Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux

Type de document

COMMUNICATION AVEC ACTES INTERNATIONAL (ACTI)

Langue

anglais

Auteur

DUHAMEL ; LUO ; YIN

Résumé / Abstract

Nowadays, the increasing number of urban railway lines has gradually become one of the major environmental annoyances in cities. Noise barrier, as the most effective method to control the impact of noise, are widely applied as an engineering application in urban railway transit. Compared with the conventional and multiple-edged profiles, fully-enclosed barriers can reduce railway noise much more effectively. Aiming at understanding the acoustic performance of fully-enclosed barriers, a series of experiments have been carried out in Ningbo, China. It can be seen from experimental results that the fully-enclosed barrier shows good performance in the frequency range of the main source of urban railway noise. However, low frequency noise has not been controlled effectively and the pressures at low frequencies are even larger than those in the test field without barriers. In order to make clear the cause of the negative effect at low frequencies, a two-dimensional model of a fully-enclosed barrier on a boxed girder simulating the actual conditions of the experiments has been established. With a simulated point source on the side of the track closed to the barrier, the model can be developed and solved using the Boundary Element Method (BEM). The numerical results from the BEM analysis show that sound pressures at many low frequencies are amplified excessively and these peaks of sound pressure are sharp and high. Since the appearance of sound level distribution at the frequencies of these peaks seems to be the natural frequency responses of acoustic resonance, the acoustic resonance of the air cavity formed by the fully-enclosed barrier is highly suspected to be the cause. Therefore, the acoustic modes of the air cavity were solved by the Finite Element Method. Compared with the results of the BEM model, several frequencies of the acoustic modes approximately coincided with those of the peaks, and the corresponding distributions of sound pressure inside the barrier were in good agreement with those of the BEM model. Hence the peak values of sound pressure at low frequencies in the model with the fully-enclosed barrier are mainly caused by the acoustic resonance of the air cavity. In conclusion, the acoustic mode of the air cavity formed by a fully-enclosed barrier can be excited by the source inside the barrier to amplify the sound pressure in the vicinity of urban railways, which results in unsatisfactory performance of the fully-enclosed barrier at low frequencies.