A storage pond model is developed which can treat inundation of both ground and underground spaces in urban area. The continuity equation, momentum equation without advection, and drop formula are used in the model. The model is applied to Fukuoka city with the underground spaces in JR Hakata station, and Fukuoka flood (1999) is simulated. The computation results show good agreement with the actual record. In the case of Kyoto city, overflow from the Kamo river is assumed. As a result, the underground malls downtown and adjacent subways are inundated. Also the underground spaces which are far from inundation area of ground are inundated by the water flowing through subways.

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A flooding to an urban underground space may cause the serious damage on a life of human. The effective simulation that handles directly individual action of human being has not been applied to the refuge from inundated urban underground space, up to now. In this study, the distinct-element-method type humanaction model is built and improved for the simulation of crowd behavior in the flow field, which is calculated by the shallow-water-flow analysis. In the human action model, an individual recognizes the situation of circumference, and actively moves based on self decision making. Interaction zone of individuals is set with assuming that individuals decide their moving direction based on the visual information of their circumference. The driving force of active motion of individuals is set by taking previous observation of moving speed of crowd into account.

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As the prevention of all water disasters by using of structural measures is very difficult, the present task is to construct non-structural disaster measures as well as the usual structural ones. The importance of overland flood flow analysis increases for examination of these various counter measures. The aim of this study is to develop the synthetic system for analysing water phenomenon in river, sea and urban region in flooding. The heavy rain in Tokai district is treated in this study. The suitable distribution of inundation water depth is obtained in the inundation states of the urban area. From the simulation results, the validity of the numerical analysis models systematized here and the effect of the sewer system in flood is discussed.

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A filed study and dynamic flood simulation on the Onga River heavy rainfall disaster in July 18-21, 2003 were conducted. Firstly, the flood process in the Iizuka-city area, which suffered the greatest damage in the Onga basin, was examined based on field study. Secondly, the flood simulation model was applied to the Iizuka-city area. The water movement in the urban area including the Onga River, main branch rivers was simulated simultaneously and the computed results compared with the flood process examined in the field study. Finally, the effect of the river improvements on the flood damage was examined through the numerical simulation. It shows that the model is a useful tool for examining the effects of the improvement work of a main river to inundation flows from tributary rivers.

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Rivers possesses the function of storage and peak discharge attenuation of flood water. Author's recent studies have deepened basic understanding of these important characteristics of the flood flow. At the river confluence, downstream boundary conditions of a tributary change with time. The water flowing from the upstream and going against a stream is stored in the tributary.
Furthermore, at the river confluence, a water level changes with time and a reverse water surface slope occurs under the time change in the downstream boundary conditions. It is difficult to estimate accurate flow rate of the tributary in such hydraulic conditions. This study aims to estimate by new method discharge hydrograph and storage rate in the neighbourhood of the confluence of the Tone River and the Watarase River.

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To realize more accurate measurements for pollutant loads in an urban river, in the present study, a high-resolution, acoustic Doppler current profiler (HR-ADCP) was used to measure the vertical distributions of current and SS in an urban river under rainy conditions. The field measurements with the bottom-mounted HR-ADCP were carried out at the downstream point of the Oohori River, one of main inflow rivers in Lake Teganuma. The observed results show that characteristic vertical structures of the current and SS appear in hydrologic events and then the vertical distribution of SS flux in the streamwise direction vary considerably in rising and falling stages. With the HR-ADCP measurements, we grasp the temporal variation for the dependence of the erosion rate of sediments on flow conditions.

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Velocity measurements were carried out in a river of straight reach with a series of groynes on one side of the main channel. An Acoustic Doppler Current Profiler (ADCP) mounted on a small boat was used. The measurements were performed under three depth conditions including two submerged cases. Flow patterns induced in groyne fields, exchange processes between the main channel and the groyne field, and local flow peculiar around groynes, are of interests.
2-D large circulation flow is dominant in the non-submerged condition, whereas a vertical vortex is formed just behind a groyne in the shallow submerged case, then these circulating patterns in a groyne field are totally washed away in the deep submerged case. The maximum velocity filament in the main channel appears at different positions as the water depth changes owing to the groynes' effect. A slow water body leaving a groyne and showing a boil-like motion is clearly detected.

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This paper analyzes velocity fluctuation of 30min to 60min period observed in the Tone River Estuary. First, the influence of the fluctuation on resuspension of sediment is assessed by analyzing near-bottom turbulence data. The result indicates that the fluctuation may enhance resuspension considerably. Second, the characteristics of the fluctuation are investigated. Spectrum analysis of cross-sectional average velocity and water level shows that there are several dominant oscillations whose frequencies coincide with the characteristic frequencies of seiches in the estuary. This result indicates that the velocity fluctuation is caused by higher harmonics of seiche. Furthermore, the external force causing the seiches and the response of the estuary against it are examined by comparison of frequency response functions estimated from observation and analysis. It reveals that the seiche is mainly caused by offshore water level fluctuation.

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Data of current, water density, and suspended sediment (SS) were collected for about 3 months in the Ohta floodway to clarify characteristics of SS transport in tidal estuary where flow and density conditions change significantly. The SS transport intermittently occurs, and most of that occurs just before and after lower low water slack. Moreover, it is found out that the long term variation of SS transport is concerned with river discharge and tidal range. Peaks of the SS transport on the flood tide are higher than those on the ebb tide during the spring tide. Spatial variation of SS transport is examined from observations at longitudinal three measurement positions, which are located at about 2.8km, 5.8km and 8.8km.upstream from the mouth.

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Long-duration observations of tidal current and stratification have been conducted in the Ohta flood-way. The data demonstrate a semi-diurnal stratification cycle driven by tidal straining of freshwater-induced horizontal density gradient, i. e., the stratification during the ebb is stronger than that during the flood. As a result, the data of current profilers show that the velocity distribution during the ebb deviates from logarithmic law. The nonlinearity of tidal wave and tidal straining mainly bring about the asymmetry of tidal current and bottom shear-stress. At 2.8 km upstream from the mouth, the maximum bottom shear-stress during the flood is twice as large as that during the ebb. A numerical model incorporating a level 2.5 turbulence closure scheme reproduces the main feautures of the observations and is used to investigate the behaviour of the current and bottom shear-stress.

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A simple modification is proposed to compute free-surface flows with HSMAC type iteration method of computing incompressible flows. It solves for the position of the moving free surface boundary as part of the iteration to satisfy the continuity equation in a non-boundary conforming fixed grid system. It does not need any additional transport equation for tracking the moving boundary as in most methods and a stable and accurate solution can be obtained. The method is verified in a benchmark test case of standing wave and applied to LES computation of a turbulent open-channel flow past a backward-facing step. The results indicate that both instantaneous flow is simulated well and the mean quantities agree with experiment and other methods. It is proved to be a viable method of computing practical free-surface flows

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An large-eddy simulation of a turbulent flow using a dynamic two-parameter model has been carried out for a straight open channel with one flood plain at a Reynolds number of 5, 300, based on the hydraulic radius and bulk mean velocity. This can be viewed as an extension of Satoh's simulation [J. Hydr., Coastal and Envir. Engrg. JSCE 628/II-48 (1999) 115] in which the standard Smagorinsky model was employed as an SGS stress model. Overall, the computational results agree quite well with laboratory measurements by Tominaga and Nezu [J. Hydr. Engrg. ASCE 117 (1991) 21] in spite of difference in their Reynolds numbers and show that the present method is a promising tool for natural river predictions.

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The unstructured collocated grid can be easily adapted to the complicated boundary shapes. Thus, it is effective when the incompressible flow is predicted for the numerical actual phenomena. A C-ISMAC method is an implicit algorithm, which had been shown to be effective on the structured collocated grid. This method is based on an implicit-SMAC method in the stagged grid, and can be used with higher-order schemes for spatial discretization as done in an explicit scheme. In this paper this method is applied to unstructured collocated grid. To show the validity, the incompressible flows in the square and triangullar cavitys is calculated with a C-ISMAC method. It is shown that the calculation time is decreased and the calculation accuracy is almost same when a C-ISMAC method is used.

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To perform a three-dimensional current simulation in a wide region of a river with reducing computational load, we attempt to introduce a two-way nesting procedure, recently presented by the authors, into a three-dimensional numerical model for river flow. To examine the fundamental performance of the present model, we conduct the flood flow computation in the Edo River with the present numerical model. The results show that the computational results for the time sequences of discharge and lateral and vertical distributions of the streamwise velocity give good agreements with the observed data done by the authors. This fact demonstrates the fundamental applicability of the present numerical model with the nesting procedure to flood flow computations.

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A new numerical scheme to solve a water flow with a free water surface and arbitrary curved ground surface is proposed. In the proposed method, by using a soroban grid system proposed by one of the authors, computational mesh is reconstruct easily at each time step so that some grid points locate on a free water surface exactly. Time development of velocity components and water surface are calculated according to an incompressible inviscid flow equation without any transformation of the equation. Advection effects are calculated by direct interpolation of the CIP method in 3rd order accuracy in spatial. After the advection is solved, acceleration of velocity components due to the pressure gradient is solved using a FDM approach on a soroban grid system. The proposed method is applied to some problems and computational results are examined through comparisons with results of other FDM scheme and theoretical result.

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Applicability of some numerical schemes in generalized curvilinear coordinate forms on a density current is examined focusing on the conservation and numerical diffusion. Various models with different spatial schemes for convective terms, grid fineness, turbulence models and methods of pressure calculation are applied to the mixing of two fluids with different density in a simple rectangular domain (Flat Model), a rectangular domain with a small mound (Mound Model) and a trapezoidal domain with steep bed slope (Slope Model). The numerical results show that the un-conservative spatial schemes yield significant error in total salinity and grid fineness affects not only the vertical density profile but also the phase velocity of density wave. A simple modification is also proposed in order to suppress unreasonable current in a stable stratified flow over a steep bed slope.

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In this paper, a volume correction method for free surface flow analysis using density function method is proposed. The proposed volume correction method consists of two steps. The first step is to correct the volume of fluid phase. The second step is to correct the mass in the whole computational domain. The effect of the proposed method was checked by solving a dam break problem. Especially, volume conservations and mass conservations are checked. It is found that the proposed volume correction method is effective and this method makes an air-water interface sharp.

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It is very important to reveal the hydrodynamic properties in open-channel flows including the rising-bubbles, when we consider effective control techniques of aeration in actual rivers, sedimentation basins and reservoirs. However, such a bubbly open-channel flow has very complicated phenomena, and thus there are few previous studies that have been tried by high-accurate measurements and numerical simulations. Therefore, in this study, the bubbly open-channel flow was calculated by using a discrete vortex method (DVM). The DVM is a gridless model and applicable to multi-phase flows such as air-induced flows. As the numerical results, it was found that the present model was able to predict the hydrodynamic properties observed in the experimental data.

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In this study, a direct numerical simulation for analyzing the immiscible incompressible two-fluid flows was carried out with the 3-dimensional MARS method, and the applicability of this scheme was verified in the water column collapse phenomenon, 2-dimesional channel flows between two walls and 3-dimensinal air-water co-current flows between a non-slip wall and a free-slip wall. It was shown that the present numerical simulation was in good agreement with previous experimental and numerical results, and that the volume of fluid in flows was sufficiently conserved for the long simulation time step. However, it is pointed out in the 3-D air-water co-current flows that lack of simulation grids and inadequate averaged time generates the inaccurate results in this DNS.

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A method for predicting turbulent gas-liquid two-phase flows is developed. A level set method is used to capture the motion of the interface and a k-ω model is introduced as a turbulence model. The turbulence damping effects near the interface are modeled by considering the jump in the density profile across the interface as a special case of density-stratified flows. This multiphase approach enables us to treat a wide range of flows involving free surfaces in the same way, irrespective of the importance of the motion in the air phase. Computational results for a two-dimensional, fully-developed open-channel flow are given to illustrate the properties of the method along with a discussion of the future implications of these results for better performance.

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Sewage thermal energy is a kind of untapped one that we can easily obtain in a big city. To apply sewage heat to road heating in winter, a heat extraction test was carried out using a heat exchange pipe sank in fluid in a mimic sewer pipe. A longitudinal temperature profile of heat carrier fluid was measured along the heat exchange pipe. The extracted heat increased as the flow rate of sewage or of heat carrier fluid (heat exchange fluid) became high. A quasi-Nusselt number, N_uq was proposed to predict the overall heat transfer coefficient of the heat exchange pipe. The value of N_uq was normalized by the overall heat transfer coefficient, and the heat conductivity and diameter of the heat exchange pipe. As a result, the following relation, N_uq=2.483×10³R_eh^0.34R_es^0.2P_r^0.4 was obtained, where R_eh and R_es are the Reynolds number of heat exchange pipe and sewage and P_r is the Prandtl number.

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A quasi steady heat and mass transfer model of a Tubular Solar Still taking account of humid air properties inside the still is presented in this study. Time variations of saline water, humid air, cover and trough temperatures and production and condensation fluxes are derived under a steady meteorological condition. In order to validate the proposed model, an indoor production experiment on a Tubular Solar Still was carried out in a thermostatic room at the University of Fukui. A special technique to investigate the water-vapor movement in the still was also developed and could detect a time lag between the evaporation flux and the condensation flux. It is found from the production experiment that the analytical solutions derived from the present model could reproduce the experimental results on the saline water temperature, the humid air temperature, the cover temperature and production and condensation fluxes.

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We investigate the influence of terrain on the slow spreading of isothermal lava by numerically solving initialvalue problems for a Bingham fluid. Under the lubrication approximation, systematic computation is carried out for two types of terrains: an inclined channel of finite width and a hill on a sloping base. The transient evolution and the final extent of lava are calculated for a dry bed. In the open channel the effects of bank steepness, Bingham parameter, and the total volume on the final extent of spreading are examined in detail. A simple formula is found by synthesis to relate the final elongation ratio of the deposit to these factors. For a hill on an inclined base, both symmetrical and asymmetrical spreading from a hillside are studied. The transient motion of the lava flow is found to follow essentially the direction of local path of steepest descent.

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The transportation of sedimentation in 2D branched and non-uniform duct flows is numerically predicted with a computational method, which has a conservative scheme for convection terms in 5th-order accuracy with a flux control technique (FVM-QSI scheme). The governing equations including a turbulence model are discretized with strong conservative forms in curvilinear coordinates on the collocated grid system. The predicted results are compared with the measured values and its applicability is discussed.

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Flow/particle and particle/particle interaction are key-factors to investigate internal structure of the bed load layer from the viewpoint of computational mechanics of sediment transport. In addition, interaction between bed load layer and fluctuating free water surface is also key-factor under high bottom shear condition. In this paper, the particle/ particle interaction was evaluated by the Distinct Element Method (DEM), the flow/particle interaction was evaluated by drag force and the free water surface was traced by the Lagrangian massless marker particles. Developing process of the bed load layer was simulated by the Euler-Lagrange coupling model, furthermore, the internal structure of the bed load layer was discussed by the velocity profile, ineter-particle force and so on.

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This paper concerns the evaluation method for contact force in the Distinct Element Method (DEM) in terms of the energy conservation. The contact force is usually determined from the relative displacement of the particles, using analogy of spring-dashpot system. Since this form of contact force does not take account of the mechanical energy of the particles, unexpected sudden increase of the kinematic energy can be occured. In this paper, an evaluation method for contact force that conserves the kinematic energy is newly proposed. A basic validation is carried out to confirm the validity of the proposed model.

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The applicability of the computational method for multiphase flows, MICS (Multiphase Incompressible flow solver with Collocated grid System), is investigated for the incipient motion of a cylinder under the shielding effects in a duct flow. In order to understand the actual phenomena, hydraulic experiments are conducted with two cylinders, one fixed and another movable. In the experiments, the distance of the two cylinders are widely changed and critical flow rates that rotate the movable cylinder are measured. As a result, resistance force and sheltering coefficients are derived and the defects of the usual evaluation method to derive these values are pointed out. The incipient motion of the cylinder is numerically investigated with MICS. As a result of the computations, it is shown that the behaviors of the movable cylinder are reasonably predicted with MICS, while MICS needs no empirical coefficients regarding the resistance force and sheltering effects.

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Graphics of falling-water texture are produced by the frame work to combine the sub-particle-scale (SPS) texture model for splash with the particle method for a physical skeleton. A texture of splash is described as the diffusion process of mist by the random walk model. A gas-liquid two-phase-flow model is used for a calculation of falling-water and resultant air-flow field. Governing equation of the pressure that express the compressibility of gas phase is applied. The computational program is improved so that a stable solution is provided in the gas-liquid interface under high-level change of pressure. A conventional diffusion model is improved so that the unsteady and non-uniform structure of air flow affects directly on the motion of mist. The hybrid tracking model of a droplet and an air bubble is proposed on the basis of a random walk model. Finally, the graphics of falling water are drawn by the ray tracing technique.

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the spur dikes has gathered great public attentions from a point of view not only in river engineering but also in water environment, because the spur dikes offers a comfortable environmento aquatic lives and plants as well as human beings in eco-systems. At present, some artificiality side-cavity has been constructed in the rivers for the purpose of the maintenance of the river environment. However, there is little information of form effects of the spur dikes on the bed shape and hydraulic characteristics. In this study, the bed topography and velocity in and around spur dikes in an equilibrium condition were measured with changing the aspect ratio (=streamwise distance of each spur dike/spanwise length of spur dike). It was found that the maximum depth of the scour hole increases with an increase of the aspect ratio and also that crest is located near the junction between the main-channel and side-cavity. The latter result is corresponding to the phenomenon of the Kiso River.

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When a flow over backward-facing step or consolidation work includes both subcritical and supercritical flows, a very complicated local scouring is generated by interaction of a wave jump and a submerged jet at the downstream of these structures. Since the local scouring decreases the stability of these structures, it is a very important problem on disaster prevention. In this paper, we present a 2-dimensional numerical model which can reproduce the local scouring by the complex flow over backward-facing step. The numerical model is based on the MacCormack scheme, and the FAVOR method is introduced into the basic equations. A bed load and a suspended load are taken into consideration by the bed evolution model. The numerical results reproduce the local scouring by repetition of each flow well.

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A generalized method to determine maximum and temporal evolution of scour-depth at river structures, based on large range of data set from independent physical model studies, has been developed. A relative grain-size-like parameter referred to as alpha parameter was proposed. Likewise, a method was proposed to determine time factor in terms of a parameter, so called, sediment Strouhal number that can be employed as a similarity number in any time dependent phenomenon. It is evident that temporal development of local scour can widely be generalized using this parameter. Proposed method can be applied for structures protruding from the river bank (spurs, abutment etc) as well as pier-like structures. This method can be applied for live-bed scouring case as well. The method was verified using large range of laboratory data from independent investigations on maximum and temporal scour. Likewise, method was tested against field investigation on temporal scour development at pier during flood event.

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Nature-friendly hydraulic structures such as a rubble mound weir have attracted researcher's attention in recent years. Therefore, it is important to establish a numerical model to predict a possible failure process. In this research, the distinct element method which is used for modeling the aggregate of discontinuous elements is applied to model a failure process of the rubble mound weir. Hydrodynamic forces acting on the rubble-mound weir such as drag force and seepage force which are required in the calculation of DEM was obtained by the flow analysis using VOF technique. It is confirmed that the numerical results using the proposed method can reproduce the movement of particles in the early stage of failure under the steady flow condition. It is also clarified that the contact angle of DEM particles has a significant effect on the failure process.

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Bed protective works are installed just downstream of weirs and ground sills to prevent failure and collapse of the structure due to bed scouring. Because a failure of bed protective works exposes the main structure in danger, it is importantf or river technologya nd managemento maintain the safety of the bed protectivew orks. In this paper, themodel of a vertical two-dimensional analysis for the flow with complex boundary shape of blocks is presented, in order to evaluateh ydrodynamic forces acting on the blocks. Then, the numerical analysis for deformation and failure mechanism of the blocks based on the criteria for determining whether a block moves are performed. It is clarified through the comparison between measured and computed results that the model can simulate the deformation and failure mechanisms with flow fields.

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The hydraulic characteristic of submerged overflow is not fully solved as compared with perfect overflow. Moreover, in the research on a weir, the hydraulic model test is conducted in many cases. However, if the flow over a weir can be reproduced in sufficient accuracy by numerical analysis, it will be able to contribute to the elucidation of its hydraulic characteristic greatly. Then, in this research, numerical analysis of the submerged over flow on trapezoidal weir is performed. Consequently, the flow change by the difference in Ht/Ho is in good agreement with experimental measurements (Ho: water depth at upstream of weir, Ht: water depth at downstream of weir, both from weir crest). Additionally, by not disregarding approaching velocity head and evaluating discharge from the channel floor to the water surface, the possibility of deriving the discharge formula which can be applied when Ht/Ho is close to 100% is shown.

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The discharge formula of the side-weir, which can predict spill discharge per unit width in open-channel flows, involves the discharge coefficient. A lot of discharge coefficients have been suggested by many researchers. However, each researcher uses its own parameters in the discharge coefficient, irrespective of that Subramanya & Awasthy pointed out that the discharge coefficient is controlled by four parameters such as the inlet Froude number, the ratio between the height and length of the weir, the ratio between the inlet flow depth and length of the weir and the ratio between the length of the weir and channel width. In contrast, it is quite difficult to change one parameter under the condition that the other three parameters are kept. In this study, the experiments were conducted with changing all parameters under the condition that the ratio between the height and the length of the weir is set to zero. A new spill discharge coefficient of the side-weir with zero height in subcritical open-channel flows is proposed.

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Numerical simulation of flow over stepped channel is performed here in. All the previous studies on the flow over stepped channels have been done in the experimental way. It is because that in the Eulerian method, which is popular as the method for analyzing the free surface flow, it is too difficult to treat complicated boundary condition of this phenomenon. On the other hand, the particle method shows good performance to simulate the fragmentation and coalescence of liquid. The previous numerical simulations by particle method in hydraulic engineering were executed in 2-D field because it was impossible to track the sufficient number of particles required to execute 3-D simulation, due to a limitation of computational memory. But, in these days, the hardwear is rapidly developping and we can control sufficient number of particles to execute 3-D simulation under the rather small computational domain. In this study, 3-D simulation model of particle method is applied to the flow over stepped channels.

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Fishways are river constructions which give a helping to fish migration. The rea re three types of flow formations in pool-and-weir fishways such as a plunging flow, streaming flow and intermixed flow of plunging and streaming flows. Rajaratnam et al. proposed a criterion formula that predicts the flow formations. However, this criterion formula has no physical meaning. Further the accuracy of prediction of their for mula is not high. In this study, the criterion formula, which can predict the flow formation in a pool-and-weir fishway, is derived semi-theoretically. The experiments were conducted with changing the aspect ratio and discharge in the pool-and-weir fishway. The water surface profiles were measured and also three components velocities were measured with a 3-D electromagnetic current meter. A new criterion formula, which is able to predict the flow formation, is proposed under the condition that the channel slope is 1 on 12.

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Manyr esearchersin vestigatejdu mp characteristicisn slopingc hannels, b ut the effecto f an aeratedi nflowo n flowcharacteristicosf hydraulicju mps has not been shown at all. This paper presents the effect of aerated in flow on flow characteristics of hydraulic jumps in steeps lopingc hannels (i. e., 30 and 55 degrees). The experimental in vestigation reveals the relationship between velocity decay, jumps length, and air-concentration distribution in hydraulic jumps under different air-concentration of aerated inflows. Further, an air-concentration distribution in hydraulic jumps has been characterized, and the magnitude and distributionp atterno fair-concentratioin n jumps has been discussed betweena erateda nd non -aeratedi nflows.

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Stepped channels are effective for dissipating the energy of supercritical flows that occur at steep channels, dams, weirs, and drop structures. As stepped channel flows are characterized as aerated flows, it is important to estimate the energyh ead of the aerated flow for a hydraulic design of the stepped channel. Recently, the authors proposed a method for estimating an energy head of skimming flow E_w by using a clear water depth. But, an energy head of air-water flow E_res in stepped channels has not been estimated. In this paper, a method for estimating the energy head of air-water flows E_res in stepped channels is presented. Also, the relationship between E_w and E_res is discussed under given discharge, channel slope, and step height. The experimental investigation reveals that the magnitude of E_res is nearly equal to E_w. Further, the relation between the actual velocity of an aerated flow and the velocity obtained according to the clear water depth in stepped channels is shown.

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The characteristics of the circulation flow were investigated for the water flow with the air entrainment slightly from the free water surface in a three-dimensional rectangular outlet pit. At first, the air entrainment pattern was classified into two types by the visual observations.
Measurement of the flow velocity distribution in the pit revealed that the dominant types of flow include circulating flow and vertical eddies. And relation of the three-dimensional steady flow field and the primary factor of the air entrainment were clarified. The primary factor of air entrainment made clear that it was the velocity of the radiated surface flow from the end wall, the flow velocity along the side wall and the instantaneous velocity of downward flow at water surface in outlet pit. Turbulent flow velocities in the three-dimensional flow field near the water surface were also investigated. It was concluded from these results that air entrainment is caused by interference between the steady circulating flow and instantaneous velocity variations near the water surface.

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This paperp resents the results of a numerical investigation on the flow field and the fluid force acting on a yawing blade of a new type waterwheel in unidirectional flow. Because the performance of the waterwheel heavily depends on the behavior of the spring-supported blades, we examined the effects of the spring stiffness coefficient and the rotational speed of waterwheel on the torque magnitude. Flow was simulated by solving the unsteady Navier-Stokes equations, in the Arbitrary Lagrangian-Eulerian formulation. Descriptions are given of the interaction between the viscous fluid and the blade. The results indicate that properly controlling of the spring coefficient is important to get alarger net force during one rotation. The net force becomes large when the wheel rotates at a speed of about 0.4 timesas fast as the velocity of the main flow. Fairly good agreementsh ave been obtained between the numerical results and the experimental for the relationship between the net force and the rotational speed.

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This paper presents the results of numerical simulations on the unsteady flow fields around a circular cylinder placed in asymmetric oscillatory flows. The corresponding fluid forces acting on the cylinder are also examined. Systematic computations are carried out for the two-dimensional Navier-Stokee equations in a generalized curvilinear coordinate. The asymmetric velocity profile of the cnoidal waves is adopted for the far field flow conditions. The effects of the asymmetric velocity variation on the vortex motion and the fluid forces are investigated for a wide range of Keulegan-Carpenter numbers. The structures of the wake vortices are described in detail, and the dependence of the maximum fluid force on the flow asymmetry is clarified. The results indicate the significant influence of flow asymmetry. The applicability of the Morison type formula for the in-line fluid force is then examined. The variationso f the drag and inertia coefficients in asymmetric oscillatory flows are als opresented.

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A habitat for the migratory fish, such as salmon and ayu, is separated after construction of a large drop in a river. This is because the fish cannot migrate over the large water difference. Recently, a construction method by making use of both a steep channel and pool has attracted a great deal of public attention, due to the migration is possible in this structure. In contrast, the hydraulic jump may occur in the pool when the river is flooded. The length of the hydraulic jump in open-channel flows with an abrupt rise is controlled by the Froude number and the ratio between the inlet flow depth and the height of the abrupt rise. On the other hand, the location of the toe of the hydraulic jump is not able to predict at present. If the location of toe and length of the hydraulic jump can be controlled, the cost of construction decreases. In this study, USBR-type III was constructed in the pool and the effects on the location of toe and length of the hydraulic jump is investigated with changing the inlet Froude number and inlet flow depth.

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A simplified evaluation method of the surface area and volume of coastal forest trees is proposed by using the Pipe Model based on the physiology of the vegetation. When inundation depth is higher than the tree height, the surface area and volume of tree evaluated by this method were simply determined by the height and diameter of tree. In addition, coastal forest trees' lodging resistance to a reproduced inundated flow by tsunami was investigated. The result of examination was equivalent or smaller than conventional values used for river channels. A quantitative evaluation of coastal forest trees' lodging resistance to tsunami was suggested.

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This paper presents results of a scale model experiment on internal flow field of newly developed selective withdrawal equipment with elevating rubber sheets. In order to clarify the flow pattern, a visualization-measurement was conducted using a 2-D PIV system. Horizontal and vertical cross sections of the flow field were measured under different conditions of the flow rate and the depth of the intake. The obtained data were described in the form of the vector map, and a generation limit of the airentraining vortex was also shown. These results will be utilized for validation of prediction models using CFD.

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Flow structures around colony-model on a flat plate, one of the vegetation type in river, were investigated by water flume experiment. Considering the characteristics of the colony of Phragmites australis, Typha angustifolia and Phragmites japonica, three parameters, distance between cylinders (L/D), aspect ratio and inclination, were decided. The two types of vortex street were visualized behind the colony-model, large eddy street and Kármán vortex street. The Strouhal number was not change with changing mean velocity. The value of drag coefficient, C_d, was changed based on L/D. When the aspect ratio was low, the C_d increased gradually with increasing L/D. But, it become almost constant value when the ratio was larger than 4. Moreover, the C_d decreased significantly with increasing the inclination of the colony-model. The C_d of the colony-modelc an be arranged by using L/D, aspect ratio and inclination of it.

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The effect of dry-wet history on the erosion process of cohesive sediment was investigated experimentally in the present study. Detailed discussion on the mechanism of this process was conducted here on the basis of enormous number of experimental data. In this experiment, the test sample keeps under dry or wet conditions every 6 hours, and erosion test was conducted just after each period. It wasfound that this process can be classified into two parts in their mechanisms according to the total period of this history. The erosion rate of test sample which experienced this history more than one day keeps almost constant value which agrees well with the predicted value of the erosion rate formula.

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In the computational mechanics of sediment transport, which approaches to movable-bed phenomena from the viewpoint of a computational dynamics, the numerical movable bed, or the numerical model of granular material, plays an significant role. A numerical movable bed is the tool which is based on the distinct element method analyzing the interparticle collision directly. Although the conventional numerical movable bed has been applied to a comparatively small domain, the application of numerical movable bed to the practical problems of movable-bed phenomena requires the handling of complicated boundary condition and resultant extreme increases of number of the calculation particles. Therefore the parallel computation by the three dimensional numerical movable bed is developed in this study, to enable the calculation with the 1, 000, 000 numbers of the particles. The performance of numerical movable bed is clarified, in a scale of practical problems, through the velocity of sediment in the fill and overflow processes of sediment control dam.

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In flow and sedimentation processes of the debris flow, an approach by considering particles motion and motion of water individually is more appropriate. This study has presented such a numerical calculation method by using the distinct element method (DEM) coupled with flow analysis and has analyzed the development of debris flow through the erosion process of bed-layer caused by the dam break. Especially, we focus on the effects of grain rotational motion and its friction on the debris flow simulation and find that when rotational motion of particles is not considered, total erosion volume in bed layer decreases. It is also shown that the appropriate spin motion considering rolling friction was indispensable for the DEM simulation of debris flow.

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Results obtained from both of flume data and theories suggest that equilibrium bed slope in flow over an erodible bed are determined uniquely by sediment discharge rate when the movements of sediment particles are laminar and thus no suspended transportation take place. This means that the static friction force is dominant in debris flow and that sediment concentration is determined by shear stress balance on the bed surface as seen in our previous studies. On the other hand, if part of sediment particles in debris flow body is transported in suspension, sediment concentration will be larger and the equilibrium bed slope will decrease. These facts are supported by Egashira et al.'s flume data and others' experimental data.
The present study discusses experimentally an influence of flow scales on an equilibrium bed slope and flow structure, based on experimental data and emphasizes that the equilibrium bed slope decreases with increasing of flow scale if part of debris flow body is turbulent.

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