Modeling of multiple reflections between noise barriers and trains using the boundary element method

Christian H. Kasess

Acoustics Research Institute, Austrian Academy of Sciences

Time : Wednesday 11 may 2022 from 09:00 to 09:30

Room: Gæstesalen

Abstract :

In addition to the desired acoustical effect, noise barriers also pose an optical barrier obstructing the view. Transparent elements, which are typically highly reflecting, could reduce this visual barrier effect. Unfortunately, in particular for railway traffic highly reflecting surfaces oriented towards the noise source may produce considerable multiple reflections between train and barrier, potentially reducing the insertion loss of the barrier. Current noise mapping methods such as the EU directive 2002/49/EC (Annex II) provide means to approximately consider such reflections assuming parallel planes and a constant absorption coefficient of the barrier. There is, however, the need for detailed investigations how the placement and dimensions of sound hard elements, the distance of the train to the barrier, the train cross- section, the distance to the observer, and other variables influence the insertion loss of the barrier. The work presented here aims at investigating the different factors systematically using 2.5D-boundary element (BE) calculations as well as an extensive measurement campaign where acoustic passby measurements of 4 different barrier variants combining highly absorbing and reflecting materials were performed. These measurements provide the basis for the validation of the BE calculations. Based on this calibration, simulations of many different configurations are performed and a simplified, practical calculation model will be derived which can be used in noise mapping applications. Measurement results show reductions in the shielding effect of the barrier, depending on the position and the train type. Concerning the simulations, the BE method proved suitable for modeling the effects of reflecting panels, however, in particular the source positioning can produce considerable variance in the BE calculation results and thus the derivation of an adequate source model is the current challenge.

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