Jinxin Cao | Tongji University (original) (raw)
Papers by Jinxin Cao
Acta Optica Sinica
Conclusions Trans-HONO and N 2 O 4 gases are continuously measured at the same time, and the spec... more Conclusions Trans-HONO and N 2 O 4 gases are continuously measured at the same time, and the specific absorption line frequencies of the two gases in the range of 1279. 5-1282. 5 cm-1 are obtained by using a 7. 8 μm roomtemperature CW-QCL and a long pathlength absorption cell. The decay time of HONO in a closed absorption cell made of quartz is obtained by fitting and analyzing the decay curve of HONO. According to the known absorption line intensity of trans-HONO at 1280. 4 cm-1 , the level of trans-HONO in the sample to be measured is calculated to be (0. 72±0. 04) ×10-6 , the corresponding minimum detection limit of the system is about (11. 15±0. 50)×10-9. As the absorption line intensity of N 2 O 4 has not been reported in the spectral database and published articles, the level of N 2 O 4 in the sample to be tested has not been calculated. The absorption line frequencies of HONO and N 2 O 4 obtained in the experiment provide a reference for realtime continuous gas monitoring, sources and sinks analysis of atmospheric HONO, and analysis of the N 2 O 4 chemical reaction process.
Atmosphere, 2021
For the analysis of the aerodynamic characteristics of the buildings immersed in the atmospheric ... more For the analysis of the aerodynamic characteristics of the buildings immersed in the atmospheric boundary layer (ABL), it is necessary to generate a turbulence velocity field with similar temporal and special characteristics to the ABL to obtain a reliable result. In this paper, an improved precursor simulation method called the recycling and reshaping method (RRM) is proposed to generate a turbulent boundary layer in an LES model. The laminar inflow is firstly disturbed by the virtual roughness blocks realized by adding drag force term in the momentum equation, then the inflow velocity profile is reshaped every several steps to adjust the streamwise velocity profile in the downstream target area to meet the requirements. The final turbulence field generated by RRM with virtual roughness blocks is in good agreement with the target velocity conditions. Then, the simulation of the wind-induced pressure on an isolated low-rise building surface is carried out, using the generated turbul...
Journal of Wind Engineering and Industrial Aerodynamics
Journal of Wind Engineering and Industrial Aerodynamics
Journal of Wind Engineering and Industrial Aerodynamics, 2020
In addition to strong wind, tornado-borne flying debris is a major contributor to large destructi... more In addition to strong wind, tornado-borne flying debris is a major contributor to large destructions caused by tornadoes. However, research on flying debris is still very rare. In the present study, a specific tornado observed in nature is reproduced using large eddy simulations. The debris is assumed to consist of compact wooden objects with diameters of 2, 5, and 10 cm. The wooden objects are released at heights of 1, 5, 10 m, and 20 m. Instantaneous debris distributions, debris concentration, and statistics of debris velocities were systematically examined. The model shows that releasing debris at lower elevations or enlarging the size of the debris lead to greater debris dispersion and decrease the speed of debris. The fluctuations and maxima of debris velocities are globally less than those in wind. Among all of the cases studied, debris velocities can be estimated using wind velocities only when the debris diameter is 2 cm. The largest difference between the debris velocit...
Current wind-resistant design of wind-sensitive structures including large-scale cooling towers i... more Current wind-resistant design of wind-sensitive structures including large-scale cooling towers is generally carried out with respect to synoptic boundary-layer-type strong winds. A swirling tornado can produce significantly different wind pressures than conventional boundary-layer wind. This paper presents both stationary and translating tornado effects on a cooling tower in a tornado vortex simulator developed at Tongji University, China. Wind pressures acting on the external surface of cooling tower model were measured at a fixed swirl ratio (S = 0.54) in the present study. Different radial distances between a cooling tower and stationary tornado vortex center were considered. Translating tornadoes with three different translation speeds (u = 0.04 m/s, 0.12 m/s and 0.2 m/s) were simulated. The results show that a tornado vortex can produce high negative wind pressures on a cooling tower surface due to the negative pressure drop accompanying a tornado. A cooling tower exposed to a...
Journal of Wind Engineering and Industrial Aerodynamics
Buildings
The vector form intrinsic finite (VFIFE) method is a new and promising structural analysis techni... more The vector form intrinsic finite (VFIFE) method is a new and promising structural analysis technique that has many advantages as compared with the conventional finite element method (FEM) in analyzing the complex behaviors of a structure. However, despite the popularization of its application in civil and infrastructure engineering, there is no available unified general analysis framework for it, which limits the applications and developments of VFIFE. This work develops and implements a platform (termed openVFIFE) based on a new proposed object-oriented framework to facilitate the development and application of the vector form intrinsic finite method as well as the efficient and accurate analyses of complex behaviors for civil structures. To validate the platform, a series of numerical examples are conducted. Furthermore, to extend the applications of VFIFE, the nonlinear dynamic and collapse processes of a transmission tower under earthquake load are studied using openVFIFE. The r...
Frontiers in Built Environment
With the trend of variable cross-sections for long-span bridges from truss-stiffened to quasi-str... more With the trend of variable cross-sections for long-span bridges from truss-stiffened to quasi-streamlined, and then to multiple-box cross-section geometries, the importance of aeroelastic performance is becoming increasingly significant in wind-resistant design. This article shows that there is clearly insufficient qualitative as well as quantitative understanding of turbulence effects on bridge aerodynamics, particularly the mechanisms behind them. Although turbulence might help the stabilization of long-span bridges, and is thus not a conclusive parameter in wind-resistant design, turbulence effects on the aerodynamic and aeroelastic behaviors of a bridge need to be better understood because interaction between a bridge and turbulence always exists. This article also briefly introduces a newly developed multiple-fan wind tunnel that is designed to control turbulence to assist the study of turbulence effects.
Journal of Wind Engineering and Industrial Aerodynamics
Journal of Fluids and Structures
Frontiers in Built Environment, Dec 11, 2017
With the trend of variable cross-sections for long-span bridges from truss-stiffened to quasi-str... more With the trend of variable cross-sections for long-span bridges from truss-stiffened to quasi-streamlined, and then to multiple-box cross-section geometries, the importance of aeroelastic performance is becoming increasingly significant in wind-resistant design. This article shows that there is clearly insufficient qualitative as well as quantitative understanding of turbulence effects on bridge aerodynamics, particularly the mechanisms behind them. Although turbulence might help the stabilization of long-span bridges, and is thus not a conclusive parameter in wind-resistant design, turbulence effects on the aerodynamic and aeroelastic behaviors of a bridge need to be better understood because interaction between a bridge and turbulence always exists. This article also briefly introduces a newly developed multiple-fan wind tunnel that is designed to control turbulence to assist the study of turbulence effects.
Journal of Wind Engineering and Industrial Aerodynamics
Abstract Tornado risks for highly important long-span bridges in tornado-prone regions can not be... more Abstract Tornado risks for highly important long-span bridges in tornado-prone regions can not be neglected. Rigid-model wind pressure measurements on a streamlined bridge deck were conducted using a tornado vortex simulator, to clarify tornado-induced surface pressure distributions, aerodynamic load coefficients and total force coefficients. We focused on two main parameters: swirl ratio and horizontal distance from tornado center to deck. Obvious discrepancies were observed between tornado-induced wind loading and results from conventional boundary-layer wind tunnels. Strip theory was not applicable since pressure distributions vary for different sections of the deck along the bridge axis. The absolute values of mean pressure coefficients for the deck section near tornado center are largest among all tested sections along the bridge axis. The most unfavorable mean sectional drag force coefficients were found when the bridge model is located at the tornado core radius and largest mean sectional lift force coefficients at the tornado center. With increase in swirl ratio, magnitudes of mean pressure coefficients as well as mean and fluctuating sectional aerodynamic load coefficients become smaller. The unfavorable locations for fluctuating rolling moment coefficients are different from those for mean values, which indicates that the quasi-steady assumption becomes invalid for tornado-induced rolling moment coefficients. Total force coefficients over the entire deck were investigated to evaluate the non-uniform loading characteristics. The findings will be helpful for predicting tornado-induced responses and risks for highly important long-span bridges.
Journal of Structural Engineering
AbstractWind pressures acting on a cubic building with openings exposed to stationary tornadolike... more AbstractWind pressures acting on a cubic building with openings exposed to stationary tornadolike vortices were studied experimentally. The effects of opening ratio, single central opening azimuth,...
Journal of Wind Engineering and Industrial Aerodynamics
Abstract This paper presents large-eddy simulation of tornado-induced pressures and forces on fla... more Abstract This paper presents large-eddy simulation of tornado-induced pressures and forces on flat-roofed and gable-roofed low-rise buildings. The simulation is carried out with respect to an ISU-type tornado simulator and the simulation results are compared with available laboratory and field data. The present study shows that tornado-induced wind pressures have very different characteristics than those caused by boundary layer flows. The distribution and magnitude of wind pressures around the building models depend significantly on the distance between tornado vortex and building model. The roof angle does not alter the integrated wind loads on the gable-roofed building models significantly, but the local pressure on building surfaces, especially on the roof, depends obviously on the roof angle. However, this dependence is similar to that in boundary layer winds, although the value of the pressure coefficient is different due to pressure drop accompanying the tornado. In addition, the present study shows that the same horizontal profile of mean tangential velocity do not necessarily result in the same wind loads on building models in a tornado because of the difference in vortex structures.
Journal of Wind Engineering and Industrial Aerodynamics, 2016
Abstract Wind load characteristics of a structure exposed to a swirling tornado are different fro... more Abstract Wind load characteristics of a structure exposed to a swirling tornado are different from those in a boundary-layer-type straight-line wind. This paper presents wind pressures around a cooling tower caused by a translating tornado-like vortex with two different swirl ratios at three different translational velocities. The translational motion is scaled so that the durations of tornado force on both prototype and model structures are identical. The effects of translational motion are studied by comparing the pressure characteristics caused by a translating tornado-like vortex with quasi-steady results obtained for stationary tornado-like vortices located in different radial locations relative to the cooling tower model. Results of the present study show that translational motion does not significantly influence the peak external and internal pressures, although peak pressures and forces decrease slightly with translational velocity. A peak pressure coefficient does not necessarily appear after the passage of a tornado. The running-window cross-correlation analyses show that the correlation is actually lower than that of stationary tornadoes, although greater correlation occurs if it is calculated by the traditional steady analysis method that includes the effects of pressure variation trend.
Acta Optica Sinica
Conclusions Trans-HONO and N 2 O 4 gases are continuously measured at the same time, and the spec... more Conclusions Trans-HONO and N 2 O 4 gases are continuously measured at the same time, and the specific absorption line frequencies of the two gases in the range of 1279. 5-1282. 5 cm-1 are obtained by using a 7. 8 μm roomtemperature CW-QCL and a long pathlength absorption cell. The decay time of HONO in a closed absorption cell made of quartz is obtained by fitting and analyzing the decay curve of HONO. According to the known absorption line intensity of trans-HONO at 1280. 4 cm-1 , the level of trans-HONO in the sample to be measured is calculated to be (0. 72±0. 04) ×10-6 , the corresponding minimum detection limit of the system is about (11. 15±0. 50)×10-9. As the absorption line intensity of N 2 O 4 has not been reported in the spectral database and published articles, the level of N 2 O 4 in the sample to be tested has not been calculated. The absorption line frequencies of HONO and N 2 O 4 obtained in the experiment provide a reference for realtime continuous gas monitoring, sources and sinks analysis of atmospheric HONO, and analysis of the N 2 O 4 chemical reaction process.
Atmosphere, 2021
For the analysis of the aerodynamic characteristics of the buildings immersed in the atmospheric ... more For the analysis of the aerodynamic characteristics of the buildings immersed in the atmospheric boundary layer (ABL), it is necessary to generate a turbulence velocity field with similar temporal and special characteristics to the ABL to obtain a reliable result. In this paper, an improved precursor simulation method called the recycling and reshaping method (RRM) is proposed to generate a turbulent boundary layer in an LES model. The laminar inflow is firstly disturbed by the virtual roughness blocks realized by adding drag force term in the momentum equation, then the inflow velocity profile is reshaped every several steps to adjust the streamwise velocity profile in the downstream target area to meet the requirements. The final turbulence field generated by RRM with virtual roughness blocks is in good agreement with the target velocity conditions. Then, the simulation of the wind-induced pressure on an isolated low-rise building surface is carried out, using the generated turbul...
Journal of Wind Engineering and Industrial Aerodynamics
Journal of Wind Engineering and Industrial Aerodynamics
Journal of Wind Engineering and Industrial Aerodynamics, 2020
In addition to strong wind, tornado-borne flying debris is a major contributor to large destructi... more In addition to strong wind, tornado-borne flying debris is a major contributor to large destructions caused by tornadoes. However, research on flying debris is still very rare. In the present study, a specific tornado observed in nature is reproduced using large eddy simulations. The debris is assumed to consist of compact wooden objects with diameters of 2, 5, and 10 cm. The wooden objects are released at heights of 1, 5, 10 m, and 20 m. Instantaneous debris distributions, debris concentration, and statistics of debris velocities were systematically examined. The model shows that releasing debris at lower elevations or enlarging the size of the debris lead to greater debris dispersion and decrease the speed of debris. The fluctuations and maxima of debris velocities are globally less than those in wind. Among all of the cases studied, debris velocities can be estimated using wind velocities only when the debris diameter is 2 cm. The largest difference between the debris velocit...
Current wind-resistant design of wind-sensitive structures including large-scale cooling towers i... more Current wind-resistant design of wind-sensitive structures including large-scale cooling towers is generally carried out with respect to synoptic boundary-layer-type strong winds. A swirling tornado can produce significantly different wind pressures than conventional boundary-layer wind. This paper presents both stationary and translating tornado effects on a cooling tower in a tornado vortex simulator developed at Tongji University, China. Wind pressures acting on the external surface of cooling tower model were measured at a fixed swirl ratio (S = 0.54) in the present study. Different radial distances between a cooling tower and stationary tornado vortex center were considered. Translating tornadoes with three different translation speeds (u = 0.04 m/s, 0.12 m/s and 0.2 m/s) were simulated. The results show that a tornado vortex can produce high negative wind pressures on a cooling tower surface due to the negative pressure drop accompanying a tornado. A cooling tower exposed to a...
Journal of Wind Engineering and Industrial Aerodynamics
Buildings
The vector form intrinsic finite (VFIFE) method is a new and promising structural analysis techni... more The vector form intrinsic finite (VFIFE) method is a new and promising structural analysis technique that has many advantages as compared with the conventional finite element method (FEM) in analyzing the complex behaviors of a structure. However, despite the popularization of its application in civil and infrastructure engineering, there is no available unified general analysis framework for it, which limits the applications and developments of VFIFE. This work develops and implements a platform (termed openVFIFE) based on a new proposed object-oriented framework to facilitate the development and application of the vector form intrinsic finite method as well as the efficient and accurate analyses of complex behaviors for civil structures. To validate the platform, a series of numerical examples are conducted. Furthermore, to extend the applications of VFIFE, the nonlinear dynamic and collapse processes of a transmission tower under earthquake load are studied using openVFIFE. The r...
Frontiers in Built Environment
With the trend of variable cross-sections for long-span bridges from truss-stiffened to quasi-str... more With the trend of variable cross-sections for long-span bridges from truss-stiffened to quasi-streamlined, and then to multiple-box cross-section geometries, the importance of aeroelastic performance is becoming increasingly significant in wind-resistant design. This article shows that there is clearly insufficient qualitative as well as quantitative understanding of turbulence effects on bridge aerodynamics, particularly the mechanisms behind them. Although turbulence might help the stabilization of long-span bridges, and is thus not a conclusive parameter in wind-resistant design, turbulence effects on the aerodynamic and aeroelastic behaviors of a bridge need to be better understood because interaction between a bridge and turbulence always exists. This article also briefly introduces a newly developed multiple-fan wind tunnel that is designed to control turbulence to assist the study of turbulence effects.
Journal of Wind Engineering and Industrial Aerodynamics
Journal of Fluids and Structures
Frontiers in Built Environment, Dec 11, 2017
With the trend of variable cross-sections for long-span bridges from truss-stiffened to quasi-str... more With the trend of variable cross-sections for long-span bridges from truss-stiffened to quasi-streamlined, and then to multiple-box cross-section geometries, the importance of aeroelastic performance is becoming increasingly significant in wind-resistant design. This article shows that there is clearly insufficient qualitative as well as quantitative understanding of turbulence effects on bridge aerodynamics, particularly the mechanisms behind them. Although turbulence might help the stabilization of long-span bridges, and is thus not a conclusive parameter in wind-resistant design, turbulence effects on the aerodynamic and aeroelastic behaviors of a bridge need to be better understood because interaction between a bridge and turbulence always exists. This article also briefly introduces a newly developed multiple-fan wind tunnel that is designed to control turbulence to assist the study of turbulence effects.
Journal of Wind Engineering and Industrial Aerodynamics
Abstract Tornado risks for highly important long-span bridges in tornado-prone regions can not be... more Abstract Tornado risks for highly important long-span bridges in tornado-prone regions can not be neglected. Rigid-model wind pressure measurements on a streamlined bridge deck were conducted using a tornado vortex simulator, to clarify tornado-induced surface pressure distributions, aerodynamic load coefficients and total force coefficients. We focused on two main parameters: swirl ratio and horizontal distance from tornado center to deck. Obvious discrepancies were observed between tornado-induced wind loading and results from conventional boundary-layer wind tunnels. Strip theory was not applicable since pressure distributions vary for different sections of the deck along the bridge axis. The absolute values of mean pressure coefficients for the deck section near tornado center are largest among all tested sections along the bridge axis. The most unfavorable mean sectional drag force coefficients were found when the bridge model is located at the tornado core radius and largest mean sectional lift force coefficients at the tornado center. With increase in swirl ratio, magnitudes of mean pressure coefficients as well as mean and fluctuating sectional aerodynamic load coefficients become smaller. The unfavorable locations for fluctuating rolling moment coefficients are different from those for mean values, which indicates that the quasi-steady assumption becomes invalid for tornado-induced rolling moment coefficients. Total force coefficients over the entire deck were investigated to evaluate the non-uniform loading characteristics. The findings will be helpful for predicting tornado-induced responses and risks for highly important long-span bridges.
Journal of Structural Engineering
AbstractWind pressures acting on a cubic building with openings exposed to stationary tornadolike... more AbstractWind pressures acting on a cubic building with openings exposed to stationary tornadolike vortices were studied experimentally. The effects of opening ratio, single central opening azimuth,...
Journal of Wind Engineering and Industrial Aerodynamics
Abstract This paper presents large-eddy simulation of tornado-induced pressures and forces on fla... more Abstract This paper presents large-eddy simulation of tornado-induced pressures and forces on flat-roofed and gable-roofed low-rise buildings. The simulation is carried out with respect to an ISU-type tornado simulator and the simulation results are compared with available laboratory and field data. The present study shows that tornado-induced wind pressures have very different characteristics than those caused by boundary layer flows. The distribution and magnitude of wind pressures around the building models depend significantly on the distance between tornado vortex and building model. The roof angle does not alter the integrated wind loads on the gable-roofed building models significantly, but the local pressure on building surfaces, especially on the roof, depends obviously on the roof angle. However, this dependence is similar to that in boundary layer winds, although the value of the pressure coefficient is different due to pressure drop accompanying the tornado. In addition, the present study shows that the same horizontal profile of mean tangential velocity do not necessarily result in the same wind loads on building models in a tornado because of the difference in vortex structures.
Journal of Wind Engineering and Industrial Aerodynamics, 2016
Abstract Wind load characteristics of a structure exposed to a swirling tornado are different fro... more Abstract Wind load characteristics of a structure exposed to a swirling tornado are different from those in a boundary-layer-type straight-line wind. This paper presents wind pressures around a cooling tower caused by a translating tornado-like vortex with two different swirl ratios at three different translational velocities. The translational motion is scaled so that the durations of tornado force on both prototype and model structures are identical. The effects of translational motion are studied by comparing the pressure characteristics caused by a translating tornado-like vortex with quasi-steady results obtained for stationary tornado-like vortices located in different radial locations relative to the cooling tower model. Results of the present study show that translational motion does not significantly influence the peak external and internal pressures, although peak pressures and forces decrease slightly with translational velocity. A peak pressure coefficient does not necessarily appear after the passage of a tornado. The running-window cross-correlation analyses show that the correlation is actually lower than that of stationary tornadoes, although greater correlation occurs if it is calculated by the traditional steady analysis method that includes the effects of pressure variation trend.