Ground Effect due to Periodic Resonant Roughness
Invited paper
The Open University
Tuesday 2 june, 2015, 17:00 - 17:20
0.8 Rome (118)
Abstract:
Traffic noise is an ever-increasing problem due to the gradual urbanisation
and
growing popularity of motorised means of travel. Land between roads and
nearby
noise-sensitive receivers can be used to support a series of low-rise
roughness
structures as an alternative to conventional earth berms and noise barriers.
Through measurements in an anechoic chamber and numerical computations
using a
two-dimensional boundary element method, we have investigated the effect of
periodic roughness elements above a smooth hard surface on sound
propagation.
First, an array of solid rectangular roughness structures was studied to
investigate the effect of the periodicity-induced diffraction. The broad-
band
insertion loss with reference to smooth hard surface was found to be
considerable
for near-grazing incidence. However, at frequencies below the first
roughness-
induced destructive interference, negative insertion loss was also observed
both
experimentally and numerically due to the creation of surface waves by the
roughness elements. To improve the insertion loss in this low-frequency
range, we
have investigated the use of hollow resonant elements with slit openings
constructed from pairs of aluminium angles, and observed the desired effect
while
maintaining the insertion loss at higher frequencies. Also we have created
doubly-resonant roughness elements by inserting pairs of smaller aluminium
angles
within the larger structures and have measured associated multiple
resonances.
At near-grazing incidence, the doubly-resonant roughness array is found to
produce a 3 dB increase in insertion loss compared to the array of single-
resonance structures.