A quasi-elastic regime for vibrated granular gases

Using simple scaling arguments and two-dimensional numerical simulations of a granular gas excited by vibrating one of the container boundaries, we study a double limit of small $1-r$ and large $L$, where $r$ is the restitution coefficient and $L$ the size of the container. We show that if the particle density $n_0$ and $(1-r^2)(n_0 Ld)$ where $d$ is the particle diameter, are kept constant and small enough, the granular temperature, i.e. the mean value of the kinetic energy per particle, $/N$, tends to a constant whereas the mean dissipated power per particle, $/N$, decreases like $1/\sqrt{N}$ when $N$ increases, provided that $(1-r^2)(n_0 Ld)^2 < 1$. The relative fluctuations of $E$, $D$ and the power injected by the moving boundary, $I$, have simple properties in that regime. In addition, the granular temperature can be determined from the fluctuations of the power $I(t)$ injected by the moving boundary.

Retrofitting housing with lightweight green roof technology in Sydney, Australia, and Rio de Janeiro, Brazil

© 2015 by the authors. The built environment contributes around half of total greenhouse gas emissions and with 87% of residential buildings that we will have by 2050 already built, it is vital to adopt sustainable retrofitting practices. The question is: what are the viable solutions? One answer may be green roof retrofitting. The environmental benefits include reduced operational carbon emissions, reduced urban heat island effect, increased bio-diversity, housing temperature attenuation and reduced stormwater run-off. The economic benefits are the reduced maintenance costs and lower running costs. The social gain is the creation of spaces where people have access to green areas. However, the barriers to retrofitting include the perceptions of structural adequacy, the risk of water damage, high installation and maintenance costs, as well as access and security issues. Many Australian and Brazilian residential buildings have metal sheet roofs, a lightweight material with poor thermal performance. During the summer, temperatures in Sydney and Rio de Janeiro reach 45 degrees Celsius, and in both cities, rainfall patterns are changing, with more intense downpours. Furthermore, many residential buildings are leased, and currently, tenants are restricted by the modifications that they can perform to reduce running costs and carbon emissions. This research reports on an experiment on two small-scale metal roofs in Sydney and Rio de Janeiro to assess the thermal performance of portable small-scale modules. The findings are that considerable variation in temperature was found in both countries, indicating that green roof retrofitting could lower the cooling energy demand considerably

Retrofitted green roofs and walls and improvements in thermal comfort

© 2017 Author(s). Increased urbanization has led to a worsening in the quality of life for many people living in large cities in respect of the urban heat island effect and increases of indoor temperatures in housing and other buildings. A solution may be to retrofit existing environments to their former conditions, with a combination of green infrastructures applied to existing walls and rooftops. Retrofitted green roofs may attenuate housing temperature. However, with tall buildings, facade areas are much larger compared to rooftop areas, the role of green walls in mitigating extreme temperatures is more pronounced. Thus, the combination of green roofs and green walls is expected to promote a better thermal performance in the building envelope. For this purpose, a modular vegetated system is adopted for covering both walls and rooftops. Rather than temperature itself, the heat index, which comprises the combined effect of temperature and relative humidity is used in the evaluation of thermal comfort in small scale experiments performed in Sydney - Australia, where identical timber framed structures prototypes (vegetated and non-vegetated) are compared. The results have shown a different understanding of thermal comfort improvement regarding heat index rather than temperature itself. The combination of green roof and walls has a valid role to play in heat index attenuation

Modelling green roof stormwater response for different soil depths

© 2016 Elsevier B.V. Green roofs have been proposed as a way to mitigate stormwater run-off in urban areas due to the possibility of retrofit to existing buildings. The amount of run-off is influenced by the, humidity, evapotranspiration, as well as soil type and depth. A modelling approach was undertaken to evaluate the response of different soil depths to cumulative rainfall and the efficiency in stormwater flow rate attenuation. The soil hydraulics were modelled using HYDRUS-1D software developed for modelling water flow in variably saturated porous media. Model runs were carried out for three quarterly scenarios to determine run-off peak flow rates and the overall retention, based on evapotranspiration rates of succulent plants and rainfall registers from Auckland, New Zealand. The soil depths modelled ranged from 5 to 160 cm. The efficiencies in peak flow attenuation by the shallowest soil considered were reduced under extreme and longer rainfall events by 3%. Therefore shallow soil or extensive green roofs may, on a wide scale, overcome the performance of deep soils due to their lighter weight which adds limited loads to existing roof structures thereby making them suited to retrofit greater numbers of buildings

Efeitos da fertirrigação com chorume bovino sobre características físicas e químicas de solos.

O experimento foi conduzido no Departamento de Solos e Engenharia Rural do Centro de Ciências Agrárias da Universidade Federal da Paraíba, Areia-PB com o objetivo de avaliar os efeitos da aplicação de chorume bovino em diferentes proporções em água: 0:1; 1:5; 1:4; 1:3 e 1:2 correspondentes aos percentuais de 0; 17; 20; 25 e 33% de chorume respectivamente, sobre características físicas e químicas de dois solos: um de textura argilosa e outro de textura arenosa. O delineamento experimental foi inteiramente casualizado em esquema fatorial 5 x 2 com três repetições. Para cada tratamento a aplicação da solução foi feita imediatamente após o volume de 5kg de solo terem sidos acondicionados em sacos de polietileno preto com 30cm de altura de 20cm de diâmetro e aos dez e vinte dias após a primeira aplicação. Os efeitos do chorume foram mais expressivos sobre a retenção de água pelo solo, densidade do solo, soma de bases, capacidade de troca catiônica do solo mais argiloso em relação ao solo mais arenoso. A aplicação do chorume não contribuiu no aumento da condutividade elétrica a ponto de tornar os solos salinos

Evaluating the Thermal Performance of Retrofitted Lightweight Green Roofs and Walls in Sydney and Rio de Janeiro

© 2017 The Authors. With increasing densification in urban settlements, environmental issues are a challenge in the sustainable development of all cities globally. Considering that the built environment releases almost half of the total greenhouse gas emissions, an effective solution to mitigating the impacts of increasing temperatures can be the improved performance of existing buildings. Furthermore 87% of the buildings we will have in 2050 are already built. Retrofitting roofs and walls with a living vegetated system such as green roofs and walls could be an upgrade option, increasing sustainable construction. The benefits are improved thermal performance but also improved air quality, stormwater attenuation, increased bio-diversity and lower heating and / or cooling energy consumption. No empirical data exists for Sydney and Rio de Janeiro and the question is; what is the extent of thermal improvement with retrofitted green walls and roof in timber framed and blockwork structures? This study analyses both effects and benefits of the green roofs and walls through an experiment in two countries: one in Sydney, Australia; a timber framed construction, and another one in Rio de Janeiro, Brazil; with blockwork construction. This difference in the material choice was made according to the most common type of construction for housing in each country. In each site, the walls and the roof of one of the prototypes were covered with plants and compared to the performance of an unplanted but otherwise identical prototype. The thermal performance was analysed by observing the temperature variation simultaneously in a non-vegetated and vegetated structure. The initial findings show that the combination of green roof and green walls have a relevant role in temperature attenuation. These results indicate, that this lightweight retrofit green technology could not only represent an important advance on sustainable development, but can that it also lead to more comfortable internal conditions for humans living in dense urban environments