The present report introduces main results of investigations on precise tsunami evaluation methods, which were carried out from the viewpoint of safety evaluation for nuclear power facilities and deliberated by the Tsunami Evaluation Subcommittee. A framework for the probabilistic tsunami hazard analysis (PTHA) based on logic tree is proposed and calculation on the Pacific side of northeastern Japan is performed as a case study. Tsunami motions with dispersion and wave breaking were investigated both experimentally and numerically. The numerical simulation method is verified for its practicability by applying to a historical tsunami. Tsunami force is also investigated and formulae of tsunami pressure acting on breakwaters and on buildings due to inundating tsunami are proposed.

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This paper investigates the appropriate lumping scale for rainfall-runoff models. Since the location of rainfall inside the lumping scale cannot be reflected to the simulations, it is important to identify the scale in which the spatial variability of rainfall does not affect significantly to the discharge at the outlet. It defines Model Building Unit (MBU) as a maximum catchment size in which explicit consideration of rainfall location is not required for flood predictions. The simulation results in the Yodo River basin showed that MBU is restricted mainly by river channel effects and quantified as absolute size if the catchment size is between 150 km² and 1500 km². MBU is 200 km² for 5 % of allowable relative peak discharge error.

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Considereing the methane migration processes in the closed coal mine, this paper describes the numerical experiment by two multiphase models, the basic two-phase (gas, water: hereinafter 2P) model and the two-phase (gas, water)/three-component (air, methane and water: hereinafter 2P/3C) model newly developed by the authours. The major difference between these two models is that the 2P/3C model can simulate the mass transfer processes between the phases such as the methane dissolution into the liquid phase, while the 2P model cannot. The methane migration proceeces in a hypothetical coal mine were simulated by these two models and compared. This study exhibited an interesting aspect that the 2P model can simulate the basic methane migration processes and the interphase mass transfer model (2P/3C) proposed can well simulate, in addition, the methane segregation in the subsurface. The results obtained herein typically indicate the importance of multiphase models for the water-gas simulation in the subsurface, as well as the further importance of the model concept selection.

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Subramanya & Awasthy pointed out that the discharge coefficients are affected by four parameters, i.e., the Froude number, relative flow depth, relative weir height and relative weir length. The discharge coefficients in the previous studies were obtained from the experiments under the condition that the four sets of parameters were not changed systematically, due to it is not easy to conduct such systematic experiments. Recently, it is pointed out that the relative flow depth does not affect on the discharge coefficient so much in comparison with the other parameters. In this study, all four parameters except for the relative flow depth were changed systematically in supercritical open-channel flows with a side-weir. A new discharge coefficient is suggested.

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A model for predicting not only the three-dimensional beach changes but also the planer change in grain size distribution was developed based on the contour-line-change model. In the past model, there were some problems with respect to the stability of the calculation related to the selection method of the local beach slope in response to the grain size of the seabed materials, and in this study these problems were solved by reconsidering the fundamental characteristics of the equilibrium slope. Assuming that the equilibrium slope at a location of the beach is strongly governed by the equilibrium slope of the dominant grain size population existing at the location with forming a thick layer and the effect due to the composition change in the surface exchange layer is less important, the concept of the dominant grain size population was introduced in the model. The model was applied to the prediction of the beach changes on Kemigawa Beach and around the Shimohara fishing port in Chiba Prefecture, and the appropriateness of the model was confirmed.

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In this paper, using data from consecutive observations of Lake Biwa water quality and existing long-term weather observation data, the authors clarified the mechanism in which water temperature and dissolved oxygen (DO) concentration in deep layers of Lake Biwa change during the period from autumn to winter, i.e. from the stratification collapse period to the circulation period. The relationship between the DO recovery of deep layers and the air temperature in the circulation period was also studied. The amount of the DO supply to the deep layers by circulation was then calculated as a trial, and compared to the results of investigations related to water temperature and water quality in Lake Biwa.
As a result, it was clarified using measured data that the oxygen supply by lake water circulation through the surface of the lake was predominant in the mechanism of DO supply to the deep layers in Lake Biwa than the DO inflow caused by melted snow. It was also pointed out that the coldness of winter which hits during the circulation period was essential in the DO recovery of deep layers.

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In this study, attempts were made to provide a group of complete heat and mass transfer correlations, and to propose a new heat and mass transfer model for a Tubular Solar Still (TSS) by taking account of thermal properties of the humid air inside the still. We developed a new experimental technique for directly measuring the evaporation rate from the saline water surface in the TSS and evaluated the evaporative mass transfer coefficient. Indoor experiments were conducted to investigate the production performance and the heat and mass transfer coefficients of the TSS. It was found that i) the heat and mass transfer coefficients, h_cha, h_cw, h_cdha, h_ew can be expressed as functions of the temperature difference between the saline water and the cover, and ii) the conventional formula available for a basin type still overestimates the convective heat transfer coefficient, h_cw for the TSS. Furthermore, in this study, the long-wave radiation interaction between the water surface and the tubular cover was shown theoretically.
We also proposed a new heat and mass transfer model of TSS. The mass balance of water vapor inside the still was formulized for the first time. The proposed model was successful in the calculation of humid air properties (temperature, vapor density and relative humidity) and condensation flux on the tubular cover inner surface besides the saline water temperature, tubular cover temperature, trough temperature and evaporation flux. The validity of the model was evaluated from the comparison with field experiments in Fukui, Japan and in Hamuraniyah, UAE. It was seen that the calculated results also had a good agreement with the field data.

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