Scattering by a cylinder covered with an arbitrary distribution of impedance and application to the optimization of a tramway noise abatement system

International audienceA semi-analytical solution for the two-dimensional scattering of a line source by a cylinder with an arbitrary distribution of surface impedance and its image with respect to a vertical baffle is derived. This description is used to model the shadowing due to a low-height semi-cylindrical noise barrier close to a tramway. After validation against the boundary element method, this solution is used in a gradient-based optimization approach of the admittance distribution to maximize the broadband insertion loss in a given receiver zone. First, a hypothetical but passive distribution is found, showing an improvement of more than 20 dB(A) with respect to a purely rigid barrier. Second, a feasible optimized surface treatment made of a porous layer and a micro-perforated resonant panel is proposed, with an improvement of 14 dB(A) with respect to an entirely rigid barrier and 8 dB(A) with respect to a uniform absorbent barrier. The optimization provides an automatic way of tuning the resonant panel so that the attenuation is enhanced in the frequency band where the source has the most spectral content. The benefit of using a non-uniform admittance distribution is evaluated in this idealized context to be about 8 dB(A)

Application of admittance optimization to the design of a low-height tramway noise barriers

International audienceAn urban low-height barrier meant to attenuate tramway noise emission for nearby walking pedestrians or cyclists is studied. A numerical method coupling the two dimensional BEM and a gradient-based optimization algorithm is proposed to optimize the admittance distribution on the barrier in order to enhance the broadband insertion loss in the shadowing zone. The gradient of the broadband attenuation is calculated e ciently using the adjoint state approach which makes it possible to use a large number of parameters without significant increase of computation time and to consider a barrier of arbitrary shape. A few admittance designs coupling porous layers and micro-perforated resonant panels covering barriers of classical shapes are proposed, all showing an improvement of several dB(A) compared to more simple admittance distributions

Sensivity-based shape optimization of a rigid tramway low-height noise barrier

International audienceAn urban low-height barrier meant to attenuate tramway noise for nearby walking pedestrians or cyclists is considered. The efficiency of this type of device is known to depend on the shape of the cross section and the acoustic properties of the surface treatment. Some sort of absorptive material is often required to enhance the performance by preventing the multi-reflection phenomenon, however such materials can be costly compared to acoustically rigid materials such as concrete. In this study, a rigid barrier is assumed but its shape is optimized using a sensitivity-based shape optimization algorithm coupled to the two dimensional BEM. The shape is here described in a very general fashion by mesh nodes coordinates, which can involve a large number of variables. Sensitivities with respect to all coordinates are calculated efficiently using the adjoint state approach, without significant increase of computation time. Numerical results show that optimized shapes tend to be quite irregular but provide a significant improvement compared to simpler shapes, especially in the mid and high frequency range. Intensity calculations seem to suggest that this improvement is due to scattering of the incident acoustic energy in the upwards direction, therefore reducing the diffracted energy which reaches the shadow zone. Extra calculations show that the benefit of the optimized shapes can still be significant even in more realistic situations

Scattering of a cylinder covered with an arbitrary distribution of admittance and application to the design of a tramway noise abatement system

International audienceAn urban low-height barrier meant to attenuate tramway noise emission for nearby walking pedestrians or cyclists is studied. A semi-analytical solution for the two-dimensional scattering of a line source by a cylinder covered by an arbitrary distribution of impedance and its image with respect to a vertical baffle is derived. This description is used to model the shadowing due to a semi-cylindrical noise barrier close to a tramway. This solution is used in a gradient-based optimization approach of the admittance distribution to maximize the broadband insertion loss in a given receiver zone. A feasible optimized surface treatment made of a porous layer and a micro-perforated resonant panel is proposed, with an improvement of 14 dB(A) with respect to an entirely rigid barrier. The optimization gain with respect to a uniform absorbent admittance is about 8 dB(A). Extra tests with the boundary element method show that this gain is reduced but still significant if more realistic conditions are considered

Accuracy of outdoor sound propagation prediction in a complex environment using some reference numerical models

The paper presents principles which can be used in reference numerical models to make easy calculations for predicting long-range outdoor sound propagation under complex environment. Limits, assumptions as well as approximations used are discussed here in terms of accuracy for typical road traffic configurations, depending on range of frequency, geometry of the site and atmospheric conditions. Part of this work has been achieved during the European Project Harmonoise

Using natural means to reduce surface transport noise during propagation outdoors

This paper reviews ways of reducing surface transport noise by natural means. The noise abatement solutions of interest can be easily (visually) incorporated in the landscape or help with greening the (sub)urban environment. They include vegetated surfaces (applied to faces or tops of noise walls and on building façades and roofs ), caged piles of stones (gabions), vegetation belts (tree belts, shrub zones and hedges), earth berms and various ways of exploiting ground-surface-related effects. The ideas presented in this overview have been tested in the laboratory and/or numerically evaluated in order to assess or enhance the noise abatement they could provide. Some in-situ experiments are discussed as well. When well-designed, such natural devices have the potential to abate surface transport noise, possibly by complementing and sometimes improving common (non-green) noise reducing devices or measures. Their applicability strongly depends on the available space reserved for the noise abatement and the receiver position

Association between Ambient Noise Exposure and School Performance of Children Living in An Urban Area: A Cross-Sectional Population-Based Study

16 pages Article disponible à l'adresse suivante : http://link.springer.com/article/10.1007%2Fs11524-013-9843-6International audienceMost of the studies investigating the effects of the external noise on children's school performance have concerned pupils in schools exposed to high levels due to aircraft or freeway traffic noise. However, little is known about the consequences of the chronic ambient noise exposure at a level commonly encountered in residential urban areas. This study aimed to assess the relationship between the school performance of 8- to 9-year-old-children living in an urban environment and their chronic ambient noise exposure at home and at school. The children's school performances on the national standardized assessment test in French and mathematics were compared with the environmental noise levels. Children's exposure to ambient noise was calculated in front of their bedrooms (Lden) and schools (LAeq,day) using noise prediction modeling. Questionnaires were distributed to the families to collect potential confounding factors. Among the 746 respondent children, 586 were included in multilevel analyses. On average, the LAeq,day at school was 51.5 dB (SD= 4.5 dB; range = 38-58 dB) and the outdoor Lden at home was 56.4 dB (SD= 4.4 dB; range = 44-69 dB). LAeq,day at school was associated with impaired mathematics score (p = 0.02) or impaired French score (p = 0.01). For a + 10 dB gap, the French and mathematics scores were on average lower by about 5.5 points. Lden at home was significantly associated with impaired French performance when considered alone (p < 10(-3)) and was borderline significant when the combined home-school exposure was considered (p = 0.06). The magnitude of the observed effect on school performance may appear modest, but should be considered in light of the number of people who are potentially chronically exposed to similar environmental noise levels