DDA (Discontinuous Deformation Analysis), a numerical method used to analyze the discontinuous media, is used to simulate the deformation mechanism of a sand model in this paper.The microscopic mechanism of deformation properties of a sand model such as elasto-plastisity, dilatancy, strain softening, hysteresis loop during unloading-reloading, volume contraction during unloading and formation of shear zone are analyzed and explained by the DDA simulation.The method that takes sand as discontinuous particles provides a powerful approach in the field of soil mechanics.

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A rigid-plastic analysis of an assembly of regularly arranged circular elements with an equal diameter was made to consider the relationship between the micro- and macro-mechanisms of cohesive granular materials. No elastic constant for elements was employed whereas rolling and plastic sliding at the contact points were considered. It is the main subject to estimate bearing capacity by this model.

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The inter-particle force due to meniscus at a contact point of soil particles is derived and then the relationship between suction and apparent cohesion is numerically obtained based on some probabilistic consideration on the soil particle size. A new slope stability analysis is proposed to analyze the stability of Shirasu slopes, in which Janbu method is applied to the slope failure caused by heavy rainfall. In the proposed stability analysis the change in apparent cohesion with the change in water content due to rainfall can be taken into account. The current safety factor can be calculated by a personal computer when the data on total amount and intensity of rainfalls are obtained in the real time.

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Discontinuous Deformation Analysis (DDA) was developed by G.H.Shi and has been often applied to rock mechanics problems.The original DDA handles only a polygonal element, therefore the judgment of penetration between elements is complicated.The authors develop elastic circular element for DDA and applied to impact analysis. From several numerical analyses, we could find the spring parameter that satisfies 1-dimensional wave equation.The developed method are applied to contact issues between falling rock and sand cushion, then good results are derived which agree with the past experimental resul s. It is shown that the developed method is effective to impact analysis of granular materials.

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This study aims to clarify analytically mechanical behaviors of a sand-structure system subjected to static and cyclic loadings.In particular, the settlement-lateral deformation behaviors of the ground bearing a structure are focused.A series of FEM analysis based on Mohr-Coulomb formulas with non-associated flow rule was carried out to accomplish the purpose.The analysis results obtained were detailedly compared with those of the model static and cyclic tests performed on the two-dimensional soil box.On the basis of these results, the applicability of FEM analysis to evaluate the deformation behaviors of the ground-structure system was made clear.

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The technique of X-ray TV visualization is described in this study as applied to seepage failure experiments of a sand and gravel two-layer system. This technique allows for the precise visualization of the microscopic internal deformation processes, the dynamic development of a liquefaction front in a sand layer, the transport of sand particles into a gravel layer, the failure mode of a whole system and so on. This experimental technique provides a powerful and promising tool for understanding the dynamic interaction mechanisms of granular media/pore fluid systems.

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Recently, seismic observation networks of various scales from local to global have been established. They contain the infra-network of seismic surveys and observations, and high concentration strong motion seismograph. Our concern is now how to make the best use of such a huge observation system for a science and disaster mitigation plan. In this project: real-time seismology, we attempt to extract the detailed information on seismic source and strong ground motions at an early stage by using seismic data provided by this huge system immediately after earthquakes or daily. In addition, we aim to develop effective methods to utilize such information for disaster mitigation, and to contribute to th further advancement of earthquake source physics and disaster science.

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An inversion method to infer dynamic rupture parameters of earthquake faults is presented. An earthquake fault is divided into subfaults. Assuming that stress drop occurs within the subfault and that stress drop in other area of the fault is 0, the ground motion generated by each subfault is calculated. The seismic wave of an earthquake can be expressed as the sum of the waves of each subfault. The rupture time and the stress drop of each subfault are used as dynamic rupture parameters. I applied the inversion method to a simple model using synthetic seismogram generated numerically by 3-D finite difference method. The inferred parameters are exactly the same as the ones used to calculate synthetic seismogram.

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This paper proposed an estimation method of JMA intensity using a multi-regression formula with acceleration response spectrum. The estimated JMA intensities from the multi-regression relationship agree well with observed values. Combination of the proposed method with the attenuation relation of acceleration response spectrum and the amplification factors of subsurface can predict the distribution of JMA intensities for large area. Furthermore, this estimation method was applied to the inversion of earthquake fault by using genetic algorithm. From numerical experiments, it is confirmed that the identified results show enough accuracy to predict an isoseismal map for large area.

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In this study, the applicability of the method to identify the location of earthquake fault after the eventusing the records of peak acceleration observed at ground surface is described. The applicable limit is defined as the standard deviation of the identified location of an fault line in relation to the magnitude and the length of fault line. Finally, the results of identification in 1995 Hyogoken-Nanbu eathquake is discussed

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The earthquake ground motions are efficiently simulated using a discrete three fold Fourier transform of the analytical forms of seismic wave field in frequency wavenumber domain. They are derived by a stiffness matrices based formulation of the physical processes of propagation of seismic waves, which are radiated from a kinematic rupturing fault model. It is found from a numerical example that the seismic wave field on free field ground surface near a strike slip fault is like a vortex of sea water.

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The structure design method, which takes into consideration the influence of the earthquake faults on the ground, has not yet been established. The purpose of this paper is to do MDEM simulation, which a boundary condition was decided as from the experiment result of the deformation of model grounds, shear zones and bedrock stress. This paper presents the results of a series of MDEM simulation of two speeds about the reverse dip-slip faults of bedrock, which made the granular materials in the subsurface ground. The results have an influence greatly by the setup of about the reverse dip-slip faults step of bedrock.

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In this paper, a finite element model is formulated to simulate the crustal of deformation of faultbend folding with the large scale features using the large deformation theory in which the fault surface is represented with the master-slave method. The viscous-plastic material properties modeled by the Perzyna viscoplasticity theory are used to simulate the pressure solution creep and cataclasis respectively. Moreover, an interfacial viscous-plastic model is adopted to represent the nonlinear behavior of the fault surface. Effects on different structural models and parameters of fault-bend folds are simulated. Contours and development of the stress invariant, horizontal strain, equivalent viscous plastic strain by following an individual particle and traction on the fault surface are shown. The numerical results comparing with kinematic models are also discussed in order to infer a sequence of the deformation mechanisms.

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In order to simulate the formation process of surface earthquake faults, we develop a new stochastic finite element method for an elasto-plastic body with randomly varying material properties. The method is based on the Karhunen-Loeve and the polynomial chaos expansions to efficiently estimate complete probabilistic characteristics of responses, such as average, variance, and a probability density function. The method is compared with the Monte-Carlo simulation, and the agreement is satisfactory. Also, it is shown that the proposed stochastic finite element method is able to simulate complicated bifurcation phenomena associated with the fault formation process.

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The objective of this study is to develop a theoretical framework for conditional random fields (CRFs) which consists of non-stationary stochastic processes. For this purpose, we use the probability density function of Fourier amplitudes and phases in frequency domain. The problem area of CRFs in this study is limited in the estimation of stochastic processes conditioned by realized values of time series. To represent the properties of non-stationary processes, we will introduce group delay time spectra, which are gradient of phase spectra with respect to frequency. Using the style of likelihood method, the conditional probability density functions of Fourier phases are updated by information of group delay time. On this basis, a method to generate numerically the conditional random fields containing non-stationary processes is developed and it is verified through the numerical examples that the method can give reasonable results.

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A spring-mass model for structures on pile foundations is proposed in this paper. Research on spring-mass models for pile foundation is reviewed, and a comparison with other such models in terms of the governing equations shows the features of the proposed model. Moreover, it is explained that the model is very much practical for the evaluation of the effects of both soil nonlinearity and soil liquefaction on the behavior of pile-structure system. The model is applied to two case studies whose results can simulate both seismic behavior of an instrumented structure and well-investigatedp ile failureo f a heavily damageds tructure.T hese can lead us to a conclusiont hat the applicability of the model is well verified.

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This paper discusses the quick inspection technique for earthquake damaged railway bridges using vibration measurement and new numerical model for nonlinear analysis of structures. The accuracy of the Applied Element Method (AEM), used in this study, is verified by comparing with the experimental result of change of natural frequency of the RC column due to damage and also actual earthquake damage to existing two-storied RC rigid frame viaduct. Next, the methodology to obtain the relation between the change in natural frequency and damage levels of real structures is discussed.

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Demand for the large scale nonlinear FEM analysis is increasing and the efficient computation of such FEM is becoming important. This paper proposes a non-iterative time integration scheme that is applicable to the dynamic FEM analysis, in which the model is partitioned into subdomains for the purpose of parallel computation.
The proposed scheme is implemented as the combination of the explicit scheme and the implicit scheme. Detail of the algorithm of the proposed scheme is described and some aspects of the proposed method such as its stability is discussed based on the numerical study. Applicability of the method is shown by numerical examples of the dynamic analysis of the model which is partitioned into two subdomains. The computation results show the efficiency and accuracy of the proposed method.

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New finite element analysis algorithm based on the constitutive relationship database is studied. Since this method does not require the calculation of constitutive equation at each time step, there is huge advantage for the numerical analysis of the material whose constitutive equation is complicated. In this study, the process of database construction and the feasibility of proposed algorhythm are discussed.

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The present study deals with dynamic nonlinear analyses of reinforced concrete columns in order to examine the failure modes and maximum displacement response.In the paper, first, the three kinds of failure modes are defined: shear failure, shear failure after the yielding of main reinforcement, and bending failure.In particular, the shear strength degradation in the truss analogy is modeled by introducing the reduction formula given by Priestley, et al.
The various numerical simulations of single type of columns are carried out under the two types of the recorded strong ground motions.The degradation process of shear strength of concrete are realistically observed during the random time-history response.The reduced shear strength is compared to the design values specified in the Japan's seismic design codes.

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Compaction and separation work are popular countermeasures to prevent floating of underground structure due to liquefaction of sandy soil. However, it is difficult to decide the extent of densification, the width of area to be compacted and the rigidity of sheet pile wall rationally. In this study, a series of 1g shaking table tests on a underground structure surrounded by loose sand were carried out with compaction around thestructure, separation by sheet pile wall and both of them to investigate its effect on the dynamic stability of underground structure. No serious damages were observed when the ratio of the width of compaction area to the thickness of liquefied layer is greater than 1.0 in a series of tests. The greater the rigidity of sheet pile wall, the less floating of the underground structure was observed due to shaking. The increment of the restraint of floating to the rigidity of sheet pile wall gradually tends to decrease as the value of its rigidity increases.

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It is important to clarify activities of geological structures until earthquakes occur.In this paper, we propose a theory for numerical analysis to predict initiation and development of faults.The formulation is based upon the multiscale analysis and the faults are treated as localized deformations.Considering high order terms in the singular perturbation method, we deduce a nonlocal constitutive law, such that stresses are determined by not only strains but also strain gradients, whose effect dissolve a problem that the numerical results depend on the mesh size in finite element analysis.

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Mathematical viewpoints of the eigenvalue problems provide geometrical aspects forintegral equations used in various phisical ploblems. One of the authers Touhei previously showed spectral representation of Green's function concerned with the scattering problem for a layered acoustic half-space. This paper shows a representation of SH wave-fields for a layered medium having an irregular interface in terms of eigenfunctions for the continuous spectra and verifies applicablity of these expressions to the boundary integral equations.

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We have been developing artificial seismic sources which generate harmonic wave fields with highly accurate frequency. In this paper, we study the wave fields genarated by these sources. We evaluate the effect of embedding the sources in the underground and the efficiency of transformation from electrical energy to seismic wave energy. We also show the ability of a phased array of the sources to control the wave fields.

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This paper presents a method to judge a huge earthquake for an early warning system. The judgement is made by assessing a wave form at an initial stage. In this paper, rate of acceleration is studied, as a possible decision index that is used for the judgement. The following results are shown: 1) the system performance simulation using the physical model of the fault with built-in fault fracture process and, 2) statistical verification of the system accuracy by processing and examining measured data.

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Numerical simulations of the flows around rectangular cross-sections are carried out to examine the aerodynamic sound generated by the flows and its sources on the body surface. The flows are simulated by solving the unsteady two-dimensional incompressible Navier-Stokes equations. The aerodynamic sound is evaluated by using the Curie's solution of the Lighthill aeroacoustic analogy.It is found that the intensity of the aerodynamic sound sources are strong near the reattachment points of the separated shear flows on the body surface, and the reattachment to the body surface closer to the trailing edge generates stronger aerodynamic sound.Furthermore, it is shown that some sound sources have the effect of reducing the aerodynamic sound.

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This paper deals with a study on calculating unsteady aerodynamic forces of a bridge deck section using computational fluid dynamics (CFD). The large eddy simulation (LES) with the Smagorinsky sub-grid scale (SGS) model is applied for the turbulent model. The IBTD/FS finite element formulation is applied for the methodology of the numerical flow simulation. For a treatment of the flow around an oscillating structure. the whole domain rigidly moves the same translational and rotational motions as the structural motions without any deformation of the finite element mesh. In order to confirm the effectiveness of present technique, the flow analyses around a flat plate with vertical and rotational forced motions were performed, and present results were compared with the theoretical solutions.

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Viaducts have been constructed in a large city to solve traffic congestion in the city. In recent year, the long viaducts are constructed from the viewpoint of the construction cost reduction. In some cases, a parallel viaduct is adopted. Since most viaducts in the city have the sound-barrier wall, they are susceptible to vibration under the wind action. The present paper deals the aeroelastic. instability of the parallel long viaduct with sound-bather wall and the suppression of the vibration by T M D. In the experiments, the leeward viaduct of the parallel viaduct vibrated under wind action by the influence of the wake of the windward viaduct. The divergence force worked on the leeward viaduct was very strong. It was considered that it was difficult to adopt the aerodynamic countermeasure on the leeward viaduct for suppressing the aeroelastic vibration. The another method was T M D. In this paper, it is introduced that the T M D is effective for the control of the aeroelastic vibrations of the leeward viaduct under wind action.

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Three dimensional simulations of the flow around a rectangular cylinder with depth-to-height ratio, d/h =0.6, are carried out by means of a finite difference method for a Reynolds number of 1000.First, the influence of the numerial viscosity caused by a third-order upwind scheme for the convection terms, on the results is investigated.Second, the effect of the spanwise aspect ratio under periodic boundary conditions on the flow around a rectangular cylinder is also examined. As the coefficient of the numerial viscosity term is changed from 0.2 to 3, a cylinder with d/h =0.6 clearly shows characteristic fluctuations in base pressure, indicating high and low values alternatively at an irregular interval.As the span length is extended from 2h to 8h, a three dimensional flow structure becomes dominant.

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A two-dimensional numerical simulation of stably-stratified flows past a cosine-shaped hill is made by using a finite-difference method (FDM) with a third-order upwind-difference scheme at Re=2000. In order to simulate the flow around the hill with high accuracy, a boundary-fitted coordinate (BFC) grid is used. First, effects of the grid resolution in the streamwise direction on numerical results are discussed, and it is shown that for the calculation with the stably-stratified flow the grid resolution is more important than that with the non-stratified flow. Next, effects of the numerical method on the convergence of the successive over relaxation (SOR) method in solving the pressure Poisson equation are examined, because the iteration solution of the pressure Poisson equation is the most time-consuming part in the overall solution procedure. The numerical method based on a collocated grid shows much more efficiency for the CPU time than that with a regular grid.

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Wind field over real topography has been simulated using a Large-Eddy Simulation (LES) technique. The results are compared with physical simulation results obtained in a low-speed wind tunnel. Emphasis has been placed on the effects of the simulation region and the effects of the ground surface roughness. Local wind field over the region of a few kilometers is found to be well predicted by the present numerical simulation, though detailed and precise validation is not possible due to differences between the conditions for the numerical computations and the wind-tunnel measurements.

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Free-surface effects have been incorporated in a two equation turbulence model and applied to computation of fully developed two-dimensional open-channel flow. A semi-empirical relation is used to determine the surface fluctuation and is used as a parameter that reflects the surface effects. A semi-empirical formula for the surface fluctuation has been obtained and used in actual calculations. The results are compared with experiments to show its effectiveness in representing the surface effects for a range of Froude and Reynolds numbers.

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Direct numerical simulation of a fully-developed open-channel flow has been carried out for the friction-velocity Reynolds number of 180.The free surface is approximated by a rigid slip wall.After verifying the computational accuracies, the budgets of various turbulence statistics including the budget of the triple velocity correlations have been obtained.The behavior of these quantities near the free surface has been examined in detail and implication for modeling is discussed.

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Direct numerical simulations of fully developed turbulence in an open channel flowwere performed to clarify the effects of coherent structure on flow dynamics under a free surface. A numerical analysis method was constructed in a generalized curvilinear coordinate system to apply arbitrary complicated boundary conditions. First, a fifthorder accurate upwind difference scheme for the convective tam was considered in a one-dimensional linear convection problem to develop the appropriate discretization of the spatial derivatives. The results showed that the fifth-order upwind scheme yielded a superior performance in comparison with UTOPIA, conservative six-point scheme, TVD Lax Wendrofi CIP and sixth-order central difference method. Furthermore, the direct numerical simulations were in good agreement with velocity fluctuation statistics of a conventionally obtained DNS data base and clarified the interaction of a coherent vortex with both a free surface and fixed wall.

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To solve the global warming problem, one of the environmental ones presented all over the world, we need to evaluate accurately the quantitative and qualitative characteristics in the global circulation process of th e issued gas, such as CO₂. However, there is little basic information about kinetic relationships between water and air at the water sphere in the earth. As we reveal the gas transport phenomenon across the air-water interface, we find it very important to investigate the mutual turbulent structures in each phase of the wavy interface. Therefore in this study, we examined the element motion in the interface instantaneously, by making use of Particle-Image Velocimetry (PIV) which enables us to measure the simultaneous velocity components at all points in laser-light sheet, and analyzed turbulent structures with phase -averaged method. This study resulted in the fact that the effect of both water disturbance and air entrainment is superior to the one of turbulen ce in terms of gas transfer mechanism on the flow with breaking wave.

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Characteristics of open-channel backstep flows with a trench are experimentally investigated. The experiments were conducted by controlling a tailwater depth so that a hydraulic jump was generated downstream of the trench. In the one-dimensional investigation relative energy head losses and locations of the hydraulic jump were measured for various aspect ratios of the trench. Two-dimensional velocity measurements were also performed at the trench section by using a high-resolution video camera with 1304x1024 pixels. Mean and turbulent velocity distributions and the Reynolds stress distributions at a longitudinal cross-section were measured by applying a particle tracking velocimetry (PTV) technique. It was made clear that energy loss due to backstep is closely related to the aspect ratio of the trench and the size of recirculating region. In addition, it was observed that quite a periodic oscillation of a hydraulic jump was produced for a specific aspect ratio of the trench and its frequency characteristics were examined in detail.

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A method has been proposed to compute instantaneous turbulent bottom shear stress from the variation in free stream velocity under irregular waves for plane bed condition. Instantaneous free stream velocity and a modified relationship for turbulent wave friction factor have been introduced as the basis for the correlation with bottom shear stress. Instantaneous bottom shear stress computed by the proposed method has been compared with experimental data. Proposed method presents a good agreement and has been found to be very convenient to use from the viewpoint of practical application.

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To predict and control sediment transport and water quality exchange by using submerged spur-dike, it isnecessary to clarify three-dimensional flow structures and instantaneous vortex structures around spur-dikezones. In this study, relative height of super dike to water depth is chosen as a design parameter and its effectson flow structures in spur-dike zones are investigated by using PIV method. Two-dimensional PIV analyses ofvertical and horizontal planes reveal the time-averaged flow structures in spur-dike zones with reasonableaccuracy. The vertical vortices caused by the top flow and transverse vortices caused by the side flow interactwith each other and produce characteristic three-dimensional vortex structures. The vertical profiles of thelongitudinal velocity indicate similarity with respect to the top level of the spur dike. The inverse flow strengthbecomes larger at an inner part of the spur-dike zone with an increase of the relative height

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There are several embayments so-callde “Wando”, which are located at riverbank andhave dead zones, in Japanese natural rivers. The characteristics of water fluctuations and their frequency have been investigated to some extent. In contrast, turbulence measurements in an around embayments have not been conducted as yet. However, it is quite important to investigate the turbulent characteristics in and around embayments, because mass and momentum exchanges between the main channel and embayment are generated by the turbulence.
In this study, the turbulence measurements in and around embayments were conductedby making use of a two-component laser Doppler anemometer (LDA) and ultrasonic water-wave gages. The aspect ratio of the downstream length L and spanwise length of embayment B_w were changed widely. Further, the behavior of the coherent vorticies was measured by Particle-image Velocimetry (PIV). Several new findings, such as the mass and momentum exchange rates were investigated experimentally.

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Structure of overbank flow in compound sinuous channel is discussed based on experimental results obtained by visualization methods. Secondary flow is most important in this flow. In this paper, the influences of bed form and roughness on the flow structure are investigated by using same conditions of channel and flow except for the bed and roughness. Scouring and deposition of bed are induced by the secondary flow and vice versa. Roughness on the flood plain reduces the surrounding velocity and this reduction causes the local modification of bed. From these results the interaction between secondary flow and bed configuration can be explained.

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