The strong crustal magnetic fields significantly alter the structure of the Martian space environment,including all plasma boundaries.The stretches of mini-magnetospheres formed by crustal fields from the location of ...The strong crustal magnetic fields significantly alter the structure of the Martian space environment,including all plasma boundaries.The stretches of mini-magnetospheres formed by crustal fields from the location of the Martian bow shocks were first found from the Mars Atmosphere and Volatile EvolutioN(MAVEN)observations.The present study aims to test whether this effect is also present in the shocks observed by Mars Express(MEX).We find that the bow shocks above the crustal field regions are enlarged,resulting in a north−south asymmetry and a longitude dependence in the shock size.The longitude dependence is more pronounced for near-subsolar shocks,and more dispersed for near-terminator shocks.The enlarged shocks are also observed to have shifted tailward from the longitudes of the strongest crustal fields.Due to a dawnside bias in MEX shock crossings,the enlarged shocks generally display a westward shift from the strongest crustal field region.These results confirm that stretches of the mini-magnetosphere are also present in the MEX shock observations.展开更多
Observational analyses and convection-permitting simulations are conducted to study an extreme event of damaging surface winds within a bow-shaped squall line over South China.Prevailing explanations for the formation...Observational analyses and convection-permitting simulations are conducted to study an extreme event of damaging surface winds within a bow-shaped squall line over South China.Prevailing explanations for the formation of damaging surface winds were applied to investigate the detailed processes at the mature stage of a squall line in a complicated real-world scenario.It is shown that environmental vertical wind shear was adequately strong to cause a shearing vorticity,and the shearing vorticity was comparable to the baroclinic vorticity by a cold pool.The balance led to strong upward motions at the leading edge of the squall line and brought plenty of rainfall.The descending rainfall cooled the surrounding air and entrained the upper-level cold air downward to the lower level,strengthening the cold pool by excessive evaporation and melting.The cold pool accelerated the propagation speed of the squall line and caused extensive wind damage at the surface.Meanwhile,the horizontal vortex lines at the leading edge of the cold pool were lifted by frontal updrafts and tilted to form the anti-cyclonic vortex at the middle level.This maintained and intensified the rearinflow jet behind the apex of bow echo in association with a notable midlevel pressure gradient.The rear-inflow jet was then transported downward to the surface by descending condensate,leading to damaging winds there.Other factors,such as environmental flows,however,contributed less to the damaging surface winds.展开更多
随着地面无人平台(Unmanned Ground Vehicles,UGVs)在复杂作业环境中的潜在应用和战略价值日益凸显,确保其自主行为的安全性变得至关重要。提出一种结合系统理论过程分析(System-Theoretic Process Analysis,STPA)和Bow-Tie模型的地面...随着地面无人平台(Unmanned Ground Vehicles,UGVs)在复杂作业环境中的潜在应用和战略价值日益凸显,确保其自主行为的安全性变得至关重要。提出一种结合系统理论过程分析(System-Theoretic Process Analysis,STPA)和Bow-Tie模型的地面无人平台系统安全分析方法。围绕遥控操作地面无人平台系统安全,通过STPA方法识别UGV系统中的不安全控制行为及其潜在风险,并利用Bow-Tie模型分析从损失致因场景到可能事故后果的事件链,得到风险传播路径和风险扩散路径。最终,基于Bow-Tie分析结果确定主被动安全分级控制措施,并通过自主安全控制器实现了系统安全管理。展开更多
Wave breaking at the bow of a high-speed ship is of great importance to the hydrodynamic performance of high-speed ships,accompanied by complex flow field deformation.In this study,the smoothed particle hydrodynamics(...Wave breaking at the bow of a high-speed ship is of great importance to the hydrodynamic performance of high-speed ships,accompanied by complex flow field deformation.In this study,the smoothed particle hydrodynamics(SPH)method under the Lagrange framework is adopted to simulate the breaking bow wave of the KCS ship model.In order to improve the computational efficiency,the inflow and outflow boundary model is used to establish a numerical tank of current,and a numerical treatment for free surface separation is implemented.Numerical simulations are carried out at Fr=0.35,0.40,0.5,0.6,and different types of wave breaking such as spilling breaker,plunging breaker,and scars are captured by the SPH method,which is consistent with the experimental result,demonstrating that the present SPH method can be robust and reliable in accurately predicting the breaking bow wave phenomenon of high-speed ships.Furthermore,the wave elevation and velocity field in the bow wave region are analyzed,and the evolution of the bow wave breaking is provided.展开更多
Based on previously released data,this paper first presented the criteria for recognizing bow echoes and divided their life cycle into three stages:the development stage,the mature stage,and the attenuation stage.Base...Based on previously released data,this paper first presented the criteria for recognizing bow echoes and divided their life cycle into three stages:the development stage,the mature stage,and the attenuation stage.Based on Doppler weather radar data during 2011-2020,43 bow echo events(including 54 individual bow echoes)in western South China were identified.The spatial and temporal distributions,formation and dissipation modes of these bow echoes,and the severe weather they caused were statistically analyzed.The results show that:(1)The bow echo events were unevenly distributed year-to-year,but all occurred from March to July,with the highest in April and May and the lowest in July.The period from night to early morning was found to be the main period for bow echo generation and intensification.(2)A banded area from Hechi City on the southeastern edge of the Yunnan-Guizhou Plateau to Wuzhou City in southeast Guangxi was identified as a high-incidence area of bow echoes.The length of bow echoes was correlated with their life cycle.(3)The origins of the bow echoes could be divided into five locations,most of which were in the eastern Yunnan-Guizhou Plateau.After entering western South China,their moving paths were categorized into three types,among which most bow echoes moved southeastward,generally because of the effect of cold air.Specifically,bow echoes generally moved eastward when cold air was weak or in the warm zone.Meanwhile,the fewest bow echoes moved northeastward.(4)Four modes of bow echo formation were identified:linearly organized,broken areal,linearly merging,and broken line.Dissipation could also be classified into four types.(5)The probability of convective weather generated by a bow echo was largest in the mature stage.展开更多
The outlet flow fields of a low-speed repeating-stage compressor with bowed stator stages are measured with five-hole probe under the near stall condition when the rotor/stator axial gap varies. The performances of th...The outlet flow fields of a low-speed repeating-stage compressor with bowed stator stages are measured with five-hole probe under the near stall condition when the rotor/stator axial gap varies. The performances of the straight stator stages are investigated and compared to those of the bowed stator stages. The results show that using bowed stator stages could alleviate the flow separation at both upper and low corners of the suction surface and the endwalls, and decrease the losses along the flow passage as well as the outlet flow angle. As the rotor/stator axial gap decreases, although the diffusion capacity of the compressor increases obviously, the outlet flow field in the straight stator stages deteriorates quickly. By contrast, little changes occur in the bowed stator stages, indicating that as the rotor/stator axial gap decreases, improved performance is achieved in the bowed stator stages.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2022YFF0503204)the National Natural Science Foundation of China(Grant No.42388101)+3 种基金Youth Innovation Promotion Association CAS(2020065)Young Elite Scientist Sponsorship Program by CAST(YESS20200152)the Key Research Program of the Institute of Geology&Geophysics,CAS(IGGCAS-202102)the Key Research Program of Chinese Academy of Sciences(Grant ZDB-SSW-TLC00103).
文摘The strong crustal magnetic fields significantly alter the structure of the Martian space environment,including all plasma boundaries.The stretches of mini-magnetospheres formed by crustal fields from the location of the Martian bow shocks were first found from the Mars Atmosphere and Volatile EvolutioN(MAVEN)observations.The present study aims to test whether this effect is also present in the shocks observed by Mars Express(MEX).We find that the bow shocks above the crustal field regions are enlarged,resulting in a north−south asymmetry and a longitude dependence in the shock size.The longitude dependence is more pronounced for near-subsolar shocks,and more dispersed for near-terminator shocks.The enlarged shocks are also observed to have shifted tailward from the longitudes of the strongest crustal fields.Due to a dawnside bias in MEX shock crossings,the enlarged shocks generally display a westward shift from the strongest crustal field region.These results confirm that stretches of the mini-magnetosphere are also present in the MEX shock observations.
基金Research(2020B0301030004)National Natural Science Foundation of China(42275002)+3 种基金Natural Science Foundation of Chongqing(CSTB2022NSCQ-MSX0890)Scientific and Technological Project of Chongqing Meteorological Service(YWJSGG-202124)Key Innovation Team of China Meteorological Administration(CMA2022ZD09)Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(SML2023SP209)。
文摘Observational analyses and convection-permitting simulations are conducted to study an extreme event of damaging surface winds within a bow-shaped squall line over South China.Prevailing explanations for the formation of damaging surface winds were applied to investigate the detailed processes at the mature stage of a squall line in a complicated real-world scenario.It is shown that environmental vertical wind shear was adequately strong to cause a shearing vorticity,and the shearing vorticity was comparable to the baroclinic vorticity by a cold pool.The balance led to strong upward motions at the leading edge of the squall line and brought plenty of rainfall.The descending rainfall cooled the surrounding air and entrained the upper-level cold air downward to the lower level,strengthening the cold pool by excessive evaporation and melting.The cold pool accelerated the propagation speed of the squall line and caused extensive wind damage at the surface.Meanwhile,the horizontal vortex lines at the leading edge of the cold pool were lifted by frontal updrafts and tilted to form the anti-cyclonic vortex at the middle level.This maintained and intensified the rearinflow jet behind the apex of bow echo in association with a notable midlevel pressure gradient.The rear-inflow jet was then transported downward to the surface by descending condensate,leading to damaging winds there.Other factors,such as environmental flows,however,contributed less to the damaging surface winds.
文摘随着地面无人平台(Unmanned Ground Vehicles,UGVs)在复杂作业环境中的潜在应用和战略价值日益凸显,确保其自主行为的安全性变得至关重要。提出一种结合系统理论过程分析(System-Theoretic Process Analysis,STPA)和Bow-Tie模型的地面无人平台系统安全分析方法。围绕遥控操作地面无人平台系统安全,通过STPA方法识别UGV系统中的不安全控制行为及其潜在风险,并利用Bow-Tie模型分析从损失致因场景到可能事故后果的事件链,得到风险传播路径和风险扩散路径。最终,基于Bow-Tie分析结果确定主被动安全分级控制措施,并通过自主安全控制器实现了系统安全管理。
基金The Guangdong Basic and Applied Basic Research Foundation(2024B1515020107)the National Natural Science Foundation of China(Grant Nos.52171329)+1 种基金the State Key Laboratory of Disaster Prevention&Mitigation of Explosion&Impact(Grant No.NOLGD-SKL-202201)the Fundamental Research Funds for the Central Universities,Sun Yat-sen University(Grant No.231gbi023).
文摘Wave breaking at the bow of a high-speed ship is of great importance to the hydrodynamic performance of high-speed ships,accompanied by complex flow field deformation.In this study,the smoothed particle hydrodynamics(SPH)method under the Lagrange framework is adopted to simulate the breaking bow wave of the KCS ship model.In order to improve the computational efficiency,the inflow and outflow boundary model is used to establish a numerical tank of current,and a numerical treatment for free surface separation is implemented.Numerical simulations are carried out at Fr=0.35,0.40,0.5,0.6,and different types of wave breaking such as spilling breaker,plunging breaker,and scars are captured by the SPH method,which is consistent with the experimental result,demonstrating that the present SPH method can be robust and reliable in accurately predicting the breaking bow wave phenomenon of high-speed ships.Furthermore,the wave elevation and velocity field in the bow wave region are analyzed,and the evolution of the bow wave breaking is provided.
基金National Natural Science Foundation of China(52239006,41975001,41930972)Natural Science Foundation of Guangxi Zhuang Autonomous Region(2022GXNSFBA035565)。
文摘Based on previously released data,this paper first presented the criteria for recognizing bow echoes and divided their life cycle into three stages:the development stage,the mature stage,and the attenuation stage.Based on Doppler weather radar data during 2011-2020,43 bow echo events(including 54 individual bow echoes)in western South China were identified.The spatial and temporal distributions,formation and dissipation modes of these bow echoes,and the severe weather they caused were statistically analyzed.The results show that:(1)The bow echo events were unevenly distributed year-to-year,but all occurred from March to July,with the highest in April and May and the lowest in July.The period from night to early morning was found to be the main period for bow echo generation and intensification.(2)A banded area from Hechi City on the southeastern edge of the Yunnan-Guizhou Plateau to Wuzhou City in southeast Guangxi was identified as a high-incidence area of bow echoes.The length of bow echoes was correlated with their life cycle.(3)The origins of the bow echoes could be divided into five locations,most of which were in the eastern Yunnan-Guizhou Plateau.After entering western South China,their moving paths were categorized into three types,among which most bow echoes moved southeastward,generally because of the effect of cold air.Specifically,bow echoes generally moved eastward when cold air was weak or in the warm zone.Meanwhile,the fewest bow echoes moved northeastward.(4)Four modes of bow echo formation were identified:linearly organized,broken areal,linearly merging,and broken line.Dissipation could also be classified into four types.(5)The probability of convective weather generated by a bow echo was largest in the mature stage.
基金National Natural Science Foundation of China (50646021)Chinese Specialized Research Fund for the Doctoral Pro-gram of Higher Education (20060213007)
文摘The outlet flow fields of a low-speed repeating-stage compressor with bowed stator stages are measured with five-hole probe under the near stall condition when the rotor/stator axial gap varies. The performances of the straight stator stages are investigated and compared to those of the bowed stator stages. The results show that using bowed stator stages could alleviate the flow separation at both upper and low corners of the suction surface and the endwalls, and decrease the losses along the flow passage as well as the outlet flow angle. As the rotor/stator axial gap decreases, although the diffusion capacity of the compressor increases obviously, the outlet flow field in the straight stator stages deteriorates quickly. By contrast, little changes occur in the bowed stator stages, indicating that as the rotor/stator axial gap decreases, improved performance is achieved in the bowed stator stages.
