pressure waves by the bottom materials has an important effect on the distribution of pressure are shown.

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Field measurements were performed to investigate the effects of the Kuroshio current fluctuation on the 3-D characteristics of currents and material transport in Tokyo Bay in stratified conditions. When coastal warm water intrusion induced by the fluctuation of the Kuroshio current occurs, the bay water both in the surface and bottom layers with high temperature, low salinity and high turbidity and with low temperature and high turbidity, respectively, flows toward the ocean; the coastal warm water with high temperature, high salinity and low turbidity intrudes into the bay with a complicated 3-D feature. This current system with the three-layer structure, in contrast to the two-layer current system of the estuary circulation, may effectively transport the turbid water in the bay toward the ocean.

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In the stratified closed water systems, the unique phenomena caused by the density differences are observed. Numerical simulation is useful tool for investigating such phenomena. In this paper, a three-dimensional numerical model which is based on the Body Fitted Coordinates is constructed for the purpose of calculating incompressible density current under the influence of complicated ground shape. The model is cross-checked by the results of an experiment of density front migration in a stratified closed water system. Then the model simulates wind driven density flow which causes aosio phenomenon. As a result, availability of our model is confirmed and the simulation result of wind driven density flow gives important information.

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It is the purpose of this report to present and verify a prediction method developed to analyze behaviors of water temperature and turbidity in a pumped storage reservoir. The features of this method are (1) to treat a density current by applying a numerical method for incompressible flow with density variation, (2) to calculate a fluid density stratification by using κ-ε turbulent model and (3)to be applied to a flow involving free surface with VOF method. The prediction method is applied to local measurements in Shin-Takase pumped storage reservoir and its 1200-scale model experiments. The obtained numerical solutions of water temperature and the turbidity distributions agree well with those results.

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General applicability of recently-developed low-Reynolds number two-equation turbulence models using isotropic eddy viscosity, is examined by conducting calculations of flows past a backward-facing step and over a rectangular cavity in the bottom bed of open channels, and by comparing with experimental results and direct simulation results. These flows contain features of many general complex flows, such as separation and stagnation, and are suitable for the present purpose. Though it may not be necessary to represent the near-wall behavior of stresses in detail, overall Reynolds number and normal-stress effects need to be represented with some accuracy. Low Reynold-snumber k-ε model has been seen to perform consistently and has the best general applicability.

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In this study, we propose to solve the traveling time of the first arriving wave of a tsunami as the shortest route problem in which the submarine topography is given. It is proved that the accuracy of analysis can be improved by the design of wave orthogonal from each node where the water depth is allocated, when the nodes are located at regular intervals. It is also shown that the accuracy of analysis can be understood quantitatively by the relation with the interval of located nodes. Finally, it is demonstrated that the phenomena such as diffraction and refraction of wave can be simulated using the proposed method.

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