Updated: 25-10-2017

Computational methods
Contemporary urban environments suffer from excessive levels of road traffic noise. A strategy has been adopted where access to closed courtyards is essential in order to offer urban sound environments of high quality with regard to health and perceived sound. From 2004 to 2009 the conveyed research has been focused on developing prediction methods of sound propagation to these close courtyards. One such method is the urban PE method (see paper C2 of publications). Later, I have worked with the 2.5-dimensional equivalent source method, ESM (see paper J02, J04 of publications) and developed the time-domain method PSTD (papers J06, J07) for this purpose. The latter method, has also been applied to atmospheric sound propagation applications. The methods have in common that they are wave equation based methods, in contrast to the engineering prediction methods. As such, the role of reflection and diffusion processes in the urban environment and the effect of meteorological conditions can accurately be studied. The models have been validated by a scale model study (papers C03, C05, C08 and J06) and by mutual comparison with the FDTD method (paper J11). Further developments within PSTD include a multi-domain PSTD method (paper J9) and the curvilinear PSTD method (J23) to model non-staircase geometries.
The PSTD method has also been used to improve engineering methods with the purpose of fast generation of noise maps. The improvement is related to the computed noise levels at non-exposed urban areas (paper J13).
From 2012, the PSTD method has been developed in the openPSTD project towards an open-source software for modelling sound propagation (paper C37). A 2D version of openPSTD is available at www.openpstd.org.
From 2013, PhD research is being conducted to improve boundary conditions in PSTD (C39) and to model source directivity with PSTD (C38).

Animation from openPSTD software.

Urban propagation effects
Propagation effects in the urban environment are investigated for understanding the urban sound environment and to investigate potential noise reduction measures. The effect of measures as façade absorption, walkways, and roof treatments like vegetation roofs and roof screens has been calculated for using the ESM method in a 2.5 approach (paper J04) and the PSTD method for a full 3D urban configuration (paper J08). The PSTD method has been exploited to investigate urban vegetation in a EU-funded project, the effect of greening the buildings on noise levels both in the closed courtyards as on the streets directly exposed to road traffic noise has been studied (papers J10, J11, J20) and the effect of ground roughness constructed out of low-height bricks has been computed (paper J14). Also, the effect of low height noise barrier inside streets has been studied (paper C25) as well as the sound scattering from a tree structure (paper C22). Another application that has been investigated with the numerical methods is the influence of meteorological conditions on sound propagation over de urban roof level (papers J05 and C30).
From 2014, research is devoted to investigating the in-situ effect of meteorological conditions (as rainfall) on the acoustic performance of green roofs, and on the acoustic effect of trees in the urban context. Urban_Green

Urban vegetation as noise reduction measure.

Human echolocation
Blind people may master the skill of human echolocation, i.e. they can explore their surroundings by listening to self-produced tongue clicks and the acoustical response from the physical environment. In a research project (2013-2015), the ability to successfully carry out echolocation is studied depending on different locations of the acoustic source and the frequency content of the signal.

 Dutch TV program ‘de Kennis van Nu’: 19 October 2017

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