In order to establish a simple and rational impact response analysis method for lightweight shear-failure type Reinforced Concrete (RC) beams with stirrup, three-dimensional elasto-plastic finite element analysis was conducted for total fourty-seven RC beams under falling-weight impacting. Here, tensile strength of concrete was assumed as 1/16th of compressive one. An applicability of the proposed analysis method was confirmed by comparing with the experimental results of fourteen beams. From this study, following results were obtained: 1) impact response waves and crack patterns can be rationally predicted by using proposed analysis method, and 2) ultimate shear capacity of the RC beams under impact loading can be rationally predicted by means of the proposed numerical analysis method considering a safety margin of 15 %.

View full abstract

Cracks and spalling of concrete are the effects that can be seen on a reinforced concrete structure giving a warning of the occurrence of damage. An image of these effects can be taken and analyzed to estimate the damage of the structure. In this analysis image processing is necessary to extract crack data effective to characterize the damage of a particular type of structure. Characterization of geometrical properties of cracks is important in the preparation of digital crack data. In this study a set of indices to characterize the geometrical properties of cracks are examined for various RC structures.

View full abstract

Prestressed concrete (PC) girders with corrugated steel webs have recently been utilized for superstructures of highway bridges. For structural design of such girders, the shear strength characteristics (including shear buckling capacity) of the corrugated steel web must be well understood, and thus several design formulas have been provided. However, because of possible semi-rigid characteristics of the shear connecter between the conugated steel web and the concrete flanges, the shear characteristics of the connecter may affect the overall shear strength of the PC girder with corrugated steel web. Thus, this study aims to clarify the shear strength characteristics of the PC girder with corrugated steel web by considering the characteristics of the shear connecter using 3D finite element analysis.

View full abstract

In this paper, we examine the implicit soil/water coupling elastic-plastic calculation algorithm with contact conditions on the crack surfaces in order to obtain stress and strain fields near a crack tip under the biaxial compressive loads. It is important to elucidate the fracture criterions under compressive loads such as the explanation of the existence and the creation of long faults, landslide in slope ground and so on. We find that the mode II crack extension can be explained by plastic effect near a crack tip using Cam-Clay model under the undrained condition. We also find, under the drain condition, that localized strain region appears perpendicularly from a crack tip, which caused by the softening plasticity with absorbency.

View full abstract

The traditional elastoplastic constitutive equation, which is independent of the stress rate component tangential to the yield surface predicts an unrealistically stiff mechanical response for the nonproportional loading process in which the stress rate has a component tangential to the yield surface. In this article, the generalized constitutive equation is then formulated by incorporating the inelastic strain rate due to the stress rate tangential to the subloading surface into the subloading surface model exhibiting a smooth elasticplastic transition.

View full abstract

This paper investigates bifurcation behavior of an elasto-plastic material under plane strain deformation. A simple and isotropic material in finite strains based on the multiplicative decomposition of the deformation gradient and Hencky's hyperelastic model is employed, and the expressions of instantaneous modulus of the material in rate form are explicitly derived. We present a theoretical approach for bifurcation analysis, and calculate bifurcation stresses of diffuse modes. The analysis reveals that elastic nonlinearity due to the hyperelastic constitutive model significantly changes general characteristics of the governing partial differential equation, and, moreover, this change influences occurrence of bifurcation. Finally, we conduct numerical bifurcation analysis based on FEM. Comparison between the theoretical and numerical results shows that the numerical approach provides good accuracy for estimate of the bifurcation stress.

View full abstract

For pertinent countermeasure of rockfalls, rockfall simulation was studied many times. Any rockfall simulation has not gotten consistency between the simulation result and real rockfall. There are a few causes. One is whether method of calculation used the simulation approaches the mechanics of real rockfall. Two is whether parameters using the calculation are assigned pertinent value in. This study suggests direct measurement of rockfall's detail motion which as method of closuring of the problems. It would be possible to determine pertinent value in parameter by comparing the detail motion to calculation result. In this research, 3-demensional rockfall simulation developing in this laboratory is explained. Then the problems and improvement of the simulation is shown. Finally the result of experiments on impact acceleration that applies to rockfalls is shown.

View full abstract

Mechanical behaviors of granular materials, which are developed from the interaction of grains, are very complicated to understand. In such a field, the computational mechanics is a powerful tool to investigate various features by the simulation in the grain level. To model the behavior of granular materials, geometrical structures should be represented precisely since stability of the material is secured by contact between grains. In this paper, we present an image-based modeling based on the distinct element method for granular materials. The 3-D image data of a gravel specimen obtained by CT scan are utilized to represent a real geometrical structure and individual grains are separated in the geometrical model by an image processing technique. The distinct element method that deals with grains with irregular shape obtained by the image data is also presented.

View full abstract

In usual analysis using the granular element method, global stiffness matrix is rarely applied. The main reason is that inverse matrix calculation for a large matrix was considered to be inefficient. However, from the author's experience there is an efficiently calculated case in which the global stiffness matrix is applied in comparison with a calculation performed without applying the global stiffness matrix for the same problem. Therefore, formularization of the granular element analysis in which the global stiffness matrix is applied is presented. Irregularly shaped elements composed of circles or spheres are used in the formularization. Analytical results of reproducing shear tests on stacks of aluminum rods are also presented.

View full abstract

To investigate how the incremental behavior of granular media deviates from the conventional plasticity theory, a series of numerical tests by Granular Element Method were carried out. The numerical tests were the combination of several proportional shear loadings in the π plane and subsequent series of stress-probe tests. Plastic responses for these stress probes were characterized in terms of a reference plane generated by the shear loading path and the line that connects the origin of stress space and the current stress point. Only for stress probes within this reference plane, plastic responses were approximately predicted by the non-associated flow rule. However, general incremental plastic responses never obeyed the classical flow rules.

View full abstract

A method of multiscale analysis based on mathematical homogenization theory has been developed for quasi-static equilibrium problems of granular media. The micro-scale problem is analyzed by a discrete numerical model assuming elastic and frictional contact between rigid particles. This two-scale analysis enables us to obtain the macroscopic/phenomenological inelastic deformation response of a representative volume element (RVE). To examine the macroscopic deformation properties of the assumed RVE, a series of numerical experiments involving pure rotation of the principal stress axes are carried out. The necessity of incorporating the non-coaxiality induced by the tangent effect and the anisotropy in the yield condition is revealed in the phenomenological constitutive description of the deformation under principal stress axes rotation.

View full abstract

In order to design the soil-recycling machine, it is necessary to understand the breaking performance for viscous clay. However, experimental investigation needs much costs and long experimental period. If the simulation model is developed, the effective and economical design will be possible. Therefore, in this study, the simulation model to estimate the breaking performance for viscous clay was developed by using DEM, and simulation result for size distribution of soil particles was compared with the experimental one. Simulation result was almost agreeable with experimental one. Therefore, it was confirmed that the simulation model developed in this study is almost reasonable.

View full abstract

The physical process of granular shear flows is very complex, and the mechanical properties such as the dependency on the shear-rate or the influence of confining pressure have not been fully investigated. This paper discussed the dynamic characteristics of granular shear flows with the aid of numerical tests by the Granular Element Method that was recently extended to a dynamic version. It was found from a series of simulation tests that the flow patterns were strongly influenced by the confining pressure, as well as the shear rate. It was also shown that the localization developing in the dynamic deformation field weakened the shearing toughness of granular specimen.

View full abstract

This paper investigates liquefaction induced lateral spreading using a 2D Smoothed particle hydrodynamics (SPH) based numerical method in the framework of fluid dynamics. Owing to the fact that the induced displacement during lateral spread may reach several meters and the shear strain develops till 100%, a method which is essentially a Langrangian meshfree particle was developed to deal with large displacement. By assuming the liquefied subsoil to behave as a viscous fluid during earthquake shaking, a Bingham type model is used to model the liquefied soil. The ability of the method is checked using results from shaking table experiments to reproduce free surface shape, flow velocity and to investigate the relationship between time history of flow velocity, liquefied soil thickness and surface ground slope.

View full abstract

Mechanical behavior of particle-fluid systems is extensively studied in various engineering field such as geotechnical engineering, mechanical engineering and powder technology. Although observation of complicated behaviors including interaction between particles and pore fluid is essential, very few efficient techniques are available for this purpose. From this point of view an observation technique based on LAT (Laser-Aided Tomography) and PIV (Particle Image Velocimetry) was developed and applied to the permeability experiments involving a seepage failure. The LAT-PIV technique enables us to visualize not only the particle motion but also the pore fluid motion and evaluate them quantitatively

View full abstract

It is difficult to estimate the properties of rock masses before construction. This paper presents a new coupling key block analysis using stochastic-deterministic method for the prediction of the key blocks before all the discontinuity traces of the blocks have not appeared on the cutting face of the tunnel, in other words, in the moment some of the discontinuity traces of the block have appeared The coupling key block analysis using stochastic-deterministic method developed by the authors is applied to a large tunnel excavation site where real discontinuity information was obtained In order to illustrate the validity and applicability of this numerical analysis for stability evaluationin tunnel construction, the analytical results are compared and examined.

View full abstract

The Shirate Bridge, an old rock arch bridge located in Oita, has become weathered over the years and is slightly damaged at its base of abutment. This paper describes two-dimensional static and dynamic discontinuous numerical model studies of rock bridge using discontinuous deformation analysis. The discontinuous numerical model of a bridge consists of an assemblage of polygonal stone blocks, abutment, roadbed and rockmass. The logistical function-shaped subsidence curves and then sinusoidal earthquake waves were inputted into the model. Block activities in a narrow area of rock bridge were evaluated with such parameters as: increase in void volume (dilation); horizontal, vertical and rotational displacements; and kinetic energies of rock blocks at different points. The relationship of base subsidence on the failure mode and the development process are presented in detail. Results indicate that the larger the base subsidence, the more discontinuous motions become dominant, and that higher frequencies engender the dominance of vertical and rotational motions of blocks.

View full abstract

This paper presents the development of measurement-based multiagent simulator for evacuation process. The major features of the simulator are i) the capability of simulating nonlinear phenomena in the evacuation process such as congestion, ii) the objective input parameters for an agent. The simulation result and measured behavior of a crowd walking on an intersection show good agreement. Also, the result from multiagent simulation coupled with the structural analysis is presented.

View full abstract

A method to evaluate the network redundancy based on a recursive decomposition algorithm (RDA) introduced by Li and He in 2002 was employed to calculate the reliability of lifeline networks. A redundancy index proposed by Hoshiya and Yamamoto in 2002 was used to represent the redundancy of networks. RDA is shown to be much more effective, as compared with results of Monte-Carlo simulation. In addition, a limitation of the redundancy index is revealed by case studies.

View full abstract

The objective of this research is to develop the multipoint displacement measurement system for infrastructures. This paper describes the developed prototype of this system and shows the results of the field experiments. This system consists of a GPS server and sensor nodes. A low cost Ll GPS receiver and a wireless LAN device are equipped on the sensor nodes. A GPS server is able to gather the GPS data received at sensor nodes and to estimate their accurate positions by analyzing the Ll carrier phases. Field experiments were conducted with three sensor nodes. The results show that the positions of the sensor nodes are monitored by the accuracy of a few centimeters. The integer ambiguities, that are needed to estimate the accurate position, are correctly determined in 10 minutes in the experiment.

View full abstract

This paper presents an implementation of acoustic ranging and proposes a distributed algorithm for localization of sensor network. Relative positions between sensor nodes are estimated based on acoustic ranging through the inverse Delaunay algorithm. This algorithm localizes all the nodes simultaneously, thus, the accumulation of the error in the localization is suppressed. Noise tolerant acoustic ranging algorithm that employs digital signal processing techniques is implemented in an off-the-shelf sensor platform (Mica2). Experiments show that this acoustic ranging algorithm is sufficient to give average range estimation error below 10 cm. Field experiment was conducted with twenty-one sensor nodes to evaluate the accuracy of the localization of the system.

View full abstract

Quantitative prediction of the damage of a heterogeneous earth structure induced by earthquake is very important However, any rational method for such a prediction has not been proposed yet. The soil as a material of the earth structure is generally heterogeneous. Therefore, a probablistic approach for the evaluation of the physical properties of the soil is advantageous. In this study, the residual settlement of a heterogeneous earth structure induced by earthquake is predicted based on the Monte Carlo simulation. The dynamic elasto-plastic finite element analysis is used in each calculation. In order to realize the reliability based design of an earth structure, a fundamental study such as introduced in this paper is indispensable.

View full abstract

The present paper proposes an application of spectral stochastic approach to dynamic analysis of stochastic structures in the presence of phase uncertainty of input motions. An analytical expression of the expectation value of the product of complex exponential and polynomial chaos. This allows efficient computation of the projection of the function to the homogeneous chaos space. Efficiency of the proposed scheme is discussed based on the comparison with the results obtained by Monte Carlo Simulation. It is found that the proposed method exhibits good performance even when variety of uncertainty amplitude and structural parameters are assumed.

View full abstract

Elastic waves generated by a controlled dynamic load applied on the surface of soil deposits yield useful tools for non destructive testing of the systems to determine the elastic properties of the soils and their variation with depth. A number of methods for the non destructive testing have been developed and are being used in practice. The objective of this paper is to examine some of the basic concepts related to P-SV wave propagation in layered media and their dynamic response due to the vertical harmonic point load applied on the soil surface. A proper understandings of these concepts is necessary for a correct interpretation of the field data and for improving the accuracy of the estimation of the soil properties at low strain values by using the spectral analysis of surface waves or the Rayleigh wave method.

View full abstract

The objective of this report is to propose the procedure to evaluate the characteristics of fragility specified for civil engineering structure such as road bridge considering with site and source specific seismic action. First of all, limit states specified serious damaged rank associated with either reconstruction or repair of the structure are defined by the damage degree of a structure member. The uncertainty with respect to the material properties and the strength is evaluated quantitatively for obtaining the response of structure. Furthermore, a input motion which needs to obtain a seismic action at the site is evaluatede by considering the uncertainty of rupture process on the fault. The probabity of a damage rank is evaluated by use of Monte carlo simulation technique.

View full abstract

From the results of the past experiments, it is reported that the friction force and coefficient of frictional isolators are strongly dependent on the sliding velocity and pressure.In addition to them, the temperature is also the important factor for the property of materials.In this study, based on the tribology theory, a numerical model for frictional isolators, which consist of PTFE and SUS, is proposed. Compared with the experimental results of the shaking table tests, it is found that the model can simulate well the behavior of frictional isolators under variational normal pressure, sliding velocity and displacement.

View full abstract

This study addresses the simultaneous influence of soil-structure interaction, non-uniform ground excitations and pounding on the required seating length of bridge girders. The recently published Japanese design specification for bridge girder relative displacement and the recommendation of many current design codes for mitigating pounding and unseating potential are also discussed. The spatially varying ground excitation is simulated stochastically using an empirical spectrum and coherency loss function. The ground is a half-space or a soft layer of different thickness on hard soil. The results show that non-uniform ground motions together with soft subsoil can strongly amplify required seating length and pounding forces, and consequently increase unseating and pounding damage potential of bridge girders.

View full abstract

We investigated the influence of time discretization of ground motions on their spectral characteristics, and response of multi-degree of freedom systems. Two interpolation functions are investigated; a piecewise linear interpolation, and a cubic spline interpolation. Response spectra of three earthquake motions indicate that difference appears for frequencies above 5Hz. Similar earthquake response analyses of model ground show a very small difference in acceleration time history, but large differences in response spectra for frequencies above 20Hz. The analyses show that the effect re-sampling of ground motions are negligible in the most frequency range of engineering interest For some cases effect on high frequency range might be important.

View full abstract

Earthquakes are the typical examples of failure phenomena of the crust materials. Especially, prediction of failure behavior of the faults is important for disaster mitigation. However, physical and mathematical modeling of failure phenomena is very difficult. In this sense, we need a highly efficient numerical analysis tool for failure behavior. This paper presents the application of FEM-β to analyze failure problems of earthquake. The major characteristic of FEM-β, the high efficiency in solving failure problem, is explained in the viewpoint of function discretization and failure criterion treatment.

View full abstract

Dynamic rupture model was proposed to simulate source rupture processes based on physical relationship between the stress and strain field near the fault plane. However, if we use dynamic rupture model for inversion analysis, it is difficult to find a global minimum because of a high nonlinearity caused by the inversion method. We propose a stage by stage inversion process, in which the number of the estimated parameters increase as the stage proceeds, in order to give adequate initial values and to estimate the optimal resolution of the inversion problem.

View full abstract

In this paper, a geomechanical model is proposed to study the influence of CO₂ (carbon dioxide) geological sequestration on the mechanical changes of faults around the injection well by the finite element simulation. Through the numerical parametric studies, such as the thickness and spread width of CO₂ plume, the injection pressure, the depth of injection well and the caprock permeability, effects of the injection pressure and the buoyancy of CO₂plume on the mechanical changes of faults are clearly interpreted. The study shows that the shear stress change along the fault surface is sensitive to the variation of the injection pressure, the thickness and spread width of CO₂plume. The relative slip displacement of fault surfaces is significantly small in current studies. Finally, some suggesting remarks are concluded to decide ideal geological disposal sites for CO₂ sequestration.

View full abstract

Recently, a construction method by making use of both a steep channel and stilling basin has attracted a great deal of public attention. This is because fish migration is possible in this structure due to the slope is about 1/10. In contrast, the hydraulic jump may occur in the pool when the river is flooded. Unfortunately, the location of the toe of the hydraulic jump cannot be controlled. If the location of toe and length of the hydraulic jump can be controlled, the cost of construction decreases. Onitsuka et al. suggested an improved USBR-type ICI for the river, i.e., the slope of chute block is changed. However, the performance of this stilling basin was not investigated. In this study, the performance of this stilling basin was investigated with changing with changing the inlet Froude number and inlet flow depth.

View full abstract

At the location where a backward-facing step or, in the river engineering sense, a drop structure is installed in an open-channel, flow separates and generates a relatively large recirculating region while actively shedding separation vortices in the downstream direction. The shedding of the vortices can be reduced by installing a mild slope at the downstream side of the step, by which the downstream and the upstream flows are more smoothly connected with less energy loss at the step. It is also advantageous for fish to run upstream through the structure when the streamlines are smooth. In this study, the flow at the step with various slope angles are examined experimentally by using the image analysis method with a high speed video camera. It was made clear that a characteristic vortex structure affecting the water surface configuration is generated for a mild slope condition.

View full abstract

In this study, a numerical analysis and a laboratory experiment were carried out in respect to an open channel flow field with a group of permeable groins installed. By using a two-dimensional depth-averaged numerical model, flow fields and water surface profiles were analyzed and compared with the laboratory data. The model was developed by taking consideration of flow resistance and permeability of the rubble mound structures, which is expected to be a powerful tool for making hydraulic design of rubble mound groins as well as other permeable river structures. The agreement between the analysis and experiment was fairy satisfactory. Effects of rubbles' porosity and diameter and geometry of the group of groins on the flow structure and flow force were discussed based on the experimental and the numerical data.

View full abstract

This paper treats the analysis of aerodynamic response characteristics of a rectangular cross section (the proportion between the long side and the short side was 4:1) by computational fluid dynamics (CFD). The Improved Balancing Tensor Diffusivity/Fractional Step (IBTD/FS) finite element formulation was applied to a CFD method and two dimensional calculations were performed. The Spalart-Allmaras (SA) model was applied to a turbulent model, and the Arbitrary Lagrangian-Eulerian (ALE) method was applied to a dynamic analysis. Aerodynamic force and displacement were calculated by CFD. In addition, the range of wind velocity in which a characteristic aerodynamic phenomenon occurs was investigated. The animation of the flow area in the velocity was made to be observed on the causes for the occurrence of characteristic phenomena.

View full abstract

The goal of study described in this paper is to develop the three dimensional analytical model to simulate a flow around a porous structures. The VOF method was used for the free surfacce flow field considering the future applicability to the rapid changes of the flow such as a surge flow. The flow in porous media was modeled by the Brinkman-Forchheimer extended Darcy's equation. As the experimental verification, three dimensional velocities around a spur dike were measured by using Acoustic-Doppler Velocimeter (ADV). The numerically obtained flow profile around a permeable spur dike was compared with the experimental results. It is confirmed that agreement between proposed numerical result and experiment is good under sub-critical flow condition. Some limitations according to mesh size and boundaries were exposed, nevertheless applicability of the model was proved. The present study enables the future simulation of rapidly varied flow around permeable hydraulic structures.

View full abstract

This study gives a description and some applications of a three-dimensional mathematical model, through which the local scour holes around hydraulic structures can be simulated. This model calculates the flow field by solving the Reynolds-averaged Navier-Stokes equations with the widely-used k-ε model for the turbulence closure. The local scour holes are assumed to take place in the form of bed load transport and modeled with a modified Ashida-Michiue formula. A finite volume method based on a moving unstructured mesh is employed in the formulation, which is able to resolve the flow and sediment transport in complex geometries with changeable boundaries. This is of significant meaning for engineering practices. The model is applied to predict two laboratory experiments. It is shown that the local sour profiles, together with the flow characteristics, have been reasonably reproduced.

View full abstract

The instability of shallow water flow has been studied since a long time ago. It has been found from linear stability analysis that, when the Froude number is larger than approximately two, uniform flow becomes unstable, resulting in the evolution of a terrain of waves, which are called roll waves. In this study, a linear stability analysis is performed with the use of the shallow water equation extended for flow on permeable beds in order to investigate the instability of flow on permeable river beds and the resulting water exchange between river flow and the seepage flow beneath the beds. The analysis reveals that flow is unstable in the range of sufficiently large wavenumbers and Froude numbers when the permeable layer is sufficiently thicker than the flow on the bed. In the range of instability, water exchange between river flow and the hyporheic layer beneath river beds is expected to be activated.

View full abstract

The object of the present study is to investigate 3-D turbulent structure in a meandering compound open-channel flow with floodplains. This complex flow consists of a meanderingmain-channel flow and the associated straight floodplain flows, and thus the significant interactions areobserved between the meandering flow in a lower-stage and the straight flow in a higher-stage. It is therefore very important to reveal that the interaction may have strong effects on turbulent structure and the transport of suspended sediment In particular, it is inferred strongly that hydrodynamic characteristics vary significantly in the transition region from the straight to meandering channels.
In this study, the detailed turbulence measurements were conducted by using 3-Delectromagnetic velocimetry. As the results, the distributions of bed-shear stress and velocity components and the relation between the velocity and the corresponding turbulence were examined in the straight to meandering compound open-channel flows.

View full abstract

This paper describes the numerical study of a non-stratified airflow past a two-dimensional escarpment in a uniform flow. The Reynolds number, based on the uniform flow and the height of the escarpment, is about 10⁴. The slope gradient of the escarpment is 25, 35 and 45 degree. Attention is focused on an influence of a slope gradient on airflow characteristics in a wake region. Through comparison between the numerical results, the significant difference in the airflow characteristics is confirmed in the wake region. This is mainly due to the size in the separation bubble. Furthermore, the size in the separation bubble with the surface roughness is much larger than the one without it. In the case under an imposition of the surface roughness, the velocity is strongly defected near the slope surface. As a result, the production of the vorticity in the separated shear layer is also inhibited, leading to the elongation in the separation bubble.

View full abstract

In this study, the sloshing characteristics in a cylindrical tank on an oscillation table are investigated. Firstly, laboratory experiments were conducted under various hydraulic conditions and sloshing characteristics were examined. To simulate the flow fields in experiments, the depth averaged flow model in generalized curvilinear moving coordinate system was used, in which a pressure distribution was assumed to be hydrostatic, and linear solution was derived. The sloshing characteristics obtained from the linear solution were verified by comparing with the experimental results. Good agreement between the linear solution and measurements was observed in case that the water surface profiles were under the first mode.

View full abstract

This paper describes the development of a depth averaged model of open channel flows based on a generalized curvilinear coordinate system attached to the bottom surface. The model was applied to simulate the water surface profile of flows over a circular surface. An experiment was conducted in the laboratory to validate the model. Good agreements in comparison between both steady and unsteady analysis results with observation suggest that, the model can simulate flows in open channel with highly curved channel bed.

View full abstract

The necessity to understand and predict flows that carry large suspended sediment and wash loads has become acute in the Yellow River Basin where significant erosion and siltation associated with hyperconcentrated flood give rise to many river problems. Mud flows, debris flows or slurries, made up of a large amount of clay and/or silt particles suspended in water, often show non-Newtonian properties but remain poorly understood concerning the impacts of their rheological properties on fully developed turbulent structure.
In this paper, we experimentally investigated the effects of non-Newtonian fluid on the separation vortex over fixed dune type bed by using Particle Image Velocimetry (PIV). The results showed that rheological properties significantly dissipated the turbulent flow fluctuations over the dune bed and augmented the flow resistance by comparison with the clear water flow.

View full abstract

Free surface water waves generated by plunging of debris flow cause devastating damage on human life. In this study, a numerical scheme for interaction of debris flow and free surface water wave is developed based on shallow water approximation. Numerical scheme for interaction of debris flow and free surface wave is suggested newly. Generation of waves byplunging of debris flow is highly non-linear phenomena. Classical CIP method and 1^st orderup-wind scheme mixed with 2^nd order central derivative scheme are adopted to simulate collision of two initially separated fluid (debris flow and still water). Numerical results for interaction of debris flow and generated water wave quite satisfactory and reasonable.

View full abstract

Resent studies have shown that group of non-submerged spur dikes can provide a valuable habitat for fishes and macro invertebrates in addition to the function to established a more desirable river for a flood, navigation and bank erosion. In this study, we investigated experimentally the effects of non-submerged spur dikes on bed configurations, water surface oscillations and mean flow characteristics in the cases that spur dikes were positioned facing upstream, downstream and normal to the main flow. The results showed that the spur dikes facing downstream led to the maximum scour at the tip of the dikes, the maximum one in the main channel bed. In addition, it was found that in the case with a facing downstream, resistance is largest.

View full abstract

The excavation of the flood plain sometimes makes three-stage flow, which is composed of a main channel, a flood plain and a mid-level concavity land. In order to maintain this type ofconcavity in the flood plain, it is necessary to understand the flow structures. In this study, three-dimensional flow structures in concavity zones in compound open channels were investigated experimentally. The time-averaged flow structures in concavity zones were revealed by using PIV method. The shape of concavity and the relative level of the concavity bed was changed and investigated their effects on the flow structures in the concavity zones. Furthermore, sediment deposition tests was conducted in the same laboratory flume and the relation offlow structures to sediment transport process was investigated. In rectangular concavity case, the longitudinal scale of the transverse vortex becomes larger relative to the vertical vortex with an increase of the depth of the concavity. In trapezoidal concavity, a skew step produces inclined transverse vortex and generates different flow patterns from the normal step case. The bed level difference provides dissimilar flow structures and sediment deposition rate in the concavity zones.

View full abstract

We developed a multi-layer scanning 3-D PIV system successfully, in which the different elevated laser light sheets were projected into the water flume almost simultaneously using a specially-designed rotation instrument This PIV system is capable to measure instantaneous velocity components in all three dimensional volume at the same time, and was applied to open-channel flows over a triangle-shaped mound.
In this study, the out of plane component can also be evaluated by using the continuity equation. Furthermore, in order to examine the accuracy of this sheet-scanning PIV method, these PIV results were compared with the data measured by a laser Doppler anemometer (LDA), and it was recognized that the measured data of the present PIV was in good agreement with LDA data.

View full abstract

This study describes experimental investigation on particle-fluid interaction and turbulence modulation in suspended sediment-laden open-channel flow over sand dunes by using a discriminator particle tracking velocimetory (D-PTV), which was developed by Nezu and Azuma (JHE, ASCE, 2004). In this D-PTV system, sediment particles and fluid tracers are discriminated accurately by their occupied particle size, and thus, the particle velocity U_p and fluid velocity U_f can be measured simultaneously.
As the results, significant interactions between sediment particles and water were observed in the separation bubble (a reverse flow occurs) and near the rettachment point behind dune. Furthermore, it was revealed that the turbulence intensity of fluid became smaller in sediment-laden flow than in clear water flow without sediment.

View full abstract

This study describes an experimental investigation on turbulence characteristics and the water-surface fluctuations in adverse wind-driven open-channel flows by using both a laser Doppler anemometer (LDA) and a wave gauge simultaneously. Furthermore, a dissolved oxygen (DO) meter was used to investigate the gas transfer across the interface between the water and air.
In this study, it was shown that the velocity fluctuations of water flow near the interface in not only co-current flow but also adverse flow are affected significantly by the water-surface fluctuations in every range of frequency. However, turbulence characteristics and gas transfer phenomena in water layer in adverse wind-driven open-channel flows are different from those in the corresponding co-current flow, and there exists a high correlation between turbulence and the surface fluctuations in predominant frequency due to high-sheared wind flow.

View full abstract

An Immersed Boundary Method (IBM) has been incorporated in a finite-difference code to solve the three-dimensional incompressible fluid flow using the boundary-fitted general curvilinear coordinate system. IBM has been developed for solving flows over complex boundary shapes on rectangular grids. In the present work it has been extended to be used in the boundary fitted coordinate system in order to represent complex objects on curving boundaries, such as undulating terrain with buildings and other objects. Basic verification study has been conducted by computing laminar flows over a model terrain and model rectangular objects to verify merits and efficiency of such a procedure compared with conventional methods. It is found that the IBM technique incorporated in a sigma-coordinate system in which the first coordinate follows the boundary representing the terrain and the second coordinate axis is taken in the straight vertical direction is most appropriate in both accuracy and efficiency, and is suited for calculating flow over topography with objects of various shapes.

View full abstract