Diffraction-assisted rough ground effects

Imran Bashir , Shahram Taherzadeh , T.J Hill , Keith Attenborough

Sound propagation over a smooth hard surface can be significantly altered by introducing roughness. For near grazing sound propagation over a smooth hard surface, the first destructive interference occurs at relatively high frequencies. However, the ground effect dips, corresponding to the first destructive interference, observed in Excess Attenuation (EA) spectra measured over rough surfaces, are at significantly lower frequencies. Sound propagation over periodically spaced roughness elements and randomly spaced roughness elements with different cross-sectional profiles (semi-cylindrical, rectangular and wedge-shaped strips) is investigated. Periodic spacing results in multiple distinct maxima, compared with the single broad EA maxima observed for random spacing. Roughness also causes surface waves. These surface waves are strongest near grazing incidence and their amplitudes and the frequencies at which they occur depend on the roughness height and mean centre-to-centre spacing. Numerical models such as Multiple Scattering Theory (MST) and the Boundary Element Method (BEM) are used to make predictions of the EA spectra which are compared with measurements. [Work supported by European Community FP7 project number 234306].

Domaines: Acoustique [physics.class-ph]

Imran Bashir, Shahram Taherzadeh, T.J Hill, Keith Attenborough. Diffraction-assisted rough ground effects. Acoustics 2012, Apr 2012, Nantes, France. ⟨hal-00810794⟩