E. Salomons

The Harmonoise sound propagation model

The Harmonoise model for predicting environmental noise is expected to provide a basis for the development of a future method for environmental noise mapping in Europe. In this article a detailed description is presented of all steps involved in a calculation with the Harmonoise sound propagation model. The description is restricted to point-to-point propagation, which is a basic element of a full (engineering) model for environmental noise. The description provides all details that are required for developing a computer code for the Harmonoise pointto-point model. The development and the theoretical justification of the model was described by D. van Maercke and J. Defrance in Acta Acustica united with Acustica 93 (2007) 201-212. In the present article some recent improvements of the model are included. Numerical examples are also presented. Results of the Harmonoise model are compared with results of the Nord2000 model, and also with accurate reference results. Also included are reference results that illustrate the effect of linearizing logarithmic wind profiles, which is relevant as Harmonoise and Nord2000 assume linearized wind profiles.

Urban background noise mapping: the general model

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 facade. Multiple reflections between facades in street canyons and inner yards are commonly neglected and facades 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, facade 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 facades whereof 3 were at inner yards in the city of Ghent, Belgium. At shielded facades, a strong improvement in prediction accuracy is obtained.

Urban background noise mapping : the multiple-reflection correction term

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.

Erratum: Urban background noise mapping: The general model (Acta Acustica united with Acustica (2014) 100 (1098-1111) DOI:10.3813/AAA.918789)

Erratum : Urban background noise mapping: The general model (Acta Acustica united with Acustica (2014) 100 (1098-1111) DOI:10.3813/AAA.918789)