A scale model study of parallel urban canyons

Shielded urban areas are of importance regarding urban citizens’ annoyance and adverse health effects related to road traffic noise. This work extends the existing knowledge of sound propagation to such areas by a scale model study, rather than by model calculations. The scale model study was executed for two parallel urban canyons at a 1 to 40 scale, with a point source located in one canyon. Cases with acoustically hard façades and absorption and diffusion façade treatments were in vestigated. To correct for excess air attenuation of the measurements, a wavelet-based method has been applied. The measurement results in the shielded canyon show that, in contrast to the directly exposed street canyon, the levels and the decay times are quite constant over the length of the canyon. The energy-time curve in the shielded canyon is characterized by a rise time, which can be related to the sound pressure level. The rise times and decays can be explained by separate reflection, diffraction and diffusion processes. A closed courtyard situation enlarges the level difference between acoustically hard façades and applied façade absorption or diffusion treatments at both the directly exposed and shielded side. A comparison between measurements with two different diffusion mechanisms, horizontal and vertical diffusion, reveals that vertical diffusion yields lower levels at the shielded side compared to horizontal diffusion for the investigated situations

Meteorological effects on the noise shielding by low parallel wall structures

Numerical calculations, scale model experiments and real-life implementations have shown that the insertion of a closely spaced array of low parallel walls beside a road is potentially a valuable road traffic noise abatement technique. However, all previous studies have assumed a non-refracting and non-turbulent atmosphere. This study carries out a numerical assessment of the extent to which the noise reduction is preserved in the presence of wind gradients and turbulence. Several full-wave calculation techniques have been used to model the noise reduction provided by parallel walls subject to moderate and strong winds, and in a turbulent atmosphere. While meteorological effects do not deteriorate the insertion loss of the parallel wall array in the low frequency range, higher sound frequencies are strongly negatively affected. These numerical results are compared to the noise shielding of traditional highway noise walls with different heights including refraction

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 A(can). Firstly, it is shown by numerical calculations that A(can) may be divided into independent source and receiver environment terms, A(s) and A(r). 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 A(s) and A(r) 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

The potential of building envelope greening to achieve quietness

Reduction of noise is one of the multiple benefits of building envelope greening measures. The potential of wall vegetation systems, green roofs, vegetated low screens at roof edges, and also combinations of such treatments, have been studied by means of combining 2D and 3D full-wave numerical methodologies. This study is concerned with road traffic noise propagation towards the traffic-free sides of inner-city buildings (courtyards). Preserving quietness at such locations has been shown before to be beneficial for the health and well-being of citizens. The results in this study show that green roofs have the highest potential to enhance quietness in courtyards. Favourable combinations of roof shape and green roofs have been identified. Vegetated façades are most efficient when applied to narrow city canyons with otherwise acoustically hard façade materials. Greening of the upper storey’s in the street and (full) façades in the courtyard itself is most efficient to achieve noise reduction. Low-height roof screens were shown to be effective when multiple screens are placed, but only on conditions that their faces are absorbing. The combination of different greening measures results in a lower combined effect than when the separate effects would have been linearly added. The combination of green roofs or wall vegetation with roof screens seems most interesting

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

On the improved point-to-point calculations for noise mapping in shielded urban areas

Noise mapping of 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 these 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, the attenuation terms describing these propagation paths are extended by terms including geometrical aspects of the urban environment both in the source and in the receiver area. In the present work, it has been studied to what extent these terms may be treated as being independent of the source-receiver distance. Also, the validity of treating the propagation path in a 2D plane rather than in 3D is investigated. Results obtained from a wave-based acoustic propagation model have been used for this assessment

Työpaikalla homealtistuksesta oireilevien ja sairastuneiden sosiaaliturva ja kuntoutus

Opinnäytetyön aiheena on työpaikalla homealtistuksesta oireilevien ja sairastuneiden sosiaaliturvan ja kuntoutuksen toteutuminen. Tutkimuksen viitekehys muodostuu homealtistuksen aiheuttamien terveyshaittojen, sosiaaliturvan ja kuntoutuksen sekä psyko-sosiaalisen tuen käsitteistä. Tutkimukseni perustuu kvantitatiiviseen tutkimusotteeseen ja se on luonteeltaan survey-tutkimus. Tutkittavien joukkoon kuului sekä Työpaikalla homealtistuksesta sairastuneiden eli TYHOSA ry:n jäseniä että sellaisia työpaikalla homealtistuksesta oireilevia ja sairastuneita, jotka eivät kuulu homesairaiden yhdistykseen. Kyselylomakkeita lähetettiin kaikkiaan 135 työpaikalla homealtistuksesta oireileville ja sairastuneille. Kyselyn vastausprosentti oli 57 %. Tutkimusaineisto koostui sähköposti- ja postikyselyistä, jotka suoritettiin huhtikuussa 2004. Tiedonkeruussa käytetty kyselylomake sisälsi strukturoituja ja avoimia kysymyksiä yhteensä 10. Kyselylomakkeessa kysyin taustatiedot, kosteusvauriomikrobien aiheuttamat oireet ja sairaudet, sosiaaliturvan ja kuntoutuksen toteutumista sekä millaista tukea tutkittavat ovat saaneet. Tutkimusaineisto käsiteltiin manuaalisesti laskemalla. Tutkimuksestani kävi ilmi, että työpaikalla homealtistuksesta oireilevien ja sairastuneiden sosiaaliturvan, kuntoutuksen ja psykososiaalisen tuen saaminen ei toteudu asianmukaisesti. Rahalliset tukimuodotkin ovat sekavia eivätkä toteudu kaikkien kohdalla tasavertaisesti. Homealtistuksessa sairastuneet kaipaavat viranomaisilta, työyhteisöltä, lääkäreiltä ja työterveyshuollosta enemmän tietoa ja tukea oireilunsa ja sairastamisensa vuoksi sekä tietoa kuntoutuksesta ja ammatillisesta kuntoutuksesta. Ammattitautitutkimuksiin pääseminen on ollut myös vaikeaa ja sairastuneet ovat usein joutuneet hakemaan lähetteensä yksityislääkäreiltä, koska työterveyslääkäri ei ole suostunut sitä kirjoittamaan. Homesairaita on kaikissa ammattiryhmissä. Eniten homesairauksia oli hoitoalan työntekijöillä (21 %), toimistotyöntekijöillä (18 %) ja opettajilla (17 %). Suurin osa sairastuneista (45 %) oli ollut sairauslomalla alle puoli vuotta, mutta jopa seitsemän ja kahdeksan vuoden sairausloma-aikoja oli, henkilöiden saamatta kuitenkaan eläkettä. Työnantajat olivat irtisanoneet neljä työntekijää ja kahdelle oli ehdotettu irtisanoutumaan vapaaehtoisesti työstään, koska työnantajalla ei ollut osoittaa homeetonta työpaikkaa oireilevalle työntekijälle. Vakuutusyhtiöltä sai tapaturmaeläkettä 24,7 % vastaajista. Yksi henkilö sai viimesijaista tukimuotoa, eli toimeentulotukea. Vastaajista 54 % oli saanut kuntoutusta ja 46 % vastaajista ei ollut saanut mitään kuntoutusta. Neljä henkilöä oli hakenut kuntoutusta, mutta heidän hakemuksensa oli hylätty, koska heillä ei ollut diagnoosia sairaudestaan