THE VIBRO-ACOUSTIC MODELLING OF SLAB TRACK WITH EMBEDDED RAILS

The application of concrete slab track in railways has certain advantages compared with conventional ballasted track, but conventional slab track structures generally produce more noise than ballasted track. For this reason a “silent slab track” has been developed in the Dutch ICES “Stiller Treinverkeer” project (silent railway traffic) by optimizing the track. In the design, the rails are embedded in a cork-filled elastomeric material. The paper discusses the vibro-acoustic modelling of this track using the simulation package “TWINS”, combined with finite element techniques. The model evaluates the one-third octave band sound power spectrum radiated by train wheels and track, and provides for a tool to optimize the track design. Three track types are compared using the vibro-acoustic model: an existing slab track with embedded UIC54 rails, a newly designed, acoustically optimized slab track with a less stiff rail embedded in a stiffer elastomere, and, as a reference, a ballasted track. The models of the existing tracks have been validated with measurements. Calculations indicate that the optimized slab track will emit between 4 and 6 dB(A) less noise than the ballasted track. The existing slab track produces between 1·5 and 3 dB(A) more noise than the ballasted track; this is caused by resonances in the elastomeric moulding material in the frequency range determining the dB(A)-level.