CONTINUOUS investment in research and development (R&D) is vital in order for railways to maintain a competitive advantage over other modes. The Railway Technical Research Institute (RTRI) has a long history as an integrated railway technology research institute and has conducted extensive R&D ranging from basic to applied railway technologies since its foundation.
We have successfully implemented 10 inter-disciplinary projects every five years since 2000 under the R&D for the Future of Railways programme. We set four R&D goals for the five years starting in 2010:
- increasing safety
- improving harmony with the environment
- reducing costs, and
- improving convenience.
To achieve these goals, our R&D projects comprised four comprehensive research themes:
- improving the safety and reliability of railway systems
- highly-efficient use of energy
- revolutionary maintenance, and
- expanding and maintaining railway networks.
We also focused on creating railway simulators as an additional research tool to act as a common foundation on which to develop advanced simulation technologies for railways. Simulation technology helps to clarify phenomena whose observation or reproduction by conventional methods is difficult while helping to make R&D processes more efficient. Together with theoretical analyses and experiments, we regard simulation technologies as one of the pillars of R&D, and simulation-based R&D is one of our most important challenges.
In the past, RTRI has developed simulators in a variety of areas such as rolling stock, railway structures, electric power supply, and railway operation, and used them for various R&D projects. Many of these simulators were built using traditional methodology that simplifies complex phenomena significantly and adopts minimum physical models. However, advances in high-performance computing in recent years have been accompanied by the creation of an environment in which it is possible to practically apply simulations that directly reproduce complex phenomena on a computer by minimising approximations or assumptions for simplification in modelling, such as multi-scale multi-physics simulations.
In 2010, RTRI started to develop groups of simulators that could provide a comprehensive understanding of the underlying operating environment. Each simulator is capable of reproducing complex, and often large-scale phenomena that are difficult to reproduce and observe experimentally using a single simulator or through on-track testing. The railway simulator operating environment utilises coupled calculation to link multiple simulators in order to achieve this comprehensive analysis. Development of this concept is already underway, and a number of individual simulators have been produced.
In addition, following several larger than anticipated earthquakes in recent years, a seismic hazard simulator was developed as a powerful tool to provide a virtual training environment to prepare for large-scale earthquakes, perform prior investigations of various damage scenarios to railway structures, and evaluate the risk inherent in each scenario.
This simulator consists of three separate units: the earthquake motion simulator that calculates the propagation of seismic motion in deep subsurface, including that in the hypo-central region; a simulator that calculates the behaviour of the surface ground, including the foundations of structures; and a simulator that calculates the dynamic behaviour of railway structures during earthquakes.
The analysis models used for the calculations are provided automatically on the basis of data stored in three information archives covering deep subsurface, surface ground, and structure.
To validate this enhanced simulator, it was used to assess damage to railway structures caused by large earthquakes in comparison with the damage which actually occurred. The simulator predicted that damage requiring repair would occur at 18 out of a total of 69 railway structures (26%) in the region, while in reality, damage requiring repair occurred at only 10 structures (14%). This confirmed that this simulator can evaluate structural damage caused by earthquakes with practical precision and with caution.
With trains travelling faster than ever before, addressing aerodynamic problems is becoming increasingly important. Therefore, we developed the airflow simulator/aeroacoustic sound simulator as a tool to clarify the aerodynamic phenomena mechanism.
This simulator consists of two sub-simulators: one for airflow and the other aeroacoustic sound. The former is based on the Cartesian grid method, which can automatically generate a calculation grid from 3D CAD data to achieve a large reduction in the time required for grid generation. Figure 4 shows an example of the computational result of a flow field around a pantograph. Riken's K-computer was used for the calculation, whereby the vortex induced around the pantograph head was successfully computed on a scale of less than 1mm.
The aeroacoustic sound simulator calculates aeroacoustic sound in a field far from the results of flow field calculation using Howe's theory of vortex sound. This enables quantitative evaluation of spatial structures of the aeroacoustic sound-source distribution near a structure, providing useful information by clarifying aeroacoustic sound generation mechanisms. The simulator can evaluate aeroacoustic sound generated by a column with an error of about 3dB based on wind tunnel test results.
We are building the virtual railway test track simulator group to reproduce dynamic behaviour of railway systems during train operation under a variety of conditions in order to perform virtual running tests. We have developed four prototypes covering: vehicle dynamics, the pantograph/catenary, wheel/rail rolling contact, and ballasted track. Figure 1 shows examples of computational results from the latter two.
As its name implies, the wheel/rail rolling contact simulator will simulate the dynamic rolling contact behaviour between wheels and rails, which is difficult to clarify experimentally or by using trains in service. It was developed through joint research with Professor Okuda of Tokyo University. This simulator can accurately analyse contact behaviour up to a high frequency, which are unobtainable by contact models such as that based on Kalker's creep theory which is widely used at present. This simulator is also useful for evaluating sharp wheel load variations occurring at rail joints.
The ballasted track simulator was developed through joint research with the Japan Agency for Marine-Earth Science and Technology to simulate the motion of a large number of crushed stones with several sleepers, including their elastic deformation. Figure 2 shows an example of simulation of the initial settlement behaviour of a section of ballasted track immediately after compaction. As this shows, the simulator can analyse detailed dynamic behaviour of a section of ballasted track as a train travels over it, and it will be used to clarify the ballast settlement mechanism and verify the effectiveness of countermeasures.
Coupled computation of these two simulators has permitted numerical simulation of dynamic behaviour of wheels, rails, sleepers, and ballast during the passage of a train up to the high-frequency region. Several points regarding long-term deterioration phenomena pertaining to wheels, rails, and tracks still remain unclear, but the use of this simulator is expected to eventually resolve such problems.
RTRI intends to complete the development of railway simulators by the end of FY2019, and the railway simulator is expected to become a powerful tool for developing revolutionary concepts to advance railway R&D.