The centralized smoke exhaust system of shield tunnel is an important determinant for tunnel fire safety,and the use of different design parameters of the tunnel smoke exhaust system will affect the smoke exhaust effe...The centralized smoke exhaust system of shield tunnel is an important determinant for tunnel fire safety,and the use of different design parameters of the tunnel smoke exhaust system will affect the smoke exhaust effect in the tunnel,and the influence of different design parameters on the smoke exhaust effect and temperature attenuation of the tunnel can help engineers in designing a more effective centralized smoke exhaust system for the tunnel.In this paper,the Fire Dynamic Simulator(FDS)is utilized to examine smoke exhaust vent settings for a centralized exhaust system in shield tunnel with both flat and sloped conditions,including slopes of+4.5%and−4.5%,under a 30MWfire power with a 150m^(3)/s smoke exhaust rate.The results suggest that maintaining a vent spacing of 60m and a vent size of 4.0 m×1.5 m is a reasonable configuration for centralized smoke exhaust systems in both flat and slope shield tunnels.This choice helpsminimize construction costs and prevent excessive smoke accumulation.It also promotes favorable conditions for maintaining temperature distribution at 2-m height,visibility,smoke spread distance,and temperature below the ceiling,all below the threshold values,while ensuring high smoke extraction efficiency.However,in the slope section,the chimney effect can disrupt exhaust efficiency,visibility,ceiling temperature,and temperature distribution at a height of 2 m.Employing different opening methods,such as having 2 vents up and 4 vents down in a+4.5%slope and 4 vents up and 2 vents down in a−4.5%slope,can help mitigate these effects.Furthermore,the temperature decay formula for shield tunnels follows a bi-exponential decay pattern,and different design parameters of centralized smoke exhaust systems have minimal effects on temperature decay in shield tunnels.展开更多
The optical properties of LaCl3：Ce crystal are reported in this paper. Optical transmission spectrum, photoluminescence and time resolved photoluminescence spectra at different temperatures are investigated. It is fo...The optical properties of LaCl3：Ce crystal are reported in this paper. Optical transmission spectrum, photoluminescence and time resolved photoluminescence spectra at different temperatures are investigated. It is found that optical transmittance is as high as 80% between 320 nm and 600 nm, and no obvious absorption band is found in this region. Emission intensity and decay time of photoluminescence are quite stable with the change of the temperature between 80 K and 500 K. No thermal quenching is present up to 500 K, and decay time keeps at 17±2 ns. With the increase of the temperature, the whole emission bands and excitation bands present broadening and overlapping, leading to the strengthening of re-absorption of the Ce^3＋ emission, which makes the emission spectra have a red shift trend.展开更多
Jet ventilation is widely used in the ventilation design of highway and railway tunnels as an important air supply method during tunnel operation and disaster periods.This ventilation method has also been applied for ...Jet ventilation is widely used in the ventilation design of highway and railway tunnels as an important air supply method during tunnel operation and disaster periods.This ventilation method has also been applied for fire control in immersed tunnels.We conduct numerical simulations using computational fluid dynamics(CFD)to study positive ventilation in the upstream and reverse ventilation in the downstream(P-R)for an extra-wide immersed tunnel.The effects of fire source location and jet fan air velocity response strategy on the ceiling temperature decay,carbon monoxide(CO)distribution,and smoke exhaust efficiency were investigated for varying fire source locations.The results show that flames will be tilted to the side of the jet fan with a smaller air velocity.Additionally,the jet fan air velocity should be adjusted based on the relative distance between the fire source and the smoke vent.Among the studied scenarios,the most effective outcome was achieved when the air velocity was adjusted to 25 m/s on the side near the smoke vent.Also in this scenario,the phenomenon of smoke deposition was effectively mitigated and the average smoke exhaust efficiency reached 87%.Moreover,we found that the temperature decay of the tunnel follows an exponential decay law.The temperature decay rate is significantly higher on the side closest to the smoke vent compared to the farther side.This research provides a theoretical basis for smoke control strategies for fires that occur in immersed tunnels.展开更多
Experiments were conducted in a 1:20 arced tunnel model to investigate the effect of canyon cross wind on buoyancy induced smoke flow characteristics of pool fres,involving smoke movement behaviour and longitudinal te...Experiments were conducted in a 1:20 arced tunnel model to investigate the effect of canyon cross wind on buoyancy induced smoke flow characteristics of pool fres,involving smoke movement behaviour and longitudinal temperature distribution of smoke layer.The canyon wind speed,longitudinal fre location and fre size were varied.Results show that there are two special smoke behaviours with the fre source positioned at different flow feld zones.When the fire source is positioned at the negative pressure zone,with increasing canyon wind speed,the smoke always exists upstream mainly due to the vortex,and the smoke temperature near the fire source increases frst and then decreases.However,when the fre source is located in the transition zone and the unidirectional flow zone,there is no smoke appearing upstream with a certain canyon wind speed.Meanwhile,the smoke temperature near the fre sources are decreases with increasing canyon wind speed.The dimensionless temperature rise of the smoke layer OT:*along the longitudinal direction of the tunnel follows a good exponential decay.As the canyon wind speed increases,the longitudinal decay rate of△T.*decreases.The longitudinal decay rate of AT*downstream of the fire is related to the fre location and canyon wind speed,and independent of the fire size.The empirical correlations for predicting the longitudinal decay of OT:*downstream of the fre are established.For a relatively large-scale fre,the longitudinal decay rate of AT:*upstream of the fire increases as the distance between the fire source and the upstream portal increases,especially for larger canyon wind speeds.展开更多
文摘The centralized smoke exhaust system of shield tunnel is an important determinant for tunnel fire safety,and the use of different design parameters of the tunnel smoke exhaust system will affect the smoke exhaust effect in the tunnel,and the influence of different design parameters on the smoke exhaust effect and temperature attenuation of the tunnel can help engineers in designing a more effective centralized smoke exhaust system for the tunnel.In this paper,the Fire Dynamic Simulator(FDS)is utilized to examine smoke exhaust vent settings for a centralized exhaust system in shield tunnel with both flat and sloped conditions,including slopes of+4.5%and−4.5%,under a 30MWfire power with a 150m^(3)/s smoke exhaust rate.The results suggest that maintaining a vent spacing of 60m and a vent size of 4.0 m×1.5 m is a reasonable configuration for centralized smoke exhaust systems in both flat and slope shield tunnels.This choice helpsminimize construction costs and prevent excessive smoke accumulation.It also promotes favorable conditions for maintaining temperature distribution at 2-m height,visibility,smoke spread distance,and temperature below the ceiling,all below the threshold values,while ensuring high smoke extraction efficiency.However,in the slope section,the chimney effect can disrupt exhaust efficiency,visibility,ceiling temperature,and temperature distribution at a height of 2 m.Employing different opening methods,such as having 2 vents up and 4 vents down in a+4.5%slope and 4 vents up and 2 vents down in a−4.5%slope,can help mitigate these effects.Furthermore,the temperature decay formula for shield tunnels follows a bi-exponential decay pattern,and different design parameters of centralized smoke exhaust systems have minimal effects on temperature decay in shield tunnels.
文摘The optical properties of LaCl3：Ce crystal are reported in this paper. Optical transmission spectrum, photoluminescence and time resolved photoluminescence spectra at different temperatures are investigated. It is found that optical transmittance is as high as 80% between 320 nm and 600 nm, and no obvious absorption band is found in this region. Emission intensity and decay time of photoluminescence are quite stable with the change of the temperature between 80 K and 500 K. No thermal quenching is present up to 500 K, and decay time keeps at 17±2 ns. With the increase of the temperature, the whole emission bands and excitation bands present broadening and overlapping, leading to the strengthening of re-absorption of the Ce^3＋ emission, which makes the emission spectra have a red shift trend.
文摘Jet ventilation is widely used in the ventilation design of highway and railway tunnels as an important air supply method during tunnel operation and disaster periods.This ventilation method has also been applied for fire control in immersed tunnels.We conduct numerical simulations using computational fluid dynamics(CFD)to study positive ventilation in the upstream and reverse ventilation in the downstream(P-R)for an extra-wide immersed tunnel.The effects of fire source location and jet fan air velocity response strategy on the ceiling temperature decay,carbon monoxide(CO)distribution,and smoke exhaust efficiency were investigated for varying fire source locations.The results show that flames will be tilted to the side of the jet fan with a smaller air velocity.Additionally,the jet fan air velocity should be adjusted based on the relative distance between the fire source and the smoke vent.Among the studied scenarios,the most effective outcome was achieved when the air velocity was adjusted to 25 m/s on the side near the smoke vent.Also in this scenario,the phenomenon of smoke deposition was effectively mitigated and the average smoke exhaust efficiency reached 87%.Moreover,we found that the temperature decay of the tunnel follows an exponential decay law.The temperature decay rate is significantly higher on the side closest to the smoke vent compared to the farther side.This research provides a theoretical basis for smoke control strategies for fires that occur in immersed tunnels.
基金supported by National Natural Science Founda-tion of China (Grant No.51974361)Natural Science Foundation of Hunan Province of China (No.2020JJ3046)the Fundamen-tal Research Funds for the Central Universities of Central South University (Grant Nos.2021zzts0762,502501004 and 502045009).
文摘Experiments were conducted in a 1:20 arced tunnel model to investigate the effect of canyon cross wind on buoyancy induced smoke flow characteristics of pool fres,involving smoke movement behaviour and longitudinal temperature distribution of smoke layer.The canyon wind speed,longitudinal fre location and fre size were varied.Results show that there are two special smoke behaviours with the fre source positioned at different flow feld zones.When the fire source is positioned at the negative pressure zone,with increasing canyon wind speed,the smoke always exists upstream mainly due to the vortex,and the smoke temperature near the fire source increases frst and then decreases.However,when the fre source is located in the transition zone and the unidirectional flow zone,there is no smoke appearing upstream with a certain canyon wind speed.Meanwhile,the smoke temperature near the fre sources are decreases with increasing canyon wind speed.The dimensionless temperature rise of the smoke layer OT:*along the longitudinal direction of the tunnel follows a good exponential decay.As the canyon wind speed increases,the longitudinal decay rate of△T.*decreases.The longitudinal decay rate of AT*downstream of the fire is related to the fre location and canyon wind speed,and independent of the fire size.The empirical correlations for predicting the longitudinal decay of OT:*downstream of the fre are established.For a relatively large-scale fre,the longitudinal decay rate of AT:*upstream of the fire increases as the distance between the fire source and the upstream portal increases,especially for larger canyon wind speeds.
