Comparison of the performance of absorbing and rigid -edged barriers by using experimental and numerical methods

The purpose of this study was to optimize the geometry and the acoustical properties of noise barriers for traffic noise applications. The approach consisted of performing scale-model experiments in a laboratory environment and developing corresponding boundary element models. Field measurements were also performed in order to confirm the findings of the scale-model experiments and numerical studies. First, the simple geometry was chosen to validate the use of boundary element models for the prediction of scattered diffraction. More complicated geometries were investigated to study the effects of geometry on sound barrier performance. The performance of straight-edge barriers with various top geometries and sound absorptive treatments was then investigated. Experiments were performed using a finite-size barrier in an anechoic chamber. The results confirmed that a sound absorptive treatment near the edge has a performance advantage over corresponding rigid barriers. A design optimization study of the most effective shape of acoustical treatments concluded that a circular shape works best. The performance of two different acoustical materials was also compared. The results from the boundary element model agree well with the experimental results up to 6300 Hz. Insertion loss distribution proved the numerical model\u27s capability of reproducing the complicated interference pattern on the receiver plane. Space-averaged insertion loss over different size receiver planes was also used to confirm the numerical results. Boundary element models for barriers with sound absorptive edges were created using a multi-domain formulation by prescribing a complex sound speed and density. It was found that the multi-domain numerical model could be used to predict diffraction phenomena through and around the absorptive material, and can therefore be used to identify the sound absorptive top geometry and material properties that yield optimal barrier performance. A full-scale barrier-top add-on device was designed based on laboratory experiments and numerical studies, and was shown to be effective in a realistic highway environment