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Acoustics

Noise has always been a part of freight and passenger transport by rail. Reducing this noise will make trains more socially and environmentally acceptable.

Acoustics is a field of research and technical progress dealing with the generation, propagation, and perception of sound and vibration waves. From a physical standpoint, working on noise and acoustics in rail transport calls for identifying and acquiring a good understanding of the origins, i.e. the sources, of noise.

  • In rail transport, the main source of noise at speeds from 80 to 300 km/h is rolling noise, that is, the noise generated at the contact between the wheel and the rail by vertical irregularities in the running surfaces.
  • The second source of noise is the auxiliary equipment, e.g. the motor and the ventilation system, that is needed to operate the train. Though noticeable at low speeds, this noise is quickly drowned out by rolling noise.
  • Last, at very high speeds, the predominant source of noise is aerodynamic phenomena related to the disruption of the air flow over structural components such as bogies and pantographs. This is part of the noise we hear when a TGV passes.

 

To comply with increasingly stringent regulations and make rail transport more socially and environmentally acceptable, railways are investing to reduce noise at the source and attenuate it on the propagation path. They are also developing new experimental and numerical means to describe acoustic phenomena so as to help guide the design and maintenance of trains.

Acoustics is a major issue for SNCF and the rail industry generally, since noise annoyance is an obstacle to expanding the use of trains for both freight and passenger transport.

Railway acoustics involves a SYSTEM in which both infrastructure and rolling stock play a role.

Will reducing noise boost competitiveness?

TECH SNCF’s acoustics specialists are convinced it will.

So how can the sound environment of local residents and SNCF personnel be improved?

A solid foundation of physical knowledge built on years of scientific research already exists, but it must be broadened, notably to questions related to the perception of rail traffic noise and to the field of simulation. As for technologies, many “off the shelf” solutions are available today, but more needs to be done, especially in the area of on-board measurement systems and new acoustic materials.

  • When it comes to rolling noise, the solution begins with effective rail and wheel maintenance. By keeping the surfaces in good condition, noise-generating excitation at the rail–wheel contact point is eliminated. Structural vibration resulting from their contact can be partially mitigated by placing dynamic absorbers on the rails and/or wheels.
  • In the area of equipment noise, there is a long list of possibilities, from the enclosure of certain electrical units to the electrification pure and simple of rail lines. To reduce aerodynamic noise, work must be done to arrive at more streamlined train designs.
  • Propagation of acoustic energy can be partially curbed with installations such as screens, while under-sleeper pads and sub-ballast mats will reduce ground vibration.

And a lot has already been accomplished!

For example, a reduction of 14 dB (A) has been achieved between the first-generation TGVs and the ones operating today.