Barriers to consistent results: the effects of weather
Abstract
Calculating the attenuation provided by barriers and other screening elements is an essential part of practical noise control engineering. There are well-documented approaches to this problem, with noise propagation standards often specifying which approach to take. A noticeable exception is CONCAWE: the principal prediction method used in Australia. CONCAWE provides complex calculation methods for ground and meteorological effects, but not for barrier attenuation. The sound prediction software SoundPLAN uses the barrier attenuation algorithm from the General Prediction Method (GPM) in its implementation of CONCAWE. In Victoria, noise assessments are performed under neutral meteorological conditions, but the GPM assumes downwind propagation conditions. SoundPLAN therefore can under-predict the performance of the barrier. While predicting noise propagation under favourable conditions has merit, this paper discusses several barrier-attenuation algorithms and their suitability for modelling noise propagation in neutral meteorological conditions.
... The present paper presents the detailed analysis of computing the noise attenuation using acoustic barriers using four different approaches: Maekawa-Tatge formulation [1,2], Kurze and Anderson algorithm [3], general prediction method (GPM-ISO 9613) [4,5], and Menounou formulation [6]. The noise attenuation of the barrier was computed based on the Kirchhoff diffraction theory, which implies that the Huygens-Fresnel theory is applied to a semi-infinite acoustic thin barrier. ...
... The GPM [4,5] provides a relation for the sound attenuation based on a modified Fresnel number N 1 as mentioned in ISO 9613-2 [5], taking into consideration a correction factor for the downwind meteorological effect Kmet, given by the relation: With this correction factor K met , the modified Fresnel number N 1 of the source is: (8) and therefore, the sound attenuation of a thin rigid barrier, considered by GPM, is: ...
... Using Relations (1)-(14), a MATLAB software was developed to compute the sound attenuation of pure tones for the previously mentioned acoustic rigid semi-infinite thin barrier considering: Maekawa-Tatge formulation [1,2], Kurze and Anderson algorithm [3], general prediction method (GPM-ISO 9613) [4,5], and Menounou formulation [6]. The simulations were all represented without the ground effect and the atmospheric sound absorption. ...
The aim of this research is to provide a better prediction for noise attenuation using thin rigid barriers. In particular, the paper presents an analysis on four methods of computing the noise attenuation using acoustic barriers: Maekawa-Tatge formulation, Kurze and Anderson algorithm, Menounou formulation, and the general prediction method (GPM-ISO 9613). Accordingly, to improve the GPM, the prediction computation of noise attenuation was optimized for an acoustic barrier by considering new effects, such as attenuation due to geometrical divergence, ground absorption-reflections, and atmospheric absorption. The new method, modified GPM (MGPM), was tested for the optimization of an y-shape edge geometry of the noise barrier and a closed agreement with the experimental data was found in the published literature. The specific y-shape edge geometry of the noise barrier contributes to the attenuation due to the diffraction phenomena. This aspect is based on the Kirchhoff diffraction theory that contains the Huygens-Fresnel theory, which is applied to a semi-infinite acoustic barrier. The new method MGPM of predicting the noise attenuation using acoustic barriers takes into consideration the next phenomena: The effect of the relative position of the receiver, the effect of the proximity of the source or receiver to the midplane of the barrier, the effect of the proximity of the receiver to the shadow boundary, the effect of ground absorption-reflections, the effect of atmospheric absorption, and the meteorological effect due to downwind. The conclusion of the paper reveals the optimization of the method for computing the noise attenuation using acoustic barriers, including the necessary corrections for ISO-9613 and the Sound PLAN software, as well as the optimization on a case study of a specific geometry of the edge barrier.
... NORD 2000 (Nordic noise prediction method), Harmonoise/Imagine (Improved Methods for the Assessment of the Generic Impact of Noise in the Environment) or SonRoad (Swiss noise prediction method)). These methods have they own equations for calculation of noise barrier sound reduction, many of them have corrections, based on the measurements performed by Maekawa [17,18]. To simulate performance of more complex material and shape noise barriers in a certain interval of frequencies, numerical methods are more suitable comparing methods listed before. ...
This paper presents investigation of traffic noise barriers enhancement potentiality at low frequencies: regarding measurements results near motorway with 43.3-49.8 percentage of heavy duty, the investigation assesses efficiency of existing (modelled and built according predicted overall A-weighted rated sound levels) noise barriers and simulates (using finite element method) improving of them by adding most common T-shape and octagon-shape tops at low frequencies. According simulation results (model deals with divergence loss, diffraction from obstacles, absorption and reflection from surfaces of cylindrical sound waves), noise barrier enhancement with those tops has influence on additionally 0.6-6.5 dB reduction of SPL at low frequencies in a noise shadow zone.
Barrier experiments were conducted in a low speed wind tunnel in which
the flow simulates the mean and fluctuating components of the turbulent
velocity of the atmospheric boundary layer over uniform terrain. The
tests consisted of 1:32 scale model experiments of sound propagating
over grassland, both with and without an acoustic barrier, and also with
and without the presence of turbulent winds. Results show two effects of
the wind on the performance of barriers: (1) the barrier attenuation is
increased for upwind propagation and decreased for downwind propagation,
and (2) the fluctuations in the measured levels of the wind reduction
were of the same order as the mean value.
This paper presents experimental data on the diffraction of sound round a semi-infinite plane screen in a free field and describes a method for calculating the shielding effect of a real screen employed for the purpose of noise reduction, with the assistance of a single graph and without the aid of a computer.
Environment Protection Authority Victoria ISO 9613-2, Acoustics -Attenuation of sound during propagation outdoors -Part 2: General methods of calculation
EPA Information Bulletin 280 1991, Environment Protection
Authority Victoria
ISO 9613-2, Acoustics -Attenuation of sound during propagation outdoors -Part 2: General methods of calculation 1996, International Standards Organization, Genève,
Switzerland, 1996.
- P Nelson
Nelson, P. 1987, Transportation Noise Reference Book, Butterworths, Sydney.