In Japan, stakes that collect driftwood have long been used to prevent the blockage of bridges. However, design codes are not established; thus, stake installations differ for individual bridges. It is important to clarify the function of these stakes; for example, stakes can be used to prevent rubbish from accumulating near a pier. In this paper, we demonstrate a fundamental experiment that explored the function of traditional stakes as a countermeasure against driftwood accumulation. It was found that driftwood passes between piers after rotation about the stake. The functionality of these countermeasures against natural debris was confirmed. Consequently, it is suggested that stakes should be installed vertically at bridges to divert both drift wood and natural debris and protect the bridge.

抄録全体を表示

 In this paper, Frazil slush variation mechanism and a method of frazil slush variation estimation on ice-covered river are studied. This study did develop a frazil slush generation, transport and accumulation calculation model. The continuous input values of this model are air temperature, wind velocity, sunshine duration, snowfall depth and water level. We carried out field observation of frazil slush accumulation using the ADCP and the SWIP. It was shown that the calculation model built by this study can reproduce the frazil slush variation of the real river. The increase of frazil slush transport, the increase of frazil slush generation and the upstream frazil slush accumulation volume are important values when considering frazil slush blockage of water intakes.

抄録全体を表示

 Recently localized torrential rain has hit many urban areas to cause inundation partly owing to the insufficient drainage capacity of sewer system. Drain cover or grating, which serves as an inlet of road runoff to sewer system, needs to have high drainage capacity to minimize inundation. This study demonstrates through experiments that the introducing component members to conventional grating can significantly enhance its drainage capacity over a wide range of incoming discharge and road slope. Flow visualization and velocity measurement have shown that the enhancement is realized by the rectangular shape of the component member to alter the coming flow downwards and that the decrease in velocity over the grating due to the component member is too small to explain the increase in drainage capacity.

抄録全体を表示

 We examined the methods of the nested flood simulation model using unstructured grids. Water depth and discharge were used for connection of nesting calculation, and these results were compared with the reference calculation that did not employ the nested calculation. In order to compare the result with the previous studies, we performed flooding calculation with structure-unstructured grids nesting and unstructured-unstructured grids nesting, and they were applied to an uneven terrain of the Jamuna River basin in Bangladesh. As a result, nested calculation using water depth showed good agreement with the reference calculation, and result with discharge showed over estimation. For the further research, applicability of these methods should be confirmed in the cases where high flow velocity is observed.

抄録全体を表示

 Though the shallow water equations are highly precise in the inundated area where the water is continuous, it is not appropriate at the wave fronts which are neighboring with dry bed, for the reason that the derivative of water surface does not exist due to the discontinuous. Present research gave a focus to the wave fronts. It is shown that different treatments at the wave fronts may give much different results for the water depth and the wave celerity. A pseudo fractional-step method which splits momentum equation into advection phase and weir overflow phase is proposed here. It is then validated by comparing the numerical results with analytical solutions for 1D dam break wave of an ideal fluid, experimental data of water and other researcher's semi-theory.

抄録全体を表示

 The design of the confluence is one of the most difficult aspects of the implementation of a compound channel because the streamlines during high water may deviate from the banks of the low-water channel depending on the inflow conditions. This paper reports a field study on flood flow at the confluence of the Tone River and Watarase River. Stereo image analysis of the aerial photographs taken at a flood peak in 1981 revealed the flow divergence and convergence across the low-water channel banks as well as flow stagnation around the tree communities in the high-water channel. A quasi-3D shallow water model with unstructured triangular mesh system was used to simulate the flow field. The drag force of the tree communities was also taken into consideration based on the results of a field survey. The simulation fairly well reproduced the surface flow field obtained by the image analysis. The calculated difference between the streamlines at the surface and the bottom of the water suggested that large dispersive stress in the flow near the low-water channel banks, especially around the tree communities.

抄録全体を表示

 The Shakujii River basin is a highly urbanized area which is located in northwest of the 23 wards of Tokyo. The drainage system with high density was constructed in this area. This basin has been suffered from flood damage twice in the last decade. In this study, we conducted numerical prediction to investigate both a process of urban inundation and flooding. As a result, inundation risk in this basin was made clear with high accuracy and high resolution. In this study, we focused on the water exchange which occurred between the drainage system and the Shakujii River. In order to realize real-time prediction of inundation, another attempt about the simplification of computation was also conducted.

抄録全体を表示

 This paper presents a set of numerical flow simulations to investigate the flood control capacity of the Hyakken-gawa which was constructed as a floodway of the Asahi River for preventing inundation of Okayama Castle City in the 17th century. The river channel topography and hydraulic conditions for calculation were assumed almost same as the previous study, but the inundation to the eastside alluvial plain was calculated together to estimate its effect on the reduction of food damage in the castle city. The numerical simulation showed that the backwater caused by the transverse dikes in the floodway induced the inundation to the eastside plain just before the inundation would start in the castle city. The result suggests that the flood control planning in the age took the inundation to the eastside plain into account at the time of unusual flood events.

抄録全体を表示

 This paper discusses the development of a coastal sedimentary prism in recent 100 years that has taken place on an initially rocky coast (Teradomari-Nozumi beaches) facing the Japan Sea. The interesting case history actually began in 1922 when the Ohkouzu diversion channel started operation for safely conveying large quantities of flood water of the Shinano River into the ocean. Based on field studies, the discussion explores the fate and delivery of the fluvial sediment in waters up to forty meters and beyond, thereby emphasizing the importance of muddy flood layers in deciphering the complex coastal sedimentary architecture. The approach and outcome should facilitate insights into the nature of a sediment routing system, including the likely evolution of the catchment area over a prolonged period of time.

抄録全体を表示

 Estuaries of the large river discharge river waters and sediment to the sea. The discharged sediment is mainly the wash load, which is affected by density currents, tide, inertia forces of river discharge. Sediment which has repulsive force in pure water, lost electrical charge when it meets sea water and finally made flocculation caused by molecular attractive force. To understand distribution of the sediment in sea bottom, above mentioned phenomena should be included in numerical simulation algorithm for sediment transport model. In this study, a numerical algorithm for sediment particle transport under the effects of flocculation is originated. The algorithm is mainly based on the Lagrangian method. The performance of the numerical method is confirmed by the Lock-exchange flow in laboratory scale case. Application of the method to field scale calculation is conducted for the Okozu diversion channel in the Shinano River mouth. Settling of the sediment through the pycnocline is visualized with high resolution.

抄録全体を表示

 Morphology of Cua Dai River mouth and adjacent sandy beaches in Hoi An City, central Vietnam has been being eroded severely in recent years. Results of Landsat image analysis reveal that morphology of river mouth in the period from 1975 to 1991 is highly similar to one in the period from 2003 to 2015; long sand spit on the left side and cuspate shoreline (cuspate foreland) on the right side. Meanwhile, welding of two sand spit occurred in the period from 1995 to 2002. The river mouth topography formed during the 40-year long period are classified into three types. The right bank of river shifted to the south about 250m. That is corresponded to the period with elongation of sand spit on the left after welding from offshore sandbar. The tip of cuspate shoreline on the right side was also observed to move to the south during the period that right river bank shift to the south. The shifting to south of main river channel resulted in more sediment deposit on the right side of the river mouth, resulting in serious erosion on the left beach.

抄録全体を表示

 Breaching of sandy coast was commonly observed on Yamamoto Coast, southern Miyagi Prefecture during the 2011 tsunami. That made the shoreline having concave shape after the tsunami. Concave shoreline is bounded by two headlands. The recovery of concave shoreline is discussed through the analysis of satellite images. The relationship between dimensionless elapsed time with dimensionless recovery of shoreline at the central line of concave portion, and dimensionless of area of backfilling in the concave portion are studied based on analytical solutions of the one-line model. For those two relationships, results obtained for case with rigid boundaries is asymptotic when the ratio between length of the bounded coast and width of concave portion is getting larger. Good agreement between measured data and theoretical results can be obtained.

抄録全体を表示

 In this study, numerical simulations of the flow and sediment transport in the lower reach of Chikugo River are implemented. The objective of this study is to evaluate functions of Wakatsu Port training levee quantitatively by considering the flow, salinity and sediment transport characteristics in the lower reach of Chikugo River. It has been found that the presence of the training levee plays a role in accelerating flow velocity of left bank side even during river floods. The result of sediment transport analysis revealed that the sediment deposition had affected the river mouth blocking before the training levee construction.

抄録全体を表示

 Okayama city is susceptible to tsunami disaster when Nankai Trough earthquake occurs because its coastal area is mainly occupied by a vast below-sea-level area. It is indispensable to predict tsunami behavior hitting the city previously for taking appropriate countermeasure under the earthquake. Although real-time tsunami forecast method by inverse analysis has been developed, it is difficult to predict tsunami waveform in a shallow inland sea where Okayama city faces. This research constructs a model for forecasting waveform of tsunami reaching Okayama city's coast before its arrival from tsunami waveform observed at Naruto or Akashi Channel which is located in east of the Seto Inland Sea. As the results of this research, relatively large tsunami at Yamada port is reproduced by this model as being numerically simulated. And this research shows the prediction model is usable for estimating highest tsunami height at Yamada port even if a tide is taken into consideration.

抄録全体を表示

 The Nankai Trough Earthquake Tsunami is predicted to occur in the near future in Japan. One of the countermeasures to be taken against the tsunami attack is to predict how long salt water carried by a river-runup tsunami would stay in the river to prevent a water purification plant from taking in salt water.
 In this study, an application of a hybrid 2DH-3D model to salt water behavior caused by a river-runup tsunami was conducted. The hybrid model is useful for coupling of tsunami propagation from the wave source in 2DH to the flow in the estuary area in 3D, where the density current should be considerable. Two conditions of river flow rate were considered to analyze the effects on the vertically-distributed salinity transport. It was shown that although free surfaces were similar between 2DH and 3D models, significant vertical distributions of the density were present in the 3D region, indicating applicability of the hybrid model to the situation.

抄録全体を表示

 This study is conducted for clarifying the energy dissipation effects of coastal lagoon for more than Level-1 tsunami that can overtop the sea embankment and propagate inland. The numerical model is validated for reproducing the 2011 Great East Japan tsunami at Torinoumi Lagoon. The time series and maximum values of inundation depth, current velocity, fluid force at three selected locations were calculated with/without lagoon. Moreover, the storage capacity effect was analyzed with different tsunami conditions. Lagoon can reduce the velocity and fluid force especially at cross-stream direction because of the low velocity of the overflow current from the lagoon which mixes with the inundated tsunami from seaward, thus reducing the percentage of washout houses. The effect is greatly changed with the rate of tsunami inundation flux to lagoon and storage capacity of the lagoon.

抄録全体を表示

 The Great East Japan tsunami has revealed the limit of hard solution by only sea embankment. Thereafter, a multiple defense system for Level2 tsunami that combined coastal forest and sea embankment is planned. This study is conducted to clarify the change of overflow rate from embankment with the location and thickness of coastal forest. Flume with sudden opening gate for making tsunami-like unsteady flow was used to investigate the change with various multiple defense models. The results indicates that seaside coastal forest can reduce overtopping flow rate than landward. Even when the seaside forest is thin, the flow pattern change in front of embankment increases the total reflection and decreases the overflow rate around 10%, although the forest itself does not increase the reflection.

抄録全体を表示

 Laboratory experiments were performed to study wave transmission and reflection capacity by pervious structures as coastal protection from waves. The energy dissipated in pervious structures may be evaluated by using the drag forces acting on the pervious structures and particle velocities of principal waves in structures. A theoretical analysis based on application of the continuity and energy equations to the flow through the pervious structures were made to evaluate wave transmission and wave reflection capacity of structures. The transmission coefficient K_t and reflection coefficient K_r of a) Porous media, b) Blocks of detached breakwater and c) Wave dissipating caisson with circular cylinders in front of wall were also studied experimentally and theoretically.

抄録全体を表示

 Lattice Boltzmann Method (LBM) is one of the new, robust and efficient Computational Fluid Dynamics (CFD) solvers. One of the key features of LBM is that implementation in parallel computing is more efficient compared with the other conventional CFD solvers. In the current study, we developed a novel Tsunami simulation model applying Impedance boundary condition for offshore non-reflecting boundary to Subgrid-scale LBM based on Shallow Water Equations. The model was tested in the benchmark with solitary wave incident waves. As a result, the model can reduce amount of wave reflection compared with the conventional non-reflective boundary condition based on linear long-wave approximation in the Finite Difference Method. Through the model verification, we found that Impedance boundary condition has a sufficient accuracy for Tsunami offshore non-reflecting boundary condition.

抄録全体を表示

 There are two major factors which make it difficult to simulate tsunami run-up in the Kitakami River by the 2011 Tohoku Earthquake. Since the water level gauges in the bay or estuary broke due to the huge tsunami, inflow volumes from the ocean and tsunami waves could not be estimated. And, the water running up in the river flowed out to the inundation area not only by overflowing but also levee breaches. It is considered that these flows have significant effects on the behavior of tsunami run-up in the river.
 This study aims to discuss the observed data based on the simulation of the tsunami run-up and inundation in the Kitakami River. First, we conducted the simulations using two fault models and discussed the reproducibility, particularly of the inflow conditions of the tsunami. Second, we investigated the simulations with and without levee breaches. Through comparisons between the simulations and observation results, the effects of levee breaches on the tsunami were discussed.

抄録全体を表示

 Separation of permanent water body and temporal water body is essential for the grasp of global water distribution. Global 3-second Water Body Map (G3WBM) is a global scale high-resolution water body map recently-developed by the authors, which separates water body types by the idea of water frequency, using multi-temporal Landsat data. In this paper, we further improved the accuracy and computational efficiency of G3WBM algorithms, and refined the resolution from 90m to 30m. The validation against U.S. National Hydrography Dataset revealed that, although some small water bodies could not be visualized, more than 85% of permanent water bodies were classified correctly. Comparison between the water body mask constructed in this paper and G3WBM in the U.S. showed that water judgment accuracy was improved and over 2600km² of temporal water has been newly separated from permanent water.

抄録全体を表示

 A HYPE (HYdrological Prediction for the Environment) model considering impervious land cover in an urbanized watershed is set up to improve prediction precision of storm runoff. The set-up of the model is based on the Urban Atlas that is polygonal land cover data with impervious information. Firstly accurate impervious area ratios in a target watershed are calculated using the Urban Atlas, and the ratios are set to the HYPE model. Secondly, appropriate parameters to describe hydrological property in an urbanized area are implemented for the HYPE model. The model was applied for the watershed including urbanized area of Svedala, Sweden. It was demonstrated that impervious information obtained by polygonal impervious area ratio data contributed precision improvement of runoff prediction by HYPE model in urbanized area.

抄録全体を表示

 We built a model to estimate catchment-scale stream integrity using a hydrothermal model and biomonitoring techniques. First, we prepared habitat suitability indices of 32 benthic macroinvertebrates developed using the hydrothermal simulation and several landscape variables. We also adopted multiple metrics as stream integrity; average score per taxon (ASPT), EPT, benthic index of biotic integrity (B-IBI), Shannon-Weiner's diversity index and principal component scores. Most of the integrity metrics exhibited increasing trends along with elevational gradients, while ASPT showed a somewhat different trend. The integrity score of ASPT varied in developed area, and increased with catchment area even though other metrics such as EPT and B-IBI showed opposite pattern. Finally, according to the result of one-way analysis of variance, land-use strongly contributed variation of the integrity metrics within the catchment, suggesting a need of further consideration in outcomes where applying integrity metrics to another geographical domain because it is surely comprised of different land-use.

抄録全体を表示

 Spawning redds of Ayu fish (Plecoglossus altivelis) have been degraded by decrease in sediment supply and increase in turbidity derived from reservoir sedimentation in the lower reaches of the Tenryu River, Japan. In order to restore the riverbed for their suitable spawning redds, both newly deposited gravel riverbed and clear water flow are required. We conducted a series of habitat surveys in the two reaches of the Tenryu River to seek the spawning redds and suitable physical conditions. Then, we found the spawning redds of the fish in the upwelling-zones of hyporheic water in the secondary channels. Based on the results we conducted a sediment replenishment work in the secondary channel to create a new riffle and upwelling zone of hyporheic water. The work resulted in successful creation of upwelling zone but it lasted only a month and amount of hyporheic discharge decreased within three month. Results of the work also indicated that effective distance from the sediment replenishment site to the target riffle is very short less than 100m.

抄録全体を表示

 We evaluated the relative importance of flow regimes, water temperature, and water quality influencing on the inter-annual population variability of 20 fish species (1993-99) in the Sagami River, Japan, using a random forests approach. A result indicated that flow regime conditions before and after spawning season (April-August and October-December, respectively) and temperature after spawning season influence the population variability of many species most dominantly (relative importance >15% for 10, 8, and 5 species, respectively). Hence, to mimic the natural variability of these factors particularly in the suggested seasons may contribute to better sustain the ecological healthiness in the Sagami River.

抄録全体を表示

 According to an observation record, long-term discharge at Fukakusa station in the Kamo River basin has been decreasing, which may affect water-related landscapes and the ecosystem. This study conducts a forensic analysis to investigate the dominant reasons for the streamflow reduction and attempt to quantify the contribution of each factor based on water balance analysis, trend analysis and hydrologic model simulation. The results suggest that the decreasing trend is primarily caused by the increase of drainage areas of the sewage system in Kyoto city and the reduction of intake from Lake Biwa canal to the Kamo River. These effects diminish the impact of slight increase in the annual precipitation and suppress the increase in evapotranspiration in the Kamo River basin.

抄録全体を表示

 This article aims to compute the probability density function of radioactivity in the human body and the effective dose based on lumped hydrological method. We treat the fluctuations of radioactivity in the human body as the stochastic process. There are three types equivalent formalisms regarding the stochastic processes, that is, Langevin equations, stochastic differential equations (SDEs), and Fokker-Planck equations. We adopt the Langevin equation as the starting point for discussion. We can get the Langevin equation of radioactivity in the human body by adding the random fluctuation term to the continuity equation of radioactivity in the human body. Deforming the Langevin equation to the equivalent Fokker-Planck equation, we compute the probability density function of radioactivity in the human body. We attempt to formulate the stochastic process of the effective dose. Although we cannot put the mathematical footing, we propose the likely stochastic process to consider the convergence in the average.

抄録全体を表示

 Bayesian approach becomes widely spread over the verious fields of statistical applications of sciences and engineering in the computer intensive manner. No exception will be frequency analysis for heavy rains in hydorological engineering. The preliminary survey is neccessary in the theoretical sense of the intrinsic property of extremes. Extrapolation in extreme value analysis can be conducted in two paths: one is an externally equipped path, the other is a path enclosed in the same footing with the observed data. The latter path is rational but actually the former is employed in practice. The same goal should be achieved essentially in both paths. The agreement and disagreement are demonstrated in the numerical sense.

抄録全体を表示

 The glacial area changes of 173 glaciers in the Andes (15°45'S~17°00'S, 67°15'W~68°30'W), Bolivia were determined using satellite data between 1988 and 2012. Total of glacial areas in 2012 decreases to 78% from 1988. The decrease rate of large-scale glaciers more than 5.0km² was high. The aim of this paper is to analyze glacier retreating with glacier characteristics, which are area, latitude, longitude, maximum/minimum/average elevation, area-aspect, area-slope, and area-hill shading. The values of glacial area, average elevation, and area-slope are very sensitive to glacier retreating. On the other hand, the value of the area-aspect is not sensitive. In addition, we constructed the estimated formula of glacier retreating volume. This adjusted R-square is 0.693. The total area estimated in 2036 is 170.2 km² which is the 64% of 1988.

抄録全体を表示

 Better estimation of snow water equivalents for a dam basin and dam inflow is important for dam operation in cold and snowy regions. In this study, the relationship between snow depth and topography was analyzed using airborne laser scanning data. The linear relationship between snow depth in the forest area and elevation and the relationship between snow depth in the non-forest area like the area above the forest line and overground-openness were clarified. Moreover, three types of snowfall distribution were set and the dam inflow was calculated using snowmelt runoff model. The calculation applied snowfall distribution considered snow depth transport by wind at high elevations had the highest accuracy.

抄録全体を表示

 This paper proposes the derivation method of an approximate solution of shallow water equations for dam break flows, applying a perturbation method. The basic equations are firstly transformed into the equations in a moving coordinate system with the celerity of the negative wave front. The depth and velocity are denoted as the power series of the spatial coordinate of the moving coordinate system. After denoting the time dependent coefficient of each term of the power series as the perturbation expansion with the bottom friction coefficient, all unknown coefficients are derived using the known variables such as the initial depth and gravitational acceleration. The analytical solutions are compared with the numerical results obtained using a Finite Volume Method. Although the results indicate that further investigations are needed to obtain a better analytical solution, it is considered that in this study a mathematical framework is presented to study the asymptotic behavior of the depth distribution with negative infinite gradient at the front position to the Ritter solution when the friction coefficient tends to 0.

抄録全体を表示

 Based upon the shallow water equations, linear stability analysis is conducted on an open-channel flow with velocity retardation on one side. The analysis is applied to a steady turbulent base flow which is characterized by a sub-depth scale turbulence derived from a logarithmic profile of vertical velocity. The linear stability analysis is performed for the case of spatially growing disturbances and compared to the case of temporally growing disturbances. We found that discrepancies between results from the spatial and the temporal approaches were less relevant when the bed friction effect and the kinematic eddy viscosity effect were more significant.

抄録全体を表示

 The consideration of slump blocks in the coupling fluvial erosion and cantilever failure model is the recent advancement toward dealing the phenomena of riverbank failures. In this study, we developed a numerical modeling of a cantilever failure that uses a triple-grid approach to simulate the behavior of a cantilever within the framework of fluvial erosion, the cantilever's subsequent failure, slump block effect and bedload sedimentation. Two cases of cohesive materials with the different percentages of silt-clay content were simulated under the similar hydraulic conditions with and without slump block consideration. The simulated results in terms of the fluvial erosion and cantilever failure showed significantly difference due to inclusion of slump block consideration. The present numerical model with slump block consideration satisfactorily reproduced the riverbank failure phenomena and showed good agreement with the experimental results in terms of the spatial-averaged bank width along the riverbanks.

抄録全体を表示

 In this study, we conducted numerical experiments to investigate the influence of the wall and bed roughness to the secondary flow in a bend part in open channel flows. The nays CUBE distributed by the iRIC project was used in this study. Firstly we conformed that the nays CUBE has good accuracy to predict the three dimensional flow by comparing with our laboratory experimental data.
 We conducted numerical experiments under the five cases. In the cases that the wall roughness is smaller than or equal to the bed roughness, the circulation near the inner bank wall became bigger as the side wall roughness increased in the entrance of the bend part. On the other hand, in the cases that the wall roughness is greater than the bed roughness, the circulations near the outer bank wall were not clear at the middle of the bend part.

抄録全体を表示

 A three-dimensional numerical model is recently applied to simulate flows in a complicated flow domain more accurately, and basic equations in the Cartesian coordinate with some gas-liquid interface capturing method or in the generalized curvilinear movable coordinate system along water surface and river bed are commonly used. In this study, a three-dimensional numerical method in open channel flow in boundary fitted coordinate system with density function method is firstly developed, since boundary fitted coordinate system is easier to treat boundary conditions such as a river bed and bank, and a density function method solves water surface variations in unsteady inundated flood flows. The developed model is applied to flows in curved channel and overtopping flows, and it is shown that this model can reproduce complicated flow fields reasonably by comparing with the experimental and numerical results.

抄録全体を表示

 The flow structure around the bed, especially in gravel layer, is very important and needs to be clarified because the detailed topography of the bed exerts a significant influence on generation and dissipation of turbulent energy. A lot of channel hydraulics has considered smooth bed conditions but there are still many unsolved problems awaiting clarification for gravel bed rivers. This study investigates how the turbulence characteristics i.e. vertical distribution of longitudinal velocity, Reynolds stress distribution and effect of boundary layer development on velocity distribution can differ in a shallow gravel bed river with high effective roughness height when bed conditions change. The flume experiments using particle image velocimetry (PIV) were performed with varying surface roughness elements spacing and results were compared with the frictional resistance, mixing length and constant mixing length theories, which allow studying vertical components of velocity in the flow.

抄録全体を表示

 We carried out a direct numerical simulation of open-channel flow with the free-surface fluctuation to investigate the effect of the fluctuation on the secondary flow and the air-water gas transfer. The DNS reproduces turbulent characteristics of the secondary flow such as the velocity-dip phenomena and counter-rotating vortex pairs, and they are almost similar to numerical results without the free-surface fluctuation. However, the maximum secondary flow velocity and the depth at which the streamwise velocity becomes maximum are changed by the influence of the free-surface fluctuation. The numerical results show the free-surface fluctuation enforces the secondary flow. The turbulent field near the sidewall that controls the air-water gas transfer is investigated on the basis of a statistical treatment such as the VITA technique. We can visualize the surface renewal eddies due to the secondary flow through the VITA technique.

抄録全体を表示

 The basic method of smoothed particle hydrodynamics (SPH) has been applied to simulate two-phase flow of water and air, of which motion near the interface influences that of water, as in the case of breaking waves and in skimming flows in steep sloped channels. The form of the particle interpolation for the divergence and the pressure gradient are chosen so that the stability of the calculation is maintained. The method has been verified in the calculation of dam-break flow with air trapped under water and used to simulate the skimming flows in stepped channel. The calculation results agree with the experiments. In the calculation of the flow over the steps, not only is the trapped air but entrained air bubbles are reproduced fairly well. The detailed variation of the time-averaged mean quantities will have to be further examined but overall prediction with relatively small number of particles performed well.

抄録全体を表示

 Three dimensional and unsteady flow structures generated at a river confluence are still not fully understood. In the present study, a fully-resolved LES (Large Eddy Simulation) with a VOF (Volume of Fluid) method capable of treating free surface boundary was performed to investigate three dimensional structures of turbulent flow and water surface variations at a right-angled confluence. The averaged flow structures and water surface variations obtained by the LES were compared with detailed measurement data obtained by PIV. As a result, it was shown that the LES was able to predict a size of a recirculation region in the streamwise direction and a width of that in the spanwise direction. Moreover, the LES was also able to predict that the width of the recirculation region varies in the depthwise direction in a complicated manner.

抄録全体を表示

 A series of direct simulations of a fully-developed turbulent flow along a mesh-screen type permeable plate whose geometrical property is systematically changed is performed to identify the effect of wall permeability on wall-bounded turbulent flows. The present system includes as two extreme limiting cases the classical impermeable channel flow and the perfectly-permeable channel flow of Yokojima (J. Phys. Soc. Jpn. 80 (2011) 033401), which have an identical solution in the laminar state. The numerical experiment demonstrates that, by increasing the porosity of the plate or by decreasing the pore size, the coherent structures visualized near the boundary show a qualitative transition from the streamwise vortices ubiquitous in a wide variety of wall-bounded flows to thin vortical structures elongated to the transverse direction and the flow resistance is increased. These findings are in good accordance with those observed in the perfectly-permeable channel flow. It is also found that the drag is closely associated with the blowing/suction intensity through the mesh screen.

抄録全体を表示

 The riverside concavity sometimes loses its function by heavy siltation. In this study, a spur dike placed upstream is used to control the sand deposition in a side concavity. The effects of a spur dike on flow structures and sand deposition in a side concavity were investigated experimentally. The length and height of spur dike and the location distance of the spur dike from the upstream end of the concavity zone were changed. The recirculation vortex strength and the exchange coefficient in the concavity become larger by setting spur dike at just upstream of the concavity, but it is slightly reduced when the sur-dike location is far upstream. The morphological shape and total amount of sand deposition were affected by the strength of recirculation vortex and sediment transport rate along the open interface of concavity.

抄録全体を表示

 For irrigation open channels with gradually width-contracted part, we aimed to evaluate the effects of changes in structure of the contracted part on the coefficient f_qc of conversion loss based on laboratory experiments. The experimental results showed that f_qc increased corresponding to the increase in the reduction-angle θ at the contracted part from 12.5° to 90°. Additionally, f_qc decreased when the reduction-ratio B₂/B₁ of the downstream to the upstream channel width at the contracted part increased from 0.5 to 0.7. We conclude that the optimum value of f_qc is 0.1 for designing the irrigation open channels with B₂/B₁ greater than 0.7. These findings are useful for determining the value of f_qc for channel repairs, especially in facilities management project.

抄録全体を表示

 Local scouring which occurs at the downstream bed of weirs is a very important problem because the local scouring reduces the stability of the structures. Since the local scouring progresses rapidly at the time of submerged jet flow, it is very important to calculate the submerged jet flow with high accuracy on the prediction of the bed deformation. In the previous studies, two-dimensional vertical (2DV) model has been used mainly for the predicting of the flow and the bed deformation. However, a possibility that the 2DV model cannot reproduce the submerged jet flow accurately by the hydraulic conditions has been indicated. Therefore, in this study, we conducted comparisons between 2DV model and three-dimensional (3D) model for the reproducibility of the submerged jet flow. Consequently, in the case of the constant width-to-critical flow depth ratio (B/h_c), it was clarified that the 2DV model cannot reproduce the flow with high accuracy when the width-to-weir height ratio (B/W) and the width-to-downstream flow depth ratio (B/h_t) become small.

抄録全体を表示

 In shallow water conditions, open-channel flows are subject to the influence of channel bottom roughness because the boundary layer or vortices generated at the bottom interact with water surface. Such an influence become more pronounced when the bottom is composed of discrete roughness such as a strip roughness. In the present study, water surface variations were investigated experimentally by varying the water depth relative to the roughness height. Although the water surface is kept almost horizontal for a relatively large depth of water, it tends to show significant differences with decrease of water depth. As an example, the water surface exhibits three dimensional topographical features with various arrangement of lumps depending on hydraulic conditions. Moreover, water surface begins to oscillate quite periodically with a hydraulic jump under specific hydraulic conditions. A new image analysis technique was developed to capture such surface flow features.

抄録全体を表示

 River vegetation fosters a rich ecological environment and creates a friendly riverside environment. Importance is attached, therefore, to the question of what vegetation should be like when designing and improving river channels. In view of concerns and problems such as the diversity of rivers, continuity of ecosystems and the deterioration of water quality caused by stagnant water in vegetation communities, it is desirable that regions where the exchange of flows with the main flow region are promoted be provided. In this paper, the influence that arrangement patterns of longitudinal discontinuous vegetation zones gave to the flow resistance and turbulent structure in an open-channel was examined experimentally. Results showed that the relationship between flow depth and discharge significantly depended on the arrangement patterns and the reason could be explained by the difference of turbulent structure and spatial gradient of the dynamic pressure.

抄録全体を表示

 In general intake facilities of hydroelectric power stations, intake vortices cause the air-hammer phenomena in the intake tunnel and the cavitation phenomena at blades of a water turbine generator by air-entrainments. In order to understand hydraulic characteristics of a vortex-suppressing device in a vertical intake facility, flow fields in the basic model of a vertical intake facility that combined a rectangular linear channel and a vertical pipe have been measured using a Particle Tracking Velocimetry (PTV). As a result, the relationship between installation positions of a vortex-suppressing device and number of occurrences of intake vortices indicates that the vortex-suppressing device installed near free surface and near vertical pipe is more effective.

抄録全体を表示

 In this study we investigated the accuracy of the lateral over flow discharge formulations for the curved channel of which the radius of curvature is constant. From the experimental results we found that the lateral over flow discharges are in proportion with the power to 3/2 of the over flow depth, so that we use the same formulation form as Honma formulation for the front over flow discharge.
 The Froude number, the ratio of channel width and lateral weir width, the ratio of weir height and weir width and the ratio of channel width and radius of curvature were used as the parameters of the discharge coefficient. We assumed that the discharge coefficient is the simple product of theses parameters and these parameters have the power. The powers of theses parameters were determined with the experimental data. It was confirmed that the accuracy of the proposed formulation is good.

抄録全体を表示

 In the rainwater discharge chamber of the combined sewer system, it is difficult to control the flow rate of the intercepted sewage to the sewage treatment plant at the time of heavy rain, and a part of the sewage from the sewage treatment plant is discharged untreated into the sea. To overcome this problem, it is necessary to develop the facility which can control the flow rate in the interceptor sewer. Recently, by authors, a new technology of sewer system has been proposed in which the rainwater discharge chamber has multiple regulation tanks and which has the high performance of controlling the water level in the regulation tanks and flow rate of intercepted sewage into the treatment plant. In the new rainwater discharge chamber with two regulation tanks, the interception error (excessive flow rate of intercepted sewage/planned flow rate of intercepted sewage) becomes 3% to 8%.

抄録全体を表示

 Stepped channels are effective for dissipating the energy of supercritical flow that occurs at steep channels. For a large discharge and/or small dam height, the nonaerated region occupies a large portion of the skimming flow in stepped spillways. For hydraulic design of stepped channels, it is important to know the depth and the velocity in nonaerated skimming flows in order to estimate the specific energy. However, most experimental studies for stepped channels have focused on aerated skimming flows, and characteristics of nonaerated skimming flows have not yet been clarified. This study shows reasonable equations for estimating the boundary layer development and the water surface profile along the channels for nonaerated skimming flows. The energy head along the channel is obtained, indicating that the energy dissipation for the stepped channel becomes larger than that for the smooth channel.

抄録全体を表示

 The characteristics of power generation using non-linear vortex-excited vibration of a circular cylinder in steady open channel flow were estimated with considering the variation of a) the amplification of hydrodynamic forces acting on the vortex-excited vibrating cylinder in comparison with the hydrodynamic forces acting on the test cylinder stationary mounted and b) the amplitudes of transverse vibration of the test cylinder were evaluated quantitatively. The maximum values of power generation using vortex-excited vibration of the test cylinder were appeared in the range of 2< K_sa <4.

抄録全体を表示