A FEM/Kirchhoff-Helmholtz integral model for noise diffractors on low height noise barriers

So-called noise diffractors are a novel way to reduce traffic noise. As opposed to blocking or absorbing noise, diffractors bend noise in an upward direction, creating a shadow zone of reduced noise levels behind the diffractor. The diffraction is most effectively induced by quarter-wavelength resonators. The resonators can be placed in the ground but can also be mounted on top of a (low height) noise barrier, which provides additional reduction. In this paper, we describe a finite element/Helmholtz integral model for a diffractor mounted on a low height noise barrier. The finite element model is used to calculate the scattered acoustic field in the proximity of the diffractor for a noise source sufficiently far away from the diffractor. The acoustic pressure and particle velocity on the outer boundary of the finite element domain are subsequently used in the Kirchhoff-Helmholtz integral formulation to evaluate the acoustic field in the far field. The major benefit of this approach is a large reduction of the model size and reduced calculation times. This allows us to assess the reduction values at different barrier heights, larger distance from source to diffractor and larger distances from diffractor to evaluation points, with an example shown for highway traffic noise.