A review of simulation models for railway systems

Abstract

With the advances in computer hardware and software
development techniques in the past 25 years, digital
computer simulation of train movement and traction
systems has been widely adopted as a standard
computer-aided engineering tool [1] during the design
and development stages of existing and new railway
systems. Simulators of different approaches and scales
are used extensively to investigate various kinds of
system studies. Simulation is now proven to be the
cheapest means to carry out performance predication
and system behaviour characterisation.
When computers were first used to study railway
systems, they were mainly employed to perform
repetitive but time-consuming computational tasks, such
as matrix manipulations for power network solution and
exhaustive searches for optimal braking trajectories.
With only simple high-level programming languages
available at the time, full advantage of the computing
hardware could not be taken. Hence, structured
simulations of the whole railway system were not very
common. Most applications focused on isolated parts of
the railway system. It is more appropriate to regard
those applications as primarily mechanised calculations
rather than simulations.
However, a railway system consists of a number of
subsystems, such as train movement, power supply and
traction drives, which inevitably contains many
complexities and diversities. These subsystems interact
frequently with each other while the trains are moving;
and they have their special features in different railway
systems. To further complicate the simulation
requirements, constraints like track geometry, speed
restrictions and friction have to be considered, not to
mention possible non-linearities and uncertainties in the
system.
In order to provide a comprehensive and accurate
account of system behaviour through simulation, a large
amount of data has to be organised systematically to
ensure easy access and efficient representation; the
interactions and relationships among the subsystems
should be defined explicitly. These requirements call
for sophisticated and effective simulation models for
each component of the system. The software
development techniques available nowadays allow the
evolution of such simulation models. Not only can the
applicability of the simulators be largely enhanced by advanced software design, maintainability and
modularity for easy understanding and further
development, and portability for various hardware
platforms are also encouraged.
The objective of this paper is to review the development
of a number of approaches to simulation models.
Attention is, in particular, given to models for train
movement, power supply systems and traction drives.
These models have been successfully used to enable
various ‘what-if’ issues to be resolved effectively in a
wide range of applications, such as speed profiles,
energy consumption, run times etc.