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A practical approach to modelling railway vehicle interior acoustics

A practical approach to modelling railway vehicle interior acoustics
A practical approach to modelling railway vehicle interior acoustics
The aim of the current work is to propose a practical approach for modelling the interior acoustics of railway vehicles by investigating the spatial decay of sound within the vehicle and its relation to the reverberation time and absorption. Measurements are presented of the longitudinal distribution of sound level inside five railway vehicles as well as the corresponding reverberation times. Both quantities are determined using an omnidirectional sound source located near one end of the vehicle. The measured sound pressure level follows a roughly linear dependence with longitudinal distance and the rate of decay is found to follow a consistent trend over all five datasets when plotted against reverberation time. To interpret these results, three different modelling approaches are considered: ray tracing, Statistical Energy Analysis, and an analytical corridor model. Ray tracing models with a simple geometry resembling the interior of a railway carriage are used to explore the dependence of the spatial decay and reverberation time on the absorption and scattering coefficients of the surfaces. For high values of scattering coefficient, the reverberation time approaches the Sabine estimate but for low values of scattering coefficient it can be up to a factor of 2.5 greater than this estimate. This implies difficulties in deducing the average absorption coefficients from the measured reverberation times. The spatial decay rates obtained from the ray tracing model do not have the same consistent dependence on reverberation time as the measured results, although the results for low values of scattering coefficient are closer to the measured trend than those for higher values. Investigation of the Statistical Energy Analysis approach shows that it predicts a spatial decay rate that depends explicitly on length of the subsystems used in the model; consequently, the results do not converge as the model is refined. It is possible to use modified coupling loss factors based on an analytical corridor model to give a better approximation to the spatial decay. This corridor model is shown to give results that are consistent with the measurements if the average absorption is obtained from the reverberation time using a modified formula for the mean free path length, and if the cross-section area is reduced to allow for the blocking effect of the seats. This provides a practical way forward for using SEA for the interior sound in railway vehicles.
rail vehicle acoustics, reverberation time, spatial decay, scattering, statistical energy analysis
0003-682X
Sun, Wenjing
697ae912-77f1-43f4-b7ee-38cf7fb986b2
Thompson, David J.
bca37fd3-d692-4779-b663-5916b01edae5
Zhang, Zhanfei
9d71b5cb-3244-4900-916d-1c57e191beda
Squicciarini, Giacomo
c1bdd1f6-a2e8-435c-a924-3e052d3d191e
Sun, Wenjing
697ae912-77f1-43f4-b7ee-38cf7fb986b2
Thompson, David J.
bca37fd3-d692-4779-b663-5916b01edae5
Zhang, Zhanfei
9d71b5cb-3244-4900-916d-1c57e191beda
Squicciarini, Giacomo
c1bdd1f6-a2e8-435c-a924-3e052d3d191e

Sun, Wenjing, Thompson, David J., Zhang, Zhanfei and Squicciarini, Giacomo (2022) A practical approach to modelling railway vehicle interior acoustics. Applied Acoustics, 200, [109055]. (doi:10.5258/SOTON/D2398).

Record type: Article

Abstract

The aim of the current work is to propose a practical approach for modelling the interior acoustics of railway vehicles by investigating the spatial decay of sound within the vehicle and its relation to the reverberation time and absorption. Measurements are presented of the longitudinal distribution of sound level inside five railway vehicles as well as the corresponding reverberation times. Both quantities are determined using an omnidirectional sound source located near one end of the vehicle. The measured sound pressure level follows a roughly linear dependence with longitudinal distance and the rate of decay is found to follow a consistent trend over all five datasets when plotted against reverberation time. To interpret these results, three different modelling approaches are considered: ray tracing, Statistical Energy Analysis, and an analytical corridor model. Ray tracing models with a simple geometry resembling the interior of a railway carriage are used to explore the dependence of the spatial decay and reverberation time on the absorption and scattering coefficients of the surfaces. For high values of scattering coefficient, the reverberation time approaches the Sabine estimate but for low values of scattering coefficient it can be up to a factor of 2.5 greater than this estimate. This implies difficulties in deducing the average absorption coefficients from the measured reverberation times. The spatial decay rates obtained from the ray tracing model do not have the same consistent dependence on reverberation time as the measured results, although the results for low values of scattering coefficient are closer to the measured trend than those for higher values. Investigation of the Statistical Energy Analysis approach shows that it predicts a spatial decay rate that depends explicitly on length of the subsystems used in the model; consequently, the results do not converge as the model is refined. It is possible to use modified coupling loss factors based on an analytical corridor model to give a better approximation to the spatial decay. This corridor model is shown to give results that are consistent with the measurements if the average absorption is obtained from the reverberation time using a modified formula for the mean free path length, and if the cross-section area is reduced to allow for the blocking effect of the seats. This provides a practical way forward for using SEA for the interior sound in railway vehicles.

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More information

Accepted/In Press date: 30 September 2022
e-pub ahead of print date: 10 October 2022
Published date: 10 October 2022
Keywords: rail vehicle acoustics, reverberation time, spatial decay, scattering, statistical energy analysis

Identifiers

Local EPrints ID: 471471
URI: http://eprints.soton.ac.uk/id/eprint/471471
ISSN: 0003-682X
PURE UUID: 2dfdd398-d6ba-4cd8-97e3-7dfc0e34338d
ORCID for David J. Thompson: ORCID iD orcid.org/0000-0002-7964-5906
ORCID for Giacomo Squicciarini: ORCID iD orcid.org/0000-0003-2437-6398

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Date deposited: 08 Nov 2022 19:02
Last modified: 21 Jun 2024 04:01

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Author: Wenjing Sun
Author: Zhanfei Zhang

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