Whole system railway modelling

There has been a general view articulated within the railway industry that there needs to be greater systems thinking and systems engineering applied to major projects within the industry (Network Rail, 2013 and Rail Safety and Standards Board, 2012). However, there are many differing ideas held by practising engineers of exactly what systems engineering is and how it is applied within the industry. There are also barriers within industry in general, management and practising engineers to using systems engineering techniques. They can be seen as an overhead in terms of, training, tooling, effort and costs. Also the benefits to be gained from applying these techniques are not easily seen when they work well. A key pillar of systems engineering and systems thinking is the ability to look at a system as a whole. Part of this is getting to grips with what a system really is, it’s interaction with its operational environment and the world around it and to understand the various subsystems that the system is comprised of and their interaction, including people. This is particularly difficult when it comes to complex systems like railways. This project attempts to develop an approach to modelling a whole railway system (or Guided Transport System (GTS) as it is defined in this project) by implementing a Model Based Systems Engineering (MBSE) approach and techniques. It also proposes definitions of a system and system engineering that are applicable to the Railway industry. Through a common view of a GTS as a whole and a common approach to modelling it, it should be possible to address some of the barriers to systems engineering techniques that currently exist. MBSE has three pillars, a method, a modelling language and a modelling tool (Delligatti, 2014, pp. 4-7). The author has developed a method that can be applied to a whole complex system, such as a GTS, supported by the SysML modelling language implemented through the Enterprise Architect modelling tool (other languages and modelling tools could also be used). The method developed was then tested on a body of students studying for an MSc in Railway Systems Engineering and Integration at the University of Birmingham. This body was chosen because the course is part time and the majority of the students work full time in the industry. Thus the author was able to gain an insight into how diverse the opinions on systems engineering and its application actually are within the industry and get valuable feedback on the systems modelling methodology developed during this research. It has been demonstrated through the development of a partial model of various representative parts of a GTS, that it is possible, within a single model, to capture and represent a large and diverse amount of information about a GTS as it is defined within this thesis. This includes: • its context within the wider world and its operational environment; • its physical structure; • the relationships between its various subsystems and the outside world; • the views of a diverse stakeholder group and their Requirements; and • critical system properties and how these are derived from the various layers of abstraction within the system. The methodology drives the user to develop a model that: 1. is re-usable, e.g. applicable to different railways at different times; 2. is extendable in length (be able to model more railway) and depth (greater levels of detail); 3. allows the inclusion of existing quantitative and qualitative models from other sources; 4. encourages the use of data from existing sources; 5. is open and transparent to allow others to use and add to them; and 6. enables the production of outputs that are readily understandable across disciplinary divides e.g. common representation

System-wide assessment of intervention strategies for railway infrastructure

The existing railway infrastructure exhibits faster degradation rates and requires more maintenance effort as a result of increased utilisation. At the same time, due to increased numbers of freight and commuter trains obtaining access to the railway infrastructure to carry out maintenance and repairs, not to mention major enhancements, is becoming more problematic. Furthermore, safety measures put in place in the event of infrastructure faults or delayed completion of intervention activities will cause greater disruptions to train services in the parts of the network with intense train traffic. Taking a system wide view is, therefore, vital for developing efficient intervention strategies that could deliver the desired infrastructure outputs. In this paper we propose a modelling approach for simulation and analysis of railway track asset management strategies integrating different elements of the whole railway system. The approach uses a Petri net modelling technique to construct the railway system model. The model is built in a hierarchical, modular fashion, meaning that the system can be represented at any level of granularity and complexity, ranging from a single-asset system in a small segment of the network to a complex multi-asset system in a large geographical region. The impact of different asset management strategies on the infrastructure functionality and the operation of train services is assessed using the Monte Carlo simulation technique

Railway infrastructure asset management: the whole-system life cost analysis

Delivering the railway infrastructure whose functionality is sustainable and uncompromised in terms of safety and availability under ever decreasing budget constraints is a great challenge. The successful accomplishment of this task relies on the effective management of individual assets within a wider whole system perspective. This is a highly complex decision-making task where mathematical models are required to enable well-informed choices. In this study, a novel modelling framework is proposed for performing the whole system lifecycle cost analysis. The framework is based on two models: railway network performance and costs. Using the former model investigations of the effects of decisions can be carried out for the individual asset and the whole system. A Petri net modelling technique is used to construct the model. A form of Monte Carlo simulation is then used to obtain model results. The infrastructure performance model is then integrated with the cost model to perform the lifecycle cost analysis. A superstructure example is presented to demonstrate the application of the approach. The results show that taking into account interdependencies among the intervention activities greatly influences, not only the performance of the infrastructure, but also its lifecycle costs and thus should be included in the cost analysis

Modelling asset management of railway overhead line equipment

The overhead line equipment (OLE) is a critical sub-system of the 25kV AC overhead railway electrification system. There is a need to evaluate OLE asset management strategies through a whole life cost analysis that considers degradation processes and maintenance activities of the OLE components so that the investment required to deliver the level of performance desired by railway customers and regulators can be based on evidence from modelling results. A Petri Net model is proposed to simulate the degradation, failure, inspection and maintenance of the main OLE components and to calculate various statistics associated with the cost and reliability of the system over its whole life. The Petri Net considers all the main OLE components in one model and can simulate both fixed interval and risk based maintenance regimes. To allow such processes to be modelled accurately and efficiently, High Level Petri Net features are used. The model developed is the first of its kind, in such detail, for OLE and the applicability of Petri Nets for modelling many processes on a large system, containing numerous components, is shown

A holistic approach to railway infrastructure asset management

In the railway industry asset management decisions are focused on the maintenance, enhancement and renewal of assets in order to ensure a required level of dependability and improvement in services at the lowest whole life costs. To achieve these objectives system lifecycle models, rather than individual asset models,= offer a greater advantage. The paper presents a modelling approach developed for constructing multi asset system models to support well-informed railway infrastructure asset management decisions. The models are built using the Petri Net formalism and are analysed by a means of Monte Carlo simulations. A specific example of the railway superstructure model is presented. Its simulation results demonstrate the superiority of the system-wide model against individual asset models in terms of its accuracy in predicting the superstructure (system) performance and information available to support asset management decisions. Furthermore, by using the multi-asset system model interdependencies among maintenance regimes of different assets and different parts of the infrastructure can be modelled

Probabilistic simulation for the certification of railway vehicles

The present dynamic certification process that is based on experiments has been essentially built on the basis of experience. The introduction of simulation techniques into this process would be of great interest. However, an accurate simulation of complex, nonlinear systems is a difficult task, in particular when rare events (for example, unstable behaviour) are considered. After analysing the system and the currently utilized procedure, this paper proposes a method to achieve, in some particular cases, a simulation-based certification. It focuses on the need for precise and representative excitations (running conditions) and on their variable nature. A probabilistic approach is therefore proposed and illustrated using an example. First, this paper presents a short description of the vehicle / track system and of the experimental procedure. The proposed simulation process is then described. The requirement to analyse a set of running conditions that is at least as large as the one tested experimentally is explained. In the third section, a sensitivity analysis to determine the most influential parameters of the system is reported. Finally, the proposed method is summarized and an application is presented

Development of a whole life cycle cost model for electrification options on the UK rail system

Projects to deliver Overhead Line Equipment (OLE) electrification on the UK rail infrastructure system presents technical challenges which the rail industry in Britain have not traditionally had to consider. Whole Life Cycle assessment provides decision makers with cost estimates for the installation phase and over the entire service life of the system, including disposal. The OLE projects face a particular problem when analysing the best option for overbridges. Much of the rail infrastructure has not traditionally had to consider overhead clearances and therefore many of the bridges are only a little taller than the rolling stock. In addition to the difficulties in assessing the Life-Cycle costs of assets that have historically been used in very limited scales, the Whole Life Cycle assessment must consider the various engineering options that are available for projects. The three competing options (bridge rebuild, track lowering, reduced clearance) are all going to have very different capital expenditure (CAPEX) and operating expenditure (OPEX) costs. This work presents a model created to predict these costs over the anticipated assessment period. The developed model predicts capital expenditures, maintenance and service disruption costs and links them to the three major assets options involved in OLE underbridges

Integrating Dynamics and Wear Modelling to Predict Railway Wheel Profile Evolution

The aim of the work described was to predict wheel profile evolution by integrating multi-body dynamics simulations of a wheelset with a wear model. The wear modelling approach is based on a wear index commonly used in rail wear predictions. This assumes wear is proportional to Tγ, where T is tractive force and γ is slip at the wheel/rail interface. Twin disc testing of rail and wheel materials was carried out to generate wear coefficients for use in the model. The modelling code is interfaced with ADAMS/Rail, which produces multi-body dynamics simulations of a railway wheelset and contact conditions at the wheel/rail interface. Simplified theory of rolling contact is used to discretise the contact patches produced by ADAMS/Rail and calculate traction and slip within each. The wear model combines the simplified theory of rolling contact, ADAMS/Rail output and the wear coefficients to predict the wear and hence the change of wheel profile for given track layouts

Complex delay dynamics on railway networks: from universal laws to realistic modelling

Railways are a key infrastructure for any modern country. The reliability and resilience of this peculiar transportation system may be challenged by different shocks such as disruptions, strikes and adverse weather conditions. These events compromise the correct functioning of the system and trigger the spreading of delays into the railway network on a daily basis. Despite their importance, a general theoretical understanding of the underlying causes of these disruptions is still lacking. In this work, we analyse the Italian and German railway networks by leveraging on the train schedules and actual delay data retrieved during the year 2015. We use {these} data to infer simple statistical laws ruling the emergence of localized delays in different areas of the network and we model the spreading of these delays throughout the network by exploiting a framework inspired by epidemic spreading models. Our model offers a fast and easy tool for the preliminary assessment of the {effectiveness of} traffic handling policies, and of the railway {network} criticalities.Comment: 32 pages (with appendix), 28 Figures (with appendix), 2 Table