A hybrid method that combines a noise engineering method and the 2.5D boundary element method approximates outdoor sound propagation in large domains with complex objects more accurately than noise engineering methods alone and more efficiently than reference methods alone. Noise engineering methods (e.g., ISO 9613-2 or CNOSSOS-EU) efficiently approximate sound levels from roads, railways, and industrial sources in cities for simple, box-shaped geometries by first finding the propagation paths between the source and receiver, then applying attenuations (e.g., geometrical divergence and atmospheric absorption) to each path, and finally incoherently summing all of the path contributions. Standard engineering methods cannot model more complicated geometries but introducing an additional attenuation term quantifies the influence of complex objects. Calculating this extra attenuation term requires reference calculations but performing reference computations for each path is too computationally expensive. Thus, the extra attenuation term is linearly interpolated from a data table containing the corrections for many source/receiver positions and frequencies. The 2.5D boundary element method produces the levels for the real and simplified geometries and subtracting them yields a table of corrections. For a T-shaped barrier with two buildings, this approach reduces the mean error by approximately 2 dBA compared to a standard engineering method.
Extending standard urban outdoor noise propagation models to complex geometriesa)
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Portions of this work were presented in “The initial development of a hybrid method for modeling outdoor sound propagation in urban areas,” 170th Meeting of the Acoustical Society of America, Jacksonville, FL, USA, November 2015; “Modeling outdoor sound propagation in urban environments,” 171st Meeting of the Acoustical Society of America, Salt Lake City, UT, USA, May 2016; “Augmenting Road Noise Engineering Methods using the Boundary Element Method,” Inter-noise, Hamburg, Germany, August 2016; and “Enabling noise engineering methods to model complex geometries,” 3rd Joint Meeting of the Acoustical Society of America and the European Acoustics Association, Boston, MA, USA, June 2017.
Matthew Kamrath, Philippe Jean, Julien Maillard, Judicaël Picaut, Christophe Langrenne; Extending standard urban outdoor noise propagation models to complex geometries. J. Acoust. Soc. Am. 1 April 2018; 143 (4): 2066–2075. https://doi.org/10.1121/1.5027826
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