Accuracy of wave based calculation methods compared to ISO 9613-2 (original) (raw)
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The process of performing an Environmental Impact Assessment includes the study of noise propagation. Often, the path from a noise source to a noise sensitive location involves complicated mechanisms of sound transmission. These mechanisms may relate to diffraction & reflections from obstacles (natural or man made), ground properties, and meteorological conditions. The International Standards Organization proposes with standard ISO9613-2, methods by which to calculate these effects. While they are relatively easy to implement, they underestimate the true workings of the aforementioned mechanisms. In this paper, we present the OTL - Terrain software application, which accurately and precisely simulates outdoor sound propagation. The software application can be used for the prediction of environmental noise and the design of control measures. OTL - Terrain is an application which uses geometrical acoustics (GA) and models the propagation of sound in terms of rays. The tool makes use of the image source method (ISM) combined with visibility tracing techniques to implement a novel method of path-detection, taking both reflection and diffraction effects into account. Calculations utilize the predicted reflections from finite-sized objects with Fresnel zone corrections, an unlimited order of diffraction, and atmospheric turbulence. This paper presents a comparison of the predictions made by the OTL – Terrain application, the methods proposed by ISO, and the published results from experimental data.
Ray-tracing software, which normally uses ISO 9613-2 to calculate outdoor sound propagation, is typically used to model community noise from large facilities. It is computationally practical for large-scale models. While ray-tracing has been used successfully for designing industrial facilities, the accuracy of some empirical algorithms in 9613 is questionable. It is presumed that ground effects calculated using 9613 are generally accurate for grazing incidence of a ray to the ground, but their use at large angles of incidence and taller sources is of lesser but unknown accuracy. For example, at 100 m, a 100-m high stack has an angle of incidence of 45°, which is much far higher than grazing incidence. Full-wave software, such as Greens Function-Parabolic Equation calculates wave length-effects, and is nominally exact, but too computationally intensive for modeling large-scale industrial facilities. On the other hand, Olive Tree Lab OTL Suite software provides the wavelength effects needed to accurately calculate and model ground reflections, and is computationally practical to model large industrial facilities. The accuracy of excess attenuations of ground effects calculated using 9613 are assessed. Conclusions on the accuracy of 9613 for use in design are made.
Comparison of Some Methods Used for Prediction of Atmospheric Sound Propagation
Canadian Acoustics, 1997
The sound field in inhomogeneous atmospheric conditions above an impedance plane is computed using three different numerical procedures, to assess their advantages and disadvantages. Two implementations of the parabolic equation are considered, the Green's function method and a Crank-Nicolson method; these are contrasted with a version of the fast field program. As test cases, both upward and downward refracting conditions are considered, with and without turbulence. Calculations made using the Green's function implementation are considerably faster, making it the method of choice when large numbers of calculations (as when many realizations of turbulence are required) are necessary. However, considerable care is required in setting computational parameters and parallel calculations with one of the other techniques for validation is advisable.