Terumichi Yoshiaki

<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 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.

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 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.

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.

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.

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.

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.