Boundary element method for the calculation of correction factors of insertion loss for arbitrarily shaped noise barriers

摘要

Noise mapping software uses in general geometric methods to calculate the insertion loss of a noise barrier which is not appropriate for complex shapes with e.g. multiple edges. The aim of the current project is to derive simple formulas that can be used in noise mapping software. In this way new shapes of noise barriers can be brought into praxis. The boundary element method in 2D is used to calculate the insertion loss. The ground surface is modelled with a two parameter grassland model from Attenborough for a more realistic representation of ground reflections. Deriving the correction factors for different geometries requires a large number of different geometries to be calculated. Thus, for reduced computational effort a 2D model with a coherent line source is assumed. This assumption leads to considerable interference effects behind the barrier. Spectral and spatial averaging can reduce these effects only to a certain degree. In order to estimate the contribution of this effect, a few selected geometries will be assessed using 3D models and partially incoherent summation over a number of evaluation points along the z-axis. 3D modelling employs the fast multipole method and thus no grassland model will be used in 3D.