In this study, the pollutant dispersion within street canyons is studied by experiments conducted in an environmental wind tunnel. The vehicular exhaust emissions are modeled using a line source. The pollutant （smoke...In this study, the pollutant dispersion within street canyons is studied by experiments conducted in an environmental wind tunnel. The vehicular exhaust emissions are modeled using a line source. The pollutant （smoke） concentrations inside the canyons are measured based on a light scattering technique. The pollutant concentrations within the four different street canyons containing the galleries and the three-level flat-roofs under both the isolated and urban environments are obtained and discussed. For each of the four canyon configurations investigated, it is found that there is an obvious discrepancy between the pollutant dispersion patterns under the isolated environment and the urban environment. The three-level fiat roof is found to significantly influence the pollutant distribution pattern in a street canyon. In order to clarify the impacts of the wedge-shaped roofs on the pollutant dispersion inside an urban street canyon of an aspect ratio of 1.0, the pollutant distributions inside urban street canyons of three different wedge-shaped roof combinations are measured and analyzed. It is revealed that the pollutant distribution pattern inside the urban street canyon of an aspect ratio of 1.0 is influenced greatly by the wedge-shaped roof, especially, when an upward wedge-shaped roof is placed on the upstream building of the canyon. Images from this study may be utilized for a rough evaluation of the computational fluid dynamics （CFD） models and for helping architects and urban planners to select the canyon configurations with a minimum negative impact on the local air quality.展开更多
Long-span roof with span larger than height always has a complicated three-dimensional curve. Wind pressure on the roof is often influenced not only by the atmospheric turbulence, but also by the “signature” turbule...Long-span roof with span larger than height always has a complicated three-dimensional curve. Wind pressure on the roof is often influenced not only by the atmospheric turbulence, but also by the “signature” turbulence provoked in the wind by the structure itself. So it is necessary to study characteristics of flows around the roof. In this paper, three-dimensional numerical simulation of wind-induced pressure has been periormed on a long-span flat roof by means of Computational Fluid Dynamics （CFD） software ——FLUENT. The flow characteristics are studied by considering some parameters, such as wind direction, span-height ratio, roof pitch, flow characteristics, roughness of terrain. The simulation is based upon the Reynolds-averaged equations, in which Reynolds stress equation model （RSM） and SIMPLE technology, （Semi-Implieit Method for Pressure-Linked Equations） have been used. Compared with wind tunnel tests, the computational results have good agreement with the experimental data. It is proved that the results are creditable and the method is feasible.展开更多
The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechan...The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechanism of wind pressure pulse events, the peak over threshold method was employed to study properties of this kind of events. The event duration time, the energy contribution, the number of the pulse events, and the distribution of average peak pressure were calculated. Probability density functions of some typical samples in separation region were also given. Results show that the non-Gaussian roof pressure is strong in the flow separation region owing to the wind pressure pulse events. Evaluations of the extreme peak pressures, which can be determined by the peak over threshold method effectively, are important to the design of building cladding.展开更多
Historically,white flat roofs have been used in Israel due to the intense solar radiation and long,hot,rainless summers.However,red pitched roofs have also been frequently used for aesthetic reasons.It has been recent...Historically,white flat roofs have been used in Israel due to the intense solar radiation and long,hot,rainless summers.However,red pitched roofs have also been frequently used for aesthetic reasons.It has been recently observed that red pitched roofs have been recolored white by homeowners.The goal of this study was to compare the life cycle assessments(LCAs)of white flat roofs versus red or white pitched roofs through their production(P),operational energy(OE),and maintenance to disposal(MtoD)stages.EnergyPlus software was used to evaluate the OE stage.The ReCiPe method was used to evaluate the environmental damages in all the stages.A two-stage nested ANOVA was used to determine the significant differences between the ReCiPe result of a white flat roof and the ReCiPe result of a red/white pitched roof.It was found that(i)selection of the best roof technology(flat or pitched)requires consideration of the LCA,including the P,OE,and MtoD stages;(ii)the white(flat and pitched)roof was the best technology,while the red pitched roof was the worst technology;and(iii)the combination of the ReCiPe endpoint hierarchical six methodological options method with two-stage nested hierarchical mixed ANOVA is the best approach for assessing the differences related to the LCAs of roof technologies.展开更多
This paper studies and analyzes tall buildings with shell and flat roof responses designed for gravity and earthquake loads in different zones having different soil profiles. These tall buildings having two different ...This paper studies and analyzes tall buildings with shell and flat roof responses designed for gravity and earthquake loads in different zones having different soil profiles. These tall buildings having two different heights and different configurations are simulated with different load combinations. The responses of the simulated structural models with flat and shell roofs are studied and analyzed. These responses draw recommendations and guidelines for preliminary design of structurally efficient and reliable tall buildings with shell roof in earthquake zones. Five different earthquake zone factors (Z1 - Z5) along with the five different soil profiles (S1 - S5) are selected in this study. The non-linear dynamic response of buildings was obtained using three simulated models of buildings;square/rectangular, circular, and tube-shaped building. Total of 12 building models, four under each category, are analyzed using the finite element software (STAAD pro) subjected to the gravity as well as earthquake loading defined by UBC and IBC codes. Each building model is analyzed with two different story heights;which are 120 meters for 30 stories and 72 meters for 18 stories respectively. Horizontal and vertical displacement comparison is made among the flat roof and shell roof building for 32 and 18 stories building satisfying the ACI code of design requirement and drift index of 1/500 (0.002). The results showed that the drift index value for all the studied buildings is close to 0.002. All the maximum horizontal and vertical deflections occur under the earthquake zone-5 (0.40 gravitational acceleration) with soil profile-5 (Soft soil). The shell roof slab with less thickness than the flat roof slab did satisfy the horizontal and vertical deflection limits, therefore, it is more economical than the flat roof slab.展开更多
A systematic experimental investigation to understand the effect of heat loss and the thermoelectric aspect ratio (cross sectional area and length) on a flat plate solar thermoelectric system performance was carried o...A systematic experimental investigation to understand the effect of heat loss and the thermoelectric aspect ratio (cross sectional area and length) on a flat plate solar thermoelectric system performance was carried out. The investigation involved a series of experiments on systems with 4 different sizes of thermoelectric generators, and it was tested in 5 different vacuum levels during the steady-state. The detailed experimental investigation provided a substantial amount of data, which revealed that the system performance of both heat and electricity power were improved when the heat lost was minimised. The system’s performance strongly depended on the aspect ratio of the thermoelectric generators. This finding might have a significant impact on the cost of the system by saving the user’s and the manufacturer’s time in examining different TEGs with different aspect ratios in order to get the optimum size optimisation of the hybrid system, as well as reduce the manufacturing cost.展开更多
基金Project supported by the National Natural Science Foun-dation of China(Grant No.51536006)the Innovation Program of Shanghai Municipal Education Commission(Grant No.10ZZ95)the Hujiang Foundation of China(Grant No.B14003)
文摘In this study, the pollutant dispersion within street canyons is studied by experiments conducted in an environmental wind tunnel. The vehicular exhaust emissions are modeled using a line source. The pollutant （smoke） concentrations inside the canyons are measured based on a light scattering technique. The pollutant concentrations within the four different street canyons containing the galleries and the three-level flat-roofs under both the isolated and urban environments are obtained and discussed. For each of the four canyon configurations investigated, it is found that there is an obvious discrepancy between the pollutant dispersion patterns under the isolated environment and the urban environment. The three-level fiat roof is found to significantly influence the pollutant distribution pattern in a street canyon. In order to clarify the impacts of the wedge-shaped roofs on the pollutant dispersion inside an urban street canyon of an aspect ratio of 1.0, the pollutant distributions inside urban street canyons of three different wedge-shaped roof combinations are measured and analyzed. It is revealed that the pollutant distribution pattern inside the urban street canyon of an aspect ratio of 1.0 is influenced greatly by the wedge-shaped roof, especially, when an upward wedge-shaped roof is placed on the upstream building of the canyon. Images from this study may be utilized for a rough evaluation of the computational fluid dynamics （CFD） models and for helping architects and urban planners to select the canyon configurations with a minimum negative impact on the local air quality.
文摘Long-span roof with span larger than height always has a complicated three-dimensional curve. Wind pressure on the roof is often influenced not only by the atmospheric turbulence, but also by the “signature” turbulence provoked in the wind by the structure itself. So it is necessary to study characteristics of flows around the roof. In this paper, three-dimensional numerical simulation of wind-induced pressure has been periormed on a long-span flat roof by means of Computational Fluid Dynamics （CFD） software ——FLUENT. The flow characteristics are studied by considering some parameters, such as wind direction, span-height ratio, roof pitch, flow characteristics, roughness of terrain. The simulation is based upon the Reynolds-averaged equations, in which Reynolds stress equation model （RSM） and SIMPLE technology, （Semi-Implieit Method for Pressure-Linked Equations） have been used. Compared with wind tunnel tests, the computational results have good agreement with the experimental data. It is proved that the results are creditable and the method is feasible.
基金Sponsored by the National Natural Science Foundation of China(Grant No.50708030 and 90815021)
文摘The wind pressure pulse events, among the most important characteristics of wind pressure fluctuations on large-span flat roofs, were investigated by wind tunnel tests in this paper. Incorporating the formation mechanism of wind pressure pulse events, the peak over threshold method was employed to study properties of this kind of events. The event duration time, the energy contribution, the number of the pulse events, and the distribution of average peak pressure were calculated. Probability density functions of some typical samples in separation region were also given. Results show that the non-Gaussian roof pressure is strong in the flow separation region owing to the wind pressure pulse events. Evaluations of the extreme peak pressures, which can be determined by the peak over threshold method effectively, are important to the design of building cladding.
文摘Historically,white flat roofs have been used in Israel due to the intense solar radiation and long,hot,rainless summers.However,red pitched roofs have also been frequently used for aesthetic reasons.It has been recently observed that red pitched roofs have been recolored white by homeowners.The goal of this study was to compare the life cycle assessments(LCAs)of white flat roofs versus red or white pitched roofs through their production(P),operational energy(OE),and maintenance to disposal(MtoD)stages.EnergyPlus software was used to evaluate the OE stage.The ReCiPe method was used to evaluate the environmental damages in all the stages.A two-stage nested ANOVA was used to determine the significant differences between the ReCiPe result of a white flat roof and the ReCiPe result of a red/white pitched roof.It was found that(i)selection of the best roof technology(flat or pitched)requires consideration of the LCA,including the P,OE,and MtoD stages;(ii)the white(flat and pitched)roof was the best technology,while the red pitched roof was the worst technology;and(iii)the combination of the ReCiPe endpoint hierarchical six methodological options method with two-stage nested hierarchical mixed ANOVA is the best approach for assessing the differences related to the LCAs of roof technologies.
文摘This paper studies and analyzes tall buildings with shell and flat roof responses designed for gravity and earthquake loads in different zones having different soil profiles. These tall buildings having two different heights and different configurations are simulated with different load combinations. The responses of the simulated structural models with flat and shell roofs are studied and analyzed. These responses draw recommendations and guidelines for preliminary design of structurally efficient and reliable tall buildings with shell roof in earthquake zones. Five different earthquake zone factors (Z1 - Z5) along with the five different soil profiles (S1 - S5) are selected in this study. The non-linear dynamic response of buildings was obtained using three simulated models of buildings;square/rectangular, circular, and tube-shaped building. Total of 12 building models, four under each category, are analyzed using the finite element software (STAAD pro) subjected to the gravity as well as earthquake loading defined by UBC and IBC codes. Each building model is analyzed with two different story heights;which are 120 meters for 30 stories and 72 meters for 18 stories respectively. Horizontal and vertical displacement comparison is made among the flat roof and shell roof building for 32 and 18 stories building satisfying the ACI code of design requirement and drift index of 1/500 (0.002). The results showed that the drift index value for all the studied buildings is close to 0.002. All the maximum horizontal and vertical deflections occur under the earthquake zone-5 (0.40 gravitational acceleration) with soil profile-5 (Soft soil). The shell roof slab with less thickness than the flat roof slab did satisfy the horizontal and vertical deflection limits, therefore, it is more economical than the flat roof slab.
文摘A systematic experimental investigation to understand the effect of heat loss and the thermoelectric aspect ratio (cross sectional area and length) on a flat plate solar thermoelectric system performance was carried out. The investigation involved a series of experiments on systems with 4 different sizes of thermoelectric generators, and it was tested in 5 different vacuum levels during the steady-state. The detailed experimental investigation provided a substantial amount of data, which revealed that the system performance of both heat and electricity power were improved when the heat lost was minimised. The system’s performance strongly depended on the aspect ratio of the thermoelectric generators. This finding might have a significant impact on the cost of the system by saving the user’s and the manufacturer’s time in examining different TEGs with different aspect ratios in order to get the optimum size optimisation of the hybrid system, as well as reduce the manufacturing cost.
