OVERVIEW DEPARTMENT INFORMATION TECHNOLOGY RESEARCH GROUP WAVES ̶ How can vegetation be used to reduce physical sound pressure levels? ̶ Tree belt along road ̶ Natural berms GREENING AND SOUND ̶ Building envelope greening (green roofs) ̶ How can the noise perception improvement by vegetation be explained ? Timothy Van Renterghem 2 VEGETATION BELTS VEGETATION BELTS ̶ A lot of ad-hoc research ̶ Leaves ̶ Divergent findings leading to conservative advice and ̶ Scattering of sound prediction schemes ̶ Absorption processes ‒ Visco-thermal effects at the surface ̶ Need for design! ‒ Damped vibrations High frequencies 3 4 1
VEGETATION BELTS VEGETATION BELTS ̶ Trunks ̶ Guidelines ̶ Multiple scattering of sound ̶ Experiments ̶ Multiple interactions with partly absorbing bark ̶ Full-wave simulations ‒ Scattering by impedance cylinders ̶ Forest floor ‒ Validated forest floor models including input data ̶ Destructive interference Mid frequencies Low frequencies 5 6 How to decrease stem cover fraction without affecting shielding (too How to increase 15-m deep belt much)? shielding ? Van Renterghem, Ecological Van Renterghem, Ecological 7 8 Engineering , 2014 Engineering , 2014 2
Van Renterghem et al., Environmental methods 9 10 for surface transport noise reduction, Chapter 5. NATURAL BERMS Van Renterghem, Acta Acustica united with Acustica , 2015 11 12 3
NATURAL BERMS NATURAL BERMS 13 14 NATURAL BERMS NATURAL BERMS 15 16 4
NATURAL BERMS NATURAL BERMS v v x z , x z , grad 2 1 dz Van Renterghem et al., Van Renterghem et al., Landscape and urban Landscape and urban planning , 2012 planning , 2012 17 18 NATURAL BERMS NATURAL BERMS 19 20 5
NATURAL BERMS BUILDING ENVELOPE GREENING Van Renterghem et al., Environmental modelling and software , ̶ Enhancing quiet side 2018 ̶ Dominant sound path interacting with green roofs FDTD Van Renterghem, Nature based strategies for urban and building sustainability , Chapter 3.8, 2018 21 22 BUILDING ENVELOPE GREENING BUILDING ENVELOPE GREENING Van Renterghem, Nature based strategies for ̶ Flat roofs ̶ Non-flat roofs Van Renterghem et al., Building and Environment , urban and building sustainability , Chapter 3.8, 2011 2018 Green roof road traffic noise insertion loss (30-70 km/h, 5 % heavy traffic) Propagation path Low High Substrate length case number Vegetation cover microphone microphone depth interacting with 2.4 dBA position position green roof > 75 % (sedum + 1 20-30 mm 8 m 4.1 dBA 1 dBA mosses) single diffraction < 5 % (sedum 2 50-60 mm 2.5 m 2.3 dBA -2.4 dBA cases shoots) 3 180 mm 4.5 m 50 % (grasses) 5.5 dBA 2.1 dBA 7.5 dBA 4 30-40 mm 25 m > 90 % (sedum) 3.1 dBA 2.2 dBA double diffraction < 5 % (sedum 5 80-100 mm 25 m 3.4 dBA 5.1 dBA cases shoots) 2-4 dBA re rigid roofs 2.4 dBA Lp2>Lp1 Van Renterghem et al., Building and Environment , Lp1 Lp2 2013 23 24 6
̶ ̶ ̶ ̶ BUILDING ENVELOPE GREENING BUILDING ENVELOPE GREENING ̶ green roofs vs solar panels ̶ green roofs vs solar panels ? 25 26 BUILDING ENVELOPE GREENING NOISE PERCEPTION AND GREEN “ A significant number of respondents indicated that vegetation ̶ green roofs vs solar panels Van Renterghem, Building Acoustics , 2018 was a viable alternative to noise walls ” and “ it was claimed that their experience with vegetation supported this contention ” (Perfater, 1979). 10 m “ 90% of the subjects believed that landscape plants contribute to noise reduction ” (Yang et al., 2011). 20 m urban A cycling path exposed to 70 dBA highway noise (but covered in road traffic green) lead to 45% of the respondents still considering this zone receivers 20 m as “calm” (opposed to “busy”) (Aletta et al., 2018). ... 27 27 28 7
SOURCE VISIBILITY NATURAL SOUNDS ̶ “Attention focussing” : seeing a source will increase ̶ Masking potential annoyance ̶ Highly appreciated by humans ̶ “Audio - visual congruency” : “you should see what you hear” ̶ Contradicting conclusions (Watts, 1999 vs Zhang et al., 2003) 29 30 RESTORATIVE POTENTIAL RESTORATIVE POTENTIAL ̶ Environmental noise exposure ̶ occupies part of the workload of the human brain Van Renterghem et al., Landscape and urban planning , 2016 ̶ induces stress reactions ̶ Potential explanation by ̶ Attention Restoration Theory (Kaplan et al., 1983) ̶ Stress Recovery Theory (Ulrich, 1989) 31 32 32 8
RESTORATIVE POTENTIAL RESTORATIVE POTENTIAL % highly annoyed 95% confidence interval factor 5 ! survey Leung et al., Journal of N=105 Acoustical Society of America , 2017 Van Renterghem et al., Landscape and urban 33 33 34 34 34 planning , 2016 PERCEPTION IMPROVEMENT CONCLUSIONS ̶ Need for visible outdoor vegetation ̶ Can nature-based solutions be used to reduce ̶ Importance of green quality decibels? Yes ! ̶ Seems to work at high exposure levels ̶ Can vegetation be used to improve perception ̶ Equivalent level reduction is strong regardless of the exposure level ? Yes ! (strong effect) ̶ 15 dBA (Langdon, 1976) ̶ But must be well designed ! ̶ 5 dBA (Lercher, 1996) ̶ 10 dBA (Van Renterghem et al., 2016) ̶ 11 dBA (Leung et al., 2017) 35 36 9
Timothy Van Renterghem Associate Professor Department of Information Technology Ghent University WAVES research group @ugent Ghent University timothy.vanrenterghem@ugent.be www.ugent.be 10
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