Terumichi Yoshiaki

As the evaluation method for the extent of the damage of the wheel tread of a railway vehicle, the measurement of its length in the rotational direction has been adopted for the decision of the wheel treatment. It is derived from the assumption that the depth of a wheel flat, which is one of the most serious damages, is proportion to its length in the rotational direction. Although the length of a shallow scrape tends to be long, the profile of the wheel with the long shallow scrape has less amount of irregularities compared with an exact circle. Therefore, in order to clarify the effect of the rotating wheelset with the shallow scrape on a bogie, we focused on the behaviour of the rotating wheel with the shallow scrape and evaluated it by dynamic model simulation and bench tests for an actual bogie. By the numerical simulation, we comprehended that the shallow scrape causes the vertical acceleration of the axlebox and the impact force to increase linearly in accordance with the running speed-up, and the vertical acceleration has a local maximum value around 110 km/h in accordance with a decrease in vertical collision velocity of the wheel with the roller in a higher speed range.

Recently, as space developments have progressed, the opportunities for human beings to become active in outer space have increased. It is now expected that upsizing of manned space facilities, such as the International Space Station, will further this trend. Therefore, a means of individual transportation is necessary to ensure that human beings can move about effectively in microgravity environments. In this study, we propose a tether-based mobility system named the Tether Space Mobility Device (TSMD), which moves the user by extending and winding a tether attached to destination point within the structure. Additionally, a TSMD attitude control method is examined via numerical analysis. This model consists of one flexible and three rigid bodies. In microgravity environments, it is expected that tether motions will involve large deformations. Therefore, tether placements are formulated using the absolute nodal coordinate formulation suggested by Shabana, and coupled motions between tethers and rigid bodies are based on an augmented formulation. Furthermore, the contact force between the tether and arm is formulated by spring and damper elements. In this paper, the TSMD posture is confirmed during extension and winding operations. In our experiments, we examined the TSMD attitude control method during tether winding while focusing on changes in the system's rotational kinetic energy. The numerical results of our analysis confirm that the attitude of the system is stabilized by our proposed controller.

<p>The rights-of-way of urban railway systems contain many sharp curves. Since sharp curves can contribute to wheel and rail wear, the ability to predict the development of wheel wear is crucial to maintaining safe operation of such systems. Observation of wear development in practical railway systems is inefficient and time consuming. In order to efficiently predict wheel wear, numerical analysis using multi-body dynamics software, such as Simpack, is proposed. Contact pressure, slip ratio, and other necessary parameters are determined from Simpack's vehicle motion analysis. Wear depth is derived to create a worn wheel profile. The current wheel profile is updated using the wear profile, and is then adopted as the new wheel profile in Simpack. The rail vehicle modeled in our numerical analysis is based on a typical Japanese commuter rail vehicle. Wear depth is calculated based on the Archard wear theory. Wear development in the wheel/rail contact area is calculated, and nodes are replaced by calculated wear depth. Validity of the wear coefficient used in the simulation is discussed. The results of the numerical analysis are compared with experimental results to assess the amount of wear from the viewpoint of mechanical and tribological contact problems.</p>

<p>In recent years, railway system is attracting attention in terms of energy efficiency and environment friendliness. Rail of railway is one of the most important elements in constructing railway system. Railheads are subjected to severe contact with wheels during repeated passage of vehicles. As a results of severe contact with wheels, wear of rail or rail defect have been occurred on railheads. Rail profile will be changed due to wear development. Worn profiles of rail have changed complexity in each section because the condition of wheel/rail contact has changed gradually, according to the running condition of vehicle and track geometry condition. Therefore, it is very important to predict the worn profiles of rail based on the analysis of vehicle dynamics. Previously, we constructed the prototyped model for predicting worn profiles of rail with Simpack. However, the validation of this model has not been verified. In this study, we conducted the wear experiments by use of full-scaled wheel/rail rolling contact equipment to distinct the coefficient of wear and to measure the worn profiles for validating the prediction model. Moreover, we analyzed the worn profile of rail in the same contact condition with the wear experiments. Finally, we considered the results of wear depth and the contact patch of wheel/rail discs of this equipment in analysis and experiments. As a result of the analyses and experiment, the analytical model was confirmed being valid to predict worn profile of rail.</p>

In the present study, we propose an analytical model with a multibody system considering three-dimensional wheel/rail contact geometry and ballasted track characteristics. Suppression of contact force fluctuation between the wheel and rail is desirable from the viewpoint of ensuring running safety, track maintenance, ride comfort, and minimizing the impact of factors such as noise on the surrounding environment. In the present paper, we investigate the effects of the support characteristics of ballasted track on the interaction between vehicles and tracks. Numerical simulations and experiments are carried out for railway vehicle motion under a wide range of ballasted track rigidities. Using the proposed numerical model, we obtain analysis results that are consistent with experimental results under two different track conditions: one simulating ordinary ballasted track characteristics and one that provides sufficient space between sleepers and ballasts. The proposed numerical simulation can accurately analyze vehicle motion running over ballasted track by considering the interaction between the vehicle and the track.

A simulation model is used to calculate the rocking motion of a vehicle and how antiderailing guard rails work to prevent derailment when subject to large ground excitation and the results are verified through full scale testing. (1) The simple vehicle-track model should properly represent the rocking mechanism. (2) The effect of vehicle speed on the wheel/rail slide is also properly represented, thus the wheel/rail creep law model can be applied to the analysis of a running vehicle experiencing large rocking motion. (3) The action of the guard rail was equal in both the simulation and the full scale test, thus indicating that the simple antiderailing guard rail model sufficiently represents the dynamic interaction of the wheel/guard rail and the effect.

This study proposes an analytical model with a multibody system considering three-dimensional wheel/rail contact geometry and ballasted track characteristics. The suppression of the contact force fluctuation between wheel and rail is desirable from the viewpoint of ensuring running safety, track maintenance, riding comfort, and minimizing impacts such as noise on surrounding environments. In this paper, we investigate the effects of the support characteristics of ballasted track on the interaction between vehicles and tracks. Numerical simulations and experiments were carried out for railway vehicle motion under a wide range of rigidities of ballasted track. Using the proposed numerical model, we obtained analysis results that are consistent with experimental results under two track conditions, one that simulates the regular ballasted track characteristics and one that has sufficient space provided between sleepers and ballasts. The proposed numerical simulation accurately analyzed vehicle motion running over ballasted track by considering the interaction between the vehicle and the track.

In recent years, much dynamic analysis and structural analysis have been done while considering abnormalities, such as derailment and collisions with foreign objects. In such situations, longitudinal force that exceeds design load may be applied to the car body and the ultimate load, also known as the buckling load and the crippling load, are more important than the design load that stipulates elastic strength. This is because a buckling load is the maximum load that a structure can sustain its soundness in the event of an accident. In this paper, the longitudinal strength of a railway vehicle is evaluated in consideration of plastic deformation. First in order to evaluate the strength of the railway vehicle body experimentally and validate the finite element (FE) model for the numerical simulations, the full scale crash test is conducted. Next the numerical simulations were conducted to investigate the relationship between the ultimate load and the design load, and effects on the buckling locations caused by load conditions such as dynamics and load path. As a result, it is clarified that existing vehicle structures have much larger longitudinal ultimate strength than elastic strength as defined in standards. Finally the ratios of the ultimate load to the design load are clarified, quantitatively.

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 large earthquakes. copyright (c) 2010 by JSME.

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. Copyright (c) 2010 by JSME.

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.

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. In this research, a mobility system called the "Tether Space Mobility Device" (hereinafter called TSMD) is proposed. In general, the tether is a cable or a wire rope. The proposed system has a mechanism that uses the tether for enabling a human to move to a target point. However, this system has the problem that the center of mass of the human and that of the TSMD are different from the direct line to the target point. Then, the human is rotated by the tension of the tether. Thus, to use this device safely, rotation of the human body must be controlled. For this reason, a numerical simulation model is proposed. The numerical model is composed of three rigid bodies and one flexible body that can express motion with large deformation and large displacement. In this model, winding motion of the tether can be expressed. An experiment of the TSMD was designed to move under two-dimensional micro-gravity. The experiment confirmed the validity of the numerical simulation model. The possibility of the mobility device using the tether and the influence of the control system are discussed.

Primary study on identifying deviations in the alignment of ground coils (ground coil irregularities) for magnetically levitated systems is conducted. The ultimate goal of this study is to introduce an active suspension system with preview in the future. First, the amount of irregular forces caused by twenty four types of ground coil irregularities is calculated respectively. The calculation results clarify that the irregular forces are complexly caused by various combinations of ground coil irregularities, and this shows that identifying ground coil irregularities by vibrations of the moving vehicles is appropriate toward the preview vibration control. Next, this paper refines an identifying method, which is originally developed for conventional wheel-on-rail systems, utilizing car body acceleration and Karman filter. To exclude a harmful influence originated by the spatial filter effects of onboard magnets, application of an impulse response of a particle model, instead of a rigid body model, and correction using the second order system compensational filter are proposed. Numerical simulation results show that the proposed method enhances the identification accuracy and widens the band of frequencies in which the irregularities can be identified. Finally, fundamental experiments are conducted in the test stand which can simulate vibrations of the moving vehicles in a range of frequencies sensitive to ride quality. The ground coil irregularities in the intended band of frequencies are experimentally identified with satisfactory accuracy by the proposed method, and the experiment technically enhanced the prospect of identifying the ground coil irregularities by car body acceleration.

Rail wear is one of the phenomena caused by rolling contact of rail and wheel. Situation of rail wear changes with complexity because the contact of rail and wheel changes gradually according to the running condition of vehicles and track geometry condition. Therefore, 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 rail and wheel. SIMPACK, which is one of the Multi-Body Dynamics (MBD) software is very useful to analyze vehicle dynamics, contact conditions of rail and wheel and so on. In this research, the authors constructed a model for predicting of worn profile of rail incorporated in SIMPACK and carried out the analysis under the several conditions. Furthermore, we examined about the influential factor of wear of rail.

The derailment mechanism for when earthquakes occur has been verified in vibration bench tests and simulations in the past. However, in the past full-scale vibration bench tests including ours, the wheels did not rotate. The aims of this study are to verify the derailment mechanism in case that the railway vehicle running at a high speed is vibrated by a large lateral displacement of track during earthquakes, and to reconfirm the past other verifications. In order to realize this aim, we conducted the full-scale vibration tests with an actual series N700 bogie on roller rigs by use of the rolling stock field test simulator. This apparatus enables to simulate running tests with one or half rolling stock on roller rigs which can experience a considerable degree of horizontal displacement. As a result of this vibration test with an actual bogie on roller rigs, we were able to confirm the influence of wheel rotation on the wheel lift motion, the anti-derailing guard rail acting on a rotating wheel, and so on. © 2013 The Japan Society of Mechanical Engineers.

Recently, many researches about vehicle dynamics analysis under unusual condition like derailment and impact to an obstacle are increasing. In this paper, the behavior of train buckling when large coupler force, large displacement and plastic deformation of a coupler occur is clarified. First, in order to analyze the behavior of the coupler in large displacement, the model by finite element method (FEM) is built and analysis is conducted. Farther, impact test using real coupler to validate FEM model is conducted. Next, the hybrid train set model consisted of the FEM coupler model and a multi body dynamics (MBD) car model is build. This hybrid model constructed focusing to that coupler is connected to the car body only by contact and independent structurally. Finally, the theoretic buckling model in consideration of dynamics is shown. Using the theoretic model and the hybrid model, effects of dynamics and initial condition is verified in detail. © 2013 The Japan Society of Mechanical Engineers.

Fundamental experiments on a test stand to examine the characteristics of magnetically levitated (maglev) vehicle dynamics were conducted. In the prototype test stand, an actual bogie with weights, which correspond to a car body, is magnetically suspended and vibrated by surrounding magnetic exciting coils. This paper proposes a bench test system and a magnetic vibration method which can suspend the bogie and simulate irregular external forces originated by four types of alignment irregularities of ground coils, using a concept of equivalent irregularities. The results of the slowly swept sine excitation experiments confirmed that the bogie in the test stand is magnetically suspended in the same way as the actual bogie running at a high speed. Furthermore, vertical accelerations of the bogie and weights vibrated in the proposed way were compared with those of the moving vehicles to find similarities in a range of frequencies sensitive to ride quality. The experiments technically enhanced the prospect of the test stand to analyze the characteristics of maglev vehicle dynamics for the future. © 2013 The Japan Society of Mechanical Engineers.

Preventing railway vehicles from derailing is the most important earthquake countermeasure. Similarly, formulating measures to prevent vehicles from deviating from the track in the event of a derailment is an extremely important secondary measure for minimizing the risk of fatalities. The authors have developed a post-derailment stopper, which prevents derailed vehicles from veering off the track by catching on guard rails. We conducted running tests under derailment conditions using real bogies and tracks to develop the stopper and evaluate its efficacy. Since we observed peculiar motions of the bogie frame when the stopper was attached during running tests, we propose a 15 DOF vehicle dynamics model in order to discuss, in particular, the motion of the bogie frame and the stopper under derailment conditions. In this model, we give degrees of freedom to the motors mounted on the bogie frame because contact between the stopper and the guards was observed repeatedly during running tests. In addition, in this simulation of a derailed vehicle, static equilibrium conditions are calculated using the data obtained from running tests prior to the time history analysis. We evaluated the validity of the proposed model by comparing the calculated results with measured data.

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 interactive 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.

The purpose of the present study is to develop a three-dimensional efficient interactive model and a numerical procedure to simulate a tire on soft ground, which can be applied to multibody dynamics for off-road vehicles. For motion analysis of the tire on soft ground, it is necessary to describe the elastic deformable behavior of the tire and the behavior with large displacement and local disruption of soft ground. A three-dimensional analysis must be conducted in order to express the complex behavior of the tire on soft ground due to the deformation of the tire and the landform of soft ground, such as ground heaving in the vicinity of the tire side edge. As the tire model, we adopt a distributed lumped mass-spring model, in which a rigid wheel is connected to a number of tire-masses by Voigt elements. This tire model allows us to describe the local deformation of the tire and the distributed contact pressure between the tire and soft ground. In addition, as the soft ground model, we adopt a discrete element (DE) model, in which soft ground consists of a number of rigid soil particles. This ground model allows us to express the discrete behavior of soft ground. Furthermore, the contact between the tire and the soft ground is defined as the contact between the tire patches constructed of tire-masses and the soil particles of 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 revealed that three-dimensional motion analysis of the tire behavior on soft ground is possible, and that the proposed model and the numerical procedure could be validated through comparison with previous experimental results on the tractive and cornering performance of the tire on soft ground.

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 and the cornering performance of the tire on soft ground.

The purpose of this study was to develop an analytical model and a numerical approach for wear development of a rolling elastic body on basement, and to characterize the polygonal wear development mechanism from the numerical results. The periodical polygonal pattern due to wear is formed on the circumference of a rolling elastic body, such as a vehicle tire, and is known as one of the abnormal wear phenomena in contact problems. Although an eigenvalue analysis is often used to investigate the stability of polygonal wear, the transient behavior must be examined to clarify the mechanism of polygonal pattern formation. Since an elastic body has large deformation and a large contact patch, it is necessary to consider the distribution of the contact force and the slip in the contact patch. In this paper, an analytical model of a rolling elastic body in contact with basement is proposed for wear development. The elastic body of this model is expressed as a rigid disk and a number of masses connected by Voigt elements. The total wear amount of each mass is derived as the time integration of instantaneous wear, and is applied to the surface profile of the elastic body as the forced displacement U(t-Delta t) after time step Delta t. This model constitutes a self-excited vibration mechanism due to the time lag during wear development. Numerical analyses for the wear development of the rolling elastic body were carried out using the proposed analytical model. The numerical results confirm that the proposed model and approach clarify the mechanism of polygonal wear development.

The purpose of the present study was to develop and propose an analytical model with a multibody system and a numerical procedure for the safety analyses and assessments of railway vehicles during an earthquake. Recent reports show that railway vehicles could derail directly by the ground motions of earthquakes before any damage directly affects the vehicles and the tracks. During large earthquakes, "rocking derailment" of trains could occur due to the rocking motion of the wheelsets. In this paper, we discuss the modeling and formulation focused on the rocking motion of the vehicle in consideration of the three-dimensional vehicle motion and the wheel/rail contact geometry. Numerical simulations using the proposed model were carried out for the motion of a railway vehicle on vibrating tracks under several excitation conditions. It was observed that the rocking modes of the vehicle depend on the excitation frequencies. These modes can be classified into lower-frequency and higher-frequency excitation types, according to the phase differences between the bodies and the wheel/rail relative motions. In addition, we analyzed the vehicle responses when the yaw motion of the wheelset and the bogie frame occurs and the effects of the excitation directions in the horizontal plane.

This paper deals with the motion of a submerged tethered system subject to large deformations and displacements. A tethered system usually employs a cable or wire rope to tether an attached piece of equipment to the ground or to a vehicle, e.g., a remotely operated vehicle (ROV) in the sea. The motion of a tether was modeled using the Absolute Nodal Coordinate Formulation in which absolute slope of elements are defined as nodal coordinates. Herein, this formulation is adapted to account for hydrodynamic drag, buoyancy and added mass. By using the slope coordinates, the hydrodynamic drag acting on the curved shape of the deformed elements can be accurately calculated. Three kinds of experiment were conducted into the fundamental motion of the submerged tether when subject to large deformations and displacements. The numerical results from the proposed model agreed well with the experimental results.

To minimize the risk of fatalities in the event of earthquakes, it is extremely important to prevent the derailed vehicle from deviating from the track as well as to prevent the vehicle from derailment. Authors have developed a post derailment stopper (hereinafter referred to as, "stopper"), which attaches to a bogie frame and prevents derailed vehicles from veering of the track. For the development of the stopper and evaluation of its efficacy, we conducted running tests under derailment conditions using real bogies and tracks. Based on the results of the running tests, we have developed a 15DOF vehicle dynamics model in order to discuss the motion of the bogie in the derailment condition. In this model, focusing on the analysis of the motion of the bogie and the stopper, vertical wheel displacements which were measured at the running tests are used as input data and non-linear characteristics observed at the running tests are considered. In this paper, we analyze the motion of the bogie and efficacy of the stopper with this model and the test results.

The purpose of the present study is to develop a three-dimensional efficient interactive model and an analytical method of a tire on soft ground, which can be applied to the multibody dynamics for off-road vehicles. For the motion analysis of the tire on soft ground, it is necessary to describe the elastic deformable behavior of the tire and the behavior with large displacement and local disruption of soft ground. A three-dimensional analysis must be conducted in order to express the variety of the tire behavior on soft ground due to the difference in the deformation of the tire and the landform of soft ground such as the ground heaving in the vicinity of the tire side edge. As the tire model, we adopt the distributed lumped mass-spring model in which a rigid wheel is connected with a number of tire masses by Voigt elements. This tire model allows us to describe the local transformation of the tire and the distributed contact pressure between the tire and soft ground. In addition, as the soft ground model, we adopt the Discrete Element Method (DEM) model in which soft ground consists of a number of rigid soil particles. This ground model allows us to express the discrete fluid behavior of soft ground. Furthermore, the contact between the tire and the soft ground is defined as the contact between the tire patches constructed of tire masses and the soil particles of 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 and the analytical method could be validated through comparison with previous experimental results on the tractive and cornering performance of the tire on soft ground. Copyright (c) 2010 by JSME.

Barrel polishing is an extremely efficient processing method for surface smoothing treatment of a large number of workpieces. However, workpieces and grinding materials may separate depending on the processing conditions. Therefore, examination of the processing conditions using dynamic analysis of the behaviors of workpieces and grinding materials is strongly desired. In this study, the behavior of the particles in the planetary barrel that simultaneously rotates around a horizontal axis and revolves around a vertical axis was examined through experiments and simulations using the discrete element method (DEM). The center of the rotary barrel was set up so that the centrifugal force might act on the particles in this barrel. As a result, it was demonstrated that the distribution of two kinds of particles might be replaced by setting position of the center of the rotary barrel even if in same combination of particles.

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 indicate that railway vehicles could be derailed solely by the ground motions of earthquakes with no 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 large seismic motions, to pursue to minimize the risk of railway system against large 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.

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 unsafe case caused due to large earthquakes. Recent reports indicate that railway vehicles could be derailed by earthquake ground motions with no fatal damages of vehicles or tracks. Thus, we should further study the derailment mechanism to pursue to minimize the risk of railway system safety against large earthquakes. Particularly, for more comprehensive understanding on the derailment mechanism of high speed railway vehicle, the derailment process of the case should be directly verified. Therefore, in this study, we 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 experiment, we obtained the outcomes. (1) Two types of vehicle derailment motions are observed; one is rocking derailment and the other is sliding derailment. Derailment motions are similar regardless of vehicle speed. (2) By contrast, the excitation amplitudes for derailment decrease according to the increase of vehicle speed particularly by low frequency excitations. (3) The excitation amplitudes for wheel lift of flange height are relatively independent of vehicle speed. (4) Based on the similarity of fundamental vehicle dynamics between the 1/10 and full scale vehicles, those observed mechanisms in the scaled test should be applicable to that of full scale vehicle.

At Mid Niigata Earthquake in October 2004, a Japanese high speed train was derailed under commercial operation at the speed of 200 km/h. Investigations of the case concluded that the horizontal ground motion by the earthquake was the major cause of the derailment, which implies that railway vehicles could be derailed solely by the ground motions of earthquakes with no fatal damages of vehicles or tracks. Based on the reports and facts, we believe that we should study both the derailment mechanism and function of guard rail, to pursue to minimize the risk of railway system against large earthquakes. In this paper, we developed a simulation program to study the basic mechanism of the function of guard rail to prevent derailment due to large eathquakes. Then through numerical analysis based on the simulation program, we obtained the following results. Firstly, anti-derailing guard rail is effective to prevent derailment due to large track excitations. Secondly 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 develop and propose an efficient interaction model and an analytical method of a tire and the soft ground which can be applied to the multibody dynamics for off-road vehicles. The model presented in this paper describes the deformable behavior of the elastic tire and the behavior with large displacement of the soft ground. We adopt a distributed lumped mass-spring model as the tire, Discrete Element (DE) model as the upper soft ground and a massspring model with Bekker's theory as the lower soft ground. A tire model with the lug considering contact geometry with the soft ground is also developed on the basis of the original tire model. Numerical simulations of the tire behavior on the soft ground under several conditions using the proposed model have been conducted. The numerical results showed that the proposed model and analytical method would be validated for the vehicle dynamics simulation compared with the results of a lot of previous experiments from some references. They also indicated that the tire with low stiffness and with the small angle lug could be effective in improving the tractive performance of the tire on the soft ground.

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 5 000 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 0.5-2.0 Hz (full-scale corresponding value) is the rocking derailment and that the anti-derailing guard is effective for the rocking derailment.

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

Recent reports imply that railway vehicles could be derailed 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 large seismic motions, to pursue to minimize the risk of railway system safety against large earthquakes. We improved our original planar vehicle dynamics simulation model to a model to allow yaw motion of wheel-set, which enable to estimate the influence of the attack angle of wheel/rail and steering effort of the wheel contacting to rail at flange and yielding large radial difference. Through the analyses based on the new model, the following outcomes were obtained. (1) Most of derailments are brought as the result of the rocking motion of a vehicle by track excitations underneath. The excitation amplitudes for derailment are influenced by vehicle speed particularly in lower input frequencies. (2) Wheel climb derailment is not observed. We attribute it to the negative attack angle of wheel/rail during wheel/rail flange contact. (3) At the moment just before derailment when wheel is contacting on rail at flange top, the steering effort of wheel-set, which may contribute to avoid or delay derailment, is not observed.

Considerable numbers of earthquake disasters have been experienced in Japan. Thus the study and research of earthquake disaster prevention are highly aware in Japan. In a railway industry, for instance, infrastructures have been reinforced, and a new alert system. has been employed to regulate the operating system to stop trains immediately if a great earthquake occurs. A railway is organized by a variety of individual technologies and functions safely and properly as a system; therefore it is beneficial for the system safety to study and examine the individual potential cases of disasters caused by earth. quakes from various different viewpoints. Recent reports imply that rail vehicles could derail solely by the ground motions of earthquakes without fatal damages of vehicles and tracks. Therefore, in this paper, the vehicle safety in terms of the dynamic stability and the possibility of derailment directly caused by the track excitations of great earthquakes is specifically studied. The rail vehicles are supposed to involve severe vehicle body motions, wheel lifts, and derailing behaviors. In this study, such extreme responses of the vehicles are focused on; thus at the start, a new vehicle dynamics simulation is developed with unique modeling specifically taking account of internal slide forces between the vehicle body and the bogie resulting from large motions of vehicles. Then, the simulation. is employed to assess the safety, of vehicles on excited. tracks with sinusoidal displacement and the numerical results are analyzed. Through the assessment and the analyses, four major outcomes are obtained. First, the limit excitation amplitudes for the wheel lift of flange height, defined as safety limits in this paper, are presented in the frequency range of 0.5-2.5 Hz. Second, two types of critical vehicle motions art, captured; one is a rocking motion involving large wheel lift observed in lower frequency excitations and the other is a severe horizontal impact of a wheel to a rail observed in higher frequency excitations. In the latter cases, the vehicles derail with slightly larger excitations than those of the wheel lift of flange height. Third, the roll characteristic of a vehicle body is demonstrated as a dominant factor for the vehicle dynamic motions in terms of large wheel lift and derailment. Finally,, the unique modeling in the developed simulation is evaluated, and its advantages for precise prediction of the extreme vehicle responses are confirmed. [DOI: 10.1115/1.300790]

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 unsafe case caused by earthquakes. Recent reports imply that railway vehicles could be derailed by earthquake ground motions without fatal damages of vehicles or tracks. Thus, we should further study the derailment mechanism to pursue to minimize the risk of railway system safety against large earthquakes. Particularly, for more comprehensive understanding on the derailment mechanism of high speed railway vehicle, the derailment process should be experimentally studied. Therefore, in this study, we 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 experiment, we obtained the outcomes. (1) Two types of vehicle derailment motions are observed one is rocking derailment and the other is sliding derailment. Derailment motions are similar regardless of vehicle speed. ( 2 ) By contrast, the excitation amplitudes for derailment decrease according to the increase of vehicle speed particularly by low frequency excitations. ( 3 ) The excitation amplitudes for wheel lift of flange height are relatively independent of vehicle speed. (4) Based on the similarly of fundamental vehicle dynamics between the 1/10 scale vehicle and full scale vehicle, those observed mechanisms should be applicable to full scale vehicle.

The decrease of wheel load variation is one of the most important issues which must be solved in railway dynamics. The purpose of this study is to make clear the mechanism of wheel load variation by the numerical simulation by the analytical model which is based on the concept of the multibody dynamics. In this study, we were able to figure out the in-depth mechanism of the wheel load variation, particularly, concerning the phenomenon that the wheel load variation suddenly decreases with more than wheel velocity at which the 1st natural frequency of system consists with the irregularity passing frequency.

Considerable numbers of earthquake disasters have been experienced in Japan. Thus the study and research of earthquake disaster prevention are highly awarded in Japan. In a railway industry, for instance, infrastructures have been reinforced and a new alert system has been employed to regulate the operating system to stop trains immediately if a great earthquake occurs. A railway is organized by a variety of individual technologies, and functions safely and properly as a system, therefore it is beneficial for the system safety to study and examine the individual potential cases of disasters caused by earthquakes from various different viewpoints. Recent reports imply that rail vehicles could derail solely by the ground motions of earthquakes without fatal damages of vehicles and tracks. Therefore, in this paper, the vehicle safety in terms of the dynamic stability and the possibility of derailment directly caused by the track excitations of great earthquakes, is specifically studied. The rail vehicles are supposed to involve severe vehicle body motions, wheel lifts and derailing behaviors. In this study, such extreme responses of the vehicles is focused on, thus at the start, a new vehicle dynamics simulation is developed with unique modeling specifically taking account of internal slide forces between the vehicle body and the bogie resulting from large motions of vehicles. Then, the simulation is employed to assess the safety of vehicles on excited tracks with sinusoidal displacements, and the numerical results are analyzed. Through the assessment and the analyses, four major outcomes are obtained. First, the limit excitation amplitudes for the wheel lift of flange height, defined as safety limits in this paper, are presented in the frequency range of 0.5 to 2.5Hz. Second, two types of critical vehicle motions are captured; one is a rocking motion involving large wheel lift observed in lower frequency excitations and the other is a severe horizontal impact of a wheel to a rail observed in higher frequency excitations. In the latter cases, the vehicles derail with slightly larger excitations than those of the wheel lift of flange height. Third, the roll characteristic of a vehicle body is demonstrated as a dominant factor for the vehicle dynamic motions in terms of large wheel lift and derailment. Finally, the unique modeling in the developed simulation is evaluated and its advantages for precise prediction of the extreme vehicle responses are confirmed.

The decrease of wheel load variation is effective in enhancing stability, safety of high-speed train. In this paper, we conduct the simulation analysis on wheel load variation in order to figure out the mechanism of wheel load variation in consideration of track irregularity such as sine wave and to investigate the influence of the relation between unsprung mass and static wheel load. As a result, we figured out as follows : The wheel load variation at high speed increases according as the wheel speed because the vertical inertia force of wheel increases widely by high-speed running along the flexible rail with irregularity. If sleeper passing frequency and the irregularity passing frequency is close to the primary natural frequency of the wheel/rail system, the wheel load variation becomes larger. The decrease of wheel mass is very effective in decreasing the wheel load variation in comparison with the decrease of static wheel load.