Japan has built a mature society with advanced infrastructure in recent years. However, there are a lot of natural disasters such as earthquakes and tornadoes almost every year, we need to notice the fact that we are living in a disaster-prone country. Moreover, some of these infrastructures lagged 30 years behind the United States exist for already 50 years and the damage because of aging infrastructures begin to appear. In this current situation, I would like to point out what the applied mechanics can do, and what is expected of the applied mechanics in the construction industry. First of all, the promising technology of the applied mechanics is described in the construction industry. Secondly, some problems are listed up, and the quality control and quality assurance problems to be solved are introduced. Finally, the expectation for the applied mechanics in the future is summarized.
Geological media exhibit heterogeneities in their hydraulic properties, which lead to enhanced spreading and mixing of the transported solutes. Intermediate-scale laboratory experiments on heterogeneous porous media were conducted in a 1×1×0.03 m sandbox with small blocks of fine or coarse sand. The use of visualization of dye solute and the measurement of NaCl concentration were applied to the identification of the changes in longitudinal and transverse dispersivities caused by the presence of heterogeneities. Results indicated an increase tendency in longitudinal dispersivity with the increase of travel distance and heterogeneity, while a continuous decrease in transverse dispersivity attributed to the initial solute distribution despite of the heterogeneity. Results also revealed that dispersivity estimates from temporal moments were identical to or smaller than those from spatial moments and variation of the dispersivities showed no dependency on the seepage velocity. Moreover, identified values were in good agreement with reported studies regarding laboratory experiments in heterogeneous porous media.
Ultrasonic array transducers are widely used in nondestructive testing of structural components. Recently, not only a linear array transducer but also a matrix array transducer is introduced to evaluate the position and shape of flaws. In this study, an inverse analysis method is developed by means of a matrix array transducer in order to reconstruct three dimensional (3D) shape of flaws. The method is based on the linearized inverse scattering method in the frequency domain and can perform shape reconstruction of flaws by fast inversion algorithms with the 3D FFT. The 3D inverse scattering imaging method (ISIM) is validated by an immersion ultrasonic measurement which imitates the matrix array ultrasonic testing. Since the size of an element of the matrix array transducer is small in general, the enhancement of the signal to noise ratio is required for the application of the 3D ISIM to actual fields. Here, ultrasonic beams generated by delayed excitations with multi-elements are applied to amplify the incident spherical wave, and its performance is checked by numerical simulations and experimental measurements.
In the performance-based design concept, the accurate prediction of displacements will be required. For the demand, the observational approaches are very effective in the soft ground engineering. In this research, as an observational method, the particle filter (PF) is employed. The PF can identify the elasto-viscoplastic parameters, and furthermore, not only primary consolidation parameters, but also the secondary consolidation parameters can be identified. To verify the accuracy of the identified parameters, the model test results are used as measured data. Two-dimensional displacements can be measured by the model test, including the shear behavior due to the loading, and log-term displacement data, including the secondary consolidation are obtained. The possibility to identify the parameters affecting the deformation behavior, are verified, and the predictions of the long term settlements are discussed.
Estimation of deterioration curve of infrastructure is one of hot topics. It is preferable to separate the data according to detailed information before estimation of regression curves. This study proposes a method to perform clustering of data and regression analysis at the same time statistically. Ordinary EM algorithm can deal only linear model though real world problems are often nonlinear. EM algorithm is a kind of local minimization method with respect to likelihood. In order to overcome these drawbacks, a new algorithm is proposed. The proposed method is a combination of EM algorithm and Distributed Particle Swarm Optimization (DPSO). After examining the efficiency of DPSO with simple test functions, a group of deterioration curves are estimated by the proposed algorithm.
A numerical algorithm was proposed to solve the governing equations of compressible fluid consisting of conservation equations of mass, momentum and energy as well as the equation of state. The algorithm is based on an implicit method, in which linear system of density is solved with the temporally-estimated velocity components. Due to the implicit procedures, this algorithm is numerically stable and needs shorter computational time compared with explicit ones. In addition, since the governing equations are discretized with finite volume method, the conservation of mass and other physical properties is satisfied with sufficient accuracy. This computational method was applied to the sock wave propagation problem and natural convection flows driven by the non-uniform temperatures. The validity of the present method was discussed with these results.
Numerical resolution of advection-diffusion equations on connected graphs requires careful treatment in implementing internal boundary conditions at junctions. This study proposes a simple conforming Petrov-Galerkin finite element method with compact stencil, referred to as CPGFEM2, which effectively solves the non-conservative advection-diffusion equations on connected graphs. The CPGFEM2 utilizes the fitting technique in the spatial discretization so that the junctions are consistently handled as implicit internal boundary conditions. A selective lumping algorithm in conjunction with the local θ-scheme is applied in the temporal discretization. The CPGFEM2 is verified through several test problems. The CPGFEM2 is successfully applied to numerical analysis of conservative solute transport in an existing agricultural drainage system, showing its applicability to real problems.
A computational method was investigated to deal with the fluid-structure thermal interaction as well as the mechanical interactions. For this purpose, our multiphase model was improved in order to estimate non-isotropic thermal conductivity in the computational cell including different phases using subcell numerical procedures. The proposed computational method was applied to the natural convection flows driven by temperature difference in the fluid-saturated porous media, consisting of heat conductive solid matrix. As a result of computations, the validity of non-isotopic model was confirmed by comparing the theoretical results. In addition, it was shown that the natural convection flows, which arise in the vertical and horizontal rectangular boxes filled with many spherical objects. are reasonably predicted in the present method.
A depth averaged sediment transport model has been developed to simulate bed level changes on alluvial beds. MAC on collocated grid system for shallow water equations (MACS) algorithm was used to track the hydrodynamic module of the developed model. The sediment transport module was describing the bed deformation either by the equilibrium or the non-equilibrium approaches for the suspended- and bed-load sediment transport. The developed model was verified against different scour problems and its validity was examined. A sensitivity analysis was conducted to estimate the in uence of the non-equilibrium adaptation parameters on the numerical results. Results revealed that although the non-equilibrium model requires more computational effort and extra 10% computational time than the equilibrium one, it gives enhanced results than those that are predicted by the equilibrium approach. However, refinement of the hydrodynamic model is required for better results.
The purpose of this paper is to solve a problem of incompressible flow in a domain which includes an internal boundary on which a Dirichlet boundary condition is imposed. We use the characteristic Galerkin scheme using B-spline basis functions based on the mixed formulation for computing incompressible flow. We employ the Lagrange multiplier method on a treatment of the internal boundary, and integrate with the Nitsche's method to overcome instability which may occur on failure of the LBBK condition. In order to confirm effectivity of the present scheme, we perform the flow around a circular cylinder.
In this paper, we propose the dynamic domain decomposition for particle methods, in which the full particles domain is decomposed into several sub-particle domains according to their initial positions. In the dynamic domain decomposition, the exchange of the particle data between neighboring sub-particle domains are effectively reduced, since each sub-domain moves along the particle motions. In addition, when the portion of the boundary particle domain to the full particle domain is small, the accerelation of numerical simulations can be achieved through the parallel computing by using the libraries such as MPIs. In this paper, we apply the method of dynamic domain decomposition to the multi-GPU parallel computing and investigate the efficiency of the method for the numerical accelerations. In fact, we will demonstrate that in dam break simulations, where the balk of water is moved from one side of the wall to another, the acceleration is achieved by reducing the ratio between the volume of the boundary particle domain and that of the full particle domain.
This paper presents a numerical method for the evaluation of thermal environmental flow in urban area by a stabilized finite element method based on the SUPG/PSPG method. The incompressible Navier-Stokes equation based on the Boussinesq approximation is employed for the governing equations. The LES based on Smagorinsky model is employed for the turbulence model. The heat balance model using the Sun's insolation is employed to determine the temperature on the ground surface. The present method is applied to several benchmark problems in order to investigate the validity of the method.
To examine the geometrical effects of aggregates on fracture behavior in concrete, numerical experiments on compressive failure in concrete's meso-structures are carried out in this paper. The method for numerical experiment employed in this paper is capable of simulating compressive failure in quasi-brittle materials involving micro- or meso-scale contact on crack interfaces. First, we explain the modeling of quasi-brittle fracture and the method for numerical experiment. The discrete micro-crack behavior is introduced to a finite element framework in consideration of material inhomogeneity of cement-based materials and by using penalty springs. Then, the basic performance for simulating fracture behavior involving tensile or shear cracks is verified. Finally, the numerical experiments are performed to investigate the effect of heterogeneity due to aggregates in concrete in comparison with the fracture behavior of crushed stone and river stone.
Applicability of PDS-FEM to simulate 3D wing crack growth in brittle elastic solids is demonstrated by reproducing some experimental observations reported in literature. 3D wing crack growth phenomenon is not well understood yet, though it has been recognized a key mechanism in failure under compression. Lack of non-destructive 3D stress field measurement techniques and efficient numerical methods for modeling 3D crack propagation are some of the barriers in understanding this phenomenon. PDS-FEM is a prominent candidate for studying complex crack propagation phenomena like 3D wing crack propagation; it provides numerically efficient failure treatments and incorporates the effects of minor material heterogeneities on crack evolution. The use of non-overlapping shape functions of conjugate geometries to approximate functions and their derivatives is the key to its attractive properties like numerically efficient failure treatment. Models with fine domain discretization are used to capture fine details of 3D wing cracks which are reported in literature. Features like curving of crack surfaces at the tip of mode-I regions and the growth of petal cracks at mode-III regions are reproduced. Comparison with experimental observations, which are reported in literature, indicates that simulated crack profiles are in good agreement.
The present study applies so-called multi-scale topology optimization for minimization of compliance of three dimensional structural problems. Multi-scale topology optimization is a strategy to optimize topology of microstructures applying a decoupling multi-scale analysis based on a homogenization method. The stiffness of the macrostructure is maximized with a prescribed material volume of constituents under linear elastic regime. A gradient-based optimization strategy is applied and a semi-analytical sensitivity approach is introduced. It was verified from a series of numerical examples that the proposed method has great possibility for microscopic advanced material designs.
In this paper, essential boundary condition enforcement using multiple point constraints (MPC) technique is examined to analyze buckling/post-buckling problem of plates employing meshfree approach. In the buckling/post-buckling analysis, tying relations and periodical boundary conditions are adopted for assuming continuity and periodicity of the structures. Since the MPC technique is simple approach, it is then suitable for enforcing the boundary conditions. However, we found the MPC enforcement cannot pass so-called patch test. The problem is examined on stress-level evaluation and plate buckling/post-bukling problem are solved in numerical examples.
This paper presents a road traffic noise evaluation system based on spatialization of sound using virtual reality technology. The effects of directivity of the sound wave and delay of the arrival time are considered in the diffraction analysis to improve the reality. Furthermore, the sound source data for the auralization in VR space are generated from the various car driving tests. This system is applied to several benchmark problems in order to investigate the validity of the method.
In the BEM with the non-orthogonal spline wavelets for steady-state out-of-plane wave propagation problems, the relation between the number of non-zero entries of the coefficient matrices and the degree of freedom (DOF) N is theoretically investigated using the information on the size and the arrangement of the support of the basis functions. The coefficient matrices are compressed by truncation with a prescribed threshold value κ. The value of κ is determined so that the amount of storage is minimized without reducing the accuracy of BE solution, and shows κ ≈ ρN−β (ρ, β > 0). The number of non-zero entries of the matrices G and H, (G) and (H) increases in proportion to O(N log N) or O(N1+γ) (0 < γ < 1). The low compression rate of the coefficient matrix for a high-frequency problem can be improved using the wavelets with a higher-order vanishing momemt property.
This paper presents an implicit Runge-Kutta (IRK) based convolution quadrature time-domain fast multipole boundary element method (CQ-FMBEM). Application of a convolution quadrature method (CQM) to a time-domain boundary element method (BEM), which is called CQ-BEM, can improve numerical stability of time-stepping procedure. In recent researches, the IRK based CQ-BEM showed better performance than the conventional linear multistep based one regarding accuracy. However, the IRK based CQ-BEM requires more computational time and memory. Therefore, in this paper, the fast multipole method (FMM) is applied to the IRK based CQ-BEM for 3-D scalar wave propagation problems. The formulation of the IRK based CQ-BEM and the application of the FMM are described. The accuracy and computational efficiency of the proposal method are compared with the linear multistep based CQ-FMBEM by solving some numerical examples.
Time domain boundary integral equation method(TD-BIEM) with Lubich convolution quadrature method is considered. In TD-BIEM with Lubich CQM, the convolution integrals with respect to time in the boundary integral equation are approximated as the products of the boundary values and the sum of the Laplace transform of the fundamental solution. Because the influence coefficient matrices become dense in TD-BIEM with Lubich CQM, a lot of computational time and large memory are required in TD-BIEM with Lubich CQM. We therefore change the timing of the matrix-vector products in the algebra equations in TD-BIEM with Lubich CQM in order to reduce the computational time. We also apply Adaptive Cross Approximation to the influence coefficient matrices in TD-BIEM with Lubich CQM. Because the influence coefficient matrices are calculated approximately and become sparse using ACA, the reduction of the computational time and memory requirements is expected. We solved some simple wave scattering problems with the conventional TD-BIEM with Lubich CQM and with the proposed method. We also compared the computational time and memory requirements in each method. Using our proposed method, we can reduce the computational time and memory requirements in TD-BIEM with Lubich CQM.
This paper presents a numerical method for acoustic field analysis based on CIP method using adaptive mesh refinement (AMR) for large scale computations. The present method is applied to several 2D and 3D benchmark problems in order to investigate the validity and efficiency of the method. The computed results are compared with the existing theoretical and other numerical results.
This paper presents a convolution quadrature time-domain boundary element method for wave propagation in general anisotropic fluid-saturated porous solids. Wave analyses for general anisotropic fluid-saturated porous solids are particularly helpful for understanding wave propagation in rocks. Boundary element method (BEM) is known as an effective numerical approach for wave propagation because BEM can deal with infinite or semi-infinite regions without any modifications. Convolution quadrature time-domain boundary element method (CQ-BEM) has been studied by several researchers to improve the numerical instability of the conventional timedomain BEM. In this paper, a new CQ-BEM formulation for general anisotropic fluid-saturated porous solids is proposed. The formulation proposed herein is based on Biot's theory. Basic problems are solved to verify our proposed method.
Uniaxial compression experiments were carried out to study on strengths and failures of gypsum samples with three pre-existing contact flaws in non-overlapping geometry. Prepared samples were expected to have same strength by the stress analysis17) which is based on the simplified linear mechanism. The experimental results demonstrate the effect of the sample's geometries on the compressive strengths, and the failure mechanisms governing the strength characteristics. And then the stress analyses were improved by using the extracted failure mechanisms. The improved analyses show that the predicted compressive strength agrees fairly well with that of experiments.
In the present paper, the bi-axial cyclic loading tests of four types of RC columns under the different loading histories have been performed. Four types of RC columns are respectively RC column, SFRC column and RC columns with the intermediate reinforcements. The flexural strength and ductility of the different types of RC columns have been examined in details in the post-peak loading area. Furthermore, the energy absorption capacities, the progressive deformation of intermediate reinforcements and the buckling behavior of re-bar have been discussed during cyclic loading. It has been found that the use of intermediate reinforcements and SFRC may be effective to make the plastic hinged zone of column more ductile, particularly for the column with rough interval of hoop tie, i.e., the interval of 120 mm in the present study.
In this paper, three dimensional FEM analysis is conducted referring the experimental results about the shear strength distributional property of perfobond strip having plural perforations. Results of the FEM analysis are also compared with the experimental ones. In this analysis, the analytical conditions are refined focusing on the stress-strain relation of concrete, boundary condition of the steel plate and the surrounding concrete, treatment of the reinforcing bars and so on and most suitable case is found to reproduce the experimental results averagely. Moreover, the shear force-relative slip relation, the shear strength distributional property along the longitudinal perforation and the strain behavior of the steel plate by the FEM analysis are investigated and these results show almost similar tendency as the experimental ones.
We present an application of node-based uniform strain element to mixed rigid plastic finite element analysis. Using triangular elements in rigid plastic finite element analysis often causes locking problem. In order to avoid the locking problem, we employ the node-based uniform strain element. We solve three problems to show the validity of the proposed method. The results show the effectiveness of the proposed method.
This paper aims to develop a finite strain anisotropic elasto-plastic constitutive model for frictional materials and its stress calculation algorithm based on the return-mapping scheme. The nonlinear rotational plastic hardening is incorporated into the model in a physically and theoretically reasonable way by introducing the dual multiplicative decompositions of the deformation gradient tensor. In addition to the usual multiplicative decomposition into elastic and plastic parts, the plastic part is decomposed further into an energetic part and a dissipative part. The energetic part leads to a tensorial internal variable related to the rotational plastic hardening. The Cam-clay plasticity model is adopted as a specific constitutive model relevant to frictional materials. Fundamental behavior of the proposed model is demonstrated through several numerical examples.
Bifurcation phenomenon is highlight as a source to diversify strain localization and shear band formation in sand specimens. Compression tests on various shapes of right-angled parallelepiped specimens under two types of conditions of plane strain and axisymmetric lateral confining stress were simulated by two- or three-dimensional nonlinear finite element analysis. The Cam-Clay plasticity model incorporating the subloading surface concept was employed to model the deformation property of sands. The inception and progress of localization breaking uniformity were analyzed as a bifurcation problem. Complex localization process accompanied by the formation and disappearance of shear bands simulated by the bifurcation analysis were compared with an experimental observation of dense dry sand specimens in a true-triaxial apparatus. Some unexpected three-dimensional localization modes were found in the analysis of plane strain test as a diffuse mode of bifurcation breaking out-of-plane uniformity, while the bifurcation point was not detected in the axisymmetric case. Effects of the testing condition and the aspect ratio of specimen on the bifurcation and failure mode were also examined.
Currently, the extension of life span of concrete structure is urgently needed. Therefore, it is important to predict the future deterioration of the concrete structure. The deterioration accompanied with alkali-silica reaction is one of the factors associated with durability. Generally, the aggregate expansion which is caused by the alkali-silica reaction brings about cracking, and the crack may decrease the durability with changing the mechanical pr operties of the concrete structure. Though there are a number of researches on alkali-silica reaction, the deterioration prediction under complex stress condition such as pre-stressed concrete is not well discussed. In this study, the degradation model for pre-stressed concrete structure is proposed and the validity of the model is examined through the comparison of exposure test of alkali-silica reaction using a pre-stressed concrete specimen.
The elastic waves propagating in concrete material are interfered with each other and reflected by aggregates and then the observed waves become much complicated but must have the information of aggregates or other influential factors. Thus in this study chaotic theory is applied to evaluate the complicity of the waves transmitted throughout concrete material. Especially, we use steady waveform of chaotic waves as an input. As a result it is found that prediction error of the received signal has some correlation with the velocity and also the matrix quality, and that correlation dimension and maximum Lyapunov exponent have strong correlation with the frequency property and are influenced with the aggregates.
The author performed a fundamental examination of the attenuation characteristics and resistance forces of the railway's ballast layer subject to traffic impact loads based on in-situ field measurements. The measurements were conducted by using high-performance three-dimensional sensing stones and a special sensing sleeper, which was developed to the distribution on the sleeper bottom of assess the dynamic pressure induced by running trains with a high frequency of up to several thousand Hertz. The measured results indicated that for the impact load components over 100 Hz, the ballast layer resists because of its high rigidity. The ballast layer can reduce the impact load amplitude to 1/3 – 1/5 per 10 cm of thickness. However, the ballast layer is almost non-resistant to the low-frequency load components with a frequency of 10 Hz or less and the low-frequency load components are not reduced.
The influence of the friction between the sample and the internal peripheral surfaces of shear box on the direct shear test keeps the normal stress on the shear plane constant was examined on high-density sands by discrete element analysis. It was revealed that the normal (vertical) components of the frictional reaction forces on the internal peripheral surfaces of shear box decrease the shear strength and facilitate the positive-dilatancy. In contrast, the shear direction components on the internal peripheral surfaces of shear box increase the shear strength and hardly affect the dilatancy. Furthermore, the distribution charts of the stress on the internal surfaces of shear box were shown in with/without the internal peripheral surface friction, and the inducement mechanism was discussed. These efforts would give useful knowledge for an interpretation on the results of the constant pressure direct shear test on sands.
The author implemented the numerical analysis algorithm based on the particle based analysis method, GIMPM (Generalized Interpolation Material Point Method) and applied it for simulations of triaxial compression tests. Although GIMPM is a derivative of MPM, it has more stable numerical algorithm and removes numerical noises, which are generated when material points cross numerical grids. In this paper, to simulate triaxial compression tests, numerical damping and material non-linearity(Mohr-Coulomb constitutive model) are implemented. The results obtained through simulations are compared with experimental results. And the effectiveness of GIMPM is confirmed.
This paper reports on the results of a medium-scale experiment regarding the impact applied by ice floes with a length of 0.6m and with an impact velocity of 0.14 to 7.7 m/s against a pile structure and numerical simulation using the 3-D discrete element method. Ice caused brittle failure/splitting in most cases. The increase rate of maximum impact load due to impact velocity decreased in comparison with that in non-fracture cases. The maximum impact load did not depend on crack initiation for the splitting failure and its propagation, but on the indentation/crashing process into ice in the vicinity the pile. The impact characteristics of timbers as a kind of Tsunami debris were compared to those of ice floes. The impact load of the timber increased linearly with impact velocity, and it was much greater than that of ice floe which causes brittle failure.
In order to solve large deformation problem of geomaterials, the SPH method is used which is a kind of particle method based on the meshless Lagrangian scheme. The method can solve large deformation problems without mesh distortion. Moreover, it can handle the governing equations and existing constitutive models for geomaterials based on a continuum mechanics. To express various states of the soil, the elasto-plastic constitutive model taking account of soil skeleton structure is introduced into the method. In this paper, in order to verify the numerical scheme, a simulation of simple shear test is carried out. The obtained results are compared with theoretical solutions. Furthermore, the excavation problems for loose and dense sand ground are solved. From a series of the numerical results, the effectiveness of the method with the constitutive model of high performance is demonstrated.
The strength and deformation characteristics of granular sands are improved by mixing flexible short fibers. Many factors such as the mixture ratio, fiber materials, fiber length and orientation affect the improvement effect of the short fiber reinforced sands. Especially, the mixture ratio of short fiber plays very important role for the improvement effect and the mixture design. Although the strength of sand increases by mixing fibers, excessive mixture may reduce that of reinforced sand. In this study, we focused on the relationship between the strength and the mixture ratio of fibers by the triaxial compression experiments and the discrete element simulations. Also, we tried to find the critical point of the important effect which would be maximized for the strength of granular materials. As a result, the existence of optimum mixture ratio for the strength of granular materials was confirmed.
Cushioning materials, such as sand cushion placed on rock sheds, are attracting attention as construction devices that can effectively disperse and reduce rock fall energy before rocks collide with rock fall protection works. To support performance-based designs for rock fall countermeasures, the present study estimated rock fall behaviors and impact forces using 2D discrete element method (2D-DEM). As one of the typical behaviors, propagated impact force can exceed impact force of falling mass. We conducted two numerical analysis focused on this phenomenon; monotonic penetration test controlling under constant penetration velocity, and removing falling mass during penetration process for any time. In addition, the effects based on some condition of sand cushion, weight of falling mass and its velocity are examined from the view point of impact force-penetration relationship of sand cushion.
An equation of state (EOS) of sand deposit subjected to high speed projectile impact is discussed in this study. We first manifest an affinity between the Hugoniot EOS under shock wave transmission and the e-log p relation under quasi-static deformation. Next we construct a set of equations within a framework of Hugoniot EOS, which describe well the void ratio change due to grain crushing in one-dimensional compression tests at low strain rates. This means that the proposed EOS can be applicable not only to low strain rate but also to high strain rate behavior of sand deposit. The applicability of the proposed EOS is demonstrated by comparing the simulation with two experiments, quasi-static one-dimensional compression tests and high speed projectile impact experiment to sand deposit.
Since HYOGOKEN-NANBU Earthquake in 1995, a large number of researches on the seismic performance of steel bridge pier have been carried out. However, there is very few research for the repair method of the steel bridge pier that has been damaged in earthquake. The research on how to repair severely damaged steel bridge pier has been conducted by the authors, but the repair effect for the steel bridge pier that suffered minor damage has not been revealed. In this study, the repairing effect of filling concrete for circular steel bridge piers which have different degrees of damage is to be verified. First, four damage levels were assumed from general load-deflection relationship. Static cyclic loading tests until reaching their predetermined damage levels were conducted. After filling the concrete inside the specimens, the same static cyclic loading tests were carried out to clarify the seismic performance of repaired piers.
A seismic response simulation method based on multiple-spring (MS) model and curve approximated hysteresis rules are proposed to predict nonlinear seismic response of steel bridge piers excited by bi-directional ground motions. A series of approximated curves and hysteretic rules are adopted to de-script the complicated nonlinear equivalent stress-strain relationship of spring elements at base of steel piers. An optimizing calculation based on parameter identify method is used to decide the six parameters of the constitutive relation from results of uni-directional cyclic loading tests. By comparing the results due to the simulation and pseudo-dynamic loading tests, the validity of the proposed method is also verified.
The seismic failure of the railway embankment is divided into 5 modes according to the embankment height and subsoil properties. In this study, the appropriate seismic reinforcement methods of embankments are proposed against failure modes Type-C; the circular slip of embankment and Type-D; the spread of the toes of embankment through centrifugal model tests and finite deformation analysis. The new findings are as follow; 1) The Nailing method against Type-C decreases the settlement of embankment since the reinforced bars prevent the circular slip of embankment, while the method against Type-D is hard to decrease the settlement. 2) For Type-C, the appropriate formation of the bars in the embankment, such as number, position and length is examined to be one-sixth of the common axial force, which can be applied to the new Nailing method.
We develop a system to perform many cases of earthquake disaster estimations of large cities. By using such a system, we aim to make disaster estimations considering uncertainties in earthquake parameters such as the source or velocity structure. Soil amplification analysis and structural response analysis are combined for reflecting soil/structural properties to disaster estimation. The major bottleneck of the previous system for application to large number of cases in large areas was the large file I/O that linearly increases with respect to the number of cases. We make remedies to these bottlenecks to improve the scalability. Application shows that 100 case simulations with different input waves targeted on area with 0.25 million structures can be performed using high performance computers.
For the scrap tire rubber pad (STRP) isolator, which is intended to be used in low rise residential buildings in highly seismic areas of the developing countries, experimental, analytical and theoretical investigation is conducted to examine the influence of loading direction on the seismic performance. Finite element analysis and theoretical evaluation using Haringx theory are carried out to evaluate the stability limit of the isolation unit under shear deformation. These types of isolators provide positive incremental force resisting capacity up to shear strain level of 155%, and this value increases when the loading direction is changed up to 45 degrees from the STRP's edge direction.
Normalized energy density (NED) is one of the essential quantities for a ground transfer function of a 1D layered structure model. The cross term of the functions and the cross term of the power of the functions are defined as an extension of the NED. The cross term is physically defined as the correlation coefficient between the two ground transfer functions. The cross term detects the harmony of two transfer functions; a finite value is obtained only in the case where peak frequencies coincide. The cross term of the power of the normalized transfer functions is 1 when the peak frequencies do not coincide. The properties of the cross term and the cross term of the power are analytically proved for a two-layered case and numerically shown for three- and four-layered cases.
With the aim of estimating the effectiveness of the measures taken to smoothen and speedup the evacuation process of a large urban area, in time critical events like tsunami, a multi agent based mass evacuation simulation software is being developed. Considering the fact that it involves large number of human casualties, moderately complex agents in 2D grid environments are implemented. A vision based autonomous navigation algorithm, which enables the agents to move through an urban environment and reach a far visible destination, is implemented. The navigation algorithm is verified comparing the simulated evacuation time and the paths taken by individual agents with those of theoretical. We adopted optimal reciprocal collision avoidance algorithm for collision avoidance and validated by comparing with filed observations reported in literature. A parallel computing extension is developed for studying mass evacuation of large areas; simulating millions of agents with vision based navigation and collision avoidance is computationally intensive. A high strong scalability is attained with two millions of agents, which indicates potential to simulate mass evacuation involving many millions of people.
This study proposes a simple evaluation method of seismic safety of road embankments. The safety of the embankments is confirmed by comparing the analyzed sliding displacement with the allowable displacement. The method is simple, but it has the equivalent accuracy with the Newmark method. The proposed method consists of two-step evaluations. In the first step, the method uses the equivalent yield acceleration, which is the PGA of ground motion whose sliding displacement reaches the allowable displacement. The method extracts the embankments which have the possibility to slide longer than the allowable displacement. In the second step, the method easily calculates the sliding displacement assuming the planar sliding surface for all embankments extracted in the first step. The validity of the method was confirmed by the numerical simulation.
The cavity zone along riverside is expected to produce native habitats of various ecosystems and water-friendly environment. However, effects of side cavities on flow resistance and turbulent flow structures are ambiguous. In this paper, Effects of aspect ratio of side cavity on open-channel flow with permeable and impermeable side cavities were examined experimentally. Velocity fluctuations were measured by using a particle-image-velocimetry (PIV). We revealed the flow resistance could be explained by the difference of mass exchange and momentum transport through the interaction between the side cavity and main flow region.
The effect of a finite patch on flow and bed morphology in the open channel was investigated using laboratory experiment. Two flow conditions, which were below and above the threshold of sediment motion, were considered with various configurations. For flows below the threshold of sediment motion (case 1), the erosion took place primarily opposite the patch and near the leading edge, whereas for the other condition (case 2), sediment deposition was observed within and near the patch due to reduction of shear stress, which was strongly influenced by the flow blockage. For case 1, the degree of scouring depth increased with the flow blockage, and as the submergence ratio increased, the scour depth decreased. For case 2, as the flow blockage increased or the obstruction ratio decreased, the deposition rate within and behind the patch decreased.
This manuscript describes an experiment study on the local flow and bed variation around different types of spur dykes in sediment mixtures. The permeable spur dyke, impermeable spur dyke and three kinds of hybrid spur dykes are investigated under non-submerged clear-water scour conditions. The local scour and wake deposition properties and the characteristics of the sediment size distribution due to the differences in the type of the spur dykes are focused on. In general, both the flow structure and the bed properties around a hybrid spur dyke are a combined one of that of a permeable and an impermeable spur dykes. Sand ribbons are observed in the downstream of spur dykes, mainly caused by the sediment sorting in the transverse direction. Desirable flow patterns and bed properties may be achieved by taking full advantages of those of a permeable and an impermeable spur dykes.
Lake Izunuma is a shallow lake located in the northern part of Miyagi Prefecture, and eutrophication has become a serious problem in the lake. One of the factors hindering the improvement of water quality is sediment deterioration. In this study, field observations of sediment resuspension were conducted in summer and winter, respectively. From the observed data, we found that the sediment resuspension were much influenced by the local seasonal wind and the aquatic vegetation in the lake. A simple model was developed to express time series of suspended sediment concentration in the lake by the use of wind speed as a forcing input, and it successfully reproduced time variation of turbidity during stormy condition in winter and spring season.