Modelling the impact of tolerances on swept envelope using Monte Carlo analysis

Abstract

Rail Safety and Standards Board commissioned project T670 to investigate the industry's understanding of vehicle tolerances as applied to the gauging process, with the aim of ensuring that the processes used to calculate clearance may enable better use of the capacity of the existing railway infrastructure, and ultimately larger trains.

Modern vehicle construction methods and maintenance regimes provide different tolerances to those traditionally assumed. The research project indicates what they are, their magnitude, their life cycle, credible failure modes, and their effect on gauge. The project does not provide detailed vehicle-by-vehicle parameter lists, but gives a general guideline against which suppliers of new vehicles can indicate differences that may affect the swept envelope of their particular vehicle.

This paper focuses on the application of Monte Carlo analysis techniques in order to combine tolerances and variations, present in the vehicle swept envelope, in a realistic manner. The resultant envelope is compared with a benchmark envelope calculated using conventional methods of aggregating tolerances. The difference between the two may represent unused space which may be released at low risk.