In this study, the impact force when the body with flat bottom runs into flat water surface is treated. In this case, the compressibility of fluid must be always regarded. When approaching velocity is low, the impact force on the body is equal to the momentum given to fluid within area given by the wave equation. On the other hand, when approaching velocity is high, the impact force is equal to compressure stress of fluid just under the body. Under these considerations, two impact force equations are obtained respectively, and the boundary of two states can be defined. And then, parameters ε (x) which is defined by the compressibility of fluid and elasticity of the body, and M_e which is defined by the ratio of approaching velocity to the velocity of sound in fluid are substantial quantities which dominate the impact phenomena.

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Three dimensional coherent structure of turbulent channel flows near the wall is investigated. The hydrogen bubble method is used in experiments.
Low speed streaks lifted from the viscous sublayer make a pair. Transverse interval between two streaks in the pair is about (10-30) ν/u, where ν is the kinematic viscosity, u the friction velocity.
In the buffer layer and log region the pair concentrate and separate from the wall. Three dimensional behavior of the pair is similar to that of the streamwise vortex.

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In order to study the mass transport process produced by the thermal convection, the thermosolutal convection in the two-layered and continuously stratified systems composed of heat-salt complex is investigated, experimentally and theoretically. Our preceding results, i. e., the stability criterion for the system with arbitrary distribution profiles of two density components and the evaluation of the diffusive and convective components of the heat-salt flux across the density interface, are introduced to develop the numerical model for the mixing process. The numerical results agrees well with the experimental data. In addition, the transforming process on the internal energy into the potential energy through the vertical mixing is quantitatively understood.

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A stochastic study on saltation may be useful in order to unify the theories of bed load motion and sediment suspension, because saltation can be regarded as an intermediate state of sediment motion. Generally, several or a few dozen times of saltations are continued by repulsions with a sand bed to constitute the so-called successive saltation. The irregularity of this phenomenon is caused by repulsions of a particle with a bed, and respective paths of individual saltations may be analyzed by a deterministic equation of motion. Such a system of sediment motion is analyzed by combining a stochastic approach with a deterministic one in this paper. By a simulation based on the derived model, the characteristics of individual saltation and successive saltation have been clarified.

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The characteristics of turbulence, interfacial fluctuation and entrainment caused by an oscillating grid have been investigated. The turbulent intensities, integral length scales and organized eddy scales have been described with the distance from the grid and the physical quantities of grid oscillation. The r. m. s. values, integral time scales and predominant periods of the interfacial fluctuation have been shown as functions of turbulent Richardson number. From flow visualizations and results mentioned above, we have found how the integral scale eddies and organized eddies play roles on entrainment and suggest the -5/3 power entrainment law.

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A probabilistic model of rainfall of a single storm is presented. Each rainfall event is represented in terms of three characteristic variables, i. e., the duration, the maximum intensity and the total amount. The joint probability density function of the variables and analytical expressions of the moments, including correlation coefficients among the variables, are derived. The validity of the presented model is verified through its application to observed rainfall events. For example, the model predicts that the correlation coefficients between (a) duration and maximum intensity, (b) duration and total amount, and (c) maximum intensity and total amount are 0-0.5, 0.6-0.75, and 0.5-0.8, respectively, which show good agreement with the values calculated from observed data.

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In this paper a new and simple method for on-line detection of the time of occurrence of abnormality is proposed. The adaptive Kalman filter (AKF) coupled with a generalized likelihood ratio test is derived incorporating this method for the case of both the unknown abnormal and observed variables being vectors. Each state variable is clearly defined as a function of the unknown abnormal variable. Physical relations among the state variables and among the other variables of the AKF are also formulated. To show its effectiveness, adaptability and ability to detect abnormalities, the derived AKF is applied to a synthetically generated time sequence having an abnormality occurring at an unknown point in the sequence. The proposed method results in a more practical on-line algorithm for the AKF and much less computer loads.

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The simulation technique has been used to investigate and estimate the confined ground water behaviors through the identification process. However, it seems that we have lack of attention to the objective evaluation of the simulated results themselves. The present paper is intended to propose the evaluation method of the ground water simulation by convining the kinematical and probabilistic approaches. For this purpose, the variational formulation have been made on the ground water behaviors, which gives us a useful tool to express the relationship among errors of parameter estimation boundary and initial conditions and the accuracy of the simulated result in the whole region concerned. This relationship is convined with the probabilistic concept and leads the evaluation-index of the ground water simulation.

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A hybrid method for analyzing wave exciting forces, added-mass and damping coefficients in scattered wave field is proposed to reduce computational efforts as compared with the conventional method. The proposed method combines a boundary integral equation method and an expansion method utilizing eigenfunctions. The primary advantage of the method is that the wave height distribution can be obtained without considerable increasing of computational efforts. This is due to the fact that kernels of the integral equation are simpler than those of the conventional method, although more elements are required. Accuracy of numerical solutions obtained by the proposed method is investigated by comparing with the exact solutions. Numerical results are also presented for floating and submerged axisymmetric bodies.

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Recently water pollution due to Coli-form qroup bacteria is strikingly high. However. its pollution route or mechanism in water bodies is not clear.
This paper presents a study on the pollution load of Coli-form group bacteria. A cae study was performed on the catchment area of the koto River.
The pollution units, expressed by the number of Coli-form group bacteria per capita (or head) per day. were 1.5×10¹⁰ in night soil. 1.0×10¹⁰ in gray sewage (domestic sewage except night soil), 5×10¹¹ from aattle, 1.0×10¹¹ from pigs.
The discharge rate in each of treatment plant ranged from 10^-2 to 10^-3 Runoff rate to the river and via the lake Ono was 0.02 and 0.08 respectively.

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The JONSWAP spectrum proposed by Hasselmann et al. has been conveniently used as a standard frequency spectrum of wind waves during wave growth. However, it is difficult to obtain the analytical integration for total wave energy and various kinds of mean wave period defined by the spectral moments with respect to frequency. In this paper, their approximate expressions are proposed as a function of peak shape parameter γ under the assumption that the other parameters σ_a and σ_b are constant. All of the expressions have very high accuracy, and maximum error is less than 0.3% respectively. It is also shown that the total wave energy-fetch relation estimated from the observed data by Hasselmann et al. is inconsistent with the one derived from the other spectral parameter-fetch relations and the expression mentioned above in both the aspects of analytical form and numerical value.

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