| 1. |
- Forssén, Jens, et al.
(author)
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A model of sound scattering by atmospheric turbulence for use in noise mapping calculations
- 2014
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In: Acta Acoustica united with Acustica. - : S. Hirzel Verlag. - 1610-1928 .- 1861-9959. ; 100:5, s. 810-815
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Journal article (peer-reviewed)abstract
- Sound scattering due to atmospheric turbulence limits the noise reduction in shielded areas. An engineering model is presented, aimed to predict the scattered level for general noise mapping purposes including sound propagation between urban canyons. Energy based single scattering for homogeneous and isotropic turbulence following the Kolmogorov model is assumed as a starting point and a saturation based on the von Kármán model is used as a first-order multiple scattering approximation. For a single shielding obstacle the scattering model is used to calculate a large dataset as function of the effective height of the shielding obstacle and its distances to source and receiver. A parameterisation of the dataset is used when calculating the influence of single or double canyons, including standardised air attenuation rates as well as façade absorption and Fresnel weighting of the multiple façade reflections. Assuming a single point source, an aver aging over three receiver positions and that each ground reflection causes energy doubling, the final engineering model is formulated as a scattered level for a shielding building without canyon plus a correction term for the effect of a single or a double canyon, assuming a flat rooftop of the shielding building. Input parameters are, in addition to geometry and sound frequency, the strengths of velocity and temperature turbulence.
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| 2. |
- Forssén, Jens, 1968, et al.
(author)
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Toolbox from the EC FP7 HOSANNA project for the reduction of road and rail traffic noise in the outdoor environment
- 2014
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In: Transport Research Arena 2014, Paris, France. ; , s. 10-
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Conference paper (peer-reviewed)abstract
- This paper offers a brief overview of innovative methods for road and rail traffic noise reduction between sourceand receiver. These include using new barrier designs, planting of trees, treatments of ground and road surfacesand greening of building façades and roofs using natural materials, like vegetation, soil and other substrates incombination with recycled materials and artificial elements. The abatements are assessed in terms of numericallypredicted sound level reductions, perceptual effects and cost–benefit analysis. Useful reductions of noise fromurban roads and tramways are predicted for 1-m-high urban noise barriers and these are increased by addinginter-lane barriers. A 3 m wide 0.3 m high lattice ground treatment, a carefully planted 15-m-wide tree belt andreplacing 50 m of paved areas by grassland are predicted to give similar reductions. Tree belts are shown to bevery cost-effective and combining tall barriers with a row of trees reduces the negative impact of wind. Greenroofs may significantly reduce the noise at the quiet side of buildings.
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| 3. |
- Hornikx, Maarten, 1980, et al.
(author)
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Urban background noise mapping : The multiple-reflection correction term
- 2014
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In: Acta Acoustica united with Acustica. - 1610-1928 .- 1861-9959. ; 100:2, s. 293-305
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Journal article (peer-reviewed)abstract
- Mapping of road traffic noise in urban areas according to standardized engineering calculation methods systematically results in an underestimation of noise levels at areas shielded from direct exposure to noise, such as inner yards. In most engineering methods, road traffic lanes are represented by point sources and noise levels are computed utilizing point-to-point propagation paths. For a better prediction of noise levels in shielded urban areas, an extension of engineering methods by an attenuation term Acan has been proposed, including multiple reflections of the urban environment both in the source and in the receiver area.The present work has two main contributions for the ease of computing Acan. Firstly, it is shown by numerical calculations that Acan may be divided into independent source and receiver environment terms, As and Ar. Based on an equivalent free field analogy, the distance dependence of these terms may moreover be expressed analytically. Secondly, an analytical expression is proposed to compute As and Ar for 3D configurations from using 2D configurations only. The expression includes dependence of the street width-to-height ratio, the difference in building heights and the percentage of facade openings in the horizontal plane. For the expression to be valid, the source should be separated from the receiver environment by at least four times the street width.
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| 4. |
- Nilsson, Mats E., et al.
(author)
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Perceptual effects of noise mitigation
- 2014
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In: Environmental Methods for Transport Noise Reduction. - : CRC Press. - 9780415675239 ; , s. 195-219
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Book chapter (peer-reviewed)abstract
- Noise mitigation reduces the audibility of a noise source at the location of the receiver, making the source less annoying and less likely to interfere with activities, such as sleep, rest, and speech. Many mitigation methods change temporal and spectral properties of noise, which may influence perceived annoyance, over and above the effect related to the overall reduction in A-weighted sound pressure level. Noise reduction also may increase the noticeability of other sources, which may influence the perception of the overall acoustic environment. Finally, well-designed noise mitigation solutions may improve the visual environment, e.g., a vegetated noise barrier or earth berm can visually shield the traffic and increase the amount of visible greenery. This chapter provides examples of such perceptual effects of noise mitigation, from effects on perception of the noise itself, via effects on the soundscape, to potential effects on the overall audio-visual environment.
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| 5. |
- Wei, Weigang, et al.
(author)
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Urban background noise mapping : The general model
- 2014
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In: Acta Acoustica united with Acustica. - 1610-1928 .- 1861-9959. ; 100:6, s. 1098-1111
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Journal article (peer-reviewed)abstract
- Surveys show that inhabitants of dwellings exposed to high noise levels benefit from having access to a quiet side. However, current practice in noise prediction often underestimates the noise levels at a shielded façade. Multiple reflections between façades in street canyons and inner yards are commonly neglected and façades are approximated as perfectly flat surfaces yielding only specular reflection. In addition, sources at distances much larger than normally taken into account in noise maps might still contribute significantly. Since one of the main reasons for this is computational burden, an efficient engineering model for the diffraction of the sound over the roof tops is proposed, which considers multiple reflections, variation in building height, canyon width, façade roughness and different roof shapes. The model is fitted on an extensive set of full-wave numerical calculations of canyon-to-canyon sound propagation with configurations matching the distribution of streets and building geometries in a typical historically grown European city. This model allows calculating the background noise in the shielded areas of a city, which could then efficiently be used to improve existing noise mapping calculations. The model was validated by comparison to long-term measurements at 9 building façades whereof 3 were at inner yards in the city of Ghent, Belgium. At shielded façades, a strong improvement in prediction accuracy is obtained.
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