Analysing the acoustic performance of a nearly-enclosed noise barrier using scale model experiments and a 2.5-D BEM approach

Abstract

This paper describes scale modelling method to measure the acoustic performance of a nearly-enclosed barrier and corresponding predictions using an existing 2.5-D Boundary Element Method(BEM) program. Preliminary investigation results show the deterioration in performance of a nearly-enclosed barrier due to the resonance effect that led to high pressure levels radiating into the surroundings via the topped opening. Absorptive material added to the inner surface of the barrier can effectively improve this phenomenon. Measurements on one-twentieth scale model of barriers, viaducts and vehicle structures were carried out outdoors under controlled conditions. The measured results show the transmission loss of transparent panels on the top were not adequate to make the measured results as high as the predictions. A modified scale model, by coating all the surfaces with rubber, was remeasured. The results from retested tests and calculations were in good agreement each other, which indicate that the 2.5-D BEM code can provide a reliable description of the acoustic performance of a nearly-enclosed barrier. Then the program was able to be employed into the investigation of barrier performance on every area with different acoustic features in the surrounding environment. As expected, the attenuation of the nearly-enclosed barrier averaged around 15 dB in the near filed and around 10 dB in the far field. The number effect of incoherent point sources on the performance is discussed as well for the study of railway traffic noise. The increased number of incoherent point sources can result in smoother and lower attenuations for the whole sound field.

In-situ measurement of the acoustic performance of a nearly-enclosed barrier prototype on an existing line in the urban rail transit system

“…The magnitude of the negative value is less than 5 dB, which indicates that the nearly-enclosed prototype had a harmful but not remarkable effect on the low frequencies. As we discussed in a previous article [34], the resonance effect caused by the open air cavity inside a nearly-enclosed barrier resulted in extremely high levels at the resonance frequencies. And with the help of the absorbent treatment, the harmful resonance effect was mitigated solely for the mid-and high frequencies.…”

Finite Element Method for the Estimation of Insertion Loss of Noise Barriers: Comparison with Various Formulae (2D)

“…FEM has been used for studies for the estimation of the reflection index of multiple acoustic layered noise barriers [50], for modeling of the acoustic performance of sonic crystals [51][52][53], for topology optimization [24,54,55], for the investigation of the structural performance of a noise barrier [56], and for calculation of insertion loss [57]. However, it seems that more numerical studies have used BEM, for modeling of noise barriers with various shapes and configurations [58][59][60][61][62][63][64][65] and for barrier optimization [66][67][68][69]. The FDTD and PSTD methods have been applied for studies to a much lesser extent, [70][71][72][73] and [74,75] respectively.…”

Fatigue Life Prediction for Semi-Closed Noise Barrier of High-Speed Railway under Wind Load

“…In experimental research, Denis Duhamel, Zhang Xun, etc. studied the noise transmission path and the acoustic characteristics of the semi-closed noise barrier through the field monitoring of HSR, and verified the noise reduction effect of the semi-closed noise barrier, it was found out that the resonance effect reduces the noise reduction effect of the semiclosed noise barrier [8][9][10]; Munemasa Tokunaga studied the dynamic response characteristics of the inward-folded noise barrier of HSR through field measurement [11]. Using numerical techniques, Lu Ming and Zhou Qiang established the noise prediction model of the semi-closed noise barrier to study the noise reduction effect and application scope of semi-closed and fully closed noise barriers.…”