ADHERE Webinar 3: Train Braking and Low Adhesion Modelling
The work presented in this session fits within the ‘Fundamental Science and Modelling’ workstream of the ADHERE programme. The purpose of this workstream is to enhance industry’s knowledge and ability to model low adhesion contaminants and braking. The session covered three modelling tools that:
- Help the industry understand how rail gets contaminated and what the consequences are – LILAC
- Help the industry understand what the impact on braking is – LABRADOR
- Enable product validation and assure product quality – WSPER.
As Luisa Moisio, R&D Programme Director put it ‘understanding the interactions that occur in the contact patch—the small space where the wheel meets the rail—and being able to model these processes accurately, forms an invaluable contribution to the industry’s armoury to improve the reliability of services’.
A key benefit that RSSB’s R&D programme strives to deliver to industry is new insights but also (with the contribution of the Adhesion Research Group), the coordination of research activities. Specifically, in the area of low-adhesion to ensure that industry is aware of the tools and solutions that are at its disposal.
Overview of the facilities and capabilities available in the area of adhesion modelling. These can range from fundamental research using laboratory based testing (such as the HAROLD bogie test rig at the University of Huddersfield), to modelling simulation tools like WILAC and LABRADOR, to hardware in the loop testing facilities such as WSPER.
The LILAC model
LILAC (T1149) has been developed by the University of Sheffield, in collaboration with RSSB, the University of Huddersfield and Virtual Vehicle. The model is used to predict friction in the wheel rail interface where a leaf layer is present.
Layers of leaves, together with wet rail interfaces—also known as ‘wet-rail phenomenon’ caused by oxide and a small amount of water—are two of the key causes of low-adhesion. The WILAC model (T1077) looked at the effect a small amount of water has in the wheel/rail interface.
The LILAC model (T1149) is an evolution of WILAC as it incorporates the impact of leaf layers in the interface. The LILAC tool can be used in a variety of applications including:
- Incorporating into the LABRADOR train braking model to simulate braking in leaf layer conditions
- Feeding it into multi-body dynamics models to study full train behaviour in leaf layer conditions
The LABRADOR model
The Low Adhesion BRAking Dynamic Optimisation for Rolling stock (LABRADOR) model is a software that models the braking of passenger trains in low adhesion conditions.
LABRADOR allows specific brake control features such as WSP strategies, sanding effectiveness, dynamic brake utilisation and traction performance to be studied with a good degree of reliability. Due to its modular structure, LABRADOR is easily adaptable to various types of rolling stock as it can represents a variety of components. The aim of this model is to support industry’s efforts to provide reliable braking in low adhesion conditions.
The model sits between ‘fundamental research’ and ‘optimisation’. It can model the wheel/rail contact in low adhesion and the benefits of improved brake blending strategies. For fleet engineering, the model can be used to evaluate proposed brake system changes and determine how effective they might be to optimise low adhesion performance. The model can also look at operational issues such as the effect of driving style and policy on braking performance, but also for incident reconstruction and analysis.
The Wheel Slide Protection Evaluation Rig (WSPER) is a hardware in the loop simulation facility. This means the hardware in the loop is the customer’s wheel slide equipment or, more commonly, the brake control unit which incorporates the Wheel Slide Protection (WSP) functionality. Using a combination of computer models and hardware, WSPER can be used to model the vehicle aspects of the simulation.
Developed by British Rail in 1989 following the poor experience of UIC’s specified WSP. Since then the model has developed and introduced new features and functionalities, reflecting changing industry needs. It is primarily used to minimise occurrence of wheel flats however the emphasis has moved towards safety and braking distance performance.
DB ESG uses WSPER to undertake two types of testing:
- Standard tests—where there is a prescribed test specification e.g. EN, UK mainline Standards
- Non-standard testing—usually applied to support Automatic Train Operation performance assessments, incident investigation, product development cycle for suppliers)
All of the models presented provide the industry with the opportunity to test and trial equipment, strategies and ideas in a cost effective and reliable way before they reach full scale testing. The session highlighted various synergies between the models and the opportunities of using them for better analysis and validation. By understanding how these tools work and where they fit within the landscape potential end users can identify opportunities for future development, and ultimately improve industry performance.
Watch the video below of the recorded webinar and download the presentations from the day.
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