The process of riming significantly impacts the microphysical characteristics of clouds.This study uses aircraft and radar observation data in stratiform clouds with convection embedded that occurred in the central an...The process of riming significantly impacts the microphysical characteristics of clouds.This study uses aircraft and radar observation data in stratiform clouds with convection embedded that occurred in the central and southern regions of North China on 22 May 2017.The microphysical structural characteristics and processes near the embedded convection core and in the stratiform cloud are analyzed comparatively.Particular attention is given to the effect of riming on the microphysical properties near the upper boundary of the melting layer and to the factors influencing riming efficiency.The collaborative observations reveal that the particle size distributions observed near the convection core and in the stratiform region are close,while the particle properties like habit and riming degree are quite different.Above the melting layer,larger plate-like ice particles and supercooled water droplets(D>50μm)are more abundant near the convective core,leading to higher collision efficiencies between ice particles and supercooled water droplets.Larger fluctuation amplitudes of vertical airflow near the convective core also contribute to the increased riming activity and the formation of more heavily rimed particles,such as graupel.Furthermore,in situ measurements from airborne probes also revealed that above the melting layer,the riming process involves two stages:the mass of snow crystals grows as supercooled droplets merge internally without changing size,followed by external freezing that significantly enlarges the crystals.展开更多
Negative pressure plays a very important role in compact spinning system.To know airflow field and its distribution is helpful to look into the condensing principle of fiber bundle.Therefore,computational fluid dynami...Negative pressure plays a very important role in compact spinning system.To know airflow field and its distribution is helpful to look into the condensing principle of fiber bundle.Therefore,computational fluid dynamics(CFD)software was used to simulate airflow field in this paper.Airflow velocity distributions both in different fiber layers and under different negative pressures were discussed.The results indicate that airflow velocity in upper layer of the fiber bundle is greater than that in lower layer.Airflow velocities in both X and Y axis directions have a positive correlation with negative pressure.It can provide a theoretical base to make high quality compact yarns in productive practice.展开更多
In order to develop the technology of the controlled recircuIation of airflow in the world, some formulas about the airflow recirculation system in the working face with leaking airflow are deduced,which reduces the e...In order to develop the technology of the controlled recircuIation of airflow in the world, some formulas about the airflow recirculation system in the working face with leaking airflow are deduced,which reduces the error between calculating and real values. on the base of the application of the formulas mentioned above, the problem about lack of airflow in the working face 2712 was solved successfully in Xiandewang Coal Mine.展开更多
Cough is a defensive behavior that protects the respiratory system from infection and clears airway secretions.Cough airflow dynamics have been analyzed by a variety of mathematical and experimental tools.In this pape...Cough is a defensive behavior that protects the respiratory system from infection and clears airway secretions.Cough airflow dynamics have been analyzed by a variety of mathematical and experimental tools.In this paper,the cough airflow dynamics of 42 subjects were obtained and analyzed.An identification model based on piecewise Gauss function for cough airflow dynamics is proposed through the dimensionless method,which could achieve over 90%identification accuracy.Meanwhile,an assisted cough system based on pneumatic flow servo system is presented.The vacuum situation and feedback control are used to increase the simulated peak cough flow rate,which are important for airway secretion clearance and to avoid airway collapse,respectively.The simulated cough peak flow could reach 5 L/s without the external assistance such as manual pressing,patient cooperation and other means.Finally,the backstepping control is developed to generate a simulated cough airflow that closely mimics the natural cough airflow of humans.The assisted cough system opens up wide opportunities of practical application in airway secretion clearance for critically ill patients with COVID 2019 and other pulmonary diseases.展开更多
Classic respiratory mechanics is a branch of vectorial mechanics, which aims to recognize all forces acting on the respiratory system. Another branch of mechanics, analytical mechanics, has been used for analyzing the...Classic respiratory mechanics is a branch of vectorial mechanics, which aims to recognize all forces acting on the respiratory system. Another branch of mechanics, analytical mechanics, has been used for analyzing the motions of complicated systems with constraints through equilibrium among scalar quantities such as kinetic energy and potential energy. However, until now, there have not been any studies concerning about analytical respiratory mechanics. In this paper, the author has obtained two types of motion equations (linear and nonlinear) for the airflow limitation from formulation of the analytical respiratory mechanics. Reconstructed flow-volume trajectories of the linear equation revealed a new relationship among the slope of the linear portion of trajectory, the coefficient of the dissipation function and the coefficient of the potential function. Reconstructed trajectories of the nonlinear equation suggested that a curved flow-volume trajectory would be caused by the emergence of regional hypoventilated clusters with airtrapped lobules. In conclusion, analytical respiratory mechanics will provide the basis for analyzing the mechanical properties of the respiratory system con cerning pulmonary functional images made by newly developed technologies.展开更多
This study investigates the influence of airflow transport pathways on seasonal rainfall in the mountainous region of the Liupan Mountains(LM) during the rainy seasons from 2020 to 2022, utilizing observational data f...This study investigates the influence of airflow transport pathways on seasonal rainfall in the mountainous region of the Liupan Mountains(LM) during the rainy seasons from 2020 to 2022, utilizing observational data from seven ground gradient stations located on the eastern slopes, western slopes, and mountaintops combined with backward trajectory cluster analysis. The results indicate 1) that the LM's rainy season, characterized by overcast and rainy days, is mainly influenced by cold and moist airflows(CMAs) from the westerly direction and warm and moist airflows(WMAs) from a slightly southern direction. The precipitation amounts under four airflow transport paths are ranked from largest to smallest as follows: WMAs, CMAs, warm dry airflows(WDAs), and cold dry airflows(CDAs). 2) WMAs contribute significantly more to the intensity of regional precipitation than the other three types of airflows. During localized precipitation events,warm airflows have higher precipitation intensities at night than cold airflows, while the opposite is true during the afternoon. 3) During regional precipitation events, water vapor content is the primary influencing factor. Precipitation characteristics under humid airflows are mainly affected by high water vapor content, whereas during dry airflow precipitation, dynamic and thermodynamic factors have a more pronounced impact. 4) During localized precipitation events, the influence of dynamic and thermodynamic factors is more complex than during regional precipitation, with the precipitation characteristics of the four airflows closely related to their water vapor content, air temperature and humidity attributes, and orographic lifting. 5) Compared to regional precipitation, the influence of topography is more prominent in localized precipitation processes.展开更多
This study examines the impact of variations in side-blowing airflow velocity on plasma generation,combustion wave propagation mechanisms,and surface damage in fused silica induced by a combined millisecond-nanosecond...This study examines the impact of variations in side-blowing airflow velocity on plasma generation,combustion wave propagation mechanisms,and surface damage in fused silica induced by a combined millisecond-nanosecond pulsed laser.The airflow rate and pulse delay are the main experimental variables.The evolution of plasma motion was recorded using ultrafast time-resolved optical shadowing.The experimental results demonstrate that the expansion velocities of the plasma and combustion wave are influenced differently by the sideblowing airflow at different airflow rates(0.2 Ma,0.4 Ma,and 0.6 Ma).As the flow rate of the sideblow air stream increases,the initial expansion velocities of the plasma and combustion wave gradually decrease,and the side-blow air stream increasingly suppresses the plasma.It is important to note that the target vapor is always formed and ionized into plasma during the combined pulse laser action.Therefore,the side-blown airflow alone cannot completely clear the plasma.Depending on the delay conditions,the pressure of the side-blowing airflow,the influence of inverse Bremsstrahlung radiation absorption and target surface absorption mechanisms can lead to a phenomenon known as the double combustion waves when using a nanosecond pulse laser.Both simulation and experimental results are consistent,indicating the potential for further exploration of fused silica targets in the laser field.展开更多
The mass of high-speed trains can be reduced using the brake disk prepared with SiC network ceramic frame reinforced 6061 aluminum alloy composite （SiCn/Al）. The thermal and stress analyses of SiCn/Al brake disk dur...The mass of high-speed trains can be reduced using the brake disk prepared with SiC network ceramic frame reinforced 6061 aluminum alloy composite （SiCn/Al）. The thermal and stress analyses of SiCn/Al brake disk during emergency braking at a speed of 300 km/h considering airflow cooling were investigated using finite element （FE） and computational fluid dynamics （CFD） methods. All three modes of heat transfer （conduction, convection and radiation） were analyzed along with the design features of the brake assembly and their interfaces. The results suggested that the higher convection coefficients achieved with airflow cooling will not only reduce the maximum temperature in the braking but also reduce the thermal gradients, since heat will be removed faster from hotter parts of the disk. Airflow cooling should be effective to reduce the risk of hot spot formation and disc thermal distortion. The highest temperature after emergency braking was 461 °C and 359 °C without and with considering airflow cooling, respectively. The equivalent stress could reach 269 MPa and 164 MPa without and with considering airflow cooling, respectively. However, the maximum surface stress may exceed the material yield strength during an emergency braking, which may cause a plastic damage accumulation in a brake disk without cooling. The simulation results are consistent with the experimental results well.展开更多
目的:定量评价集成压缩气流系统扫描头辅助口内三维扫描仪(intraoral 3D scanners,IOS)获取的液体干扰表面数据精度,为集成压缩气流系统扫描头的临床应用提供精度数据。方法:选择《YY/T 1818—2022牙科学口腔数字印模仪》中标准模型作...目的:定量评价集成压缩气流系统扫描头辅助口内三维扫描仪(intraoral 3D scanners,IOS)获取的液体干扰表面数据精度,为集成压缩气流系统扫描头的临床应用提供精度数据。方法:选择《YY/T 1818—2022牙科学口腔数字印模仪》中标准模型作为扫描对象,利用ATOS Q 12M得到三维扫描数据,作为扫描正确度评价的真值。基于现有扫描仪结构,研究设计了一种新型扫描方案,以解决液体导致IOS精度下降的问题。设计新型扫描头,并集成扫描系统与压缩气流系统,实现口内三维扫描仪在液体干扰表面的高精度数据采集。以常规标准扫描方式作为对照组,探究扫描镜头遮挡、气流、液体介质、新型扫描头对扫描过程及精度的影响,并设置4组实验,且每组扫描15次,以评价基于压缩气流系统扫描头辅助IOS获取液体干扰表面的精度数据。选用Elite和Primescan两款扫描仪作为精度数值的参考。结果:在正确度和精密度两方面评价中,被液体干扰表面的扫描精度显著下降[正确度:18.5(6.5)vs.38.0(6.7),P<0.05;精密度:19.1(8.5)vs.31.7(15.0),P<0.05];使用集成压缩气流系统的新型扫描头辅助口内三维扫描仪,扫描精度显著提升[正确度:22.3(7.6)vs.38.0(6.7),P<0.05;精密度:25.8(9.6)vs.31.7(15.0),P<0.05]。结论:集成压缩气流系统的扫描头可以辅助提高IOS液体干扰表面数据的精度。展开更多
A new air distribution pattern,air curtain jet ventilation was presented.The ventilation or airflow patterns and the air velocity produced by air curtain jet were investigated in detail.To identify the airflow charact...A new air distribution pattern,air curtain jet ventilation was presented.The ventilation or airflow patterns and the air velocity produced by air curtain jet were investigated in detail.To identify the airflow characteristics of this novel air curtain jet ventilation system,a full-scale room was used to measure the jet velocity with a slot-ventilated supply device,with regards to the airflow fields along the vertical wall as well as on the horizontal floor zones.The airflow fields under three supply air velocities,1.0,1.5 and 2.0 m/s,were carried out in the full-scale room.The experimental results show the velocity profiles of air distribution,the airflow fields along the attached vertical wall and the air lake zones on the floor,respectively.The current experimental research is helpful for heating,ventilation and air conditioning(HVAC) engineers to design better air distribution in rooms.展开更多
Based on 3D modelling of typical tunnels in mines, the airflow distribution in a three-center arch-section tunnel is investigated and the influence of air velocity and cross section on airflow distribution in tunnels ...Based on 3D modelling of typical tunnels in mines, the airflow distribution in a three-center arch-section tunnel is investigated and the influence of air velocity and cross section on airflow distribution in tunnels is studied. The average velocity points were analyzed quantitatively. The results show that the airflow pattern is similar for the three-center arch section under different ventilation velocities and cross sectional areas. The shape of the tunnel cross section and wall are the critical factors influencing the airflow pattern. The average velocity points are mainly close to the tunnel wall. Characteristic equations are developed to describe the average velocity distribution, and provide a theoretical basis for accurately measuring the average velocity in mine tunnels.展开更多
Using the observations from ICOADS datasets and contemporaneous NCEP/NCAR reanalysis datasets during 1960-2002,the study classifies the airflows in favor of sea fog over the Huanghai （Yellow） Sea in boreal spring （...Using the observations from ICOADS datasets and contemporaneous NCEP/NCAR reanalysis datasets during 1960-2002,the study classifies the airflows in favor of sea fog over the Huanghai （Yellow） Sea in boreal spring （April-May） with the method of trajectory analysis,and analyzes the changes of proportions of warm and cold sea fogs along different paths of airflow.According to the heat balance equation,we investigate the relationships between the marine meteorological conditions and the proportion of warm and cold sea fog along different airflow paths.The major results are summarized as follows.（1） Sea fogs over the Huanghai Sea in spring are not only warm fog but also cold fog.The proportion of warm fog only accounts for 44% in April,while increases as high as 57% in May.（2） Four primary airflow paths leading to spring sea fog are identified.They are originated from the northwest,east,southeast and southwest of the Huanghai Sea,respectively.The occurrence ratios of the warm sea fog along the east and southeast airflow paths are high of 55% and 70%,while these along the southwest and northwest airflow paths are merely 17.9% and 50%.（3） The key physical processes governing the warm/cold sea fog are heat advection transport,longwave radiation cooling at fog top,solar shortwave warming and latent heat flux between airsea interfaces.（4） The characteristics of sea fog along the four airflow paths relate closely to the conditions of water vapor advection,and the vertical distribution of relative humidity.展开更多
Coal mine ventilation is an extremely complicated system that can be affected by many factors. Gas ventilation pressure is one of important factors that can disturb the stabilization of airflow in airways.The formatio...Coal mine ventilation is an extremely complicated system that can be affected by many factors. Gas ventilation pressure is one of important factors that can disturb the stabilization of airflow in airways.The formation and characteristics of gas ventilation pressure were further elaborated, and numerical simulations were conducted to verify the role of gas ventilation pressure in the stability of airway airflow.Then a case study of airflow stagnation accident that occurred in the Tangshan Coal Mine was performed.The results show that under the condition of upward ventilation, the direction of gas ventilation pressure in the branch is the same to that of the main fan, airflow of the branches beside the branch may be reversed. The greater the gas ventilation pressure is, the more obvious the reversion is. Moreover, reversion sequence of paralleled branches is related to the airflow velocity and length of the branch. Under the condition of downward ventilation, the airflow in the branch filled with gas may be reversed. Methane in downward ventilation is hard to discharge; therefore, accumulation in downward ventilation is more harmful than that in upward ventilation.展开更多
Effect of airflow on the dielectric barrier discharge in ambient air at atmospheric pressure is presented. The influence of airflow on the spatial distribution and intensity of a discharge were investigated experiment...Effect of airflow on the dielectric barrier discharge in ambient air at atmospheric pressure is presented. The influence of airflow on the spatial distribution and intensity of a discharge were investigated experimentally. A critical frequency of 1 kHz was found. With the frequency above 1 kHz, when a fast airflow was introduced into the discharge gap, the discharge patterns varied from filaments to curved stripes and the curvature degree rose with an increase in the airflow speed. At the same time, the discharge intensity decreased. However with the discharge frequency below 1 kHz, the discharge intensity would get greater with an increase in the airflow speed.展开更多
A more efficient mine ventilation system, the ventilation-on-demand （VOD） system, has been proposed and tested in Canadian mines recently. In order to supply the required air volumes to the production areas of a min...A more efficient mine ventilation system, the ventilation-on-demand （VOD） system, has been proposed and tested in Canadian mines recently. In order to supply the required air volumes to the production areas of a mine, operators need to know the cause and effect of any changes requested from the VOD system. The sensitivity analysis is developed through generating a cause and effect matrix of sensitivity factors on given parameter changes in a ventilation system. This new utility, which was incorporated in the 3D-CANVENT mine ventilation simulator, is able to predict the airflow distributions in a ventilation network when underground conditions and ventilation controls are changed. For a primary ventilation system, the software can determine the optimal operating speed of the main fans to satisfy the airflow requirements in underground workings without necessarily using booster fans and regulators locally. An optimized fan operating speed time-table would assure variable demand-based fresh air delivery to the production areas effectively, while generating significant savings in energy consumption and operating cost.展开更多
It is often required to know which roadway （adjustment roadway） resistances and how much values of the resis- tances should be changed to make the airflow rates in roadways （target roadways） to certain required va...It is often required to know which roadway （adjustment roadway） resistances and how much values of the resis- tances should be changed to make the airflow rates in roadways （target roadways） to certain required values in the practice of mine ventilation. In this case, the airflow rates of the target roadways and the resistances of the roadways other than the ad- justment roadways are the given conditions and the resistances of the adjustment roadways are the solutions to be found. No straightforward method to solve the problem has been found up to now. Therefore, trial and error method using the ventilation network analysis program is utilized to solve the problem so far. The method takes long calculation time and the best answer is not necessarily obtained. The authors newly defined ＂airflow element＂ as an element of the ventilation network analysis. The resistances that satisfy the airflow requirements can be calculated straight forwardly by putting the function of the airflow element into the ventilation network analysis. The air power required for the ventilation can be minimized while meeting the airflow requirements by the advanced application of the method. The authors made the computer program fulfill the method. The program was applied to actual ventilation network and it was found that the method is very practical and the time required for the analysis is short.展开更多
Volume diffuse dielectric barrier discharge （DBD） plasma is produced in subsonic airflow by nanosecond high-voltage pulse power supply with a plate-to-plate discharge cell at 6 mm air gap length. The discharge image...Volume diffuse dielectric barrier discharge （DBD） plasma is produced in subsonic airflow by nanosecond high-voltage pulse power supply with a plate-to-plate discharge cell at 6 mm air gap length. The discharge images, optical emission spectra （OES）, the applied voltage and current waveforms of the discharge at the changed airflow rates are obtained. When airflow rate is increased, the transition of the discharge mode and the variations of discharge intensity, breakdown characteristics and the temperature of the discharge plasma are investigated. The results show that the discharge becomes more diffuse, discharge intensity is decreased accompanied by the increased breakdown voltage and time lag, and the temperature of the discharge plasma reduces when airflow of small velocity is introduced into the discharge gap. These phenomena are because that the airflow changes the spatial distribution of the heat and the space charge in the discharge gap.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.42025501)the Natural Science Foundation of Hebei Province(Grant No.D2024304015)+4 种基金the Fundamental Research Funds for the Central Universities,including Grant No.020714380217the Cemac“GeoX”Interdisciplinary Program(Grant No.020714380210)the Open Grants of the Key Laboratory of Radar Meteorology,China Meteorological Administration(Grant No.2023LRM-B05)the Hebei Meteorological Service Scientific Research and Development Project(Grant No.23ky08)the Open Research Program of the State Key Laboratory of Severe Weather(Grant No.2023LASW-A01)。
文摘The process of riming significantly impacts the microphysical characteristics of clouds.This study uses aircraft and radar observation data in stratiform clouds with convection embedded that occurred in the central and southern regions of North China on 22 May 2017.The microphysical structural characteristics and processes near the embedded convection core and in the stratiform cloud are analyzed comparatively.Particular attention is given to the effect of riming on the microphysical properties near the upper boundary of the melting layer and to the factors influencing riming efficiency.The collaborative observations reveal that the particle size distributions observed near the convection core and in the stratiform region are close,while the particle properties like habit and riming degree are quite different.Above the melting layer,larger plate-like ice particles and supercooled water droplets(D>50μm)are more abundant near the convective core,leading to higher collision efficiencies between ice particles and supercooled water droplets.Larger fluctuation amplitudes of vertical airflow near the convective core also contribute to the increased riming activity and the formation of more heavily rimed particles,such as graupel.Furthermore,in situ measurements from airborne probes also revealed that above the melting layer,the riming process involves two stages:the mass of snow crystals grows as supercooled droplets merge internally without changing size,followed by external freezing that significantly enlarges the crystals.
基金Key Project in National Science & Technology Pillar Program,China(No.2007BAE41B04)
文摘Negative pressure plays a very important role in compact spinning system.To know airflow field and its distribution is helpful to look into the condensing principle of fiber bundle.Therefore,computational fluid dynamics(CFD)software was used to simulate airflow field in this paper.Airflow velocity distributions both in different fiber layers and under different negative pressures were discussed.The results indicate that airflow velocity in upper layer of the fiber bundle is greater than that in lower layer.Airflow velocities in both X and Y axis directions have a positive correlation with negative pressure.It can provide a theoretical base to make high quality compact yarns in productive practice.
文摘In order to develop the technology of the controlled recircuIation of airflow in the world, some formulas about the airflow recirculation system in the working face with leaking airflow are deduced,which reduces the error between calculating and real values. on the base of the application of the formulas mentioned above, the problem about lack of airflow in the working face 2712 was solved successfully in Xiandewang Coal Mine.
基金The research is supported by the National Natural Science Foundation of China(No.52005015)the China Postdoctoral Science Foundation(No.2019M660391)+2 种基金the Open Foundation of the State Key Laboratory of Fluid Power and Mechatronic Systems(No.GZKF-201920)the Outstanding Young Scientists in Beijing(No.BJJWZYJH01201910006021)the National Key Research and Development Project(No.2019YFC0121702).
文摘Cough is a defensive behavior that protects the respiratory system from infection and clears airway secretions.Cough airflow dynamics have been analyzed by a variety of mathematical and experimental tools.In this paper,the cough airflow dynamics of 42 subjects were obtained and analyzed.An identification model based on piecewise Gauss function for cough airflow dynamics is proposed through the dimensionless method,which could achieve over 90%identification accuracy.Meanwhile,an assisted cough system based on pneumatic flow servo system is presented.The vacuum situation and feedback control are used to increase the simulated peak cough flow rate,which are important for airway secretion clearance and to avoid airway collapse,respectively.The simulated cough peak flow could reach 5 L/s without the external assistance such as manual pressing,patient cooperation and other means.Finally,the backstepping control is developed to generate a simulated cough airflow that closely mimics the natural cough airflow of humans.The assisted cough system opens up wide opportunities of practical application in airway secretion clearance for critically ill patients with COVID 2019 and other pulmonary diseases.
文摘Classic respiratory mechanics is a branch of vectorial mechanics, which aims to recognize all forces acting on the respiratory system. Another branch of mechanics, analytical mechanics, has been used for analyzing the motions of complicated systems with constraints through equilibrium among scalar quantities such as kinetic energy and potential energy. However, until now, there have not been any studies concerning about analytical respiratory mechanics. In this paper, the author has obtained two types of motion equations (linear and nonlinear) for the airflow limitation from formulation of the analytical respiratory mechanics. Reconstructed flow-volume trajectories of the linear equation revealed a new relationship among the slope of the linear portion of trajectory, the coefficient of the dissipation function and the coefficient of the potential function. Reconstructed trajectories of the nonlinear equation suggested that a curved flow-volume trajectory would be caused by the emergence of regional hypoventilated clusters with airtrapped lobules. In conclusion, analytical respiratory mechanics will provide the basis for analyzing the mechanical properties of the respiratory system con cerning pulmonary functional images made by newly developed technologies.
基金supported by the National Natural Sciences Foundation of China (Grant Nos. 42075073 and 42075077)。
文摘This study investigates the influence of airflow transport pathways on seasonal rainfall in the mountainous region of the Liupan Mountains(LM) during the rainy seasons from 2020 to 2022, utilizing observational data from seven ground gradient stations located on the eastern slopes, western slopes, and mountaintops combined with backward trajectory cluster analysis. The results indicate 1) that the LM's rainy season, characterized by overcast and rainy days, is mainly influenced by cold and moist airflows(CMAs) from the westerly direction and warm and moist airflows(WMAs) from a slightly southern direction. The precipitation amounts under four airflow transport paths are ranked from largest to smallest as follows: WMAs, CMAs, warm dry airflows(WDAs), and cold dry airflows(CDAs). 2) WMAs contribute significantly more to the intensity of regional precipitation than the other three types of airflows. During localized precipitation events,warm airflows have higher precipitation intensities at night than cold airflows, while the opposite is true during the afternoon. 3) During regional precipitation events, water vapor content is the primary influencing factor. Precipitation characteristics under humid airflows are mainly affected by high water vapor content, whereas during dry airflow precipitation, dynamic and thermodynamic factors have a more pronounced impact. 4) During localized precipitation events, the influence of dynamic and thermodynamic factors is more complex than during regional precipitation, with the precipitation characteristics of the four airflows closely related to their water vapor content, air temperature and humidity attributes, and orographic lifting. 5) Compared to regional precipitation, the influence of topography is more prominent in localized precipitation processes.
基金funded by the International Science and Technology Cooperation Project of Jilin Provincial Department of Science and Technology(No.20230402078GH)。
文摘This study examines the impact of variations in side-blowing airflow velocity on plasma generation,combustion wave propagation mechanisms,and surface damage in fused silica induced by a combined millisecond-nanosecond pulsed laser.The airflow rate and pulse delay are the main experimental variables.The evolution of plasma motion was recorded using ultrafast time-resolved optical shadowing.The experimental results demonstrate that the expansion velocities of the plasma and combustion wave are influenced differently by the sideblowing airflow at different airflow rates(0.2 Ma,0.4 Ma,and 0.6 Ma).As the flow rate of the sideblow air stream increases,the initial expansion velocities of the plasma and combustion wave gradually decrease,and the side-blow air stream increasingly suppresses the plasma.It is important to note that the target vapor is always formed and ionized into plasma during the combined pulse laser action.Therefore,the side-blown airflow alone cannot completely clear the plasma.Depending on the delay conditions,the pressure of the side-blowing airflow,the influence of inverse Bremsstrahlung radiation absorption and target surface absorption mechanisms can lead to a phenomenon known as the double combustion waves when using a nanosecond pulse laser.Both simulation and experimental results are consistent,indicating the potential for further exploration of fused silica targets in the laser field.
基金Projects (50872018, 50902018) supported by the National Natural Science Foundation of ChinaProject (1099043) supported by the Science and Technology in Guangxi Province, ChinaProject (090302005) supported by the Basic Research Fund for Northeastern University, China
文摘The mass of high-speed trains can be reduced using the brake disk prepared with SiC network ceramic frame reinforced 6061 aluminum alloy composite （SiCn/Al）. The thermal and stress analyses of SiCn/Al brake disk during emergency braking at a speed of 300 km/h considering airflow cooling were investigated using finite element （FE） and computational fluid dynamics （CFD） methods. All three modes of heat transfer （conduction, convection and radiation） were analyzed along with the design features of the brake assembly and their interfaces. The results suggested that the higher convection coefficients achieved with airflow cooling will not only reduce the maximum temperature in the braking but also reduce the thermal gradients, since heat will be removed faster from hotter parts of the disk. Airflow cooling should be effective to reduce the risk of hot spot formation and disc thermal distortion. The highest temperature after emergency braking was 461 °C and 359 °C without and with considering airflow cooling, respectively. The equivalent stress could reach 269 MPa and 164 MPa without and with considering airflow cooling, respectively. However, the maximum surface stress may exceed the material yield strength during an emergency braking, which may cause a plastic damage accumulation in a brake disk without cooling. The simulation results are consistent with the experimental results well.
基金Projects(50778145, 50278025) supported by the National Natural Science Foundation of ChinaProject(2009ZDKG-47) supported by "13115" Science and Technology Innovation Program of Shaanxi Province, China
文摘A new air distribution pattern,air curtain jet ventilation was presented.The ventilation or airflow patterns and the air velocity produced by air curtain jet were investigated in detail.To identify the airflow characteristics of this novel air curtain jet ventilation system,a full-scale room was used to measure the jet velocity with a slot-ventilated supply device,with regards to the airflow fields along the vertical wall as well as on the horizontal floor zones.The airflow fields under three supply air velocities,1.0,1.5 and 2.0 m/s,were carried out in the full-scale room.The experimental results show the velocity profiles of air distribution,the airflow fields along the attached vertical wall and the air lake zones on the floor,respectively.The current experimental research is helpful for heating,ventilation and air conditioning(HVAC) engineers to design better air distribution in rooms.
基金supported by the Fundamental Research Funds for the Central Universities of China (No.17ZY001)
文摘Based on 3D modelling of typical tunnels in mines, the airflow distribution in a three-center arch-section tunnel is investigated and the influence of air velocity and cross section on airflow distribution in tunnels is studied. The average velocity points were analyzed quantitatively. The results show that the airflow pattern is similar for the three-center arch section under different ventilation velocities and cross sectional areas. The shape of the tunnel cross section and wall are the critical factors influencing the airflow pattern. The average velocity points are mainly close to the tunnel wall. Characteristic equations are developed to describe the average velocity distribution, and provide a theoretical basis for accurately measuring the average velocity in mine tunnels.
基金supported in part by the National Natural Science Foundation of China under contract Nos 40675013 and 40906010the China Meteorological Administration project for popularizing new techniques under contract No.CMATG2007M23+1 种基金the scientific and technological planning project from Guangdong Province under contract No.2006B37202005The work of Wang Xin is supported by City University of Hong Kong Research Scholarship Enhancement Scheme and the City University of Hong Kong Strategic Research Grants 7002329
文摘Using the observations from ICOADS datasets and contemporaneous NCEP/NCAR reanalysis datasets during 1960-2002,the study classifies the airflows in favor of sea fog over the Huanghai （Yellow） Sea in boreal spring （April-May） with the method of trajectory analysis,and analyzes the changes of proportions of warm and cold sea fogs along different paths of airflow.According to the heat balance equation,we investigate the relationships between the marine meteorological conditions and the proportion of warm and cold sea fog along different airflow paths.The major results are summarized as follows.（1） Sea fogs over the Huanghai Sea in spring are not only warm fog but also cold fog.The proportion of warm fog only accounts for 44% in April,while increases as high as 57% in May.（2） Four primary airflow paths leading to spring sea fog are identified.They are originated from the northwest,east,southeast and southwest of the Huanghai Sea,respectively.The occurrence ratios of the warm sea fog along the east and southeast airflow paths are high of 55% and 70%,while these along the southwest and northwest airflow paths are merely 17.9% and 50%.（3） The key physical processes governing the warm/cold sea fog are heat advection transport,longwave radiation cooling at fog top,solar shortwave warming and latent heat flux between airsea interfaces.（4） The characteristics of sea fog along the four airflow paths relate closely to the conditions of water vapor advection,and the vertical distribution of relative humidity.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 51774292, 51474219, 51604278)the State Key Research Development Program of China (Grant Nos. 2016YFC0801402, 2016YFC0600708)
文摘Coal mine ventilation is an extremely complicated system that can be affected by many factors. Gas ventilation pressure is one of important factors that can disturb the stabilization of airflow in airways.The formation and characteristics of gas ventilation pressure were further elaborated, and numerical simulations were conducted to verify the role of gas ventilation pressure in the stability of airway airflow.Then a case study of airflow stagnation accident that occurred in the Tangshan Coal Mine was performed.The results show that under the condition of upward ventilation, the direction of gas ventilation pressure in the branch is the same to that of the main fan, airflow of the branches beside the branch may be reversed. The greater the gas ventilation pressure is, the more obvious the reversion is. Moreover, reversion sequence of paralleled branches is related to the airflow velocity and length of the branch. Under the condition of downward ventilation, the airflow in the branch filled with gas may be reversed. Methane in downward ventilation is hard to discharge; therefore, accumulation in downward ventilation is more harmful than that in upward ventilation.
基金supported by National Natural Science Foundation of China (Nos. 50537020, 50528707 and 10775027)
文摘Effect of airflow on the dielectric barrier discharge in ambient air at atmospheric pressure is presented. The influence of airflow on the spatial distribution and intensity of a discharge were investigated experimentally. A critical frequency of 1 kHz was found. With the frequency above 1 kHz, when a fast airflow was introduced into the discharge gap, the discharge patterns varied from filaments to curved stripes and the curvature degree rose with an increase in the airflow speed. At the same time, the discharge intensity decreased. However with the discharge frequency below 1 kHz, the discharge intensity would get greater with an increase in the airflow speed.
文摘A more efficient mine ventilation system, the ventilation-on-demand （VOD） system, has been proposed and tested in Canadian mines recently. In order to supply the required air volumes to the production areas of a mine, operators need to know the cause and effect of any changes requested from the VOD system. The sensitivity analysis is developed through generating a cause and effect matrix of sensitivity factors on given parameter changes in a ventilation system. This new utility, which was incorporated in the 3D-CANVENT mine ventilation simulator, is able to predict the airflow distributions in a ventilation network when underground conditions and ventilation controls are changed. For a primary ventilation system, the software can determine the optimal operating speed of the main fans to satisfy the airflow requirements in underground workings without necessarily using booster fans and regulators locally. An optimized fan operating speed time-table would assure variable demand-based fresh air delivery to the production areas effectively, while generating significant savings in energy consumption and operating cost.
文摘It is often required to know which roadway （adjustment roadway） resistances and how much values of the resis- tances should be changed to make the airflow rates in roadways （target roadways） to certain required values in the practice of mine ventilation. In this case, the airflow rates of the target roadways and the resistances of the roadways other than the ad- justment roadways are the given conditions and the resistances of the adjustment roadways are the solutions to be found. No straightforward method to solve the problem has been found up to now. Therefore, trial and error method using the ventilation network analysis program is utilized to solve the problem so far. The method takes long calculation time and the best answer is not necessarily obtained. The authors newly defined ＂airflow element＂ as an element of the ventilation network analysis. The resistances that satisfy the airflow requirements can be calculated straight forwardly by putting the function of the airflow element into the ventilation network analysis. The air power required for the ventilation can be minimized while meeting the airflow requirements by the advanced application of the method. The authors made the computer program fulfill the method. The program was applied to actual ventilation network and it was found that the method is very practical and the time required for the analysis is short.
基金supported by National Natural Science Foundation of China(No.51437002)
文摘Volume diffuse dielectric barrier discharge （DBD） plasma is produced in subsonic airflow by nanosecond high-voltage pulse power supply with a plate-to-plate discharge cell at 6 mm air gap length. The discharge images, optical emission spectra （OES）, the applied voltage and current waveforms of the discharge at the changed airflow rates are obtained. When airflow rate is increased, the transition of the discharge mode and the variations of discharge intensity, breakdown characteristics and the temperature of the discharge plasma are investigated. The results show that the discharge becomes more diffuse, discharge intensity is decreased accompanied by the increased breakdown voltage and time lag, and the temperature of the discharge plasma reduces when airflow of small velocity is introduced into the discharge gap. These phenomena are because that the airflow changes the spatial distribution of the heat and the space charge in the discharge gap.
