Evaluation of Noise Barriers

Noise barriers are a widely used technical measure to reduce noise immission from road and rail traÿc. The simulation based prediction of their intrinsic acoustic properties, according to standardized methods for their validation, allows a cost-eÿcient product optimization in the course of the development process. This prediction requires the determination of the material parameters of absorbing materials used in the construction of noise barriers. For this purpose four mathematical models for the prediction of the reflection index of acoustic layered systems, like noise barriers, were derived in this work. The first is a simple but computationally eÿcient one-dimensional analytical model, which allows the determination of absorber parameters via a least squares fit. The second is a finite element method (FEM) which allows the simulation of a periodic unit cell of a noise barrier. The third is the transfer matrix method (TMM) which allows the calculation of the reflection index of layered absorbing systems for oblique angles. The fourth is a rotationally symmetric boundary element method (BEM) which allows the calculation of the reflection index of arbitrary absorbing layered systems for rotationally symmetric sources like point sources or directive sources. These models were then applied to a noise barrier and multiple absorbing layered systems, followed by a comparison to measurement results. Starting with the determination of the material parameters of an absorber, used inside a noise barrier, with the analytical model, the periodic FEM model was able to predict the reflection index of the noise barrier very accurately. The computationally cheap analytical model, in combination with the more accurate FEM, also allowed the optimization of said noise barrier regarding its reflection properties. The transfer matrix method and the BEM were then used to calculate the reflected sound field of multiple plane absorbing layered systems for oblique incidence and directive sources.