Analysis on the stability of oscillation in a hydraulic system equipped with a surge tank has been made. The Thoma condition of stability is modified by taking account of the effect of inertia of flowing water in the penstock, hydraulic characteristics of turbine, characteristics of the turbine speed governor, inertia of rotating part of turbinegenerator, and paralleled running of power plants. Extensive numerical computation has been made basing on the theory derived herein, and the effect of them is examined in detail. Stability regions are shown in diagrams by the use of suitably chosen dimensionless parameters.
Stability of oscillation in the hydraulic system having no surge tank has also been analysed and is compared with the result in the case when a surge tank is equipped.
Furthermore, the response of the whole hydraulic system to the periodic variation of power demand has been analysed. The theoretical result thus derived is compared with the result of field measurement in an electric power plant. Good agreement is shown between the theory and measurement.
Basing on this study, guidelines for deciding whether the installation of a surge tank is necessary or not in a relevant case are proposed.

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Bed-load transport is often influenced by transpiration (suction or injection) through a boundary of a stream. In this study, the effect of transpiration through a bottom of a fluvial open-channel on the velocity distribution and bed-load transport are investigated both theoretically and experimentally. Bed-load transport is represented as a combination of pick-up rate and step length, and they are affected indirectly by distorted velocity distribution and directly by seepage effect. Particularly, the pick-up rate is severely affected by the transpiration. The indirect effect promotes bed-load transport on suction; while the direct one promotes it on injection. Under ordinary conditions for sand and gravels, the injection through a bed promotes bed-load transport; but the transport of materials with large specific weight is suppressed by the injection. Such effects are theoretically predicted and experimentally certificated.

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The concentration distribution of suspended sediment under non-equilibrium conditions due to the change of bed shear stress was investigated by focussing the analogy between the transient process of the Reynolds-stress distribution and that of the turbulent flux of suspended sediment. The impulse response of the Reynolds-stress distribution was empirically determined by a classic wind-tunnel data, and its applicability to that of an open channel flow was certificated by the recent accurate data of turbulence measurements in the flow with abrupt change of bottom roughness. By applying this impulse response, the suspended sediment-flux distribution due to turbulence in the transient process was described. Moreover, by using the boundary condition at the water surface, the suspended sediment concentration distribution under non-equilibrium conditions was deduced. The proposed method to estimate the non-equilibrium suspended sediment concentration revealed that the so-called adaptation length of suspended load reaches a few hundred times flow depth.

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A knowledge of the nature of turbulent flow with small relative submergence plays an important role for clarifing fluvial hydraulics of mountain rivers. Because of the existance of “roughness sublayer” which is a near-bed layer affected by roughness elements, the flow with small relative submergence is different from that with sufficient relative submergence. In the present study, the fundamental characteristics of flow with small relative submergence are discussed through flume experiments of flow over rough beds which are composed of glass beads and of natural gravels. In the roughness sublayer, the velocity profile becomes more uniform than the log-law profile and the turbulence intensity is suppressed. These characteristics are proved to be closely related with the measured distribution of Reynolds-stress.

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A strong rising current can be produced by placing a V-shaped plate against a horizontal uniform flow. Vortices are formed from the plate, coalesce with the neighboring region ones in the separation zone, then shed downstream. These vortices have a horse-shoe shape and rise due to a self induced upward motion. As the dihedral angle of plates increases, the vortex shedding Strouhal number decreases due to the frequent coalescence in the separation zone. The vortices are intensified by this coalescence, resulting in the formation of higher self-induced velocity. With too large dihedral angles, however, vortices do not rise so high because of the small self-induced velocity. On the other hand, with too small angles, the vortex forms further downstream in the separation zone, which prevents coalescence with others and increases of the vortex intensity, also resulting in the small rising height. Eventually, the rising height shows optimum with the dihedral angle of around 90°. There, the height can reach more than 10 times the plate height. The Strouhal number was found to decrease with increasing Reynolds number, regardless of the dihedral angle.

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The numerical model simulating several processes in the diurnal mixed layer is constructed based on the DIM (Dynamic Instability Model) type entrainment law derived by authors. The model has three noteworthy features. The first is that the entrainment speed is estimated according to the density gradient below the thermocline. The second is that the model describes not only the mixing process but also the heating process. The third is that the model is basically one-dimensional model but it can estimate the pressure force caused by surface tilt. The third feature is realized by solving the basic simultaneous equations consisting of the momentum, continuity equations and the entrainment law. The model is tested to input meteorological conditions just after rainy season in 1988 at the Lake Kasumigaura, and the results agree well with measured temperature and velocities.

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This paper aims to make clear the percolation process of meltwater within coarse grained snowcover. For the purpose, experiments on the unsaturated vertical percolation were made, using snow columns.
The obtained results were as follows: 1) The observed propagation speed of inflow meltwater flux was close to the wave speed calculated by the gravity flow approximation. 2) Assuming that the unsaturated permeability k_w was in proportion to the n-th power of the effective saturation S_e, the mean value of n was 3.67 and the intrinsic permeability k was within the range of 1.94×10^-8 and 6.11×10^-8m². 3) The propagation speed of the flux increased with each repetition of percolation of meltwater. 4) For the inflow flux less than 6.0×10^-6m/sec, the outflow hydrographs calculated by the gravity flow model was close to the observed hydrographs except the beginning of outflow, etc..

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This paper applies the upstream weighting finite element technique, developed by P. S. Huyakorn and G. F. Pinder, to a set of newly modified governing equations of fully coupled heat and moisture transfer in porous media. The numerical solutions obtained are compared with some experimental results of the temperature, moisture content distributions and cumulative evaporation curve, which are taken for a size of 0.1×0.1×0.6m soil test column under the soil water evaporation induced by the radiation. The basic theory by J. R. Philip and De Vries is able to lead a reproduction of these experimental results by the choice of a proper value of the upstream parameter, α. For α=0 (Galerkin finite element technique) the temperature and cumulative evaporation values are larger than the experimental ones. Results indicate that this technique is superior to the Galarkin method in dealing with the problems of heat and moisture transfer through porous media during the soil surface evaporation.

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We deduced a simple evaluation method of infiltration parameters in a watershed as follows. (1) S and K of Philip's equation are determined by using a double ring infiltrometer experimentally. (2) Philip's equation is changed for Green-Ampt's one by mathematical equivalent and their parameters are transposed each other. (3) Campbell's empirical equation is deduced from the capillary theory and their parameters are also expressed by the infiltration ones. (4) Some infiltration parameters are correlated experimentally. (5) All the infiltration parameters are deduced from the above relationship and the experimental result of the double ring infitrometer in a watershed.

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First, an expression of efficiency of detention storages for water quality and supply controls, which was derived by the authors, is briefly explained. The expression contains several parameters, which represent characteristics of (1) rainfall time sequence, (2) land-use and (3) the storage-treatment system. The rainfall characteristics all over Japan are analyzed using data of AMeDAS, the automatic meteorological data acquisition system of the Japan Meteorological Agency, and, then, values of the parameters relating to the expression are summarized on the map of Japan with contours. A process of estimation of the efficiency by the proposed method is exemplified for a hypothetical and typical size of a house detention pond in the Tokyo area.

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The study of turbulent flow over a wavy surface bed such as sand ripple is very important in understanding the mechanism of onshore-offshore sediment transport.
In this paper a numerical calculation of the flow structure over sand rippled bed under wave motion is conducted using a k-ε turbulence model for low Reynolds number. The calculated results are compared with the measured data obtained with a laboratory flume with and without suspended sediment added. The calculated flow structure such as velocity vector, streamline, circulation flow and turbulence kinetic energy is in agreement with the measured results. Also the turbulent kinetic energy is found to be dampened by addition of suspended sediment.

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A time scale for preserving the similarity of beach change processes between prototype and model under the unsteady condition is studied using a series of small- and large-scale experiments. The time scale is proposed as a function of experimental scale. By appling the time scale and the scale-model relationship to model experiments, the temporal beach change such as shoreline change and relative breaker point were well reproduced within the allowable range of experimental errors. Also, time scale is derived theoretically from the continuty equation of sediments and so on. The correspondence between the experimental and the theoretical time scales is discussed. The reliability of the proposed time scale and the scale-model relationship is checked by the movable bed model of beach change in the Ogata coast during a storm.

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The oscillatory boundary layer over a sand ripple model was measured in detail by 2-D laser doppler velocimeter. The measurement was performed in an oscillatory flow tunnel for three cases with different period and amplitude. It is found that the boundary layer is governed by large organized vortices generated alternately from the crests of the ripples. The generation of the Reynolds stress is limited within the vortices, and the associated eddy viscosity shows sinusoidal variation according to the growth and decay of the vortices. Two stationary cells were observed between the crests, the velocity of which takes about 60% of the velocity amplitude of the undisturbed oscillatory flow near the crests. An inner boundary layer was observed, the thickness of which is found to be about √νT

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A correlation method has developed to obtain the instantaneous velocity fields in wave breakers and its spatial derivatives by utilizing the entrained air as tracer. The errors of the method are evaluated and reduced by data processing. The method has applied to the spilling and plunging breakers of the solitary waves. The 3 dimensional behaviors of the flow and vortex are analyzed and discussed through the distributions of the velocity, vorticity, strain rate and two-dimensional divergence of velocity taken from the side and the bottom of the breakers.

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Pyrolysis products derived from precursors (Polychlorinated benzene: CB/Polychlorinated phenols: CP) or PVC, and products generated in mixed combustion of cellulose and HCl gas were studied. The following facts became evident. PCDD and PCDF were derived from CB and CP both. But the formation quantity of dioxins derived from CP was much greater than from CB. CB, CP and HCl gas were derived from PVC, but PCDD was not derived in the existence of HCl gas. CB and CP were derived from cellulose, but PCDD was not derived in the absence of HCl gas. The existence of HCl gas is one of the determining factors of dioxin formation.

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Investing the effectiveness using sludge incinerator ash for sludge condition and its effective adding methods for improving dehydration in fluoride electrolysis sludge treatment, following items were clarified in this paper: 1) It is found that the sludge dehydration was improved in proportion to the addition of sludge incinerator ash; 2) But, generally sludge incinerator ash itself includes many fine particles with high specific gravity, which may plug filtration. Therefore, the surface reforming was required to improve the dispersibility of particulates. As a result of this, the dehydration (becomes better) in smaller adding volume than previous one; 3) Further, considering ionically the adhesion and combination of the organic fiberizing matters produced by electrolysis with sludge incinerator ash, timely change of addition time does not only decrease the amount of sludge incinerator ash but increases sludge dehydration. From these results, it was concluded that the utilization of the sludge incinerator ash for sewage sludge treatment by electrolysis is very useful.

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The flow development and the entrainment process in a two-dimensional buoyant surface jet are discussed by numerical experiments using the algebraic stress model, which has been examined through the comparison with measured turbulence quantities in the previous paper (Murota et al., 1989). The calculated results are in good agreement with the empirical relationship between the entrainment rate and the Richardson number. It also shows that the dependence of entrainment rate on the Reynolds shear stress changes drastically at the shear layer Richardson number of 0.08, whose value corresponds to the critical value obtained in stratified shear layers theoretically and experimentally.

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