FEATURE
MALCOM DOBELL
LO AD W HE SIO N
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MODELLING
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ome aspects of railways are still not completely understood, nearly 200 years after the railways were first developed. Indeed, your writer generally sees many research papers every year seeking to further advance knowledge about what is exactly happening in the tiny, one square centimetre contact patch between the wheel and rail.
The contact patch is a key reason why rail is so successful, in the form of low rolling resistance, and is also a cause of many of its challenges, such as rolling contact fatigue and, the subject of this article, adhesion issues. If there is not a complete understanding of the steel to steel contact patch, imagine the extra complication when contamination is added to the interface, be it to the rail head or the wheel or both. Great Britain has led the way in understanding how the contact patch works in terms of vehicle dynamics and for traction and braking. Understanding how friction works is vital. RSSB hosts a wide range of industry stakeholder groups including the Adhesion Research Group, which has sponsored excellent work to develop strategies, tactics, and techniques to improve the certainty that a train can stop on demand. Rail Engineer has reported on many of the ARG/ RSSB activities, particularly the development and testing of double variable-rate sanders. Other work has included the development of models to predict behaviour in low adhesion conditions at both wheel-rail contact and at train level. Low adhesion and how it affects the railway are, together, a complex problem, with simulation models and laboratory testing providing scientific understanding of complex issues confronting the operational railway.
Rail Engineer | Issue 186 | September/October 2020
Given the complexity of these issues, different models are needed to fully explore and understand the factors involved, how they contribute to low adhesion and, ultimately, how we can develop better treatment and management techniques. A recent Adhere webinar focussed on three simulation and modelling tools for braking under low adhesion conditions. This article covers the University of Huddersfield’s work on LABRADOR and Sheffield University and Virtual Vehicle on LILAC. A presentation about DB ESG’s Wheel Slide Protection Evaluation Rig (WSPER) was also included in the Webinar, but WSPER has been covered in Rail Engineer before (issue 176, July 2019) and is not repeated here.
LILAC No model is any use unless it replicates what happens in real life. Gaining the knowledge to create the model and then to validate it is often the hardest part. Roger Lewis from the University of Sheffield described the research carried out for RSSB (Project T1149) to understand in detail the impact of the leaf layer and to provide input to the Huddersfield’s LABRADOR low-adhesion braking model as a module called LILAC (Leaf
