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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Ken-yusha Inc.  

In order to evaluate the axial force of a continuous welded rail quantitatively in a simple manner, a method was developed to measure axial force based on the natural frequency. However, the accuracy of this method is insufficient because of certain variations in track condition. This study extracted factors which influence measurement accuracy and proposed an error correction method using track finite-element analysis for the purpose of improving the accuracy of this measuring method. Furthermore, measurements were taken of the natural frequency and axial force of a rail on a real track in order to validate the proposed method.

DOI： 10.2219/rtriqr.57.2_125

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

The Blasting vibration can be reduced substantially by the employment of the controled blasting with continuous slot. Despite of this capability, the behavior concerning the dynamic fracture and vibration during the blasting process have not been clarified, and a numerical analysis method which can estimate these phenomena appropriately has not been developed. We propose a DEM-based analysis method which simulates the dynamic process consisting of both dynamic fracture and vibration. In this study a blasting experiment is also achieved for concrete blocks. The developed numerical method is then applied to its simulation. Through these analyses, the validity of the present method is discussed.

DOI： 10.2208/jscejte.71.I_1

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

Parametric instability of a wheel moving at a constant speed on a railway track is discussed. For this purpose, this paper presents an analytical formulation in which the damping is considered in rail supports. Since the dynamic behavior of a railway track depends on the rail axial load arising from the temperature change, this effect is also taken into account in the present mathematical model. Through numerical analyses, it is found that the eigenvalue which characterizes the quasi-steady-state dynamic reaction of the moving wheel and track is translated toward the positive imaginary number under the existence of damping. The range of unstable velocity is then narrowed by the introduction of dissipation into the track structure. Moreover, the critical damping at which the instability zone vanishes is obtained. Although the compressional rail stress reduces the instability speed, its contribution to the critical damping is insignificant.

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

A measuring method of rail axial load based on vibration modes is discussed. In particular, the influence of the thermal dependency of rubber pads on the natural frequency of the pinned-pinned mode is investigated. To this end, in the numerical track model a rotational spring is attached at each rail support. Through numerical experiments, it is found that the thermal dependency of the rotational stiffness dominates the sensitivity of the resonant frequency to the axial load, and its consideration is essential to simulate the dynamic nature of tracks. Furthermore, the identification of the temporal equivalent rotational stiffness reflecting the rail pad and fastener is attempted. Numerical results show that the identification using the ratio of bending moment to rotation angle of rail measured around the rail support has the best performance. In this case, the measurement with error of 0.1% is required to assure the identification accuracy of ±50kN.

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This paper presents an FE-based elastic wave transmission analysis method for composite layers consisting of different periodicities. In particular, problems in which the ratio of lattice constants of both composite arrays is given by a rational number are considered. Under this condition, by the aid of the Floquet transform, the present problem is reduced to a dynamic response of a unit cell representing each periodic layer. The developed method is applied to wave transmission through composite layers formed by circular inclusions. Numerical results showed that a combination of composites having different stop bands contributes to the vibration attenuation.

DOI： 10.2208/jscejam.71.I_859

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

The FE-based coupling method with ballast settlement elastoplastic analysis and track vibration analysis considering unsupported sleepers is developed to accurately evaluate the sleeper-ballast interaction force in deteriorated track. The present method is used to investigate the evolution of the ballast settlement around a junction of concrete slab and ballast layer. In the analysis considering unsupported sleepers, the maximum of the sleeper-ballast interaction force at the sleeper away from the junction increases in progression of the number of loading cycles at higher rate than that without loose sleepers. A larger maximum force causes a larger permanent deformation of ballast layer. This is because the progression of ballast settlement leads to an increase in the number of unsupported sleepers in neighborhood of a supported sleeper.

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

The axial force of a continuous welded rail(CWR) causing buckling and break of the rail should be controlled appropriately and adequately. In order to measure the axial force of the CWR quantitatively and in a simple manner, a method of presuming the axial force based on detection of the change of the natural frequency according to the axial force is developed. However, the accuracy of this method is insufficient because not only the axial force but the variations of track conditions such as the state of the rail and the rail fastening devices affect the natural frequency of the rail. In this paper, to investigate the influence of the variations in track conditions and its correction method for accurate measurement, we develop a finite element track model. Numerical experiments show that the wear of the rail head and the variation of the sleeper bays in the range of approximately 30 meters around the measuring point affect the natural frequency. Furthermore, we measured the axial force and the natural frequency of the CWR under various temperature conditions in an actual track and compared them with the numerical results. Through these analyses, it was confirmed that the axial force is in proportion to the natural frequency. Moreover, the consideration of the wear of the rail head and the variation of the sleeper bays in the track makes it possible to reproduce the difference of the absolute value of the natural frequency between two measurement points. By contrast, the sensitivity of the natural frequency to the axial force in the experiment is higher than that of the numerical results. Furthermore, the sensitivity of the experimental results in winter is higher than that in summer.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD  

The parametric instability of a wheel moving on a discretely supported rail is discussed. To achieve this, an analysis method is developed for a quasi-steady-state problem which can represent an exponential growth of oscillation. The temporal Fourier transform of the rail motion is expanded by a Fourier series with respect to the longitudinal coordinate, and then the response of the rail deflection due to a quasi-harmonic moving load is derived. The wheel/track interaction is formulated by the aid of this function and reduced to an infinite system of linear equations for the Fourier coefficients of the contact force. The critical velocities between the stable and unstable states are calculated based on the nontrivial condition of the homogeneous matrix equation. Through these analyses the influences of the modeling of rail and rail support on the unstable speed range are examined. Moreover, not only the first instability zone but also other zones are evaluated. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jsv.2014.03.027

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：KATHOLIEKE UNIV LEUVEN, DEPT WERKTUIGKUNDE  

This paper investigates the influence of sleeper spacing on the vibration and noise of railway tracks. Through numerical experiments of stationary harmonic loading problems for different sleeper distributions, the relationship between the variance of deviation in the sleeper location and the mean value and variance of the resonant amplitude is evaluated. The influence of randomness in the sleeper spacing on the frequency response is also examined. Moreover, since the track vibration is excited due to the interaction between the track and a running train, such problems are analyzed, taking into account the roughness between the railhead and the wheel tread. Based on a number of simulations, we assess the effect of the random and optimal sleeper distributions on the vibration and noise reductions.

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This paper investigates the influence of mechanical nonlinearity at the interface between the sleeper and ballast on the critical velocity of moving lateral load acting on an axially stressed rail. To this end, a mathematical model consisting of an elastic half-space and an infinite beam is considered. Taking into account the nonlinear stiffness in the interaction system, the critical velocity is derived via dispersion corves drown in the wavenumber-frequency space. The sensitivity of the critical velocity to the disturbance represented by a lateral moving load is revealed through theoretical discussion. Furthermore, in order to verify this phenomenon, steady-state solutions governed by the hysteresis property of the ballast material are obtained numerically for a compressed beam subjected to a moving load.

DOI： 10.2208/jscejam.70.I_971

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Physics Publishing  

The time-domain boundary element method using the Haar wavelets is developed for reducing the computational cost of the BE wave propagation analysis. The Haar wavelets are used for the discretization of the boundary integral equation. The time variation of the unknown potential and flux is approximated using the conventional scheme. The small matrix entries of the coefficient matrix are truncated with the Beylkin-type matrix compression scheme at before and after calculation of double boundary integral. The present BEM has the numerical stability comparable to the piecewise constant Galerkin BEM. The sparsity of the coefficient matrix generated at an each time step rises as the time step proceeds
the memory requirement of the present method can be reduced in comparison with the conventional BEM. The reduction of the computational work from the conventional BE analysis is difficult because of the sparse system of the conventional time-domain BEM.

DOI： 10.1088/1757-899X/10/1/012222

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD  

This paper presents a level set-based topology optimization method for noise barriers formed from an assembly of scatterers. The scattering obstacles are modeled by elastic bodies arranged periodically along the wall. Due to the periodicity, the problem can be reduced to that in a unit cell. The interaction between the elastic scatterers and the acoustic field is described in the context of the level set analysis. The semi-infinite acoustic wave regions located on the both sides of the barrier are represented by impedance matrices. The objective function is defined by the energy transmission passing the barrier. The design sensitivity is evaluated analytically by the aid of adjoint equations. The dependency of the optimal profile on the stiffness of scatterers and on the target frequency band is examined. The feasibility of the developed optimization method is proved through numerical examples. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jsv.2013.05.027

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This paper proposes a newly developed method, which measures absolute axial stress of continuous welded rails (CWR), based on the change of resonant frequency of standing wave mode of rails in the periodic infinite railway track structure. First, the authors theoretically derived dominant simultaneous equations regarding the vibration motions of a three-dimensional Timoshenko-beam under compressive or tensional axial-loadings. By applying the Floquet's theorem to dominant equations of the unit cell, which is an irreducible sub-structure with periodicity of the infinite track structure, the equations are simplified into Eigen-value problems in the frequency domain. Numerical dispersion analyses of wave modes propagating in a track made clear the relation among axial-loadings, wavenumber and natural frequency and provided an evaluation of the feasibility of the proposed method for the measurement of the absolute axial stress. Furthermore, in-situ measurements in the existing CWR track experimentally confirmed the linearity between the axial stress and the resonant frequency.

DOI： 10.2219/rtriqr.54.118

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

This paper presents a numerical method for wave transmission through a periodic track having a disturbed region. The infinite track analysis is realized by attaching the transmitting boundaries at both ends of the finite sub-domain. To achieve this, an impedance matrix representing the transmitting boundary is constructed by utilizing eigenmodes for the transfer matrix of a unit cell. The developed method is applied to infinite tracks subjected to incident harmonic waves. Through numerical analyses, the influence of the stiffness of the pads on the wave transmission is examined. The relation between the transmittance and the band structure of track is also discussed.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPRINGER-VERLAG BERLIN  

This paper presents a numerical method for wave transmission through a periodic track having a disturbed region. The infinite track analysis is realized by attaching the transmitting boundaries at both ends of the finite sub-domain. To achieve this, an impedance matrix representing the transmitting boundary is constructed by utilizing eigenmodes for the transfer matrix of a unit cell. The developed method is applied to infinite tracks subjected to incident harmonic waves. Through numerical analyses, the influence of the stiffness of the pads on the wave transmission is examined. The relation between the transmittance and the band structure of track is also discussed.

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DOI： 10.2208/jscejam.67.I_95

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DOI： 10.2208/jscejam.67.I_905

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

This paper presents a BE-based shape optimization method for acoustic problems in the context of shape design of sound insulating walls. In order to avoid the convergence to a local minimal solution around an initial shape, the topological derivative is introduced. Based on the global distribution of the topological derivative, new shape or topology are attained by nucleating small scattering bodies. Evaluation of the topological derivative is achieved within the framework of the boundary element analysis. To cope with the topological change due to the nucleation and cutting of thin branches, shape is updated by the aid of the level set approach during the optimization process. Through numerical examples, it is proved that the developed method can find a shape with good performance irrespective of its initial shape. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.enganabound.2010.06.017

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Language：Japanese   Publisher：Japanese Society for Engineering Education  

A learn-by-doing engineering career education program adopted by MEXT of Japanese Government has been conducted for three years with the assistance of named “A network of 100 wise men” , which is a novel supporting organization for the students and faculties of Niigata University. The network is composed by the company engineers or social technicians who have rich experiences in the careers of the actual R&D processes. We have confirmed that the practical experiences they possessed on the course of their R&D processed are quite effective for the students to give them the practical engineering education.

DOI： 10.4307/jsee.58.5_67

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

This paper presents a numerical method to construct transmitting boundaries for periodically supported railway tracks. This is realized by the derivation of impedance matrix for a half-infinite track. To achieve this, dynamic response of the infinite track corresponding to the half-infinite model is analyzed for a series of harmonic loading modes. The infinite problems are solved by virtue of Floquet transform. The developed method is applied to a periodically supported rail having a finite irregular zone subjected to harmonic loads. It is reduced to a dynamic problem of a finite track with the transmitting boundaries attached on both ends. Through comparison with the present method and a conventional way using a very long but finite railway model, the superiority over the truncated model is demonstrated.

DOI： 10.1299/jmtl.3.44

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

This paper describes the development of prediction method for ground-borne vibration from railway tunnels. Field measurement was carried out both in a subway shield tunnel, in the ground and on the ground surface. The generated vibration in the tunnel was calculated by means of the train/track/tunnel interaction model and was compared with the measurement results. On the other hand, wave propagation in the ground was calculated utilizing the empirical model, which was proposed based on the relationship between frequency and material damping coefficient <I>α</I> in order to predict the attenuation in the ground in consideration of frequency characteristics. Numerical calculation using 2-dimensinal FE analysis was also carried out in this research. The comparison between calculated and measured results shows that the prediction method including the model for train/track/tunnel interaction and that for wave propagation is applicable to the prediction of train-induced vibration propagated from railway tunnel.

DOI： 10.1299/jmtl.3.53

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

The time-domain boundary element method using the Haar wavelets is developed for reducing the computational cost of the BE wave propagation analysis. The Haar wavelets are used for the discretization of the boundary integral equation. The time variation of the unknown potential and flux is approximated using the conventional scheme. The small matrix entries of the coefficient matrix are truncated with the Beylkin-type matrix compression scheme at before and after calculation of double boundary integral. The present BEM has the numerical stability comparable to the piecewise constant Galerkin BEM. The sparsity of the coefficient matrix generated at an each time step rises as the time step proceeds; the memory requirement of the present method can be reduced in comparison with the conventional BEM. The reduction of the computational work from the conventional BE analysis is difficult because of the sparse system of the conventional time-domain BEM.

DOI： 10.1088/1757-899X/10/1/012222

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Language：Japanese   Publisher：Japanese Society for Engineering Education  

We report the results and further problems on what we call the learn-by-doing engineering career education program which has been conducted for three years by the grant-in-aid adapted in 2006 by MEXT of Japanese government. In the paper, we attempt to estimate the processes of the internship programs which were supported by &ldquo;A Network of 100 Wisdom&rdquo; , an organization outside the university. In this year, we have accomplished the construction of three kinds of internship programs, which have been combined one after another. We confirm that we have given the university students strong motivations toward the technical studies through these practical internship programs.

DOI： 10.4307/jsee.57.5_73

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：The Japan Society of Mechanical Engineers  

This paper describes the development of prediction method for ground-borne vibration from railway tunnels. Field measurement was carried out both in a subway shield tunnel, in the ground and on the ground surface. The generated vibration in the tunnel was calculated by means of the train/track/tunnel interaction model and was compared with the measurement results. On the other hand, wave propagation in the ground was calculated utilizing the empirical model, which was proposed based on the relationship between frequency and material damping coefficient <I>α</I> in order to predict the attenuation in the ground in consideration of frequency characteristics. Numerical calculation using 2-dimensinal FE analysis was also carried out in this research. The comparison between calculated and measured results shows that the prediction method including the model for train/track/tunnel interaction and that for wave propagation is applicable to the prediction of train-induced vibration propagated from railway tunnel.

DOI： 10.1299/jmtl.3.53

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：The Japan Society of Mechanical Engineers  

This paper presents a numerical method to construct transmitting boundaries for periodically supported railway tracks. This is realized by the derivation of impedance matrix for a half-infinite track. To achieve this, dynamic response of the infinite track corresponding to the half-infinite model is analyzed for a series of harmonic loading modes. The infinite problems are solved by virtue of Floquet transform. The developed method is applied to a periodically supported rail having a finite irregular zone subjected to harmonic loads. It is reduced to a dynamic problem of a finite track with the transmitting boundaries attached on both ends. Through comparison with the present method and a conventional way using a very long but finite railway model, the superiority over the truncated model is demonstrated.

DOI： 10.1299/jmtl.3.44

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The education centre for engineering and technology was established in the faculty of engineering at Niigata University in spring 2005 so as to elevate the motivation of undergraduate students for learning through making some products. To this end, we have been practicing several new engineering education programs, such as multidisciplinary projects similar to PBL, the active involvement of the students with the collaborative research and development between university and private companies and so on. These attempts are designed for the students to have fundamental or compulsory competence for engineering. In this report, current features of these programs are mentioned, and critical issues as well as future direction of engineering education are discussed.

DOI： 10.1299/jsmetsd.2009.29

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DOI： 10.2208/journalam.11.1031

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DOI： 10.2208/journalam.11.149

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DOI： 10.11532/structcivil.54A.114

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DOI： 10.2208/journalam.10.1029

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOHN WILEY & SONS LTD  

A boundary element method is developed for the topology optimization problem. The topological change is captured using the level set method. The level set function which is defined by signed distance from the boundary contour is assigned to fixed grid points. Boundary elements are developed along the zero contour of the level set function. The design sensitivity analysis is performed for the boundary element equation, and then the boundary velocity is obtained. The velocity field which leads the level set function to optimal material distribution is obtained by the extension of the boundary velocity. Numerical examples show that the proposed method is valid for the topology optimization problems. Copyright (c) 2006 John Wiley & Sons, Ltd.

DOI： 10.1002/cnm.919

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DOI： 10.2208/journalam.9.353

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Topology optimization methods with continuous design variables obtained by the homogenization formula or the solid isotropic microstructure with penalty (SIMP) model are widely used in the layout of structures. In the implementation of these approaches, one must take into account several issues, e.g., irregularity of the problem, occurrence of the checkerboard pattern, and intermediate density. To suppress these phenomena, the employment of additional strategies such as the perimeter control or the filtering method will be required. In this paper, a topology optimization method which can eliminate these difficulties is developed based on the volume of fluid (VOF) method. In the method, shape design is described in terms of the VOF function. Since this function is defined by a volume fraction of material occupying each element, it can be recognized as a continuous material density in the SIMP model. Within the framework of the VOF analysis, the topology optimization procedure is reduced to a convection motion of the material density governed by a Hamilton-Jacobi equation as in the level set method. Through numerical examples, the validity of the proposed method is investigated.

DOI： 10.1007/s00158-005-0582-5

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DOI： 10.2208/journalam.8.1037

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We measured factors relating to track dynamic behaviour, such as dynamic wheel loads and rail seat forces near a rail joint induced by running vehicles. We also proposed a track dynamic model to consider the excitation by wheels passing over discontinuous fish plate rail joints. We then compared the measured and analytical results, and found a close agreement between them. We also proposed a prediction model of ballast settlement near rail joints and calculated the effects of countermeasures against joint dips on ballast settlement.

DOI： 10.2219/rtriqr.46.124

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In the present paper, we investigate theoretically and experimentally the number of non-zero matrix entries generated by the wavelet BEM with the Beylkin-type compression algorithm. The Beylkin-type algorithm, which is based on a prescribed level-independent threshold, retains the asymptotic convergence rate of BE solutions, like widely-used level-dependent compression schemes. The coefficient matrix compressed by the Beylkin-type scheme has O(N 1+γ) (0 &lt
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DOI： 10.2208/jsceseee.22.219s

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DOI： 10.2208/journalam.7.1313

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WIT PRESS  

The influence of the truncation schemes for wavelet BEM on the compression rates of the coefficient matrices is investigated through the asymptotic estimation and numerical experiments. In the present paper the truncation schemes given by either Schneider's level-dependent scheme or the Beylkin-type algorithm are considered. The theoretical estimation of the number of stored entries shows O(N1+a) (0 &lt; alpha &lt; 1) for the Beylkin-type compression and O(N(log N)(beta)) (beta &gt; 1) for the level-dependent truncation. However, in actual BE analysis the Beylkin-type algorithm enables us to compress the coefficient matrix at the rates comparable to those for Schneider's scheme.

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A Timoshenko beam finite element suitable for vehicle-track vibration analysis is proposed and is applied to a jointed railway track. In several simulation models, the track vibration excited by a train running on the rail is formulated as a dynamic problem where a sequence of concentrated loads moves on the discretely supported Timoshenko beam. The external force is then defined by the concentrated load. The Timoshenko beam subjected to concentrated loads deforms with the slope discontinuity at the loading points. This deformation cannot be represented by the usual finite elements, which causes the fictitious responses of the beam. The present finite element model removes the undesirable response by completely modelling the slope discontinuity. This is achieved by the TIM7 element with the piecewise-linear hat functions. The jointed track model constructed by this finite element is employed to predict the impulsive wheel-track contact force excited by the wheel passage on rail joints. The rail joints with fishplates are of great concern to track deterioration, the settlement of ballast track and the failure of track components. In the present paper the effects of train speed and gap size of the joints on the impact force are assessed from simulation results. © IMeohE 2004.

DOI： 10.1243/0954409041319687

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WIT PRESS  

An identification method is developed for unknown material parameters in a dynamic subway-track model. The proposed method is formulated in the framework of genetic algorithms (GAs). An individual in the GA is defined by a set of real unknown parameters not by a coded string. The evaluation of fitness is carried out based on a three-dimensional dynamic analysis, in which the subway track, tunnel and ground are modeled by means of the coupling of boundary element (BE) and finite element (FE) methods. To save the computational work, a neural network (NN) in which the material parameters are input data and the spectrum ratios are output data is introduced. The developed method is validated through application to numerical models and in situ measurements.

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DOI： 10.2208/journalam.6.301

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A practical strategy is developed to determine the optimal threshold parameter for wavelet-based boundary element (BE) analysis. The optimal parameter is determined so that the amount of storage (and computational work) is minimized without reducing the accuracy of the BE solution. In the present study, the Beylkin-type truncation scheme is used in the matrix assembly. To avoid unnecessary integration concerning the truncated entries of a coefficient matrix, a priori estimation of the matrix entries is introduced and thus the truncated entries are determined twice: before and after matrix assembly. The optimal threshold parameter is set based on the equilibrium of the truncation and discretization errors. These errors are estimated in the residual sense. For Laplace problems the discretization error is, in particular, indicated with the potential's contribution ∥c∥ to the residual norm ∥R∥ used in error estimation for mesh adaptation. Since the normalized residual norm ∥c∥/∥u∥ (u: the potential components of BE solution) cannot be computed without main BE analysis, the discretization error is estimated by the approximate expression constructed through subsidiary BE calculation with smaller degree of freedom (DOF). The matrix compression using the proposed optimal threshold parameter enables us to generate a sparse matrix with O(N1+γ) (O≤γ &lt
1) non-zero entries. Although the quasi-optimal memory requirements and complexity are not attained, the compression rate of a few per cent can be achieved for N ∼ 1000. © 2003 John Wiley and Sons, Ltd.

DOI： 10.1002/nme.666

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

A wavelet BEM is applied to the evaluation of the effective elastic moduli of unidirectional composites, based on the homogenization theory. This attempt is devoted to the reduction of computational cost for the BE-based homogenization analysis. Truncation for matrix compression is carried out by the Beylkin-type algorithm. A thresholding value for the truncation is set such that the discretization error of BE solution is comparable to its truncation error. Besides, rearrangement of the BE equations is proposed to attain rapid convergence of iterative solutions. Through investigation of asymptotical convergence of the effective moduli, it is found that the BE-based homogenization analysis ensures the same rate of convergence for effective moduli as for characteristic functions. By applying the wavelet BEM to heterogeneous media which have microstructures with many voids, the effective moduli with agreement of 2-4 digits can be evaluated using 20-50% memory requirements of conventional BE approaches. (C) 2003 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0955-7997(02)00154-6

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Language：Japanese   Publishing type：Research paper (other academic)   Publisher：土木学会  

DOI： 10.2208/journalam.5.101

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DOI： 10.2208/journalam.4.127

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Other Link： http://hdl.handle.net/10191/4880

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Application of Haar wavelet to h-hierarchical adaptive method is attempted to improve the performance. The wavelet boundary element method (BEM) is developed by means of the Galerkin method. In order to save memory requirement and computation time, sparse matrices are obtained by truncation of matrix coefficients. Error indicator and estimator are constructed based on the difference between the true solution and its projection onto the mesh. These values are effectively evaluated using the boundary element solution. The adaptive method is developed for 2D Laplace problems. Through numerical examples, performance of the present method is investigated concerning the sparseness of matrices and the computation time devoted to calculation of matrix coefficients and to equation solving process. © 2001 Elsevier Science Ltd.

DOI： 10.1016/S0955-7997(01)00015-7

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Language：English   Publishing type：Research paper (scientific journal)  

Non-orthogonal spline wavelets are developed for Galerkin boundary element method. The proposed wavelets have compact supports and closed-form expressions. Besides, one can choose arbitrarily the order of vanishing moments of the wavelets independently of order of B-splines. Sparse coefficient matrices are obtained by truncating the small elements a priori. The memory requirement and computational time can be controled by changing the order of vanishing moments of the wavelets. As an iterative technique for solving the boundary element equations, GMRES(m) method is employed. Diagonal scaling and incomplete LU factorization (ILU(0)) are considered for the preconditioning. The ILU(0) becomes an effective preconditioner for higher order vanishing moments. Through numerical examples, availability of the proposed wavelets is investigated. © 2001 Elsevier Science Ltd.

DOI： 10.1016/S0955-7997(01)00036-4

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WIT PRESS  

A Gauss quadrature method in which the wavelet is used as a weighting function is developed for wavelet BEM. Non-orthogonal spline wavelets that can change the order of vanishing moments as well as the order of polynomial are considered in BE analysis. Although the increase in the order of vanishing moments leads to the increase in the sparseness of matrices, that also increases the number of intervals in which the wavelet is described by a certain polynomial. The proposed quadrature method does not need to divide the support of wavelets in the calculation of matrix coefficients, while the Gauss-Legendre formula obliges us to divide the support into several intervals. Consequently the proposed method allows to reduce the computational work for generation of matrices. Estimation of the error in the numerical integration is also attempted in order to decide the number of integral points for a specified tolerance. Numerical experiments axe carried out, and the feasibility of the proposed method is examined.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WIT PRESS  

This paper presents a practical determination method for optimal threshold in wavelet BEM. The optimal threshold, used for truncation of coefficient matrix entries, is determined such that truncation error is comparable to discretization error, in order to minimize the computational cost without deterioration of the accuracy. Errors are estimated in the residual sense. The discretization error is estimated based on the asymptotical behaviour of the residual R. These enable us to determine the optimal threshold in advance, independently of prescribed analytical conditions. Through numerical example, availability and validity of the proposed strategy axe investigated.

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Language：Japanese   Publishing type：Research paper (other academic)   Publisher：Japan Society of Civil Engineers  

The steel pipe attachment method has been employed as a seismic strengthening technique for RC columns in cut and cover tunnels. In this method, two concrete-filled tubular steel columns are attached to the RC column from both sides, and they will prevent the, tunnel from collapse even if the RC columns undergo shearing failure. In order to appreciate the mechanical properties of the attached column, numerical analyses are accomplished. This paper presents the modeling of the RC and attached columns and then constructs an interaction analysis method. Several discussions are carried out through comparison between the numerical and the experimental results.

DOI： 10.11532/journalte1991.10.87

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DOI： 10.2208/journalam.3.107

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DOI： 10.2208/journalam.3.157

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Elastoplastic analysis method is developed for wire mesh of box gabions. The wire mesh is modeled as a macrocontinuum. Constitutive relation of the continuum model is derived using the principle of virtual work, in which the equivalency of energy stored in the wire mesh to that in the continuum is taken into account. The derived expression of stress-strain relationship containes the term of forces which take place at the wire ends in a unit cell of the mesh. In order to save the computational effort, evaluation of the forces is carried out by using neural network. The nonlinear behavior of the wire is then described by the neural network. The analysis method is developed base on finite element method. Numerical analyses are compared with experimental results and good agreement is obtained.

DOI： 10.2208/jscej.1999.633_205

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DOI： 10.2208/journalam.2.153

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：WIT PRESS  

An h-hierarchical method is developed using Haar wavelets for two-dimensional Laplace problems and performance of the developed method is investigated. Haar wavelets provide complete hierarchical system for approximate solution and sparse coefficient matrix by truncation. The preconditioned GMRES(m), a kind of iterative solvers, is employed to solve equations. Through numerical example, it is found that the memory requirement is decreased, however, the CPU time is not shortened because of a large cost of preconditioning.

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A time domain numerical method is constructed for dynamic interaction analysis of wheel and track, so that nonlinearity of the system can be introduced. The rail is described as an Euler beam and the deflection is expressed by a time domain integral representation. The wheel and sleepers are modeled as masses. Stability of the dynamic analysis is augmented by introducing the compatibility into contact forces acting between the three subsystems. A time integration scheme for spring, damper and mass system in which the contact forces consist with that of the beam model is derived based on integral equation method. Influence of nonliriearity in rail pad on the dynamic response is investigated using the proposed method.

DOI： 10.2208/jscej.1998.61

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Language：Japanese   Publisher：日本計算数理工学会  

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In this study, we theoretically investigate the optimized sleeper spacing which can suppress resonances. We introduced a minimization problem in which the objective function is given by the wave transmittance and the design variable is defined by sleeper distribution. In the analysis the rail is modeled by a Timoshenko beam and the sleeper is represented by a mass. The infinite track analysis is realized by attaching the transmitting boundaries at both ends of the finite optimization region. Through numerical analyses the sleeper spacing effective in reduction of the transmittance is defined. Furthermore, the feasibility of the proposed method is validated through response analyses for a harmonic load.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The 3-D deformation behaviour of the full-scale ballasted track is simulated using the finite element method (FEM) with the cyclic densification model. The present constitutive model, proposed by Suiker et al, is based on the overstress formulation like Perzyna's viscoplastic model. The simulated vertical displacement is good agreement with the test results on the full-scale cyclic vertical loading tests. The permanent strain below sleepers is accumulated by volumetric compaction in the range under 300 loading cycles. The accumulated permanent strain in the range over 300 cycles is caused by the frictional sliding.

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In the time-domain BEM with Haar wavelets for 2-D diffusion 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 using the Beylkin-type level-independent truncation scheme with a DOF-independent prescribed threshold value A. The number of non-zero entries of the matrix G^<(L,p)> and H^<(L,p)> (1 &le; p &le; L, L: current time step), N(G^<(L,p)>) and N(H^<(L,p)>), increases in proportion to the factors log N, N^<1/2>, N and N log N, except for the behavior in the smaller DOF range where N(G^<(L,p)>) and N^(H<(L,p)>) 〜 O(N^2).

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This paper presents a wave propagation analysis method for a periodic railway track having a finite irregular zone. A half-infinite periodic sub-region is represented by an impedance matrix. The infinite system is reduced to a matrix equation with finite DOF by coupling the impedance matrices with the irregular zone. Through numerical examples, influence of the heterogeneity on the wave propagation is discussed in terms of the dispersion of wave modes. It is found that the irregularity is effective to cut off the wave transmission.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The 3-D finite element analysis for cyclic vertical loading tests of a full-scale railway ballasted track is implemented using the extended subloading surface elastoplastic model with the modified material functions proposed by Hashiguchi. The modified function fulfills the convexity of the yield surface for a whole range of the friction angle. The vertical displacement of the bottom of the sleeper is good agreement to the experiment data under the prescribed cyclic loading. The large plastic strain extends from the edge of the sleeper to the bottom of the ballast layer; the frictional sliding zone can be found in the ballast layer.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The numerical algorithm for reducing the computational work of the cyclic deformation analysis using the hypoplastic model with the time-domain homogenization is proposed. 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 analysis. The proposed algorithm enables us to change the step width of the macro-chronological analysis, and to reduce the number of the micro-chronological analysis. The accuracy of the simulation results depends on convergence speed of the accumulation of the permanent deformation.

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The localization in the buckling of infinite rail due to temperature stress is studied. A tangent rail is modeled by a straight Bernoulli-Euler beam cramped by sleepers. The buckling load is derived theoretically for each wavenumber. The bifurcation path is also analyzed under periodic deformation. On that path, instability analysis is achieved for deformation rates with wavenumbers around the buckling point. From these results, a bifurcation set embedded in the space spanned by wavenumber, amplitude and temperature is developed. It is found that deformation modes corresponding to the all wavenumbers in the neighborhood of buckling point contribute to the growth of the localization in the rail deflection.

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The cyclic deformation of railway ballast is simulated using the cycle-jump type constitutive model. The cycle-jump type model is based on the overstress formulation. The reversible response is represented by a pressure-dependent, hypoelastic model. The criterion of generation of progressive plastic deformation, the shakedown stress, is assumed to depend the accumulative plastic strain. The present model is used to simulate the cyclic triaxial tests of railway ballast. The accuracy of the simulation results depends on the convergence of the strain accumulation, while the larger value of the cycle increment ΔN enables us to reduce the computational work.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

The wavelets are applied to the time-domain boundary element method for solving the 2-D scalar wave equation. In the present method, the wavelets are used for approximating the unknowns on boundary, and for Galerkin discretization. Most of the coefficient matrix entries are small due to the vanishing moment property of the wavelets. The truncation of the small entries contributes to generate the sparse coefficient matrices. The use of wavelets, in particular, enables us to reduce the number of the matrix entries required to calculation of time convolution. However, the threshold for the truncation should be determined in consideration of the accuracy of the approximate solutions.

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The 3-D simulation of cyclic vertical loading tests of a full-scale railway ballasted track is attempted using the finite element method (FEM). The ballast layer is modeled as the continuum body of which the elastoplastic behavior is described by the subloading surface model with rotational hardening. The variation tendency in the relation between the vertical displacement of the bottom of the sleeper and the vertical load can be simulated using the present FE model. The simulated permanent displacement is comparable to those of test results. The large plastic strain extends from the edge of the sleeper to the bottom of the ballast layer; the frictional sliding zone can be found in the ballast layer.

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DOI： 10.1299/jsmehs.2009.46.153

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DOI： 10.20549/jseejaarc.2009.0_142

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The 3D ascending behavior of migratory fish is modeled using the individual-based model and an agent-type movement decision scheme. The perceived stimuli strength of migratory fish are estimated with four physical variables: velocity, strain, pressure and light intensity. The fish movement at each time step is selected from among the prescribed five movement paterns. Qaulitative validity of the simulation results on the ascending behavior is verified through numerical examples.

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DOI： 10.20549/jseejaarc.2008.0_460

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DOI： 10.20549/jseejaarc.2008.0_434

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DOI： 10.20549/jseejaarc.2008.0_436

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DOI： 10.20549/jseejaarc.2007.0_754

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A Timoshenko beam finite element suitable for vehicle/track vibration analysis is proposed. In the present analysis the Timoshenko beam is introduced to model a rail. Since the rail is usually subjected to several moving and stationary concentrated loads, the slope deflection of the Timoshenko beam has discontinuity at the acting points of these concentrated loads. Hence, the use of the finite element (FE) incompatible with the slope discontinuity causes fictitious responses. In this paper the FE which is compatible with the deflection of Timoshenko beam subjected to concentrated loads is developed using the TIM7 element and the pyramid-shape function. Numerical results show that the proposed FE can remove the non-physical response.

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

A Timoshenko beam finite element suitable for vehicle/track vibration analysis is proposed. In the present analysis the Timoshenko beam is introduced to model a rail. Since the rail is usually subjected to several moving and stationary concentrated loads, the slope deflection of the Timoshenko beam has discontinuity at the acting points of these concentrated loads. Hence, the use of the finite element (FE) incompatible with the slope discontinuity causes fictitious responses. In this paper the FE which is compatible with the deflection of Timoshenko beam subjected to concentrated loads is developed using the TIM7 element and the pyramid-shape function. Numerical results show that the proposed FE can remove the non-physical response.

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Language：Japanese   Presentation type：Oral presentation (general)  

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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

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