We have been investigating the cardiovascular system over micro to macro levels by using conjugated computational mechanics analyzing fluid, solid and bio-chemical interactions. In the present study, we introduce our recent researches on the mass transport to saccular aneurysm, cerebral aneurysm growth based on a hemodynamic hypothesis, malaria-infected red blood cell mechanics using a particle method and primary thrombus formation.
A method for the inverse scattering analysis is presented by means of the volume integral equation. The wave field dealt here is an elastic half space having fluctuations for Lamé constants. The fluctuation of Lamé constants are extracted from the volume integral equation, which is to be solved by FFT and Krylov subspace iterative technique. Several numerical calculations are carried out to verify the present method. It is found from the numerical results that the present method is almost successful to determine the fluctuation of the Lame constants from the scattered wave field.
This paper presents a localized damage identification technique for structures using Fourier amplitudes at high frequency. Structural damage is accompanied by changes in element stiffness. These changes alter dynamic characteristics of the structure, which provides useful information about the location and magnitude of damage. In most damage identification techniques using vibration measurements, stiffness changes of whole structural elements are unknowns to identify. Therefore, as the structures' size increases, the number of unknowns also increases and a large number of measurement data are necessary. The proposed technique reduces the number of unknowns to the stiffness reductions of a localized area by extracting localized vibration using high frequency excitation. The number of necessary measured data can also be reduced. The validity of the proposed technique is examined through the numerical study on a continuous girder bridge.
The specifications for seismic design of structures were significantly revised after the Hyogokenn-Nanbu Earthquake, and the performance-based design method is being introduced. In this seismic design, it has been mainstream to verify the seismic performance by time history response analysis. Structural optimization has been developed with the approximation concept and approximation concept also has been improved in these years. The RBF approximation method was applied to approximate the constraints of seismic design problem. In this paper, not only the seismic performance but also the repair cost is considered. Both of the constraints and objective function must be approximated. So, the convolute approximation technique is tied to apply to this seismic design problem with several numerical examples.
A discrete method is proposed for analysing the natural vibration problem of shear deformable rectangular plates with a line hinge. The fundamental differential equations and the solutions of these equations are derived for two parts of the plate, which are obtained by dividing the plate along the line hinge. By transforming these equations into integral equations, and using numerical integration and the continuous conditions along the line hinge, the solutions of the whole plate can be expressed by the unknown quantities on the boundary and the quantities of the rotation along the hinge. Green function which is the solution of deflection of the bending problem of plate is used to obtain the characteristic equation of the free vibration. The effects of the position of the line hinge, the aspect ratio, the thickness-to-length ratio and the boundary condition on the natural frequency parameters are considered. By comparing the numerical results obtained by the present method with those previously published, the efficiency and accuracy of the present method are investigated.
This paper presents dynamic responses of rectangular Mindlin plates under the action of impulse uniform load or concentrated load using the BF-spline Ritz method and modal analysis method. The BF-spline Ritz method is used for space domain and the mode superposition method is used for time domain. To demonstrate the accuracy of the present method, several examples are solved, and results are compared with those obtained by analytical methods. Excellent accuracy is obtained by the present method. The effects of width to thickness ratio, dwell time and impulse function on dynamic responses and dynamic amplitude factors of rectangular Mindlin plates are investigated.
The purpose of this paper is to determine a shape of a body which minimizes fluid force on a surface of a two dimensional elliptical cylinder and a three dimensional disk located in the compressible viscous flow expressed by the Navier-Stokes equations. The formulation to pursue an optimal shape is based on the optimal control theory. The optimal state is defined that a performance function, which consists of integration of a square sum of fluid forces, is minimized. The compressible Navier-Stokes equations are treated as constrained equations. A gradient of the performance function is computed by adjoint variables. The weighted gradient method is used as a minimization algorithm. A volume of the body is assumed to be constant. For the discretization of basic and adjoint equations, the mixed interpolation method based on the bubble function interpolation presented previously by the authors is employed. The structured mesh around the surface is introduced and smoothing is employed for the gradient. As numerical studies, a shape optimization of an elliptical cylinder in a uniform flow field is carried out. As an initial shape, the body is assumed as an ellipse. The shape is updated minimizing the fluid forces on the surface. The stable optimal shape determination of a body in the compressible flows is obtained by the presented method. Finally, several three dimensional disks based on the final shape obtained in two dimension are calculated in the compressible viscous flows.
This paper presents a space-time stabilized finite element method for the shallow water flow considering moving boundary using the AMR (adaptive mesh refinement) method. The AMR method is introduced to the back-ground mesh in order to improve the numerical accuracy and to treat the geographical topography accurately. The stabilization method based on GLS (Galerin/least-squares) method is employed. The present method is applied to several numerical examples. The efficiency of the present method is shown by numerical results.
A violent sloshing is an important issue for ocean engineering and naval architecture and also causes resonance phenomena with a partially filled tank. The violent sloshing is connected with important water-wall interactions and breaking phenomena This violent sloshing cannot be predicted by potential flow model. In this study, using SPH method, we applied the violent sloshing in a rectangular tank with the critical filling depth and verified these severe conditions. We also applied to the violent sloshing in an elastic tank and calculated the stress field and deformation when violent water wave acts on the elastic wall.
The present paper describes a procedure to realize the wall function as the natural boundary condition of the finite element formulation for turbulent flow analysis. There are two key ingredients in the present methods: 1) definition of the local tangential plane on arbitrarily curved solid surface in which the wall law takes place; 2) transformation of element coefficient matrices in accordance with the local coordinate transformation of the wall boundary freedoms. The present wall boundary condition is applied to the turbulent flow around a three dimensional steep hill using the κ-ε model.
This paper discusses a fast multipole method for three dimensional anisotropic elastodynamics in time domain. A PWTD (plane wave time domain) approach is presented. The proposed approach is verified via a simple numerical example. The accuracy of the approach is shown to be satisfactory for engineering purposes, although its efficiency still needs to be improved.
In this paper, properties of several numerical procedures based on the Galerkin method for wave equation is evaluated. Numerical properties are characterised by numerical dispersion, which is calculated by combining errors drived from both spatial and temporal discretization. The present approach enables us to understand the function of each discretization in the overall accuracy of the schemes and indicates the guideline for the design of numerical procedures.
The approximate accuracy of the micro-macro decoupling analysis method is studied with a view to its application to predicting detailed micro-and macroscopic responses of polycrystalline metals subjected to plastic forming. A simple example problem assuming three dimensional cold-forming is set up for examining the micro-and macroscopic analysis results in comparison with the micro-macro simultaneous coupling analysis method. The qualitative reproducibility in both the micro-and macroscopic deformation states as well as the corresponding stress states is confirmed. And even the quantitative accuracy is obtained for the plastic-deformation-dominant forming process to some extent. It is also pointed that the accuracy in the responses especially during unloading process after the forming tends to depend on the employed macroscopic homogenized constitutive equation in the decoupling method.
Estimation of optimum shape of solids subjected to external loads in the context of rigid-plastic analysis is investigated in this paper. Instead of solving optimum shape directly, rigid-plastic strength distribution optimization method is used to obtain areas where their material sterengths are zero. Since it is able to constuct a statically admissible stress field without such zero-strength-areas, it can be interpreted that a certain optimum shape can be obtained by removing those zero-strength-areas. To ensure the validity of a proposed method, Bishop's complete stress solution of a punching problem and a numerical solution is compared.
In this paper, fracture analysis that uses PDS-FEM is extended to the three-dimensional setting. Monte-Carlo simulation is carried out for a plate with two parallel cracks which are located in an anti-symmetric mannter. The probability density function of the crack path is calculated in order to evaluate the statistical and spatial distribution of the crack path, and it is shown that the crack path of an idearly homogenous plate is unstable so that small local heterogeneity produces large variaibility in the crack path. The simulation results are compared with experimental data, and some discussions are made for the PDS-FEM fracture analysis.
The time-domain homogenization method for hypoplastic elastoplastic model is formulated for cyclic defor-mation analysis of railway ballast, and its numerical algorithm for stress analysis is developed. The multiple temporal scales of the stress, strain and void ratio are introduced, and the original constitutive equations are decomposed into coupled micro-chronological and macro-chronological equations using asymptotic anal-ysis. Accuracy of the simulated macro-chronological strain, corresponds to the accumulated permanent strain induced by cyclic loading, depends on the approximation of the time derivatives of temporal averages of micro-chronological response.
Directional characteristics of laser generated elastic waves are investigated. With time domain BIEM, we compute the thermally generated wave field in an aluminium test piece. We also eval-uate the velocity at inner points of the test piece. Directional characteristics of laser generated elastic waves are determined.
In most structural optimization, the stress level based on the linear structural analysis is used as objective function or constraints. In this paper new structural optimization concept is proposed, that maximize lifetime period of structure based on the crack propagation analysis using X-FEM. In the optimization, period until structure became unstable is used as objective function to maximize, and volume of material is constrained. The shape of the structure is changed using basis vector method. In the example, it is shown that the optimized shape based on the von-Mises stress level and the optimized shapes based on the crack propagation analysis are quite different
We focus on the reflection that causes on the surface of the wall, and research the two-dimensional noise propagation analysis by the cellular automata (CA) method. In our study, the CA method is confirmed that effective method about the fundamental phenomenon of the sound. However, a report of the numerical calculation by the CA method is none in the considering the sound reflection. So, we study the calculation accuracy of the reflection on the wall in using CA method. As a result, we confirm that the calculation of the CA method is comparable with the theoretical solution. Benchmark problem “AIJ-BPCA” is performed by CA method. As a result, we confirm that the calculation of the CA method is comparable with the calculation of the BEM and the theoretical solution.
An improved method is proposed to analyze the bending problem of plates. The fundamental differential equations are satisfied for the whole plate. By transforming these differential equations into integral equations in a small area, the quantities of an appointed point can be expressed by those of the other three points. By choosing the appointed point according to a regular order, the quantities of these three points can be replaced by the quantities of the boundary points. Finally, the quantities of any point can be expressed by those of the boundary points and the unknown quantities are only on the boundary. That makes the number of the unknown quantities and the computer time of the coefficient reduce greatly. The comparision of the present method with that used early is presented and the advantages of the present method are shown. Some numerical results are given by using uniform or non-uniform divisions. By comparing the numerical results obtained by the present method with those previously published, the efficiency and accuracy of the present method are investigated.
This paper presents a new time-domain Boundary Element Method (BEM) using the Operational Quadrature Method (OQM) and the Fast Multipole Method (FMM) in 2-D elastodynamics. In general, the use of direct time-domain BEM sometimes causes the instability of time-stepping solutions and needs much computational time and memory. To overcome these difficulties, in this paper, the Operational Quadrature Method developed by Lubich is applied to establish the stability behavior of the time-stepping scheme. Moreover, the Fast Multipole Method is adapted to improve the computational efficiency for large size problems. The formulation and numerical implementation of the new boundary element method, and the basic formulas for the fast multipole method such as the multipole expansion, the local expansion, and the translation relations of them in the fast multipole algorithm are presented. The accuracy, the computational efficiency and the applicability are checked by solving elastic wave scattering problems by cavities.
With a view to the development of a new dynamic fracture analysis method, the cohesive crack model is incorporated into an explicit dynamic finite element method to evaluate dynamic fracture behavior in quasi-brittle materials. In order to evaluate the softening behavior of fracture process zone, we employ a cohesive spring approximation for implementing the cohesive crack model. After briefly summarizing the formulation and the solution algorithm in the present method, in which discrete crack model is used for representing evolving cracks, we examine the mesh-size dependency and the size-effect for quasi-brittle structures subjected to dynamic loading. Finally, a numerical simulation of the dynamic failure of a brick structure is performed to demonstrate the validity and applicability of the present approach.
This paper presents an application of the explicit solution algorithm for cohesive crack model to 3-D crack propagation analysis of quasi-brittle materials. In the present method, the cohesive property between cracked surfaces is approximated as a kind of cohesive-spring based on the penalty method instead of the traction force in conventional methods. After we show the formulation of the spring-based cohesive crack model and detail the explicit solution algorithms, we assess the approximation properties and computational costs of the proposed method in 3-D tensile failure problem in comparison with that of conventional implicit algorithm with modified Newton-Raphson scheme and 2-D analysis. And we demonstrate the performance of the present method to reproduce the mechanical behavior of size effect in 3-D quasi-brittle structures.
Ant Colony Optimization (abbreviated as ACO after) is an optimization method based on the efficient foraging behavior of ant colonies. The ACO can be regarded as the specialized method for searching the shortest paths. So the method has been applied restrictively to only the impractical problem that has a concept of paths like traveling salesman problem. For such a problem like a TSP, it was concluded that the ACO showed the superiority to Genetic Algorithms in efficiency and accuracy. From such a point of view, in this paper, by studying the efficient behavior of ant colonies the searching method applicable to the road or railway planning or channel planning is proposed. The proposed method is applied to find the optimum three-dimensional road alignment and shows the practicability and validity.
In this paper, we have given the investigations of the thin plate bending problem by using hybrid-type penalty method (HPM). We apply Kirchhoff theory to the displacement field of the 3D case of HPM. For this purpose, we use quadratic form of the displacements which parameters are independently defined in each subdomain. We introduce penalty function that presents strong spring connecting each subdomain. We apply nonlinearity in penalty function such as spring system, which allow us to calculate hinge line. If hinge line makes mechanism then we can calculate limit load. We can calculate growing hinge line systematically using r-min method for the nonlinear analysis. In the first part of the paper, we have given brief formulation of proposed method, and in second part, we have given some numerical results to check accuracy of elastic solution and limit load.
In order to reduce the noise of paving slab cutting machines, several types of edge-improved noise barriers are investigated through numerical simulation. The acoustic field around the noise barriers is computed using the finite element method with Element-by-Element conjugate gradient algorithm. The noise barrier with the improved Y-shaped edge is proposed and its sound shielding efficiency is found to be equivalent to the noise barrier with the active soft edge. It is also found that the sound shielding efficiency of a noise barrier changes drastically according to the distance between the noise barrier and the sound source.
In order to simulate mechanical fatigue phenomena represented under macroscopically elastic condition, the plastic stretching within a yield surface has to be described, whilst the plastic strain is induced remarkably as the stress approaches the dominant yielding state. In this study, a logistic analysis is conducted for the description of the cyclic loading behavior observed during so-called high cycle fatigue subjected to the cyclic stresses lower than the yield stress, and also an unconventional plasticity model is proposed. The extended elasto-plastic model is applied for metals obeying not only isotropic but also kinematic hardening law. The mechanical responses under cyclic loading conditions are examined briefly and compared with the corresponding experimental results for SN490B.
The stagnation phenomenon of isotropic hardening is observed in the cyclic loading behavior of metals. An extended formulation of this phenomenon is formulated so as to describe the smooth evolution of isotropic hardening by incorporating the concept of the subloading surface, which falls within the framewodc of stress space formulation. In addition it is furnished with the controlling function of the isotropic hardening stagnation variable and thus it does not require any return-mapping algorithm.
High friction coefficient is first observed when a sliding between bodies commences, which is called the static friction. Then, the friction coefficient decreases approaching the lowest stationary value, which is called the kinetic friction. Thereafter, if the sliding stops for a while and then it starts again, the friction coefficient recovers and a similar behavior as that in the first sliding is reproduced. In this article the subloading-friction model with a smooth elastic-plastic sliding transition (Hashiguchi, 2005) is extended so as to describe the reduction from the static to kinetic friction and the recovery of the static friction. The reduction is formulated as the plastic softening due to the separations of the adhesions of surface asperities induced by the sliding and the recovery is formulated as the viscoplastic hardening due to the reconstructions of the adhesions of surface asperities during the elapse of time under a quite high actual contact pressure between edges of asperities. Further, the anisotropy of friction is described by incorporating the rotation and the orthotropy of sliding-yield surface.
Recently, many composite structures made of concrete and steel have been developed and various shear connectors are presented in order to increase their load carrying capacity. Among these connectors, a new type of shear connector called “perfobond shear connector” has been developed and design formulas of it are derived by experimental studies. The most popular and fundamental one is presented by Leonhardt. Although the formula of Leonhardt is widely used, it is pointed out that the applicable scope has not confirmed well. Thus, parametric analyses using 3D elasto-plastic FEM for the perfobond shear connector are performed in order to investigate appropriateness and applicable scope of them in this study. Furthermore, shear fracture behavior between rib and concrete is simulated in the analyses.
This paper describesa probabilistics tudy of the two dimensional bearing capacity of a vertically loaded strip footing on spatially random, cohesive soil using Random Field Numerical Limit Analyses. The analyses use a Cholesky Decompositiontechnique to represent the spatial variation in undrained shear strength within finite element meshes for both upper and lower bound analyses, assuming an isotropic correlation length. Monte Carlo simulations are then used to interpret the bearing capacity for selected ranges of the coefficient of variation in undrainedshear strength and the ratio of correlation length to footing width.
In order to develop a method for evaluating seismic damage of reinforced concrete members based on the energy concept, the energy dissipation capability of fivereinforced concrete specimens were evaluated from seismic loading tests carried out in two stages. First, the effects of the number of shear reinforcements was investigated by means of shear reinforcement ratio or nominal shear strength. This result shows that the energy dissipation capability was correlated with both values. Next, we verified the generality of this result and demonstrated that the energy dissipation capability is correlated with the nominal shear strength.
The present paper deals with the 3-D finite element deformation analyses of concrete filled steel tubular (CFT) column subjected to the lateral loading as well as the constant axial loading. The adhesive behavior between steel tube and filled concrete is modeled by the interface element to investigate the composite action and the confining effect inside the CFT column. By introducing a new index, namely, the equivalent confining pressure, the local stress-strain behavior at the Gaussian point level is investigated to evaluate the confining effect quantitatively. It can be concluded from the present numerical analyses that the adhesion inside CFT column contnbutes to an increase in the load bearing capacity and also the prevention from the local buckling of steel tube at the range of 0.5D (D: the diameter of column) from the base of column.
A new fracture criterion of the shear failure for the geomaterials is presented which predicts a straight extension of a crack in an elastic plastic material under compressive loads called “The maximum frictional shear stress criterion”. Weexamine the criterion by using both the singular and the constant terms in the asymptotic expansion of the crack tip stress fields for a non-associate linear hardening Drucker-Prager elastic-plastic material. As a result, we find that the confining pressure, the friction along the crack surfaces, the internal material friction, and the dilatancy effect are the lowering of the extensive hoop stress: Then they cause the maximum frictional shear stress to extend a crack straight
Many of earth structures on the ground keep stability in unsaturated state. Moreover, these structures are exposed to drying and wetting conditions and changes in soil moisture always occur. Therefore, the constitutive model with unsaturated soil mechanics is needed for predicting the elasto-plastic behavior of the earth structures for a long term. The objective of this study is developing soil/water coupled F. E. analysis with unsaturated soil mechanics. In this study, the constitutive model proposed by Ohno et al. is used. Their model can express typical behavior of unsaturated soil, such as shrinkage on drying process, collapse on wetting process, and the effects of hysteresis on soil-water retention characteristic curve, and have the flexibility for dependencies on soil properties. Moreover, isoparametric element is applied on spatial discretization to preventing the dependency on mesh, which can be seen in the Akai and Tamura's method. This simulation method allows us precise prediction of the behavior of unsaturated earth structures.
The mechanical behaviors of a discontinuous rock mass are strongly affected by discontinuities included in the rock mass. The surrounding rock mass around an underground cavern is sub-jected to compressive stress even after the cavern excavation. In this case, the shear properties of the discontinuity play an importantroll in the macroscopic behavior of the rock mass. Thus, the studies on the shear properties are well carried out from not only experimental but also numerical points of view so as to clarify the behaviors of the rock mass. However, there is few studies in which the mechanism of the alteration of the shear properties under various conditions is discussed. In this article, the experimental and numerical studies in terms of the material having a single discontinuity is conducted in order to seize the mechanism of the alteration of the shear properties. In the numerical study, the alteration is modeled by the concept thatthe surface ofthe discontinuity can be worn away with increasing the load which is applied to the material. Through the comparison between the experimental and numerical studies, it is turned out that the macroscopic behaviors of the rock mass are influenced by the friction of discontinuity.
We propose a new method for evaluating fracture energy, which characterizes the fracture toughness of quasibrittle materials, by means of the method of crack propagation analyses with the cohesive crack model. In the proposed method, after three-point-bend experiments are conducted on mortar beam specimens with a single notch, the fracture energy is determined as a material parameter in crack propagation analyses so that the actual fracture behavior is well simulated. Since the analysis method enables us to properly attain the energy balance in both the equilibrium and the crack opening, the identified fracture energy is independentof specimen sizes, as opposed to the other conventional evaluation methods. Therefore, the proposed method enables to solve the problem of size effect on a fracture energy.
No matter what external force is exerted to a stable truss structure, it can be stabilized without causing large displacements. This is the reason why it is called a stable structure. In the case of an unstable truss structure, however, it is not certain to support such forces in the initial configuration. It would probably change its configuration far from its initial state. The purpose of this study is to establish a simple numerical method to seek such an equilibrium stateof the unstable structure which is subject to arbitrary given forces. It will be also shown that each of member forces can be easily derived at the same time if the equilibrium state is obtained.
A numerical analysis of the swelling behavior of bentonite is presented using anelasto-viscoplastic theory. It is an extension of an elasto-viscoplastic model for unsaturated soil, which can describe the behavior of macrostructures, such aschange of suction, pore pressure and degree of saturation. The volume increase of montmorillonite minerals due to water absorption into the interlayers, is assumed to be a part of viscoplastic volumetric strain. An internal variable H whichcontrols an increase in water absorption into clay interlayers is adopted to describe the swelling behavior of microstructure. In addition, the internal compaction effect caused by swelling of clay unit is described by the expansion of the overconsolidation boundary surface and the static yield surface. Based on the proposed model, a fully coupled soil-water-air finite element analysis is conducted to study the development of swelling pressure. Comparing the experimental results and the simulated results, it is found that the proposed model can reproducethe effects of dry density and the initial water content on the swelling behavior.
A series of stress probe tests on Toyoura Sand is fully described in this paper after introducing preliminary works related to (i) the measuring system of the volume change of the specimens, (ii) creep behaviour of sandy specimens and (iii) effect of the slight scattering of initial void ratio of the specimens on the test results obtained from a hollow cylinder apparatus designed for testing sand. The tests results are interpreted based on the concept proposed by Jardine (1985&1992) who introduced three yield surfaces representing the boundary of linearlyelastic behaviour, nonlinear elastic range and elasto-plastic range. Ten series of stress probe tests in ten different range of stress area in the stress space gives a clear evidence of the isotropic hardening (proportional expansion ofyield surfaces) induced by anisotropic repeated loadings.
The microstructure of soils is, in general, anisotropic in both the “inherent” and “induced” senses described by Casagrande and Carillo, which yield anisotropic responses for both strength and plastic deformation. The undrained shear strength of clayey soils, for example, changes greatly depending on the inclination angle θ of the loading direction with respect to the consolidation plane. In the present study on constitutive modeling, a tensorial quantity called the fabric tensor is incorporated into the classical plasticity framework to simulate the effects of microstructure on the variation of undrained shear strength of Kaolin clay. The effects of inherent and induced anisotropies are considered in terms of an evolution rule of the fabric tensor. It is shown that the proposed model can simulate well the variation of undrained shear strength observed in plane strain experiments of normally consolidated Kaolin clay by Kurukulasuriya.
This paper focuses on the estimation of bearing capacity of rigid strip footing on slope by performing a number of laboratory model tests and the numerical analysis. The laboratory model tests, including unreinforced and reinforced subsoil, are carried out using three types of subsoil. A numerical procedure is proposed which is based on a smeared shear band approach and a modified initial stress method, employing Mohr-Coulomb yield criterion with a simple plastic flow rule. The proposed procedure is capable of estimating not only the bearing capacity for natural subsoil, but also under complex conditions, for example, reinforced subsoil considering stiffness and deformation of materials. In most cases, a fairly good agreement is obtained between the experimental and analytical results.
The elasto plastic model proposed by Li and Dafalias (2000) was used for the simulation of the behaviors of sand along various loading paths. Li and Dafalias model includes density and pressure dependencies using the state parameter:Ψ=e-ec, where ec is the reference void ratio on ec-log p at the critical state. The model performance along various loadings paths were examined with an emphasis on the evolution of the state parameter, which includes stain ratio constant paths and those simulating the behavior of gentle slopes subjected to the inflow of pore fluid. The conventional stability conditions of the model along various loading paths were evaluated and discussed by using the state parameter. The effect of initial anisotropy was introduced into Li and Dafalias model through the modified stress method. The performance of Li and Dafalias model was found to be satisfactory, though some modifications are necessary for better simulations.
Heavy seismic damage tends to occur in embankment slopes in which ground water table is high. The conventional limit equilibrium analysis usually evaluates the effect of ground water by the decrease of shear strength of subsoil due to the hydrostatic pressure. This paper tries to extend the method to finite element analysis, and to estimate seismic slope stability considering ground water level. This paper proposes a numerical procedure in which a seismic slope failure takes place when a cumulative plastic deformation calculated by a dynamic stress-deformation analysis exceeds a critical value of deformation determined by a static stability analysis considering seismic intensity. The proposed procedure is applied to some hypothetical and actual case studies of seismic slope stability under high ground water level. The case studies show the possibility that the procedure gives the realistic evaluation of ground water.
A consolidation apparatus equipped with a ceramic disk at the pedestal, together with a pair of bender elements (BE) at the top platen and the pedestal has been newly developed for measurhg the variations of the matrix suction s, as well as the elastic shear modulus G of unsaturated soil subjected to one-dimensional compression. In this paper, the effects of the matrixsuction on the elastic shear modulus G of unsaturated soils were carefully examined in the newly developed apparatus. The G-value of two kinds of unsaturated soils was also successfully characterized.
Empirically, it is known that the vegetation influences on the earth structure. Kawai et al. focused on the effects of water uptake induced by the vegetation. They regarded it as an effect of decreasing soil moisture and applied the effect to unsaturated soil/water coupled F. E. analysis. In this study, the soil/water coupled F. E. analysis code is rearranged with the constitutive model for unsaturated soil proposed by Ohno et al.. In their model, the effective degree of saturation are applied as a parameter expressing stiffness of unsaturated soil to enable application of unsaturated soil mechanics to actual problem in geotechnical engineering site. To verify the applicability of soil/water coupled analysis, the accident that the vegetation uptake work brought about the non-uniform settlement of the ground and damaged the building in Poland are simulated. Consequently, it was found that the uptake increased suction and encouraged non-uniform settlement of ground surface. Its effects appeared prominently in a dry ground having low groundwater level and much uptake. This method is effective to understand the effects of vegetation.
Nickel based superalloy has excellent mechanical properties at high temperatures. The key factors gov-erning its elasto-plastic characteristics are supposed to be its microstructure, including misfit strain and nonuniform plastic deformation behavior of γ matrix. However, contribution of each factor to the overall elasto-plastic characteristics is not investigated quantitatively. In this paper, a series of numerical experi-ment by the homogenization method are therfore conducted on a few specific microstructures in order to clarify the elasto-plastic behavior of nickel based superalloy.
Recently, the risk of derailment accident caused by over-speed, earthquake and other reasons is concerned. For a bullet train, if derailment occurs, it brings about the unimaginable catastrophic accident Thus, to prevent derailment accident of the bullet train is regarded as an important issue for the railway technology. As one of the effective measure, derailment stopper made of reinforced concrete is proposed. As it is difficult to evaluate the crashworthiness of the stopper, there are no design concepts for them against derailment accident. Therefore, this study aims at evaluating the crashworthiness by 3-dimensional non-linear FE analysis under the assumption of dynamic contact condition. From these calculations, the crashworthiness of the stopper could be predicted, and failure possibility is estimated by analytical results.
In this paper, we develop a model to describe the anisotropic hyperelastic behavior of rubber sheet reinforced by a textile fabrics of fiber. The isotropic part is modeled by the Mooney-Rivlin model, and the anisotropic behavior is also modeled by using an invariant of the right Cauchy-Green deformation tensor. In addition, we propose a simple reliability varification test for shear behavior. A couple of numerical results shows a practical efficiency, but the results of the validation using the proposed reliability test reveal limitations of the proposed model.
With the objective of finding the promising contact detection methodology in the physical experiments, assembly of idealized disc particles with different solid fractions were sheared experimentally in the 2D shear flow apparatus. A high speed video camera and subsequent image processing techniques document the positions of the center of particles involved in the flow. This setup also provides opportunity for visual inspection of the collision time and partners. The important characteristics of pre and post collision phenomena were keenly investigated in sparse to dense particle concentration cases so that the precise criteria for each of them could be determined for distinguishing contacts. Based on these observations, new contact detection algorithm is formulated which have three components: finding potential partners of collision, detecting collision partners and finding the duration of each collision. The results obtained from proposed method are compared with the visual observations in the digital video of the physical experiment with the help of motion analytical and particle tracking PTV software. Comparisons of about hundred randomly selected data in different solid fractions and shear rate reveal that the proposed method could detect the contacts with considerable accuracy than the previous methods.