Validation of rolling-stock interior noise simulation in viaduct and tunnel environments

Acoustic comfort for modern rolling stock is a standard design requirement. The use of standard measurement conditions (ballast and free-field conditions) is the best way to identify quiet vehicles but operators (specially metro operators and some suburban) prefer to set noise targets in their own infrastructure. Metro infrastructures are mainly today done with ballastless tracks either in elevated track (viaduct) or tunnels. Therefore it is critical for rolling stock suppliers to develop methodologies to simulate interior noise performances on those scenarios to be able to propose design solutions and to control the risks. In this paper, the methodology used by Alstom to simulate interior noise in tunnels and viaduct is described. Methodology uses databases of acoustic transfer functions between sound power level of noise sources and acoustic wall pressures around vehicles. These transfer functions are modified in function of the environment (viaduct or tunnel) taking into account the type of acoustic field. Then, analytical or numerical models of the train structure plus interiors are calculated. Simulation cases and validation of the models are discussed to evaluate the pertinence of using virtual validation instead of interior noise type tests.