Point to point propagation over periodic rough boundaries

Attenborough, Keith; Mellish, Steve; Taherzadeh, Shahram; Bashir, Imran and Stronach, Alex (2023). Point to point propagation over periodic rough boundaries. In: 10th Convention of the European Acoustics Association, EAA 2023, 11-15 Sep 2023, Torino.


A rough surface formed by regularly spaced acoustically hard parallel strips or grooves gives rise to non-specular diffracted modes and surface waves. Surface waves result in values greater than +6 dB in spectra of the sound field relative to the direct field (excess attenuation). As well as surface wave generation, measurements of excess attenuation over regularly spaced parallel strips show effects of the finite array dimensions. Numerical predictions of pressure contours at the frequency of main surface wave energy show that the surface waves are created by overlapping, interacting, quarter wavelength resonances in the gaps between roughness elements or within grooves. Additional peaks in EA spectra result from interference between surface waves and diffracted components travelling towards the source. The surface waves are reduced if the roughness elements resonate near the surface wave frequencies. Predictions of propagation over periodic rectangular grooves with the same width but depths varied to create a phase change of 2π over each period show non-specular behaviour associated with both surface wave generation and the diversion of energy into diffracted modes. Calculations are made of potential traffic noise insertion loss due to a periodic surface consisting of rectangular grooves with different depths.

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