Open cavities with different door-opening angles are investigated using high-speed schlieren visualization and dynamic pressure measurements in hypersonic flow with a freestream Mach number of 6.With the help of numer...Open cavities with different door-opening angles are investigated using high-speed schlieren visualization and dynamic pressure measurements in hypersonic flow with a freestream Mach number of 6.With the help of numerical simulations,the shear layer deformation and pressure increase in the cavities due to the impingement of the door-leading-edge shocks are identified via comparison with those in the cavity without doors.As the door-opening angle decreases from 90°,the shear layer above the forepart of the cavity is gradually raised by the high pressure in the cavity.When the door-opening angle decreases to 30°and 15°,the boundary layer on the upstream flat plate of the cavity separates,and separation shock is observed.The doors enhance the instability of the cavity flow and increase the pressure fluctuations in the cavities.A new oscillation pattern,referred to as coupled oscillation,is observed in the cases with separation on the upstream flat plate,in which the separation shock oscillates at the same dominant frequency as the flow inside the cavity.Compared with the cavity without doors,this coupled oscillation causes a lower oscillation frequency and a larger overall sound pressure level.Cross-correlation analyses between pressure signals indicate that the disturbances generated at the trailing edge of the cavity can propagate to the separation on the upstream flat plate and cause coupled oscillation of the separation shock.The fundamental frequencies of the coupled oscillations can be normalized to approximately the same Strouhal number as that of the cavity without doors.These findings support that the oscillation mechanisms of hypersonic cavities without and with doors are primarily dominated by acoustic feedback.展开更多
The afterburning of TNT and structural constraints in confined spaces significantly amplify the blast load,leading to severe structural damage. This study investigates the mechanisms underlying the enhanced dynamic re...The afterburning of TNT and structural constraints in confined spaces significantly amplify the blast load,leading to severe structural damage. This study investigates the mechanisms underlying the enhanced dynamic response of reinforced concrete blast doors with four-sided restraints in confined space. Explosion tests with TNT charges ranging from 0.15 kg to 0.4 kg were conducted in a confined space,capturing overpressure loads and the dynamic response of the blast door. An internal explosion model incorporating the afterburning effect was developed using LS-DYNA software and validated against experimental data. The results reveal that the TNT afterburning effect amplifies both the initial peak overpressure and the quasi-static overpressure, resulting in increased deformation of the blast door.Within the 0.15-0.4 kg charge range, the initial overpressure peak and quasi-static overpressure increased by an average of 1.79 times and 2.21 times, respectively. Additionally, the afterburning effect enhanced the blast door's deflection by 177%. Compared to open-space scenarios, the cumulative deflection of the blast door due to repeated shock wave impacts is significantly greater in confined spaces. Furthermore, the quasi-static pressure arising from the structural constraints sustains the blast door's deflection at a high level.展开更多
One of the main construction problems in permafrost regions is protecting permafrost thermal stability. Although ventilating ducts and crushed-rock layers were successfully used in railway embankment construction, the...One of the main construction problems in permafrost regions is protecting permafrost thermal stability. Although ventilating ducts and crushed-rock layers were successfully used in railway embankment construction, their effects might not meet large-width expressway requirements. The convection-intensifying composite embankment composed of perforated ventilation ducts and crushed-rock layers was numerically studied to investigate its cooling effects. Adopting a numerical model, the temperature fields for two kinds of composite embankment with and without air doors were analyzed considering air flow and heat transfer characteristics in porous media. The results show that wind velocity in the crushed-rock zone is intensified by the perforated ventilation duct. The underlying permafrost temperature obviously decreases, and the 0 °C isotherm position rises significantly due to composite embankment. The composite embankment with air doors is more effective than that without air doors. Therefore, the new convection-intensifying composite embankment is potentially a highly efficient cooling measure for construction in permafrost regions.展开更多
The doors and windows are the throat of the building. This paper discusses the fundamental role of the doors and windows of the building, and the dominant roles such as spatial organization and control of light, and t...The doors and windows are the throat of the building. This paper discusses the fundamental role of the doors and windows of the building, and the dominant roles such as spatial organization and control of light, and to study the recessive function of windows and doors from aspects of the psychological impact, cultural significance and decoration. After exploring the characteristics of modem windows and doors, it studies the design elements of modem windows and doors and summed up the features that the initiative to make use of the environment. Basic from three levels as the basic form of design; windows and buildings, and the social and natural environment of the unified design; doors and windows to take the initiative to study the nature.展开更多
growth in Africa, Ghana has been witnessing a surge in foreign direct investments. According to World Bank statistics, its economy grew by an average of 6 percent annually since 2005 before heading for an assessed 4.S...growth in Africa, Ghana has been witnessing a surge in foreign direct investments. According to World Bank statistics, its economy grew by an average of 6 percent annually since 2005 before heading for an assessed 4.S-percent growth this year. Foreign investments totaled over $12 billion from 1999 to 2009.展开更多
From September 13th-16th,2010,the Texworld show will be held at the Paris le Bourget exhibition centre.This show,735 weavers-which attests to the stability in the numbers of exhibitors
FOR 26-year-old Nigerian student Olufemi Lawal. China is home. He has set his heart on seeking employment in the country after completing his studies, but past regulations meant the inconvenience of leaving the countr...FOR 26-year-old Nigerian student Olufemi Lawal. China is home. He has set his heart on seeking employment in the country after completing his studies, but past regulations meant the inconvenience of leaving the country for a lengthy period before being able to return to job hunt.展开更多
Blesse D ncube knew there would be lucrative opportunities in learning Chinese.Therefore,the Zimbabwean chose to major in Chinese while doing her Bachelor of Arts and when she graduated in 2010,the 28-year-old found a...Blesse D ncube knew there would be lucrative opportunities in learning Chinese.Therefore,the Zimbabwean chose to major in Chinese while doing her Bachelor of Arts and when she graduated in 2010,the 28-year-old found a wealth of steady work in translation coming her way.展开更多
Current practice in analysis and design of blast doors subjected to blast loading considers only simple boundary conditions and material properties. The boundary conditions and material properties, in fact, have consi...Current practice in analysis and design of blast doors subjected to blast loading considers only simple boundary conditions and material properties. The boundary conditions and material properties, in fact, have considerable influence on the response of blast doors subjected to blast loading. In this paper, the dynamic responses of a reinforced concrete arched blast door under blast loading were analyzed by the finite element program ABAQUS, combined with a previously developed elasto-viscoplastic rate-sensitive material model. And the effect of the surrounding rock mass and contact effect of the doorframe were also taken into account in the simulation. It is demonstrated that the strain-rate effect has considerable influence on the response of reinforced concrete blast door subjected to blast loading and must be taken into account in the analysis.展开更多
At present, with the rapid development of urban construction, the number of urban population is increasing exponentially year by year. Under this background, rail transit has become the only choice for people's da...At present, with the rapid development of urban construction, the number of urban population is increasing exponentially year by year. Under this background, rail transit has become the only choice for people's daily travel because of its convenience and speed. Rail transit plays an important role in relieving the pressure of urban traffic and facilitating people's daily work and life. However, during the daily operation of rail transit vehicles, due to the frequent starting of the doors, the doors of rail transit vehicles become the most prone areas to malfunction, which not only affects the normal operation of rail transit, but also brings great hidden dangers to passengers' daily travel safety. This paper mainly analyzes the common main faults of the doors of urban rail transit vehicles, and discusses the maintenance strategies of the doors, hoping to provide reference opinions for continuously improving the operation safety of rail transit.展开更多
1 Three years ago,Virginia Squier was leading a group of middle school students on a tour of England with her 8⁃year⁃old daughter,Chambers.One evening,as they waited on a crowded London Underground platform,Chambers s...1 Three years ago,Virginia Squier was leading a group of middle school students on a tour of England with her 8⁃year⁃old daughter,Chambers.One evening,as they waited on a crowded London Underground platform,Chambers suddenly let go of her mothers hand and jumped onto a train just as the doors closed.Squier ran alongside the train,desperately trying to open the doors,but it sped away with her daughter inside.展开更多
基金supported by the National Natural Science Foundation of China(Nos.12172354,12388101,U21B6003)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB0620201).
文摘Open cavities with different door-opening angles are investigated using high-speed schlieren visualization and dynamic pressure measurements in hypersonic flow with a freestream Mach number of 6.With the help of numerical simulations,the shear layer deformation and pressure increase in the cavities due to the impingement of the door-leading-edge shocks are identified via comparison with those in the cavity without doors.As the door-opening angle decreases from 90°,the shear layer above the forepart of the cavity is gradually raised by the high pressure in the cavity.When the door-opening angle decreases to 30°and 15°,the boundary layer on the upstream flat plate of the cavity separates,and separation shock is observed.The doors enhance the instability of the cavity flow and increase the pressure fluctuations in the cavities.A new oscillation pattern,referred to as coupled oscillation,is observed in the cases with separation on the upstream flat plate,in which the separation shock oscillates at the same dominant frequency as the flow inside the cavity.Compared with the cavity without doors,this coupled oscillation causes a lower oscillation frequency and a larger overall sound pressure level.Cross-correlation analyses between pressure signals indicate that the disturbances generated at the trailing edge of the cavity can propagate to the separation on the upstream flat plate and cause coupled oscillation of the separation shock.The fundamental frequencies of the coupled oscillations can be normalized to approximately the same Strouhal number as that of the cavity without doors.These findings support that the oscillation mechanisms of hypersonic cavities without and with doors are primarily dominated by acoustic feedback.
基金financially supported by the National Natural Science Foundation of China (Grant No. 52278504)the Natural Science Foundation of Jiangsu Province (Grant No. BK20220141)。
文摘The afterburning of TNT and structural constraints in confined spaces significantly amplify the blast load,leading to severe structural damage. This study investigates the mechanisms underlying the enhanced dynamic response of reinforced concrete blast doors with four-sided restraints in confined space. Explosion tests with TNT charges ranging from 0.15 kg to 0.4 kg were conducted in a confined space,capturing overpressure loads and the dynamic response of the blast door. An internal explosion model incorporating the afterburning effect was developed using LS-DYNA software and validated against experimental data. The results reveal that the TNT afterburning effect amplifies both the initial peak overpressure and the quasi-static overpressure, resulting in increased deformation of the blast door.Within the 0.15-0.4 kg charge range, the initial overpressure peak and quasi-static overpressure increased by an average of 1.79 times and 2.21 times, respectively. Additionally, the afterburning effect enhanced the blast door's deflection by 177%. Compared to open-space scenarios, the cumulative deflection of the blast door due to repeated shock wave impacts is significantly greater in confined spaces. Furthermore, the quasi-static pressure arising from the structural constraints sustains the blast door's deflection at a high level.
基金the financial support of the National Natural Science Foundation of China (No. 41121061)the National Basic Research Program (973) of China (Nos. 2012CB026101 and 2011CB013505)+1 种基金the Western Project Program of the Chinese Academy of Sciences (No. KZCX2-XB3-19)the Open Fund of State Key Laboratory of Frozen Soil Engineering (No. SKLFSE201209)
文摘One of the main construction problems in permafrost regions is protecting permafrost thermal stability. Although ventilating ducts and crushed-rock layers were successfully used in railway embankment construction, their effects might not meet large-width expressway requirements. The convection-intensifying composite embankment composed of perforated ventilation ducts and crushed-rock layers was numerically studied to investigate its cooling effects. Adopting a numerical model, the temperature fields for two kinds of composite embankment with and without air doors were analyzed considering air flow and heat transfer characteristics in porous media. The results show that wind velocity in the crushed-rock zone is intensified by the perforated ventilation duct. The underlying permafrost temperature obviously decreases, and the 0 °C isotherm position rises significantly due to composite embankment. The composite embankment with air doors is more effective than that without air doors. Therefore, the new convection-intensifying composite embankment is potentially a highly efficient cooling measure for construction in permafrost regions.
文摘The doors and windows are the throat of the building. This paper discusses the fundamental role of the doors and windows of the building, and the dominant roles such as spatial organization and control of light, and to study the recessive function of windows and doors from aspects of the psychological impact, cultural significance and decoration. After exploring the characteristics of modem windows and doors, it studies the design elements of modem windows and doors and summed up the features that the initiative to make use of the environment. Basic from three levels as the basic form of design; windows and buildings, and the social and natural environment of the unified design; doors and windows to take the initiative to study the nature.
文摘growth in Africa, Ghana has been witnessing a surge in foreign direct investments. According to World Bank statistics, its economy grew by an average of 6 percent annually since 2005 before heading for an assessed 4.S-percent growth this year. Foreign investments totaled over $12 billion from 1999 to 2009.
文摘From September 13th-16th,2010,the Texworld show will be held at the Paris le Bourget exhibition centre.This show,735 weavers-which attests to the stability in the numbers of exhibitors
文摘FOR 26-year-old Nigerian student Olufemi Lawal. China is home. He has set his heart on seeking employment in the country after completing his studies, but past regulations meant the inconvenience of leaving the country for a lengthy period before being able to return to job hunt.
文摘Blesse D ncube knew there would be lucrative opportunities in learning Chinese.Therefore,the Zimbabwean chose to major in Chinese while doing her Bachelor of Arts and when she graduated in 2010,the 28-year-old found a wealth of steady work in translation coming her way.
基金Supported by National Natural Science Foundation of China(No.50525825)
文摘Current practice in analysis and design of blast doors subjected to blast loading considers only simple boundary conditions and material properties. The boundary conditions and material properties, in fact, have considerable influence on the response of blast doors subjected to blast loading. In this paper, the dynamic responses of a reinforced concrete arched blast door under blast loading were analyzed by the finite element program ABAQUS, combined with a previously developed elasto-viscoplastic rate-sensitive material model. And the effect of the surrounding rock mass and contact effect of the doorframe were also taken into account in the simulation. It is demonstrated that the strain-rate effect has considerable influence on the response of reinforced concrete blast door subjected to blast loading and must be taken into account in the analysis.
文摘At present, with the rapid development of urban construction, the number of urban population is increasing exponentially year by year. Under this background, rail transit has become the only choice for people's daily travel because of its convenience and speed. Rail transit plays an important role in relieving the pressure of urban traffic and facilitating people's daily work and life. However, during the daily operation of rail transit vehicles, due to the frequent starting of the doors, the doors of rail transit vehicles become the most prone areas to malfunction, which not only affects the normal operation of rail transit, but also brings great hidden dangers to passengers' daily travel safety. This paper mainly analyzes the common main faults of the doors of urban rail transit vehicles, and discusses the maintenance strategies of the doors, hoping to provide reference opinions for continuously improving the operation safety of rail transit.
文摘1 Three years ago,Virginia Squier was leading a group of middle school students on a tour of England with her 8⁃year⁃old daughter,Chambers.One evening,as they waited on a crowded London Underground platform,Chambers suddenly let go of her mothers hand and jumped onto a train just as the doors closed.Squier ran alongside the train,desperately trying to open the doors,but it sped away with her daughter inside.
