Analysis of a very low tare mass wagon concept for intermodal freight
thesisposted on 29.10.2020, 00:00 by Shah Nafis AhmadShah Nafis Ahmad
The empty weight or tare load of railway freight wagons is significant compared to the gross load (13-43% of the gross load) which not only reduces the possibility of carrying a higher payload but also increases the energy consumption per payload tonne hauled. One way to reduce the energy consumption per tonne payload is to reduce the tare load. One possibility of lowering the tare load is to reduce the number of components such as a bolster, sideframes, and axles. A two-axle wagon compared to a bogied wagon creates a possibility to reduce tare by up to 4-5t on a two-axle configuration. The fewer components on a two-axle wagon, however, result in inferior dynamic performance such as low critical hunting speed, poor curving ability, greater vehicle response to short irregularities etc, so, in spite of having low tare, the two-axle wagons are not as popular as the bogied wagons. To take advantage of the lower tare mass of a two-axle wagon, a new concept wagon was conceptualised as a wagon with maximum axle load (~41 tonnes) and with enough load space to ensure a 80 tonne gross mass. The developed concept resulted in a wagon with a deck length of ~19.8m that allows carrying three 20’, or a 20’ and a 40’, or a 65’ container. The axle spacing (13.8m), overhang length (3m), tare mass (8t) and gross mass (80t) of the developed concept wagon is considerably different to the normal two-axle wagon. The challenge then was to design a suspension that would pass dynamics and roadworthiness tests. It was reasoned that as the developed concept wagon was a new and radical concept, a more rigorous test approach to dynamic testing should be added to the normal tests and acceptance parameters in railway standards. A more rigorous test approach was developed which included consideration of test track defect lengths based on bogie centre distance (BCD) and resonance conditions for the cyclic track defects. The consideration of resonance condition requires developing equivalent amplitudes of track defects corresponding to the wavelengths in the track which are multiples of bogie centre distance for the cyclic bounce, pitch and roll track defects. Using the more rigorous testing regime an innovative axle suspension was developed and refined to a design with three stages consisting of a conventional leaf spring, and the UIC link suspension in series with two multi-stage coil springs. It was also necessary to add longitudinal stiffness to improve axle yaw stability and hunting speed. The resulting design showed excellent stability with a critical speed of 204km/h and the multi-stage suspension allowed for negotiation of isolated lateral, vertical and long twist track defects as per AS7509 up to the defect band F of the ARTC track geometry standard. The short twist tests were however problematic. The resultant concept requires a smaller short twist track defect limit (8mm over 2m) than the defect band G of ARTC track geometry standard. The developed concept performed satisfactorily on track spectra up to FRA class 6 track. Finally, the energy consumption of the developed wagon concept was evaluated and compared with similar capacity wagons such as RQTY, sgns60 and double stack container wagons in a train simulation. The energy saving ranged from 6 to 12% across various operating scenarios.