Two vibro-acoustic modelling methods were combined to validate the design of vacuum trains for the New York City subway network.
The New York City subway operates around the clock. As a result, the maintenance of the railway lines must take place alongside the commercial traffic. To guarantee user comfort, the network operator defined acoustic emission levels that must not be exceeded by its new trains tasked with vacuuming the railway lines. “In general, the specifications of construction machinery do not include very restrictive noise requirements. However, in this case, they particularly specified the noise level that must be complied with by our machines”, stated Cédric Delobel, head of the vacuum train division at Neu Railways, which won the contract for the supply of three vacuum trains for the New York City subway network.
Hybrid modelling
The French manufacturer which does not have an inhouse simulation department called on Cetim to make sure that the design of its trains complied with the specified requirements. Given that finite element modelling proved to be more complex to implement on a relatively high frequency spectrum (up to 2 kHz), it was coupled with the SEA (Statistical Energy Analysis) method via the VA-ONE software. Three models were built using this hybrid simulation methodology. “As a result, we were able to identify the most problematic frequency bands and then to propose the appropriate absorbing materials and their optimum location”, explained Thomas Gardin from Cetim. Following this study, Neu Railways these recommendations involving in particular the thickness and density of the isolating materials. The first train compliant with the acoustic requirements was delivered to New York in 2018 and will be followed by two others in early 2019.
Cetim carries out acoustic modelling over a large frequency spectrum and uses hybrid methods suited to the application to perform in-depth analysis of equipment and propose solutions that comply with specific customer requirements.
