Seigo OGATA’s research while affiliated with AAA Foundation for Traffic Safety and other places

Railway tracks must be managed appropriately because their conditions significantly affect railway safety. Safety is ensured through inspections by track maintenance staff and maintenance based on measurements using dedicated track geometry cars. However, maintaining regional railway tracks using conventional methods is becoming difficult because of their poor financial condition and lack of manpower. Therefore, a track condition diagnostic system is developed, wherein onboard sensing devices are installed on in-service vehicles, and the vibration acceleration of the car body is measured to monitor the condition of the track. In this study, we conduct long-term measurements using the system and evaluate changes in the track conditions over time using car-body vibration data. Filed test results showed that sections with degraded tracks were identified using car-body vibration data. The track degradation trend can be constructed using the results obtained. Furthermore, this study demonstrated that the track maintenance effect could be confirmed. A method for improving train position using the yaw angular velocity is proposed. The track irregularity position can be shown more clearly by monitoring the track condition using position-corrected data using the proposed method. It is also shown that the time-frequency analysis of measured car-body vertical acceleration is effective for evaluating the track condition more clearly.

When railway vehicles run on sharp curves, the coefficient of friction (COF) between the outer rail and the leading-outside wheel flange of a bogie is an important value related to problems such as wheel/rail severe wear, squeak noise arising from wheel/rail contact, and running safety against flange-climb derailment. In general, it is difficult to grasp the actual state of COF, which changes from moment to moment during commercial operations. From the viewpoint of running safety and maintenance, it is desirable to detect curved tracks with relatively high COF from the entire service line. The monitoring bogie, which can measure wheel/rail contact forces during commercial operations, has realized a long-term observation of wheel/rail contact forces. For further applications of the monitoring bogie, the simulation-based estimation method of COF at the wheel flange have been proposed in the author’s previous paper. Furthermore, an investigation based on roller-rig tests have been conducted. However, the probability of the flange wear progress cannot be determined only by COF at the wheel flange, and other factors should be involved. The wear number is used to assess rolling contact fatigue and wheel/rail wear progress. In the present paper, on the basis of a multi-body dynamics simulation model of the roller-rig equipment, the difference of the wear number among four lubrication conditions on the bogie is clarified. The estimation method of COF is extended to estimate the wear number simultaneously. The extended method is applied to the roller-rig test and the wear number is estimated. The estimated wear number shows qualitative agreement with the amount of wear debris, which is observed in the roller-rig test conducted in previous research.

Monitoring the condition of railway tracks effectively increases the safety of regional railways. A system that uses a compact on-board sensing device was previously developed for monitoring the track condition of regional railways. However, this system does not consider the running speed of the vehicle. In this study, we propose two new methods for diagnosing the condition of tracks considering the travelling speed of the vehicle: one based on the Mahalanobis distance and the other that uses Gaussian process regression. After conducting a test study to verify the effectiveness of the proposed methods, the results showed that both approaches can provide an accurate diagnosis when considering the influence of speed.

Currently, the maintenance of railway tracks is carried out based on track irregularity measurement data. The vibration data of running vehicles are easy to measure and can be the base of track maintenance, but they have not been used by basic data of track maintenance because of the shortage of repeatability. However, there are an increasing number of cases where small portable information terminals are used as simple and inexpensive vehicle vibration measuring devices. Therefore, the authors tried to construct the method for track management based on vehicle vibration data measured by permanently installed small terminals on in-service trains with high frequency. Data accumulation of vehicle vibration of in-service trains have been carried out for more than one year in a regional railway line. After the analysis of collected vibration data, the authors successfully conclude the possibility of the “vehicle-vibration-based track maintenance”. In this paper, the authors propose the method to obtain accurate positioning data of the trains from GPS speed data. The relationship between car-body vertical acceleration and track irregularity showed the possibility of track maintenance based on car-body vibration.

Monitoring the condition of railway tracks effectively increases the safety of railways. A system that uses a compact on-board sensing device was previously developed for monitoring the track condition of railways. The system's position identification method uses GPS map-matching.However, this system had an error of several tens of meters depending on GPS reception conditions. In this study, the position correction method was tested using curvature calculated from yaw angular acceleration. The results of the test study indicated that it is possible to diagnose the location of track irregularities more clearly.

Oscillation of ropeway carrier is caused by wind, track rope vibration, and vibration when the carrier passes through columns. Large roll angle of the carrier results in collision with the columns and others. In this paper, a simulation is performed to grasp the influence of the track rope vibration on the rolling motion of the carrier. The carrier is modeled as a single pendulum. The track rope vibration is controlled laterally to consider a freedom of the rope sags. The situation assumed in the simulation is that the track rope and the carrier initially have a constant displacement due to wind. After the wind stops blowing, the carrier begins to move freely. On the other hand, the vibration of track rope is restrained, because the rope sag decreases as the carrier runs towards the column. The paper shows effects of amplitude and period of the track rope vibration on the roll angle of the carrier when the carrier passes thorough the column.

The coefficient of friction (COF) between the outer rail and the leading-outside wheel flange of a railway bogie running on sharp curved track is an important parameter for the progress of wheel/rail wear and running safety. Therefore, it is desired to grasp the actual state of COF of wheels especially at the leading-outside wheel flange. In the author’s previous studies, a roller-rig experiment was conducted with changing lubrication condition of each wheel of the bogie to figure out relationship between lubrication conditions and wheel/rail contact forces such as tangential, lateral and vertical directions. In this paper, a method to estimate the value of COF of leading-outside wheel with look-up tables built by repetitive numerical simulations is explained. In the construction of the look-up tables, friction coefficients for each wheel in the numerical simulation model are changed while collecting calculated wheel/rail contact forces. A railway bogie running on roller-rig test is considered for both numerical simulations and experiment with different lubrication condition, therefore look-up tables are built with a half-vehicle model running on the roller-rig. By inputting the wheel/rail contact forces measured in roller-rig test into the look-up tables built by simulations, and the COF of leading-outside wheel flange is estimated. The result shows that the lubrication condition of leading-outside wheel flange can be estimated by the proposed method especially when the value of COF is large and is useful for the detection of high COF condition.

Oscillation of ropeway carrier is caused by wind, track rope vibration, and vibration when the carrier passes through column. In a certain ropeway installation, a carrier without lateral sway damping device significantly rolled after passing through column, and consequently collided with the wayside wall. In this paper, measurement of rope sag and motion of the carrier is conducted to investigate the phenomenon. The measurement result shows that roll angle of the carrier under loaded condition tends to grow when the carrier runs toward column even if effect from crosswind is small. It is estimated that transition of the rope sag affects the roll motion of the carrier. This paper also shows dynamics simulation to grasp the influence of freedom of track rope on the rolling motion of the carrier. In the simulation, the carrier is modeled as a single pendulum. Time variation of rope sag is expressed as a change of length of pendulum or lateral vibration of fulcrum of pendulum. Transition of roll vibration period and growth of roll angle are discussed.