On the modeling of sound propagation over multi-impedance discontinuities using a semiempirical diffraction formulation

Abstract

Several approximate extensions of the semi-empirical De Jong model ͓De Jong et al., J. Sound and Vib. 86, 23-46 ͑1983͔͒ are considered for the prediction of sound propagation over multiple impedance discontinuities. A limitation in the original formulation of the De Jong model is highlighted and a modified form that overcomes this limitation is derived based on reciprocity. This leads to the development of a model for multiple impedance discontinuities that can be used for the investigation of sound-wave propagation above a mixed, striped soft ground that is created by either porous absorbent strips, embedded grooves, or wells with different depths. The accuracy of the model is validated against the boundary element method. It is then used to evaluate the importance of the imaginary part of the admittance of the ground strips on sound attenuation along welled surface. It is shown that the attenuation performance of a surface with multiple impedance discontinuities is high when the imaginary part of the average admittance is large and negative ͑with an −it convention͒, but the magnitudes of the attenuation peaks are also substantially affected by diffraction from the impedance discontinuities.

Exploiting ground effects for surface transport noise abatement

“…Both surfaces are characterised by the variable porosity impedance model [10] with effective flow resistivity values and porosity change rates of 30 kPa s m −2 and 15 m −1 and 100 MPa s m −2 and 15 m −1 for the soft and hard surfaces respectively. These comparisons confirm that the modification of the de Jong method by Lam and Monazzam [24] gives predictions that are closer to those made using BEM than the original de Jong formulation particularly for the soft to hard discontinuity.…”

“…[22] compare data from measurements over single impedance ground surface with the De Jong model predictions [21]. They show that the agreement between data and De Jong model predictions is good except when the source and receiver are placed Monazzam [24] gives predictions that are closer to those made using BEM than the original de Jong formulation particularly for the soft to hard discontinuity. …”

Effect of Absorption on the Performance of Diffusive T Shape Barriers

“…It is therefore susceptible to receiver specific interference effects caused by ground and other nearby reflections. Previous research have shown that the performance of a diffusive cover for barrier applications can be characterised by the attenuation of the sound as it propagates from one end of the cover to the other [6]. It is therefore possible to determine the performance by measuring the attenuation at the edge of the cover.…”

An analytical model for turbulence scattered rays in the shadow zone for outdoor sound propagation calculation

“…Once the reflection geometry is worked out by the numerical ray tracing, the effect of the ground at each reflection can then be approximated by the Weyl-van der Pol formulation. 12,13 The height of the upper boundary of the computational grid is set using the rule of thumb of 1 / 10 of the maximum horizontal range.…”