S L Grassie

Bio: S L Grassie is an academic researcher from Imperial College London. The author has contributed to research in topics: Track (rail transport). The author has an hindex of 1, co-authored 1 publications receiving 568 citations.

Modelling of Railway Track and Vehicle/Track Interaction at High Frequencies

Abstract: A review is presented of dynamic modelling of railway track and of the interaction of vehicle and track at frequencies which are sufficiently high for the track's dynamic behaviour to be significant. Since noise is one of the most important consequences of wheel/rail interaction at high frequencies, the maximum frequency of interest is about 5kHz: the limit of human hearing. The topic is reviewed both historically and in particular with reference to the application of modelling to the solution of practical problems. Good models of the rail, the sleeper and the wheelset are now available for the whole frequency range of interest. However, it is at present impossible to predict either the dynamic behaviour of the railpad and ballast or their long term behaviour. This is regarded as the most promising area for future research.

Fundamentals of vehicle–track coupled dynamics

Abstract: This paper presents a framework to investigate the dynamics of overall vehicle-track systems with emphasis on theoretical modelling, numerical simulation and experimental validation. A three-dimensional vehicle-track coupled dynamics model is developed in which a typical railway passenger vehicle is modelled as a 35-degree-of-freedom multi-body system. A traditional ballasted track is modelled as two parallel continuous beams supported by a discrete-elastic foundation of three layers with sleepers and ballasts included. The non-ballasted slab track is modelled as two parallel continuous beams supported by a series of elastic rectangle plates on a viscoelastic foundation. The vehicle subsystem and the track subsystem are coupled through a wheel-rail spatial coupling model that considers rail vibrations in vertical, lateral and torsional directions. Random track irregularities expressed by track spectra are considered as system excitations by means of a time-frequency transformation technique. A fast explicit integration method is applied to solve the large nonlinear equations of motion of the system in the time domain. A computer program named TTISIM is developed to predict the vertical and lateral dynamic responses of the vehicle-track coupled system. The theoretical model is validated by full-scale field experiments, including the speed-up test on the Beijing-Qinhuangdao line and the high-speed running test on the Qinhuangdao-Shenyang line. Differences in the dynamic responses analysed by the vehicle-track coupled dynamics and by the classical vehicle dynamics are ascertained in the case of vehicles passing through curved tracks.

A review of loading conditions for railway track structures due to train and track vertical interaction

Abstract: Train and track interactions during services normally generate substantial forces on railway tracks. Such forces are transient by nature and of relatively large magnitude and are referred to as impact loading. There has been no comprehensive review of the typical characteristics of the loading conditions for railway track structures, in particular, impact loads due to the wheel/rail interaction, published in the literature. This paper presents a review of basic design concepts for railway tracks, abnormalities on tracks, and a variety of typical dynamic impact loadings imparted by wheel/rail interaction and irregularities. The characteristics of typical impact loads due to wheel and rail irregularities, e.g. rail corrugation, wheel flats and shells, worn wheel and rail profiles, bad welds or joints, and track imperfections, are presented with particular emphasis on the typical shapes of the impact load waveforms generally found on railway tracks. Copyright © 2007 John Wiley & Sons, Ltd.