This study conducts 2-D elastodynamic time-reversal analysis using topological sensitivity. The time-reversal method is one of the effective inverse scattering technique to detect a defect in elastic solids. The topological sensitivity is utilized to determine the convergence area of time-reversed waves from a linear array transducer. The convolution quadrature time-domain boundary element method (CQBEM) for 2-D elastodynamics is used to obtain scattered and time-reversed wave fields. Some defect detection results obtained by using this approach are demonstrated to investigate the performance of the present method.
[講演概要📄はこちら]  

In the growth process of trees, a mechanical support function is indispensable for securing a stable structure that can withstand the own weight and wind pressure. A remarkable feature of trees is the stress uniform distribution; i.e., they grow their trunks and branches autonomously so that the stresses generated on the surface are uniform. But this established idea poses a following question: what shape of tree branches can achieve such a uniform stress distribution? In the present work, we have calculated the equilibrium state of a main branch, which was affected only by its own weight, within a small deformation range, and examined the effects of the branch tapering and cross-sectional shape variation on the deflection curve and stress distribution of the branch. We have found that the bending stress distribution can reach an almost uniform stress distribution under certain geometric conditions with respect to the outer shape.
[講演概要📄はこちら]  

The physicochemical properties of spider silk, which is a material for spider webs, have been actively studied thus far. On the other hand, the vibration characteristics of the entire spider web have not yet been elucidated, though it should be closely related to spider ecology. In this study, we aimed to establish an experimental method for investigating the vibration mechanism of a circular-shaped spider web. The effectiveness of the method was demonstrated by filming the vibration of rubber string-based spider-web model and performing Fourier analysis on the measured data.
[講演概要📄はこちら]  

There are few types of terrestrial animals that move by bipedal walking. Among them, the ostrich is famous as an animal that can move at high speed for a long time. A better understanding of the structure of the ostrich's leg and the locomotion mechanism, therefore, will open an avenue for the design of a high-speed, energy-efficient bipedal walking mechanism. This motivated us to develop a theoretical model that represents human bipedal walking and to calculate its energy efficiency, as a first step towards the long-term goal of the ostrich problem. The model led us to the conclusion that the amount of mechanical energy required for walking changes in a non-trivial manner with the step length and walking speed.
[講演概要📄はこちら]  

Bamboo is widely used as a functional and natural material in Japan and several other Asian countries. Our resent researches have shown the novel mechanical characteristics of moso bamboo (Phyllostachys pubescens ). In this study we investigate the shape difference and common structural characteristics of five bamboo species from the analysis of measurement data.
[講演概要📄はこちら]  

This study investigates the propagation characteristics of high frequency surface wave in a granite block by ultrasonic measurement. In the experiment, a surface wave field excited by a line-focus transducer is scanned finely over a rectangular aperture with a laser Doppler vibrometer. From the measured waveforms, the spatial distribution of Fourier phase is reconstructed, and the structure of the wave front configuration is investigated. Due to the heterogeneity of the granite, we find the fluctuation of the wave front measured by the distribution of spatial gradient of phase. The intensity of the fluctuation is quantified as a local wavenumber vector. As the result it is found that the granite sample can be characterized by a stochastic wave number whose probability density is frequency dependent, asymmetric and non-Gaussian with a finite support.
[講演概要📄はこちら]  

In recent years, many stainless steel (SUS) panel tanks have been installed as for water supply facilities in order to facilitate maintenance and shorten construction time. Although these tanks are designed and constructed according to the latest design standards, there have been so many cases of damage in SUS tanks due to severe earthquakes such as the Tohoku-Pacific Ocean Earthquake and the Kumamoto Earthquake. In this paper, the time history response analysis of a 3000 × 3000 × 3000mm SUS tank is carried out to show local stress behavior which can cause damages. As a result, it is necessary to study more on the relationship between SUS body stiffness in order to avoid damages under earthquake which can modify future design condition.
[講演概要📄はこちら]  

In this study, the shear lag theory using the conventional differential equation was extended to the CFRP bonded repair of the thickness-reduced plate under pure bending. The surface stress of the members obtained from this result almost agreed with the finite element analysis. Furthermore, it was found that the surface stress at the thickness-reduced section repaired by bonding CFRP is almost the same as that of the composite theory.
[講演概要📄はこちら]  

Using an image analysis method, the deformation behaviors of RC beams with artificial damage were investigated under a moving wheel load condition. The two beams were loaded simultaneously with a moving wheel under dry and wet surface condition, respectively. This study focused on the maximum principal strain and maximum shear strain of the beam with wet surface condition. Analytical results clearly showed that the deformation behaviors in the upper part of the specimen were affected by wheel load positions.
[講演概要📄はこちら]  

The reproduction and quantitative evaluation of past landslide disaster cases will lead to the evaluation of the risk of slope failure and the prediction of the damage after the collapse. The purpose of this study is to perform high-speed calculations by parallelizing 3D large-scale SPH simulations that model real ground. In the calculation for the actual ground, the calculation was performed on about 1.45 million particles, and it was shown that parallel calculation with high scalability was performed. Therefore, it is suitable as a framework for large-scale calculation.
[講演概要📄はこちら]  

The objective of this study is to establish a numerical scheme for solid represented by Helmholtz decomposition (H-d). Based on the H-d, arbitrary vector field V can be represented using scalar potential φ and vector potential ψ as follows, i.e. V= ∇φ + curlψ (divψ =0). In a previous report, I proposed an improved Helmholtz decomposition (iH-d) for displacement vector u ; i.e. u =∇φ + ∇φ^I + curlψ ( ∇²φ^I=0, divψ=0), and ∇ψ·1= ∇²Ψ, where Ψ is potential but has a similar dimension to u. By numerical model based on the finite deformation theory, the nodes must follow the Lagrangian tracking. This report proposes an adaptive nodal relocation (ANR) method, where the distortional term in the function of hexahedron play an important role for the nodal relocation. The objective to represent in iH-d is to avoid so-called numerical Locking.
[講演概要📄はこちら]  

The applicability of MPM (Material Point Method) combined with mixture theory is investigated from the perspective of predicting tsunami hazards induced by submarine landslide. By use of two overlapped layers for soil and water particles, soil-water mixture and incompressible fluid models are used to respectively represent the submarine landslide and the resulting tsunami event in a consistent manner. Numerical example is presented to simulate the collapse of an undersea soil slope on the seabed and examine the performance in reproducing the fluidized soil movement and resulting elevated waves.
[講演概要📄はこちら]  

In the wake of the 2011 the Great East Japan Earthquake, research on toughness dike structures has been done. In previous studies at, it has been clarified that steep tidewalls have a great reduction effect on tsunami energy transmission to the hinterland. Additionally, Study on scouring measures of Landside toe of slope and dike structures using geosynthetics materials to realize steep banking, obtained the knowledge of toughness resistance to long time overflow by designing using submerged unit weight. However, there are cases of collapse despite satisfying stability, and the flow of water in the foundation ground is considered. In this research, numerical analysis of the tsunami energy reduction effect is performed, including the cases that have not been implemented in the experiment.
[講演概要📄はこちら]  

Reservoirs are expected to be protected against mega earthquake damages. The immediate collapse of reservoirs due to a large earthquake, the houses around the reservoir are estimated damage due to the same fluid power as the tsunami. However, it is difficult to apply real damage to various types of reservoirs. Therefore, numerical analysis can be considered by an effective method for predicting damage. In this study, the flood analysis is conducted with reference to the damage example of a house collapsed by strong fluid force due to few data of reservoirs damage. Analyzes the hydrodynamic forces of the flood and suggests ways to use the results to determine house collapse.
[講演概要📄はこちら]  

Flood-inundation analysis using terrain-adaptive cells can flexibly describes complex terrain shapes in urban areas. However, it is difficult to generate the terrain-adaptive cells by man hands. In this study, we developed a method to mechanically generate the cells from the road network data. We also calculated using mechanically generated terrain-adapted cells are performed. As a result, 1) the mechanically generate cells can be accurately estimated the expansion speed of inundated area, and 2) contribute to the high-speed calculation.
[講演概要📄はこちら]  

During the 2011 off the Pacific coast of Tohoku Earthquake and the 2016 Kumamoto Earthquake have caused devastating damages, collapsing lots of wooden houses. Restoration and reconstruction after these huge disasters delayed to remove a large amount of debris including collapsed house members. It is estimated that the same-scale earthquakes and accordingly tsunamis in the Nankai Trough region will be happen. Therefore, it is very important not only estimating the tsunami run-up in advance but also risk management such as evaluating the total amount and spread of debris, securing rescue routes, and temporary rubble storage sites. In this study, the wooden house collapse simulation is conducted with the ASI-Gauss code, which is one of the large deformation FEM code with the Timoshenko beam element. Then, the ASI-Gauss code is enhanced in order to simulation large scale city models. In the future, it is required to carry out a city-scale seismic response analysis with the past earthquake log for a validation of our developed code.
[講演概要📄はこちら]  

This study presents a new framework for probabilistic risk assessment of buildings under seismic conditions. A part of Chiang Mai city (Thailand) is selected as a target area, and a building damage evaluation method developed in HAZUS is employed in the numerical simulations. We prepared simulated results with a variety of situations by changing locations of earthquake sources and their magnitudes. Based on the obtained results, the seismic risk of buildings in Chiang Mai is analyzed. The proposed framework can provide an efficient approach to the probabilistic seismic risk analysis, and it has a high potential for disaster risk assessment.
[講演概要📄はこちら]  

In this study, a novel implicit stress-update algorithm of the subloading surface model, a class of unconventional plasticity modes, incorporating the nonhardening plastic strain region is developed to improve the predictive capability for cyclic loading property. Ohno (1982; J. Appl. Mech., ASME) proposed an improved plasticity model equipped with nonhardening plastic strain region in order to reproduce the stagnation of isotropic harden-ing resulting in transient stabilization of hysteresis loop during cyclic loading with a fixed strain amplitude. In the plastic strain space, when the plastic strain moves inside the region, isotropic hardening does not proceed, while only kinematic hardening proceeds, and hence the region does not expand. When the plastic strain moves outside of the nonhardening region, isotropic hardening proceeds being accompanied by expansion of the region. As a specific prototype model, von Mises plasticity model is reformulated based on the hyperelastic constitutive equations within the framework of infinitesimal deformation theory. A numerical algorithm for stress calcula-tion using return mapping is developed, in which we devise a novel scheme consisting of scheme consisting of hardening/nonhardening judgment, substep technique, and nested iteration to update variables associated with nonhardening plastic strain region.
[講演概要📄はこちら]  

For metal material models, shear strength does not depend on mean stress. Aφ = 0 material such as saturated clay is also the same. For φ = 0 material, even if a mean stress is on tensile stress zone, it will not affect to failure behavior in metal material model. But, previous studies that examined the applicability of the metal material model to the failure behavior of the ground material, haven’t been found. In this paper, numerical experiments were conducted, to investigate the influences of tensile stress zone of soil on ultimate bearing capacity, using a rigid-plastic finite element method based on the lower bound theorem.
[講演概要📄はこちら]  

The two-fluid system consisting of Bingham and Newtonian fluids is sometimes seen in the area with multiple solid objects, such as mortar flows between aggregates and grouting-materials flows in rock fractures. In this study, the phase-averaged governing equations are utilized for the two-fluid system of Newtonian and Bingham fluids. The governing equations are discretized with the finite volume method with the collocated grid system. The dam-break flows of the Bingham fluids surrounded by the Newtonian fluids were calculated with the present method. From the numerical experiments, the effects of the non-dimensional yield stress of Bingham fluids are investigated together with the number of the fixed square objects in the computational area.
[講演概要📄はこちら]  

Computations of container filling with highly viscous Newtonian fluids are conducted with the finite volume method using a collocated grid system. In this study, phase-averaged governing equations are solved for the multi-phase field, which consists of two incompressible fluids with different densities and viscosities. As a result, it is confirmed that our method enables us to reasonably predict flow patterns of highly viscous liquids, such as steady filling, splashing and buckling, which arise in the specific relationships between Reynolds number and the ratio H/d, where H is the height of the container and d is the inlet width, as reported in the preceding studies.
[講演概要📄はこちら]  

This study seeks to compromise the temporal/spatial resolution (the granularity) difference in integrating different simulations. There are two approaches for the compromise, taking either average or maximum of results of the finer granularity simulation. We make numerical experiments using Integrated Earthquake Simulator for an actual urban area by integrating structural response analysis and traffic flow analysis, and demonstrate the effect of different approaches on damage evaluation. We also analyze the impacts of the structural damages on the traffic flows.
[講演概要📄はこちら]  

A numerical computation of a sound that a character moving in the virtual space hears is considered. We solve the initial-boundary value problem of wave equation using time domain BIEM and store the computed boundary values in advance. We compute the sound of the moving point with the integral representation formula in real time using Unity3D.
[講演概要📄はこちら]  

The contingency table analysis provides the interrelation between two variables and can help find interactions between them. Previously, we extended the contingency table by applying fuzzy theory and defined a fuzzy 2×2 contingency table. However, this definition cannot be extended to fuzzy m×n contingency tables. In this paper, we propose the “new” definition of fuzzy m×n contingency table and apply to similarity index calculation.
[講演概要📄はこちら]  

Cracks in concrete are visualized by using X-ray CT. Conventionally, the cracks from CT images have been extracted by binarization processing with threshold setting. The conventional method has a problem that the evaluation accuracy varies greatly depending on the set value of the threshold. In this study, concrete’s cracks are extracted by X-ray CT image processing with the decision tree method. The specimens were taken from an agricultural canal structure with frost damages. Five explanatory variables were set: Brightness, the pixel value after the DoG (Difference of Gaussian) filter, the maximum pixel value at 2 × 2 pixel, the minimum pixel value at 2 × 2 pixel, and the difference between the maximum and minimum pixel values. The decision tree method can achieve the same or better evaluation accuracy than the conventional method. Therefore, the decision tree method seems to be effective for obtaining stable accuracy under various measurement conditions.
[講演概要📄はこちら]  

Textural characteristics of visible images of corroded steel sheet pile are important information of the corroded condition. In this study, spatial distribution characteristics in visible images of the corroded steel sheet pile are evaluated by texture analysis using gray level co-occurrence matrix. As a result, by utilizing saturation channel, the textural homogeneity of a non-corroded steel sheet pile is higher value than a corroded one. Considering the spatial anisotropy, there is a difference of the homogeneity in the long length and the short one. The textural characteristics of non-corrosion and corrosion could be quantitatively evaluated by the textural homogeneity and the spatial anisotropy.
[講演概要📄はこちら]  

After a major earthquake event, there is a case that the vehicles cannot become passing on the bridge due to the damages in bearings and expansion joints caused by large dynamic displacement. In this study, the fragility analysis was conducted focusing on the vehicle passability after the earthquake event on two bridges with different structural characteristics considering the effects of deterioration damages on the existing bridges. As the results, it was shown that the deterioration damage affected the large vehicles passability after the earthquake, and may decrease the vehicle passability as the bridge structure system.
[講演概要📄はこちら]  

There have been many numerical models proposed for tsunami propagation simulations. They are all very numerically intensive, requiring days to complete the calculations. For probabilistic risk analysis, which requires many simulations, these methods are infeasible. Therefore, in this paper, we propose a framework of surrogate modeling, which introduces the potential of real-time risk assessment. To create the surrogate model, we calculated the prominent modes of the given data, after which we used RBF interpolation for mapping the input data points to their corresponding coefficients. The surrogate model this constructed is expected to be accurate, given the simulation cases used are sufficiently dense for the complexity of the results.
[講演概要📄はこちら]  

The channel width-to-depth ratio can estimate occurrence sandbars in gravel bed rivers well. How-ever, applicability of existence of sandbars by the width-to-depth ratio is unknown. In this study, we investigate the width-to-depth ratio to estimate existence of sandbars in actual 11 rivers. On this estimation, flow depth was calculated using the uniform flow formula for practical purpose. As a result, we showed that the width-to-depth ratio can estimate existence of sandbars using uniform flow formula.
[講演概要📄はこちら]  

Columnar joint is a regular pattern of cracking in igneous rock that forms an array of slender columns with polygonal cross section. In this study, we considered the geometry and topology of the polygonal crack tessellation observed at the outcrop surface of columnar joints. Aerial photo shooting of the columnar joint was conducted at four different sites in Japan to obtain a sufficient amount of image data for numerical replication of the polygonal crack patterns. Using the primary data, we examined the similarity and difference in the statistical properties of the polygon geometry between the four sites. The results imply a universal fluctuation in the skewness of polygons, which quantifies the geometric discrepancy in the polygon shape from the regular counterpart. It was also discovered that the geometric fluctuation is characterized by Gumbel distribution, irrespective to lithographic and geographic conditions under which the columnar joint formed.
[講演概要📄はこちら]  

Gravitational instability (Rayleigh-Taylor instability), which is a typical example of hydrodynamic instabilities, occurs due to density difference. When a heavy fluid lies over a light fluid in a constant gravitational field, fluctuations at the interface gradually increase and then macroscopic flows occur. The gravitational instability can be found not only in liquid-liquid interface but also in the gravitational settling of granular materials (granular-gas interface). However, the gravitational instability of liquid systems and granular systems have been discussed individually in most cases. We find a interesting relationship between the granular system and the physical gel. We also find that those behaviors are determined by the depth of the fluidization.
[講演概要📄はこちら]  

CFRP has high strength and high stiffness in addition to its low density, however CFRP exhibits a brittle behavior at the time of fracture. In this study, cross-ply laminate, helicoidal laminate within limited angle range and cross-ply laminate core with helicoidal laminate skin were tested under three-point bending, and image analysis were performed for deformation behaviors. From the image analysis, it was confirmed that the deformation behaviors did not conform to those of the beam theory. It was observed that the epoxy resin between prepregs affected the deformations and that the out-of-plane deformations of the helicoidal laminate possibly were present.
[講演概要📄はこちら]  

Monte Calro simulations are carried out to investigate the influence of the heterogeneity with respect to the grain size of coarse aggregates in concrete on the fracture properties. The concrete is regarded as three-phase composite materials composed of mortar, aggregates, and the interface. A damage model that allows a kind of mesh-free finite element analysis is used for modeling cohesive crack growth.
[講演概要📄はこちら]  

This paper investigates the surface crack propagation life based on the local elasto-plasticity response at crack tip. Fatigue crack propagation including its life and the profiles are assessed as a continuous behavior of fatigue crack initiation in this study. Firstly fatigue crack initiation life is assessed by 3-dimentional cyclic elasto-plasticity analyses and Δε-Nc criterion. Then fatigue crack growth rate is calculated as da/dN = Δa/Nc, where Δa is a fatigue crack growth length parameter. It is verified that fatigue crack propagation life in the depth and width directions is accurately assessed by comparing with the corresponding experimental results.
[講演概要📄はこちら]  

This paper presents an analytical approach on the load carrying capacity of steel pipe beams with flange joints against boulder impact by changing the impact position of boulder. First, this method was validated by comparing with the static and dynamic test results. Second, the load carrying capacities of steel pipe beams (fixed and cantilever beams) with flange joints were investigated by changing the impact positions of boulder using the static and dynamic elastic-plastic FEM analyses.
[講演概要📄はこちら]  

Shallow landslides and slope failures in Marumori, Miyagi during the October 2019 typhoon Hagibigs are acknowledged to be induced by heavy rainfall. Using rainfall intensity and soil characteristics, infiltration capacity and depth of infiltration can be estimated. In this study, the Green-Ampt equation, adapted for inclined surfaces, is used to estimate infiltration depths along critical slopes. Assigning the computed infiltration depths as the slip surface depth, the factor of safety is then calculated using the infinite slope stability model. Translating this model into raster processes, a visualization map of a time-varying factor of safety for Marumori can be generated.
[講演概要📄はこちら]  

In recent years，many cases of collapse and damage of soil structures have been reported due to the increase of sudden heavy rains (guerrilla heavy rains，typhoons，etc.) due to climate change，and they are suffering from sediment disasters every year．To date，the analysis of the causes of collapse of soil structures and their mechanisms have not been fully elucidated．However，in geotechnical engineering，long-term prediction of soil structures using numerical analysis has been conducted，and research on optimal design focusing on performance has been advanced．In this laboratory，we have clarified the behavior of the embankment and river embankment in consideration of rainfall and rising water level using the air-dissolved unsaturated soil / water / air coupled finite analysis code (DACSAR-MP)．However，since the incremental balancing equation is defined as σ'_(ji，j)=0，it is impossible to take into account the state change due to external factors，that is，the effect of the unsaturated density change．In this study，we propose an incremental balancing equation applied to unsaturated soil and reflect it in the analysis code to compare the density change of unsaturated soil due to external factors.
[講演概要📄はこちら]  

In recent years, many examples of soil structure collapse due to heavy rainfall have occurred. Because of this, it is urgent to establish a method to evaluate and examine long-term embankment structure quality. Japan's conventional design method insufficiently evaluates embankments. Although this method is shifting to a performance-based design to cope with recent abnormal weather, an effective design method has not yet been established. Therefore, this research performs an initial stress analysis of embankment, accounting for differences in construction conditions. Notable in this study, is the comparative analysis of results, considering the initial water content ratio, one layer of discharge thickness, rolling compaction, and other given structural conditions that differed from conventional design standards. Based on the dynamics of unsaturated soil, the rainfall intensity was analyzed in order to confirm the variation of the initial stress due to rainfall. Lastly, and most critically, the dynamic change in embankment performance by the aging was analytically expressed, and the optimal structural conditions of embankment, grouped by rainfall history, was examined.
[講演概要📄はこちら]  

The large compressibility with particle breakage of Ryukyu limestone sands is predicted by the power rule of logarithm void gradient. It is revealed that the different compressibility from initial void ratio is evaluated in the material constants ξ of the power rule, and the different compressibility from particle strength is evaluated in the hardening/softening coefficient K₀ of the power rule.
[講演概要📄はこちら]  

In oder to accurately determine energy loss in non uniform flow using mathematical model of open channel flow, velocities and depth of water must be simultaneously measured with high resolution. However, energy loss in non uniform flow (IeN(x)) which has spatial distribution, has been cal-culated generally using the Manning formula as energy Loss in uniform flows. In this study, to estimate IeN(x), we investigate a new solution method combining physical model analysis and in-verse analysis. We performed a simple 1-dimensional numerical analysis which estimate IeN(x)’s energy loss coefficient to confirm the applicability.
[講演概要📄はこちら]  

Both level set methods and volume of fluid (VOF) methods are popular for computation of immiscible-fluid flows. Here a comparative study of the ACLS (accurate conservative level set) method, a level set variant, and the CICSAM (compressive interface capturing scheme for arbitrary meshes) method, a VOF variant, in terms of accuracy and efficiency has been carried out. Several benchmark tests revealed that the ACLS method combined with a high-order scheme shows a remarkable ability for interface capturing. While the CICSAM is available only at low-CFL-number conditions, its accuracy comparable to the ACLS method and easiness of implementation are also desirable. Application to the steady state air bubble test, which requires coupling with a Navier-Stokes equation solver, presented that a sophisticated method for calculation of interface normal and curvature is essential for VOF methods when surface tension force plays an important role.
[講演概要📄はこちら]  

Large-eddy simulations (LES's) for a thermally convective flow above buildings and streets (an urban canopy) in the atmospheric boundary layer are performed. Special attention is paid to the effects of the buildings on turbulence heat transfer processes in the vertical direction of the atmospheric boundary layer. LES's clearly show that the buildings yield the dissimilarity between thermal and flow fields, i.e., the vertical profiles of turbulence statistics and also coherence structures in the thermal fields significantly differ from those in the flow fields.
[講演概要📄はこちら]  

Energy gradient of open channel flow has been generally estimated with the Manning’s formula for uniform flow. Therefore, almost natural river form non-uniform flow, it is unclear whether energy gradient of uniform flow can be applied non-uniform flow. We calculated the energy gradient of non-uniform flow using the Mayer–Peter–Muller formula. We showed that the difference between energy gradient in non-uniform flow and in uniform flow with roughness coefficient as constant is more than 50%.
[講演概要📄はこちら]  

In a straight gravel river, those channel width is stable and not infinite. In other hand sides, alternate bars are often spontaneously formed in gravel rivers, and a linear stream is maintained stably in response to their development. The above-mentioned stable channel width and the linear straight stream of the latter suggest some relationship. In this study, we investigated stability of channel width at the width-to-depth ratio which was obtained during the development processes of alternate bars. We showed that the ratio is a condition for suppressing the occurrence of alternate bars, and therefore, stable channel shape was kept due to the straightness of stream line is kept.
[講演概要📄はこちら]  

In this paper, we perform a numerical simulation of sand bar and channel evolution processes of the Chikuma River caused by a huge flood event observed in 2019. The numerical results show that the huge flood causes a downstream migration of sand bars, which had been fixed for last decades, resulting in a significant change of channel pattern and bank erosion. The result is reasonably consistent with the observed river evolution.
[講演概要📄はこちら]  

A multi-stage collapse process of ground structures caused by seepage flow is simulated with a coupled material point method based on the theory of porous media. The continuum of the mixture is discretized with a set of Lagrangian material points that possess the information about both the geometry and material of solid and liquid. Both explicit and implicit schemes are combined to improve the robustness and efficiency in computations. A model experiment for seepage failure is simulated to demonstrate the capability of the proposed method in dealing with the transition from the quasi-static to the dynamic state of the unsaturated soil.
[講演概要📄はこちら]  

This paper deals with the computational method for the density currents between multiple non-spherical particles with a phase-averaged model, in which no empirical formulations, like a permeability k and a drag coefficient C_d, are needed. In addition, density currents caused by wide range of density ratio can be predicted reasonably since the Boussinesq approximation is not used in our method. The numerical experiments were conducted to understand the influence of the cell-porosity resolution R, which is defined as the spatial resolution of the fluid cells against the volume that is not occupied by the solid particles.
[講演概要📄はこちら]  

A computational method was proposed for the free-surface flows between multiple absorbent particles on the basis of the finite volume method with the collocated grid system. In the proposed method, the swelling of the particle due to the water absorption is considered with the velocity boundary conditions on the particle surfaces. The proposed method was applied to the dam-break flows in the porous media, which consists of multiple absorbent particles, to confirm its applicability. As a result, it is demonstrated that the free-surface flow patterns are largely affected by the swelling particles and that the flows between particles are possibly blocked by the swelling particles in case that the water absorption speed is sufficiently high.
[講演概要📄はこちら]  

This paper describes the applicability of the two-dimensional computational method to predict the sieving filtration, which is used to trap ”moving particles” from the particle-laden liquid flows. A flexible porous structure for the sieving filtration is modeled with the ”trapping particles”, each of which connects to its initial position with a spring and dash-pot structure. The dam-break liquid flows including moving particles were calculated in the area where the trapping particles were placed. As a result, it was shown that the moving particles are retained by the trapping particles and that the sieving filtration is reasonably simulated.
[講演概要📄はこちら]  

Until now, poor understanding of the propagation characteristics of alternate bars, which are wave phenomena, is that the formulation of the theoretical equation for its celerity has not been estab-lished. In this study, we firstly derived the two-dimensional theoretical equation for celerity of riverbed waves. Secondly, we verified applicability of its equation for alternate bars using temporal and spacial high-resolution measured values. As a result, we clarified that its equation have high accuracy for estimation of alternate bars celerity if froude number is lower than 1.0.
[講演概要📄はこちら]  

Bank erosion is typical failure in gravel bed rivers. We have developed an prediction method of bank erosion point due to uneven distribution of flood flow using tractive force. However, the method is based on physical model that is not neglect any uncertainly. In this study, we try to combine new prediction method focusing on river bed shape with the previous method using flume experiment and numerical simulation of actual river. We showed that both prediction methods can estimate bank erosion point well.
[講演概要📄はこちら]  

Elevation of the phreatic surface causes instability of an earth structure. Therefore, drainage system is important on constructing an earth structure. Drain pipe is the drain system applicable even for an existing earth structure. In this study, the drain pipe was expressed in the initial and boundary problems on unsaturated soil. Here, the results of electrical prospecting were compared with seepage analysis on the embankment installed drain pipe. Consequently, qualitative agreement between them was found.
[講演概要📄はこちら]  

In recent years, localized torrential rains have frequently occurred in various parts of Japan, and frequent river levee collapses have occurred. However, the mechanism of river embankment collapse has been discussed, but not fully understood.Therefore, in this study, we performed embankment analysis considering the difference in layer thickness using the unsaturated soil / water / air coupled element finite method analysis program (DACSAR-MP), and focused on embankment reinforcement and rainfall. At that time, it was analytically confirmed that the failure mode of the embankment was different due to the difference in the rising speed of the external water level.
[講演概要📄はこちら]