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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 98
PROCEEDINGS OF THE FIRST INTERNATIONAL CONFERENCE ON RAILWAY TECHNOLOGY: RESEARCH, DEVELOPMENT AND MAINTENANCE
Edited by: J. Pombo
Paper 23

Locomotive Cab Whole-Body Vibration Assessments and Methods to Identify Seat-Motion Artifacts

A.M. DiFiore1, A.K. Zaouk1, N.J. Mansfield2, S.K. Durrani1 and S.K. Punwani3

1QinetiQ North America, Waltham MA, United States of America
2Loughborough University, Leicestershire, United Kingdom
3Federal Railroad Administration, Washington D.C., United States of America

Full Bibliographic Reference for this paper
A.M. DiFiore, A.K. Zaouk, N.J. Mansfield, S.K. Durrani, S.K. Punwani, "Locomotive Cab Whole-Body Vibration Assessments and Methods to Identify Seat-Motion Artifacts", in J. Pombo, (Editor), "Proceedings of the First International Conference on Railway Technology: Research, Development and Maintenance", Civil-Comp Press, Stirlingshire, UK, Paper 23, 2012. doi:10.4203/ccp.98.23
Keywords: whole-body vibration, engineer, locomotive, freight, seat-motion artefact, U.S. Federal Railroad Administration.

Summary
Locomotives produce vibrations and mechanical shocks from irregularities in the track, structural dynamics, the engines, the trucks, and train slack movement [1]. The different directions of the irregularities give rise to car-body vibrations in multiple axes including the following:
  • Longitudinal, or along the length of the train
  • Lateral, or the side-to-side direction of the train
  • Vertical

The structural dynamics of rail vehicles usually give rise to several resonances in the 0.5 to 20Hz frequency range [2]. Resonances are frequencies in the locomotive that cause larger amplitude oscillations. At these frequencies, even small-amplitude input can be amplified to produce large oscillations. Further exacerbating the vibration environment, coupling of the axes of movement occurs: motions in one direction contribute to or cause motion in a different direction.

The magnitude of vertical vibration in rail vehicles is reportedly well below many other types of vehicles [3,4,5]. However, there is a lack of vibration data from long-haul freight operations to adequately characterize the vibration environment of locomotive cabs. In this paper, the results of a series of long-haul whole-body (WBV) studies sponsored by the U.S. Federal Railroad Administration (FRA) are described. The results represent over 140 hours of recordings collected over more than 2800 miles of track.

For studies of whole body vibration (WBV), it is imperative to separate actual shock and vibration data from seat-motion artefacts (SMAs) that arise from operator movement. It has been suggested that seat-cushion-mounted devices may affect the validity of seat-pad measurements, because slight motion of the engineer could cause acceleration artefacts that are potentially greater than those caused by train motion [6]. Manually removing SMAs is a time-consuming process that drives up the cost of WBV assessments. Several methods have been proposed to identify SMAs automatically. This paper reports on a preliminary comparison of these methods with manual SMA identification to validate the automated methods as well as identify the most accurate automated method. Additionally, the authors report how statistical analysis can aid in determining the validity of automated SMA-removal methods.

References
1
N.J. Mansfield, "Human response to vibration", CRC Press, 2005.
2
E. Andersson, M. Berg, S. Stichel, "Rail vehicle dynamics", KTH Railway Technology, 2005.
3
H. Dupuis, G. Zerlett, "The effects of whole-body vibration", Springer-Verlag, 1986.
4
M.J. Griffin, "Handbook of Human Vibration", Academic Press, 1990. doi:10.1121/1.401606
5
E. Johanning, "Back disorder intervention strategies for mass transit operators exposed to whole-body vibration-comparison of two transit system approaches and practices", Journal of Sound and Vibration, 215(4), 629-634, 1998. doi:10.1006/jsvi.1998.1651
6
N.K. Cooperrider, J.J. Gordon, "Shock and impact levels on North American locomotives", Journal of Sound and Vibration, 318(4-5), 809-819, 2008. doi:10.1016/j.jsv.2008.04.042

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