Terumichi Yoshiaki

In recent years, some systems which contain a floating body, such as Unmanned Aerial Vehicle (UAV) connected with a tether, are used for transportation. However, the coupling motion of the system is not easily predicted with high accuracy and may induce instability of the floating body. Therefore, to control the system, comprehension of the motion of the whole system is of great importance to control the system. In this investigation, modeling and formulation of the tethered system which contains a floating body is presented using Absolute Nodal Coordinate Formulation (ANCF) and the result of the numerical simulation of the motion is discussed.

This paper proposes a method to simulate the primary bending vibration in a test stand consisting of one-third segment car body and a full-scale bogie of magnetically levitated (maglev) vehicles. The purpose of this system is to evaluate an effect of flexural vibration to the ride comfort on maglev vehicles. The system utilizes hardware-in-the-loop simulation (HILS). The HILS system calculates internal forces acting from remaining two-thirds segment car body which is missing in reality, and applies constraint forces equivalent to the internal forces to the one-third segment using electric actuators.

Behavior analysis of a coupled train under crash condition has several difficulties, because a coupled train has structural, mechanical and kinetic aspects. Many kinds of behavior can be observed when longitudinal heavy force is applied to a train set. Such as; vertical train buckling, car body deformation, coupler collapse and overriding. The objective of this study is to clarify the processes and the mechanisms of a train set behavior under these conditions, including impact force. In this study, in order to analyze the train set motion, we developed a numerical simulation model which can simulate dynamic behaviors including structural deformation, mechanical behavior and kinetic motion on a straight track. The numerical simulation model consists of both the structural models which are formulated by FEM (finite element method) and the kinematic models which are based on the MBD (multi body dynamics) theory. In this model, the FEM model was validated by comparison with the results of the collision test using the full scale test car. Simulations with large kinetic displacement and structural deformation under two types of load conditions were conducted by means of this model. One being a low speed heavy load condition, such as a relief operation, and the other a high speed light load condition, such as a collision with a relatively light weight foreign obstacle at very high speed. Large deformation processes and mechanisms data of a train set under wide load conditions ranging from low speed against a heavy obstacle to high speed against a light obstacle obtained from the simulations and experiment are comprehensively clarified.

A restraint on the wear of train wheels and rails of a railway is required to improve running safety and reduce maintenance cost. Wear is one of the problems that need to be settled in managing railway property. In order to deal with this problem, it is fundamental that we understand the mechanism of wear between rail and wheel. For this purpose, in this study an experimental approach to wear development using test stand that has controlled environment with respect to contact parameters and factors influential in causing wear is taken. In the experiments conducted, a 1/5 scaled rolling stock test stand consisting of a wheel set and two rail rollers is used. A comparison was made of the worn wheel surfaces and the creep force under various contact interface conditions such as coefficient of friction and radius of curvature. The contact interface conditions included a dry surface condition and a friction modifier-applied condition, in which low coefficient friction and high positive friction were used as friction modifiers. By studying photographs of worn wheel surfaces and the creep forces under various conditions, the mechanism of wear development at the rail/wheel contact point is examined. In particular, we clarify the influence of the creep force on the wear coefficient and the status of the worn wheel surfaces.

One method to evaluate the running stability of railway vehicles is a running test on roller rigs. In this study, we carried out running tests in order to investigate the differences in the dynamic behavior of half-body and full-body vehicle models on roller rigs in frequency response tests with vertical and rolling forced excitations. By means of a vehicle dynamics analysis by computer simulation, we evaluated the influence of the center of gravity of the body on the dynamic behavior of the vehicle. As a result, it was verified that, for both vertical and rolling forced excitations, when the gravity position of body is equal to the center of body, the dynamic behavior of the full-body vehicle model is nearly the same as that of the half vehicle model in the each excited direction. Otherwise, the dynamic behavior of the full-body vehicle model is different to that of the half vehicle model, because of a pitching movement of the body in the case of vertical forced excitations and a rolling and yawing movement of the load frame in the case of rolling forced excitations.

It is well known that enhancing safety against a large earthquake is recognized as a very important issue in Japan. So, constant effort is made to address this issue along the Tokaido Shinkansen. For example, the railway infrastructure has been reinforced and a new alert system has been deployed to regulate train operation so that trains cease running immediately should a large earthquake occur. Nevertheless, during the Mid-Niigata Prefecture Earthquake in 2004, the Shinkansen train traveling at a speed of 200km/h was derailed by the ground motion of the earthquake with no catastrophic damage to the railway tracks or structures. These fact and reports concerning that accident indicated that railway vehicle could be derailed solely by the ground motion of large earthquakes with application of the existing measures at the time. Therefore, Central Japan Railway Company (JR Central) started to study derailment mechanisms during large earthquakes and to develop new effective measures to minimize such the risk of high-speed railway vehicles derailing or and deviating. The derailment mechanism and effectiveness of an anti-derailing guardrail has been verified through full scale experiment with a real Shinkansen bogie and track, and 1/5 scale experiment. The test vehicles are standing still on shaking tracks in the experiments. So, firstly an experiment with 1 1/10 scale vehicle and roller rig was arranged providing both conditions of high speed wheel/rail rolling contact and large amplitude excitations. Then finally, as shown in Fig.1, a full scale experiment with a high-speed running real Shinkansen bogie on the roller rig of the test facility at Komaki Research Center of JR Central was carried. Also, a simulation program has been developed to approach this issue theoretically. Those results and findings obtained through the experiments and simulation indicated there was good agreement. In this paper, the test results and the analysis of the full scale experiment with a high-speed running real Shinkansen bogie on the roller rig are discussed.

This paper presents the comparison of the on-line and off-line contact algorithm. Contact force between wheel and rail is one of the most influential characteristics for evaluating running stability and safety of railway vehicles. The contact point fluctuation which affects the contact force depends mainly on the running condition and the shapes of wheel and rail. Therefore to conduct the numerical simulation for railway vehicles, there are still needs for improving the contact algorithm. In the on-line contact algorithm, contact points are calculated at the same time with the dynamic analysis by using elastic contact formulation. In the off-line contact algorithm, contact points are predicted using an assumption of rigid contacts. From this research, following conclusions were obtained. First, when the wheel tread curvature on the contact points does not change, the contact points calculated in the off-line becomes inside of the tread compared with the on-line. Despite this, the difference is sufficiently small for discussing the vehicle motion. Second, when the wheel tread curvature on the contact points changes, the difference of the vehicle motion becomes large. That is because the off-line lose the preciseness in calculation of the longitudinal creep force on the wheel tread curvature boundary points. Therefore the on-line can be more effective for the analysis when the fluctuation of the vehicle motion becomes large.

Numerical simulation is one of the effective methods for evaluating safety and stability of railway vehicles. In this paper, we formulated equations of motion of the 3D-models of vehicle and track considering 3D-contact geometry, rail flexibility and track irregularity. The simulation analysis on wheel load fluctuation was conducted to figure out the mechanism of wheel load fluctuation in consideration of rail flexibility, vehicle motion and track irregularity. As a result, following results were obtained. Rail flexibility has effect on the fluctuation of the contact force. Wheel load depends mainly on the wheel position on rail. When sleeper passing frequency becomes close to the 9th and 10th natural frequency of the vehicle/track model, the fluctuation of wheel load becomes larger due to the resonance of vehicle and track. The peak positons of wheel load and contact point between rail and wheel shift forward according to the vehicle speed. When the vehicle runs on irregularity, the effect of rail flexibility becomes less and the effect of the primary suspensions becomes larger as the wave height increases. The peak position of wheel load depends mainly on the force of primary suspension. Wheel load fluctuation on each wheel of vehicle is different because the force of the primary suspensions on each wheel is different.

Wear of rail is one of the phenomenon caused by wheel/rail contact. Wear of rail don't occur in shortly, however, there is a relation close to crack initiation. Additionally, it is possible to influence on the running stability or the curving performance of vehicle by changing the rail profile due to wear. The process of rail wear is different on each site due to the difference of wheel/rail contact condition. Up to now, predicting the worn profile of rail has been carried out by the experiment under the wheel/rail contact condition in circular curve or by the database which is accumulated the worn profiles of rail. But it is important to predict the worn profile of rail continuously in every section such as circular curve or transition curve because the condition of wheel/rail contact has changed gradually. Previously, we constructed the prediction model for worn profile of rail by use of SIMPACK. It is very useful to predict the worn profile of rail continuously according to the contact conditions at each site from the results of SIMPACK. In this research, we examined the wear predicting analysis by using the constructed model to evaluate the effect of vehicle and track conditions for rail wear.

Recently, increasing numbers of very small-sized vehicles like a personal mobility have been developed. As the mass of such small-sized vehicle is often comparable to that of their drivers, the coupling behavior between them is increasing in comparison with traditional vehicle types. Therefore, when developing small-sized vehicles, it is necessary to give ample consideration to the dynamics of the human body riding inside them. In this research, a model of a human body inside a small-sized personal vehicle is proposed. However, attempting to implement a whole body model would necessitate dealing with multiple degrees of freedom and give rise to distracting phenomena. Furthermore, the influences of human motion are uncertain and difficult to set into parameters. Accordingly, in this research, the human model is limited to the head and trunk of a human body riding inside a vehicle, and numerical simulations were used to investigate conditions that exist when lateral acceleration is applied. Then the parameters of numerical simulation is identified by Genetic Algorithm (GA). Additionally, the effect of motion control model is considered.

Recently, increasing numbers of very small-sized vehicles like a personal mobility have been developed. As the mass of such small-sized vehicle is often comparable to that of their drivers, the coupling behavior between them is increasing in comparison with traditional vehicle types. Therefore, when developing small-sized vehicles, it is necessary to give ample consideration to the dynamics of the human body riding inside them. In this research, a model of a human body inside a small-sized personal vehicle is proposed. However, attempting to implement a whole body model would necessitate dealing with multiple degrees of freedom and give rise to distracting phenomena. Furthermore, the influences of human motion are uncertain and difficult to set into parameters. Accordingly, in this research, the human model is limited to the head and trunk of a human body riding inside a vehicle, and numerical simulations were used to investigate conditions that exist when lateral acceleration is applied. Then the parameters of numerical simulation is identified by Genetic Algorithm (GA). Additionally, the influence of human behavior parameters is considered.

Rail corrugation created on the top surface of inner rails makes noise and deteriorate ride comfort due to vibration, occurred by trains passing over the rail. To solve these problems, it is necessary to identify the mechanism of the causes of generation and development of rail corrugation. So far, experimental studies have not been simulated the practical vibration systems yet, such as in terms of rail flexibility. Therefore, we set up a new type of 1/10-scale experiment machine that models real railroad vibration system. With this machine, we examined the generation and development of rail corrugation taking into consideration coupled vibration and contact problems between the wheel and rail. The condition of this experiment is R10 m (correspond to R100 m) which is the sharpest curve of conventional lines in Japan. The measurement items are the rail surface condition and the vertical acceleration of the rail. From the results of the experiments, it is thought that the surface roughness of rail and generation of vibration of dominant frequency influence generation and development of rail corrugation. Trying to find the causes that produce this vibration of prevailing frequency, we conducted an eigenvalue analysis using the simple models. As a result, the vibration system which causes rail corrugation is qualitatively thought to be caused by the vertical vibration system including contact stiffness between the wheel and rail.

This paper presents the contact force fluctuation in coupled motion between railway vehicle and flexible track. Wheel load, vertical contact force between wheel and rail, is one of an important index for evaluating stability and safety of high speed railway vehicles such as the Shinkansen. Wheel load fluctuates depending on the contact position and the coupled vibration between wheels and track. In order to figure out the influence of the track flexibility and the vehicle speed on the wheel load fluctuation, we conduct the numerical simulation with the analytical model which is based on the concept of the multibody dynamics. As main results, we figured out as follows: Track flexibility causes the fluctuation of the contact force as the coupled motion between vehicle and track. Both wheel load and lateral creep force depend on vertical contact position. The peak positions of wheel load shift forward according as the vehicle speed, because the inertia force in the running direction of wheel increases. When sleeper passing frequency is close to the 9^<th> and 10^<th> natural frequency of the vehicle/track system, the fluctuation of wheel load becomes larger. At a faster speed than the speed for the 9^<th> and 10^<th> natural frequency of the system, the wheel load fluctuation suddenly decreases. At high speed area, the wheel load fluctuation decreases according as the vehicle speed. The elastic and damping forces between car body, bogies and wheelset have the effect to decrease wheel load fluctuation in the resonance domain of the system.

Recently, increasing numbers of very small-sized automobiles like a personal vehicle have been developed. As the mass of such small-sized vehicles is often comparable to that of their drivers, the coupling motions between them is increasing in comparison with traditional vehicle types. Therefore, when developing small-sized vehicles, it is necessary to give ample consideration to the dynamics of the human body riding inside them. In this research, a model of a human body inside a small-sized personal vehicle is proposed. However, attempting to implement a whole body model would necessitate dealing with multiple degrees of freedom and give rise to distracting phenomena. Furthermore, the influences of human motion are uncertain and difficult to set into parameters. Accordingly, in this research, the human model is limited to the head and trunk of a human body riding inside a vehicle, and numerical simulations were used to investigate conditions that exist when lateral acceleration is applied. Additionally, the influence of human behavior parameters is considered.

Recently more and more small-sized vehicles like a personal vehicle have been developed. As the mass of small-sized vehicle is similar to that of driver, coupling motion between them is increasing compared with traditional type of vehicle. Therefore, it is necessary for developing small-sized vehicle to give ample consideration to the dynamics of the human body riding on a vehicle. In this research, model of the human body ridding on a vehicle is proposed. But whole body model is multiple degrees of freedom and obscurity phenomenon. Furthermore, the influence of parameters of human motion is uncertainty and it is difficult to set parameters. Therefore, in this research, human model is treated as only trunk of the human body riding on a vehicle. Then the numerical simulation is shown under the condition when lateral acceleration applied. Moreover the influence of parameter of human behavior is considered.

Recently, many researches about vehicle dynamics analysis under unusual condition like derailment and impact to an obstacle are increasing. In these conditions, longitudinal force applied to a car frame may exceed design load. In this paper, longitudinal strength of a railway vehicle at intermediate end in consideration of plastic deformation is evaluated. As a result, it is clarified that the existing vehicle structure has much larger longitudinal crippling strength than elastic strength defined in a standard. In addition, an effect of dynamics to longitudinal strength and a crippling area is evaluated.

One of methods to evaluate running stability of railway vehicles is running test on roller rigs. In this paper, in order to investigate an influence of vehicle models on dynamic behaviors of the vehicle, we carried out the running test by a frequency response with lateral forced excitations. As a result, it is verified that, there is a characteristic vibration mode in a half vehicle model, but there is not in one vehicle model.

The purpose of this study is to formulate a three-dimensional motion of a wheelset considering contact geometry by applying techniques of multibody dynamics and to analyze behavior of a wheelset on the rail with vertical track irregularity. The differential algebraic equation is solved by the augmented formulation with Lagrange multipliers, using generalized coordinates and non-generalized surface parameters that describe the contact point. The slip at the contact point between wheel and rail is generated and the creep forces are caused. Due to the creep force, the hunting motion occurs. The increase of rolling speed and the amplitude of the track irregularity is very effective on the fluctuation rate of wheel load.

The reduction of wheels and rails wear is a very important factor in improving running safety and reducing maintenance cost. We conducted an experiment to clarify the mechanism of wear development by using 1/5 scaled rolling stock test stand which composed of wheelset and roller rings. We carried out the experiment under, different curving and friction conditions. In this paper, the influences of changing track curvature and coefficient of friction on wheel wear quantity are discussed. For each boundary condition, it is clarified that wear coefficient does not depend on travel distance. Also it is pointed out that the wear parameter changes extremely at the critical curvature.

Contact force between a wheel and a rail has a significant impact on stability of a railway vehicle traveling on a curve, which is greatly dependant on the vehicle motion and the contact position. The contact position between a wheel and a rail is affected by several conditions including the cross-sectional shape of the wheel and coupled vibrations between the wheel and the rail. In order to understand wheel/rail contact accurately, the authors has built a simulation model using ANCF, taking into consideration flexibility of rails. In this paper, we show our model and the calculated results including comparisons with the results using a rigid rail model.

Wear development with polygonal shape on a rotating elastic body is a kind of pattern formation phenomenon in mechanical vibration. The polygonal deformation occurs gradually, and this causes strong vibration and noise in machine operations. This phenomenon is a kind of self-excited vibration due to time lag and eigen characteristics gives an explanation of the stability of the system. This paper deals with the experimental approach of this pattern formation in order to discuss about the polygonal numbers of the shape, giving the various rotation speed and slip ratio. The effect of the disturbance given as a groove on the surface on the stability is also examined. It is pointed out that the unexpected polygonal number appears during the rotation in the case of the large disturbance.

For high speed railway vehicles, it is very important to prevent the hunting motion. By running test with half vehicle (that is a half car body and one bogie) on roller rigs, we have investigated vibration characteristics and the dynamic behavior of the vehicle including hunting motion. In addition, we examined how the radius of inertia ratio of yaw and roll angles with half car body affected the stability of the hunting motion of railway vehicle. As a result, it is found that, the decrease of radius of inertia ratio of yaw angle makes running stability worse, and the increase of radius of inertia ratio of roll angle makes it better.

When the train accelerates/decelerates or when the failed train is in traction by the relief train, the coupler force becomes a problem from the viewpoint of tolerance against a train buckling. By analyzing the motion of the coupled train at large displacement, such as is caused when a train buckling, it is necessary to obtain knowledge on the phenomenon. Therefore, in this paper, we discuss the modeling of coupled train with a large displacement. Using the model, we make the implementation and evaluation of numerical simulations.

Recently, many researches concern vehicle dynamics analysis under derailment conditions and trainset are increasing. Although the behavior of the coupler in large displacement is noticeable, this characteristic is not necessarily clarified. In this paper, in order to clarify the behavior of the coupler in large displacement, the model by the finite element method (FEM) is built and analysis is conducted. Farther, compression test using real coupler to validate FEM model is conducted.

The environmental noise and the wear of rail occur, because the railways run while rolling wheel on the rail. Recently, the railway truck without the sleeper and the ballast is being used. The occurrences of the rolling noise and the wear of rail may be different from the previous generation. Therefore, in this study, the effect of the sleeper and the ballast were examined through experiments and analyses, when a wheel runs on the rail in passing through the connection point. As a result, the damping ratio of the truck with sleeper is higher than that without sleeper. And it was shown that there was a setting condition of ballast for the increase of damping ratio. Furthermore, it was shown that the natural frequency of rail was changed by the displacement of wheel on the rail.

Rail wear is one of the phenomena caused by rolling contact of wheel and rail. Situation of rail wear changes with complexity because contact of wheel / rail changes gradually according to the running condition of vehicles and track geometry condition. Then, it is important to predict the wear profile of rail continuously. However, predicting the change of rail profile due to wear has been mostly examined based on one contact condition of wheel / rail. SIMPACK which is one of the Multi-Body Dynamics (MBD) software is very useful to analyze vehicle dynamics, contact conditions of wheel / rail and so on. In this research, we constructed a model for predicting of wear profile of rail incorporated in SIMPACK and carried out the analysis under the several conditions.

In order to prevent the derailed vehicle from deviating from the track in the case of earthquakes, authors have developed a post derailment stopper attached to a bogie frame. For the development of the stopper, we conducted running tests under derailment conditions using real bogies and tracks. In addition, we have developed the vehicle dynamics model with the stopper based on the results of running tests. In this paper, we introduce the model for derailed vehicle and analyze the motion of the bogie frame and the stopper.

Three-dimensional motion analysis is necessary to describe the complex tire behavior on soft ground due to the deformation of the tire and the landform of the soft ground such as the ground heaving in the vicinity of the tire side edge. We developed the three-dimensional interactive model for the performance of the tire on soft ground that were composed of the distributed lumped mass-spring model as the tire, Discrete Element (DE) model as soft ground. In the present study, we have extended the previous model by dividing the soft ground into the upper and the lower soft ground, and by adding the lug to the tire with considering the contact geometry with soft ground. Numerical simulations of the tire behavior on soft ground have been carried out under several conditions using the proposed model. The numerical results showed that the three-dimensional motion analysis of the tire behavior on soft ground could be conducted, and that the proposed model could be validated through comparison with previous experimental results on the tractive performance of the tire on soft ground.

The dynamic property and behavior of the soft ground are greatly affected by the constituent grains' shape. The consideration of the elastic-plastic property of the soft ground is also important for the multipass calculation of the tire on the soft ground. We developed the efficient interaction model of the tire and the soft ground that were composed of the distributed lumped mass-spring model as the tire, Discrete Element (DE) model as the upper soft ground, and the mass-spring model as the lower soft ground. In the present study, we have improved the previous soft ground model by considering the grains' shape and the elastic-plastic property of the soft ground, and have confirmed these effects through several numerical simulations.

In this paper, two kinds of new finite element approaches are proposed for the flexible beam motion with time-varying length, large displacement and large rotation. The first approach is based on the method with variable domain and is described in the floating frame reference formulation (FFRF). Comparison with normal FFRF, calculation costs increase greatly due to time-dependent shape function. In the second approach, to avoid this disadvantage, the method of multiple time scales is applied to the above-proposed method in FFRF. A simple flexible pendulum with time-varying length has been treated for the comparison between these two approaches. In the approach used method of multiple time scales, the advantage for the calculation cost is verified.

With the increasing use of the International Space Station, humans have more opportunities to work in space. In space, a mobility device that operates efficiently is needed. But, some problems must be solved. First, the human body is suspended without the force of gravity. Second, the air cannot be polluted in the closed space of the Space Station. Thus, an air-polluting mobility device, such as a device with a gas jet using a thruster is objectionable. In this research, a mobility system called the "Tether Space Mobility Device" (TSMD) is proposed. In general, the tether is a cable or a wire rope. The tethers are expected to shift the orbit of another object without using a thruster and to move robots in space. TSMD has a mechanism that enables the tether to move an object. In this study, the TSMD model is composed of two rigid bodies and one flexible body that can express motion with large deformation and large displacement. Several modeling of TSMD is performed. An influence on motion and control of TSMD is discussed.

At Mid Niigata Prefecture Earthquake in October 2004, a Shinkansen train was derailed while being operated at the speed of 200km/h, which was the first case of the derailment of a Japanese high speed train under commercial operation through the long history. As reported, the horizontal ground motion of the earthquake was concluded to be the major cause of the derailment. Based on the reports and facts, we believe that we should study the derailment mechanism of a high speed railway vehicle due to large earthquakes, and pursue to develop an effective measure to minimize the risk of railway system against large earthquakes. In this research, a vehicle-track dynamics simulation program is developed and then employed to numerically examine the derailment mechanism and the function of Anti-derailing guard rails. The 16 DoF vehicle-track dynamics model is composed of a 10 DoF half car model and a 6 DoF track model to capture the entire dynamic response of a vehicle and rails. This reasonably simplified dynamics model should be suitable for studying the derailment mechanism and effect of guard rails. Also for more comprehensive understanding on the derailment mechanism and guard rail function for high speed railway vehicle, derailment process should be directly verified. Therefore, we also arrange an experimental setup with 1/10 scale vehicle and roller rig providing both conditions of high speed wheel/rail rolling contact and large amplitude excitations. Through the numerical analysis and experiment, we obtained the flowing outcomes. Firstly, as with the derailment pattern and process, rocking derailment is the cause of derailment due to large earthquakes. Secondly, as the measure to minimize the derailment risks, guard rails work effectively to the rocking derailments in times of large earthquakes.

In this study, the purpose is to formulate a three-dimensional motion of a wheel-set considering contact geometry by applying techniques of multibody dynamics and to discuss the errors of the constraint conditions. When the rail shape changes the constraint conditions of velocity or acceleration expression is not always satisfied. The errors of the constraint conditions are discussed by three-dimensional numerical simulation for wheel-set motion on track with irregularity.

The purpose of this study is to formulate a motion of rigid bodies system with unilateral contact problems by applying techniques of multibody dynamics and to analyze the issue of rocking conditions of the rigid bodies with slide contact or collision. The system is a coupled vibration system composed of three rigid bodies elastically supported by excited foundation. The differential algebraic equation is solved by the augmented formulation with Lagrange multipliers, using generalized coordinates and non-generalized surface parameters that describe the contact point. The influences of rocking mode and slip on the rocking motion are discussed.

The derailment mechanism and the function of Anti-derailing guard rails in times of large earthquakes have been numerically studied. The following results were obtained. (1) Rocking derailment is the major cause of derailment due to large track excitation. (2) Anti-derailing guard rail is effective to prevent derailment due to large track excitations. (3) Vertical ground motions, light weight body and curve running on canted track have relatively smaller influence on the derailment mechanism.

The purpose of this study is to clear the derailment mechanism and effect of anti-derailing guard rail on large earthquakes because the Shinkansen train was derailed by the Mid Niigata Prefecture Earthquake in October 2004. At first, in 2005, we have designed the 1/5 scale vehicle-track model and excitation device and have introduced these devices in Komaki of JR-Central and until now we have conducted the 5000 cases of excitation experiments in order to complement the result of the full-scale bogie excitation test. As a result, we conclude that the derailment occurred in the excitation frequency range of 0.5-2.0Hz (full-scale corresponding value) is the rocking derailment and that the anti-derailing guard is effective for the rocking derailment.

The derailment mechanism of vehicle on roller rigs due to large track excitation has been studied through 1/10 scale vehicle/roller rig experiment. The following results were obtained. (1) Rocking derailment is the major cause of derailment due to large track excitations regardless of vehicle speed. (2) 3mm wheel lift amplitudes are similar regardless of vehicle speed, which indicates that the effect of vehicle speed is small on wheel lift motion. (3) The derailment amplitudes generally decrease as vehicle speed increases, particularly in the cases excited by lower frequency inputs.

The purpose of this study is to develop an efficient interaction model of tire and soft ground for vehicle simulations on off-road terrain. The model presented in this paper describes the deformable behavior of the elastic tire and the behavior with large displacement and destruction of the soft ground. We adopt a distributed lumped mass-spring model as the tire, Discrete Element Method (DEM) model as the upper soft ground and a mass-spring model as the lower soft ground. A tire model with lug considering contact geometry is also developed on the basis of the interaction model. Numerical simulations of the tire behavior on soft ground using these models have been conducted. The results of the numerical simulations show that the proposed models of tire and soft ground are efficient for vehicle simulations on off-road terrain and that the lug of tire is effective in improving tractive performance of tire.

The purpose of this study is to investigate the mechanism of wheel load variation of a high-speed train running on rail track with short-wavelength irregularity effecting on the running safety. In order to investigate the mechanism, the numerical simulation is conducted. The simulation model consists of the two-axle bogie and the track. The track consists of rail, rail pad, sleeper, ballast. The rail is expressed as the flexible beam described using the Absolute Nodal Coordinate Formulation in order to obtain the rail deformation more precisely. As a result of this study, we obtained further the information of the wheel load variation while two wheels passing on the rail with irregularity. That is, the wheel load variation rate of two-axle bogie model at 270km/h becomes larger in the case of the irregularity wavelength 1.1-1.2m as well as one-axle bogie model. However, the difference between the leading wheel and the trailing wheel occurs in terms of the magnitude. And the magnitude relation between the leading wheel and the trailing wheel changes according to the wavelength with the irregularity. We discuss the mechanism of these phenomenon obtained by the simulation.

The purpose of this study is to formulate a motion of a rigid body with unilateral contact problems by applying techniques of multibody dynamics and to analyze the issue of rocking condition of the rigid bodies with slide contact. In order to deal with rocking motion with slide contact, we formulate for dynamics of simple rigid body system with unilateral contact model. Judgment for occurrence of the contact between a rigid body and a base are applied. A planar motion of the rigid body system having a simple shape and both cases with and without slide are assumed. We analyze rocking motion of the rigid body including slide and frictional force. We solve the differential algebraic equation by augmented method with Lagrange multipliers, using generalized coordinates and independent variables which describe contact points. The influence of the frequency and amplitude of disturbance given to the base are discussed.

Recent reports imply that railway vehicles could derail solely by the ground motions of earthquakes. Thus, we should further study the derailment mechanism of these cases, to pursue to minimize the risk of railway system. We developed our original vehicle dynamics simulation and employed it for numerical analyses. We obtained the following outcomes. (1) Most of derailments are brought as the result of the rocking motion of a vehicle by track excitations underneath. The derailing motions are observed similarly regardless of vehicle speed. (2) The excitation amplitudes for derailment are influenced by vehicle speed particularly in lower input frequencies.

A railway is organized by a variety of individual technologies, and functions safely and properly as a system, therefore it is necessary for the system safety to study each potential case of disasters caused by earthquakes. Recent reports imply that railway vehicles could derail solely by the ground motions of earthquakes without fatal damages of vehicles or tracks. Based on the reports and facts, we believe that we should further study the derailment mechanism of a high speed railway vehicle excited by great seismic motions, to pursue to minimize the risk of railway system safety against great earthquakes. At the start of the study, we developed our original vehicle dynamics simulation and then employed it for numerical analyses. At the present stage, through the analyses, we obtained the following major outcomes. (1) Most of derailments are brought as the result of the rocking motion of a vehicle by track excitations underneath. Interestingly, the derailing motions are observed similarly regardless of vehicle speed. (2) By contrast, the excitation amplitudes for derailment are influenced by vehicle speed particularly in lower input frequencies. This can be explained by the sensitivity of the relative wheel/rail slide due to creepage. (3) The excitation amplitudes for 30mm of wheel lift are relatively independent of vehicle speed. (4) The wheel/rail slide strongly depends on the friction coefficient if a vehicle stationed, being relatively independent of the friction coefficient at higher speeds.

In the present paper, the motion of a tethered system with large deformation and large displacement is discussed. In general, a tether is a cable or a wire rope, and a tethered system consists of a tether and the equipment attached to the tether. A tethered subsatellite in space is an example of a tethered system. In the present study, a tethered system consisting of a very flexible body (the tether) and a rigid body at one end is considered as the analytical model. A flexible body in planer motion is described using the Absolute Nodal Coordinate Formulation. Using this formulation, the motion of a flexible body with large deformation, rotation and translation can be expressed with the accuracy of rigid body motion. The combination of the flexible body motion and the rigid body motion is performed, and their interaction is discussed.<br>Experiments are performed to investigate the fundamental motion of the tethered system and to evaluate the validity of the numerical formulation. Experiments were conducted using a steel tether and a rubber tether in gravity space. In addition, an experiment of the motion of the tethered system with a rigid body in microgravity space was conducted.