China is the main silk producer in the world, whose RSS (Raw Silk Standard)is widely approved in international trade. After entering WTO, China needs to revise the RSSaccording to the changes of silk industry and deve...China is the main silk producer in the world, whose RSS (Raw Silk Standard)is widely approved in international trade. After entering WTO, China needs to revise the RSSaccording to the changes of silk industry and develop advanced electronic testing system and improvetesting means, so as to promote the internationlization of the RSS. 1. The international standingof Chinese silk The silk consisting of 18 amino acids has the similar protein structure to people'sskin. It is enjoyed by most people for it' s comfortable, magnificent and noble features and ispraised to be the second skin for its unique effects on health and adjusting the body water. In the21st century, silk is the main international fashion as the representative of green products.展开更多
In recent years, the subcontracting production for foreign trade of the Xi’an Aviation Engine Company (XAEC), a foreign trade production base of China, has achieved rapid development. In 1994, the company’s export e...In recent years, the subcontracting production for foreign trade of the Xi’an Aviation Engine Company (XAEC), a foreign trade production base of China, has achieved rapid development. In 1994, the company’s export earnings from foreign trade made a breakthrough at US$11 million, and it was commended by the State Economic展开更多
To introduce foreign capital for the municipal highway construction is a great measure to meet the development of the socialist market economy and to reform the investment system for the municipal highway construction...To introduce foreign capital for the municipal highway construction is a great measure to meet the development of the socialist market economy and to reform the investment system for the municipal highway construction. The aim of the reform lies in taking the construction and management of the municipal highway facilities as an industry to operate, widening the investment channel of the municipal highway construction and gradually forming a benign cycle of investment-construc-展开更多
According to customs statistics, China’s exports of machinery and electric products in 1996 were worth US$ 48.21 billion, an increase of 9.9 percent over the preceding year, and 8.4 percent higher than the growth rat...According to customs statistics, China’s exports of machinery and electric products in 1996 were worth US$ 48.21 billion, an increase of 9.9 percent over the preceding year, and 8.4 percent higher than the growth rate of the nation’s total exports. The proportion of machinery and electric product exports in the nation’s total foreign trade volume\ increased from 29.5 percent in 1995 to 31.9 percent in 1996, a growth at 2.4 percent.展开更多
Housing isone of the necessities of humansfor existence and development.The Chinese government hasalways attached great importanceto housing construction;especially in recent years,thepriority development of housingco...Housing isone of the necessities of humansfor existence and development.The Chinese government hasalways attached great importanceto housing construction;especially in recent years,thepriority development of housingconstruction has been seen inthe real estate and propertiesindustry.Hou Jie,Minister ofConstruction,not long ago wrotean article summarizing theachievements made in this sectorand drawing a blueprint forspeedup of housing constructionand the improvement of livingconditions in the future.It willprovide a vast vista for thedevelopment of China’s buildingindustry and its internationalcooperation.展开更多
High-speed railways have the merits of high speed, high transport capacity, low consumption of energy, less pollution, less occupation of land, and greater safety. The development of high-speed railways is suitable fo...High-speed railways have the merits of high speed, high transport capacity, low consumption of energy, less pollution, less occupation of land, and greater safety. The development of high-speed railways is suitable for the national conditions in China.The authors suggest that, with the Hu-Ning (Shanghai-Nanjing) section of the Jing-Hu (Beijing-Shanghai) Railway as the starting point, a high-speed dedicated passenger railway line be built to realize the separate transportation of passengers and goods, thus easing the strain on transport in East China, accumulating experience for the future development of high-speed railways, and bringing along the development of high and new technology industries.展开更多
This paper discusses the urgency to further develop China’s space technological industry;analyzes the gaps between China and other advanced countries in space industry,including technological level,development scale,...This paper discusses the urgency to further develop China’s space technological industry;analyzes the gaps between China and other advanced countries in space industry,including technological level,development scale,application scope and investment;describes the current severe situation that the China’s space industry is faced with and proposes the overall objective,guiding principles and major tasks of China’s space technological sector in the Ninth-Five Year Plan and the coming decade.Finally,it proposes some policies and effective measures to speed up the development of China’s space industry to meet the challenge in the 21st century.展开更多
During the hoisting process of the offshore substation,changes in the hoisting speed can affect the hoisting system.Therefore,this study set four different speed conditions for the lifting and lowering stages of the i...During the hoisting process of the offshore substation,changes in the hoisting speed can affect the hoisting system.Therefore,this study set four different speed conditions for the lifting and lowering stages of the installation process,and studied the impact of different lifting and lowering speeds on the hoisting system under the same environmental conditions through numerical simulation.The results show that during the lifting operation,as the lifting speed increases,the swing motion of the substation and the installation vessel tends to decrease,and the faster the hoisting speed,the more obvious the swing suppression of the substation and the installation vessel,and the smaller the fluctuation in the tension amplitude of the slings and mooring lines.In contrast,during the lowering operation,as the lowering speed increases,the swing motion of the substation and the installation vessel tends to increase,and the faster the lowering speed,the more obvious the swing amplification effect of the substation and the installation vessel.Therefore,during hoisting operations,increasing the lifting speed and reducing the lowering speed can mitigate the motion performance of the hoisting coupling system,reduce the tension amplitude variation of the sling and mooring,and ensure the smooth progress of the hoisting operation.展开更多
The dual challenges of critical speed prediction inaccuracies and ambiguous vibration behaviors are present in high-speed flexible rotors,particularly in free turbine rotors in turboshaft engine systems.The study begi...The dual challenges of critical speed prediction inaccuracies and ambiguous vibration behaviors are present in high-speed flexible rotors,particularly in free turbine rotors in turboshaft engine systems.The study begins with an examination of the rotor-bearing bidirectional coupling mechanism,with a primary focus on the nonlinear characteristics of the bearing.An investigation is carried out on the mechanical modeling methodologies for four-point contact ball bearings(FPCBBs)and cylindrical roller bearings(CRBs).To address the issue of excessive computational time in traditional bearing calculation methods,the sled dog optimization(SDO)algorithm is substituted for the conventional Newton-Raphson method.A rotor-bearing coupling dynamics model is developed by the finite element and lumped mass methods,with experimental validation achieved through a simulator test rig.The effects of three internal bearing parameters in FPCBBs(arching width and raceway groove curvature coefficient)and CRBs(initial radial clearance)on the critical speed characteristics and vibrational behavior of rotorbearing coupled systems are examined.The numerical simulation results show some interesting conclusions.展开更多
In the wake of the global financial crisis, China has amazed the world with the speed of its economic recovery. But what has been even more surprising is the speed of its railway evolution.
Chinese carmakers find the way to become more technologically intensive In the classic economic model, there is land,labor and capital. Each plays a role in economic development through its supply, and development can...Chinese carmakers find the way to become more technologically intensive In the classic economic model, there is land,labor and capital. Each plays a role in economic development through its supply, and development cannot occur with-展开更多
To reduce the risk of traffic accidents significantly caused by the speeding behavior of electric bicycles,this study focuses on the Beijing Yizhuang Economic and Tech-nological Development Zone.This work relies on hi...To reduce the risk of traffic accidents significantly caused by the speeding behavior of electric bicycles,this study focuses on the Beijing Yizhuang Economic and Tech-nological Development Zone.This work relies on high-precision shared electric bicycle Global Positioning System trajectory data,integrating a spatiotemporal analysis model and geographic information system(GIS)technol-ogy to explore the spatial and temporal variability law and formation mechanism of speeding behavior.Through data preprocessing,speeding events are identified,and weekday features are extracted.Four periods are identified:morning peak,midday minipeak,evening peak,and nighttime flat peak.Using the GIS platform,global spatial autocorrela-tion and local clustering analysis are conducted to identify the spatial clustering characteristics of speeding behaviors and hotspot areas.The coldspot and hotspot patterns of speeding events and the dynamic trajectories of their evolu-tion are analyzed using spatiotemporal cube technology.The results show that speeding behaviors are strongly corre-lated with the commuting peak in time and spatially concen-trated in the intersections of urban main roads,the periphery of commercial complexes,and industrial parks,with a dif-fusion tendency.The results of this study provide novel in-sights into the research and analysis of the spatial and tempo-ral characteristics of speeding risk behaviors of electric bi-cycles and effective technical support for nonmotorized traf-fic safety management.展开更多
This study focuses on coupled vibrations of rotating thin-walled composite beams subjected to hygrothermal effects.In the existing literature,many studies have been conducted on coupled bending-torsional vibration and...This study focuses on coupled vibrations of rotating thin-walled composite beams subjected to hygrothermal effects.In the existing literature,many studies have been conducted on coupled bending-torsional vibration and resonance in hygrothermal environments.Few studies considered the coupled flapwise-edgewise and resonances of composite thin-walled beams.Considering this,the flapwise-edgewise coupling effects and resonant characteristics of rotating thin-walled composite beams in a hygrothermal environment are studied.The Rayleigh–Ritz method is used to solve the equations of the beam.Results indicate that flapwise-edgewise coupling factors are essential for the vibration analysis of rectangular thin-walled beams.The ply angle and setting angle strongly affect the internal and external resonances.Large ply angles can significantly reduce the chances of primary internal and external resonances occurring when the permitted rotational speed is lower.展开更多
Previous studies have indicated a global reversal of near-surface wind speeds from a declining trend to an increasing trend around 2010;however,it remains unclear whether upper-air wind speeds exhibit a similar revers...Previous studies have indicated a global reversal of near-surface wind speeds from a declining trend to an increasing trend around 2010;however,it remains unclear whether upper-air wind speeds exhibit a similar reversal.This study evaluates reanalysis products using surface and radiosonde observations to analyze upper-air wind speed variations in the Northern Hemisphere,focusing on their seasonal and latitudinal differences.Results demonstrate that JRA-55 effectively captures wind speed variations in the Northern Hemisphere.Notably,upper-air wind speeds over land experienced a reversal in winter 2010 with significant latitudinal differences.The trend reversal of upper wind speed between the midlatitudes and subtropics presents a dipole pattern.From 1990 to 2010,upper-air wind speeds in the midlatitudes(40°-70°N)significantly declined,while the subtropical zone(20°-40°N)displayed an opposite trend.However,during 2010-2020,wind speeds in the midlatitudes shifted to a significant positive trend,whereas the subtropics experienced a significant negative trend.The variations in Northern Hemisphere winter wind speeds can be attributed to changes in low-level baroclinicity driven by tropical diabatic heating and midlatitude transient eddy feedback.Enhanced diabatic heating and weakened eddy feedback during 1990-2010 contributed to reduced wind speeds in the midlatitudes and increased speeds in the subtropics,while reduced diabatic heating and strengthened eddy feedback during 2010-2020 resulted in increased wind speeds in the midlatitudes and decreased speeds in the subtropics.The reversal of upper-air wind speeds could affect surface wind speeds by downward momentum transfer,which could contribute to the reversal of surface wind speeds.展开更多
By applying the convolution-based Hilbert transform in the zonal direction on six-hourly streamfunction fields at200 h Pa, we present the climatology and trends of the local wave period, and zonal and meridional phase...By applying the convolution-based Hilbert transform in the zonal direction on six-hourly streamfunction fields at200 h Pa, we present the climatology and trends of the local wave period, and zonal and meridional phase speeds, of Rossby waves over the globe during the solstice seasons of 1979–2023. While partly similar to and inspired by Fragkoulidis and Wirth(2020), our method differs in its ability to cover both planetary-scale and synoptic-scale waves over not only the extratropics, but also the tropics and subtropics. Based on a physically reasonable global distribution of wave periods, our key new finding is a robust prolonging of wave periods over most regions of the tropics and subtropics during both solstice seasons of 1979–2023, except for the tropical Atlantic, which experiences a shortened wave period during June–July–August of 1979–2022. Both the prolonging and shortening of wave periods are mainly associated with the changes in planetary-scale waves. Regionally varying trends of the zonal phase speed(Cpx) of synoptic waves are consistent in sign with, but smaller in magnitude than, the trends of local zonal wind, confirming the conclusion of Wu and Lu(2023)on the opposite effects of zonal wind and the meridional gradient of potential vorticity on Cpx. Meanwhile, the Cpx trends of planetary-scale waves are relatively weak, and do not exhibit a robust relation with the trend of zonal wind. These new results are helpful toward better understanding the changes in atmospheric waves and extreme events under global warming.展开更多
This work presents an adaptive tracking guidance method for robotic fishes. The scheme enables robots to suppress external interference and eliminate motion jitter. An adaptive integral surge line-of-sight guidance ru...This work presents an adaptive tracking guidance method for robotic fishes. The scheme enables robots to suppress external interference and eliminate motion jitter. An adaptive integral surge line-of-sight guidance rule is designed to eliminate dynamics interference and sideslip issues. Limited-time yaw and surge speed observers are reported to fit disturbance variables in the model. The approximation values can compensate for the system's control input and improve the robots' tracking accuracy.Moreover, this work develops a terminal sliding mode controller and third-order differential processor to determine the rotational torque and reduce the robots' run jitter. Then, Lyapunov's theory proves the uniform ultimate boundedness of the proposed method. Simulation and physical experiments confirm that the technology improves the tracking error convergence speed and stability of robotic fishes.展开更多
The high-speed reentry vehicle operates across a broad range of speeds and spatial domains,where optimal aerodynamic shapes for different speeds are contradictory.This makes it challenging for a single-Mach optimizati...The high-speed reentry vehicle operates across a broad range of speeds and spatial domains,where optimal aerodynamic shapes for different speeds are contradictory.This makes it challenging for a single-Mach optimization design to meet aerodynamic performance requirements throughout the vehicle’s flight envelope.Additionally,the strong coupling between aerodynamics and control adds complexity,as fluctuations in aerodynamic parameters due to speed variations complicate control system design.To address these challenges,this study proposes an aerodynamic/control coupling optimization design approach.This method,based on aerodynamic optimization principles,incorporates active control technology,treating aerodynamic layout and control system design as primary components during the conceptual design phase.By integrating the design and evaluation of aerodynamics and control,the approach aims to reduce design iterations and enhance overall flight performance.The comprehensive design of the rotary reentry vehicle,using this optimization strategy,effectively balances performance at supersonic and hypersonic speeds.The results show that the integrated design model meets aerodynamic and control performance requirements over a broader range of Mach numbers,preventing performance degradation due to deviations from the design Mach number,and providing a practical solution for high-speed reentry vehicle design.展开更多
This paper investigates the power generation characteristics of solar cells mounted on unmanned aerial vehicles(UAVs)under the coupled influence of flight conditions and the sur-rounding environment.Firstly,the study ...This paper investigates the power generation characteristics of solar cells mounted on unmanned aerial vehicles(UAVs)under the coupled influence of flight conditions and the sur-rounding environment.Firstly,the study reveals that the voltage,current,and power output of the solar cells undergo consistent temporal variations throughout the day,primarily driven by voltage fluctuations,with a peak occurring around noon.Secondly,it is observed that the cells’performance is significantly more influenced by temporal variations in external light intensity than by temperature changes resulting from variations in flight speed.Finally,the study finds that the impact of flight altitude on the cells’performance is slightly more pronounced than the influence of temporal variations in external light intensity.展开更多
文摘China is the main silk producer in the world, whose RSS (Raw Silk Standard)is widely approved in international trade. After entering WTO, China needs to revise the RSSaccording to the changes of silk industry and develop advanced electronic testing system and improvetesting means, so as to promote the internationlization of the RSS. 1. The international standingof Chinese silk The silk consisting of 18 amino acids has the similar protein structure to people'sskin. It is enjoyed by most people for it' s comfortable, magnificent and noble features and ispraised to be the second skin for its unique effects on health and adjusting the body water. In the21st century, silk is the main international fashion as the representative of green products.
文摘In recent years, the subcontracting production for foreign trade of the Xi’an Aviation Engine Company (XAEC), a foreign trade production base of China, has achieved rapid development. In 1994, the company’s export earnings from foreign trade made a breakthrough at US$11 million, and it was commended by the State Economic
文摘To introduce foreign capital for the municipal highway construction is a great measure to meet the development of the socialist market economy and to reform the investment system for the municipal highway construction. The aim of the reform lies in taking the construction and management of the municipal highway facilities as an industry to operate, widening the investment channel of the municipal highway construction and gradually forming a benign cycle of investment-construc-
文摘According to customs statistics, China’s exports of machinery and electric products in 1996 were worth US$ 48.21 billion, an increase of 9.9 percent over the preceding year, and 8.4 percent higher than the growth rate of the nation’s total exports. The proportion of machinery and electric product exports in the nation’s total foreign trade volume\ increased from 29.5 percent in 1995 to 31.9 percent in 1996, a growth at 2.4 percent.
文摘Housing isone of the necessities of humansfor existence and development.The Chinese government hasalways attached great importanceto housing construction;especially in recent years,thepriority development of housingconstruction has been seen inthe real estate and propertiesindustry.Hou Jie,Minister ofConstruction,not long ago wrotean article summarizing theachievements made in this sectorand drawing a blueprint forspeedup of housing constructionand the improvement of livingconditions in the future.It willprovide a vast vista for thedevelopment of China’s buildingindustry and its internationalcooperation.
文摘High-speed railways have the merits of high speed, high transport capacity, low consumption of energy, less pollution, less occupation of land, and greater safety. The development of high-speed railways is suitable for the national conditions in China.The authors suggest that, with the Hu-Ning (Shanghai-Nanjing) section of the Jing-Hu (Beijing-Shanghai) Railway as the starting point, a high-speed dedicated passenger railway line be built to realize the separate transportation of passengers and goods, thus easing the strain on transport in East China, accumulating experience for the future development of high-speed railways, and bringing along the development of high and new technology industries.
文摘This paper discusses the urgency to further develop China’s space technological industry;analyzes the gaps between China and other advanced countries in space industry,including technological level,development scale,application scope and investment;describes the current severe situation that the China’s space industry is faced with and proposes the overall objective,guiding principles and major tasks of China’s space technological sector in the Ninth-Five Year Plan and the coming decade.Finally,it proposes some policies and effective measures to speed up the development of China’s space industry to meet the challenge in the 21st century.
基金support from the National Natural Science Foundation of China(No.52271287)funding from the State Key Laboratory of Hydraulic Engineering Intelligent Construction and Operation,Tianjin University。
文摘During the hoisting process of the offshore substation,changes in the hoisting speed can affect the hoisting system.Therefore,this study set four different speed conditions for the lifting and lowering stages of the installation process,and studied the impact of different lifting and lowering speeds on the hoisting system under the same environmental conditions through numerical simulation.The results show that during the lifting operation,as the lifting speed increases,the swing motion of the substation and the installation vessel tends to decrease,and the faster the hoisting speed,the more obvious the swing suppression of the substation and the installation vessel,and the smaller the fluctuation in the tension amplitude of the slings and mooring lines.In contrast,during the lowering operation,as the lowering speed increases,the swing motion of the substation and the installation vessel tends to increase,and the faster the lowering speed,the more obvious the swing amplification effect of the substation and the installation vessel.Therefore,during hoisting operations,increasing the lifting speed and reducing the lowering speed can mitigate the motion performance of the hoisting coupling system,reduce the tension amplitude variation of the sling and mooring,and ensure the smooth progress of the hoisting operation.
文摘The dual challenges of critical speed prediction inaccuracies and ambiguous vibration behaviors are present in high-speed flexible rotors,particularly in free turbine rotors in turboshaft engine systems.The study begins with an examination of the rotor-bearing bidirectional coupling mechanism,with a primary focus on the nonlinear characteristics of the bearing.An investigation is carried out on the mechanical modeling methodologies for four-point contact ball bearings(FPCBBs)and cylindrical roller bearings(CRBs).To address the issue of excessive computational time in traditional bearing calculation methods,the sled dog optimization(SDO)algorithm is substituted for the conventional Newton-Raphson method.A rotor-bearing coupling dynamics model is developed by the finite element and lumped mass methods,with experimental validation achieved through a simulator test rig.The effects of three internal bearing parameters in FPCBBs(arching width and raceway groove curvature coefficient)and CRBs(initial radial clearance)on the critical speed characteristics and vibrational behavior of rotorbearing coupled systems are examined.The numerical simulation results show some interesting conclusions.
文摘In the wake of the global financial crisis, China has amazed the world with the speed of its economic recovery. But what has been even more surprising is the speed of its railway evolution.
文摘Chinese carmakers find the way to become more technologically intensive In the classic economic model, there is land,labor and capital. Each plays a role in economic development through its supply, and development cannot occur with-
基金The National Natural Science Foundation of China(No. 52072012)。
文摘To reduce the risk of traffic accidents significantly caused by the speeding behavior of electric bicycles,this study focuses on the Beijing Yizhuang Economic and Tech-nological Development Zone.This work relies on high-precision shared electric bicycle Global Positioning System trajectory data,integrating a spatiotemporal analysis model and geographic information system(GIS)technol-ogy to explore the spatial and temporal variability law and formation mechanism of speeding behavior.Through data preprocessing,speeding events are identified,and weekday features are extracted.Four periods are identified:morning peak,midday minipeak,evening peak,and nighttime flat peak.Using the GIS platform,global spatial autocorrela-tion and local clustering analysis are conducted to identify the spatial clustering characteristics of speeding behaviors and hotspot areas.The coldspot and hotspot patterns of speeding events and the dynamic trajectories of their evolu-tion are analyzed using spatiotemporal cube technology.The results show that speeding behaviors are strongly corre-lated with the commuting peak in time and spatially concen-trated in the intersections of urban main roads,the periphery of commercial complexes,and industrial parks,with a dif-fusion tendency.The results of this study provide novel in-sights into the research and analysis of the spatial and tempo-ral characteristics of speeding risk behaviors of electric bi-cycles and effective technical support for nonmotorized traf-fic safety management.
基金supported by the National Natural Science Foundation of China(Grant Nos.11902002 and 51705002)the Sichuan Provincial Natural Science Foundation(Grant No.2022NSFSC0275)the University Outstanding Youth Researcher Support Program of the Education Department of Anhui Province,and the Teaching Project of the Education Department of Anhui Province(Grant No.2022xxsfkc023).
文摘This study focuses on coupled vibrations of rotating thin-walled composite beams subjected to hygrothermal effects.In the existing literature,many studies have been conducted on coupled bending-torsional vibration and resonance in hygrothermal environments.Few studies considered the coupled flapwise-edgewise and resonances of composite thin-walled beams.Considering this,the flapwise-edgewise coupling effects and resonant characteristics of rotating thin-walled composite beams in a hygrothermal environment are studied.The Rayleigh–Ritz method is used to solve the equations of the beam.Results indicate that flapwise-edgewise coupling factors are essential for the vibration analysis of rectangular thin-walled beams.The ply angle and setting angle strongly affect the internal and external resonances.Large ply angles can significantly reduce the chances of primary internal and external resonances occurring when the permitted rotational speed is lower.
基金supported by the National Natural Science Foundation of China[grant numbers U2442207,42122034,42075043,and 42330609]the Youth Innovation Promotion Association[grant number 2021427]+2 种基金the West Light Foundation[grant number xbzgzdsys-202409]of the Chinese Academy of Sciencesthe Key Talent Projects in Gansu Provincethe Central Guidance Fund for Local Science and Technology Development Projects in Gansu Province[grant number 24ZYQA031].
文摘Previous studies have indicated a global reversal of near-surface wind speeds from a declining trend to an increasing trend around 2010;however,it remains unclear whether upper-air wind speeds exhibit a similar reversal.This study evaluates reanalysis products using surface and radiosonde observations to analyze upper-air wind speed variations in the Northern Hemisphere,focusing on their seasonal and latitudinal differences.Results demonstrate that JRA-55 effectively captures wind speed variations in the Northern Hemisphere.Notably,upper-air wind speeds over land experienced a reversal in winter 2010 with significant latitudinal differences.The trend reversal of upper wind speed between the midlatitudes and subtropics presents a dipole pattern.From 1990 to 2010,upper-air wind speeds in the midlatitudes(40°-70°N)significantly declined,while the subtropical zone(20°-40°N)displayed an opposite trend.However,during 2010-2020,wind speeds in the midlatitudes shifted to a significant positive trend,whereas the subtropics experienced a significant negative trend.The variations in Northern Hemisphere winter wind speeds can be attributed to changes in low-level baroclinicity driven by tropical diabatic heating and midlatitude transient eddy feedback.Enhanced diabatic heating and weakened eddy feedback during 1990-2010 contributed to reduced wind speeds in the midlatitudes and increased speeds in the subtropics,while reduced diabatic heating and strengthened eddy feedback during 2010-2020 resulted in increased wind speeds in the midlatitudes and decreased speeds in the subtropics.The reversal of upper-air wind speeds could affect surface wind speeds by downward momentum transfer,which could contribute to the reversal of surface wind speeds.
基金the support from the National Natural Science Foundation of China (Grant No. 42175070)supported by the National Natural Science Foundation of China (Grant No. 42288101)supported by the National Key Scientific and Technological Infrastructure project “Earth System Numerical Simulation Facility” (Earth Lab)。
文摘By applying the convolution-based Hilbert transform in the zonal direction on six-hourly streamfunction fields at200 h Pa, we present the climatology and trends of the local wave period, and zonal and meridional phase speeds, of Rossby waves over the globe during the solstice seasons of 1979–2023. While partly similar to and inspired by Fragkoulidis and Wirth(2020), our method differs in its ability to cover both planetary-scale and synoptic-scale waves over not only the extratropics, but also the tropics and subtropics. Based on a physically reasonable global distribution of wave periods, our key new finding is a robust prolonging of wave periods over most regions of the tropics and subtropics during both solstice seasons of 1979–2023, except for the tropical Atlantic, which experiences a shortened wave period during June–July–August of 1979–2022. Both the prolonging and shortening of wave periods are mainly associated with the changes in planetary-scale waves. Regionally varying trends of the zonal phase speed(Cpx) of synoptic waves are consistent in sign with, but smaller in magnitude than, the trends of local zonal wind, confirming the conclusion of Wu and Lu(2023)on the opposite effects of zonal wind and the meridional gradient of potential vorticity on Cpx. Meanwhile, the Cpx trends of planetary-scale waves are relatively weak, and do not exhibit a robust relation with the trend of zonal wind. These new results are helpful toward better understanding the changes in atmospheric waves and extreme events under global warming.
基金supported in part by the National Natural Science Foundation of China(62303117,T2325018,92367109)the Xiangjiang Scholar Program(XJ2023018)+2 种基金the Key Laboratory of System Control and Information Processing(Scip20240108)the Aeronautical Science Foundation of China(20230001144001)Fujian Provincial Natural Science Foundation(2024J01130098)
文摘This work presents an adaptive tracking guidance method for robotic fishes. The scheme enables robots to suppress external interference and eliminate motion jitter. An adaptive integral surge line-of-sight guidance rule is designed to eliminate dynamics interference and sideslip issues. Limited-time yaw and surge speed observers are reported to fit disturbance variables in the model. The approximation values can compensate for the system's control input and improve the robots' tracking accuracy.Moreover, this work develops a terminal sliding mode controller and third-order differential processor to determine the rotational torque and reduce the robots' run jitter. Then, Lyapunov's theory proves the uniform ultimate boundedness of the proposed method. Simulation and physical experiments confirm that the technology improves the tracking error convergence speed and stability of robotic fishes.
基金supported by the National Natural Science Foundation of China(Grant Nos.52192633,92371201,11872293,and 92152301)the Natural Science Foundation of Shaanxi Province(Grant No.2022JC-03).
文摘The high-speed reentry vehicle operates across a broad range of speeds and spatial domains,where optimal aerodynamic shapes for different speeds are contradictory.This makes it challenging for a single-Mach optimization design to meet aerodynamic performance requirements throughout the vehicle’s flight envelope.Additionally,the strong coupling between aerodynamics and control adds complexity,as fluctuations in aerodynamic parameters due to speed variations complicate control system design.To address these challenges,this study proposes an aerodynamic/control coupling optimization design approach.This method,based on aerodynamic optimization principles,incorporates active control technology,treating aerodynamic layout and control system design as primary components during the conceptual design phase.By integrating the design and evaluation of aerodynamics and control,the approach aims to reduce design iterations and enhance overall flight performance.The comprehensive design of the rotary reentry vehicle,using this optimization strategy,effectively balances performance at supersonic and hypersonic speeds.The results show that the integrated design model meets aerodynamic and control performance requirements over a broader range of Mach numbers,preventing performance degradation due to deviations from the design Mach number,and providing a practical solution for high-speed reentry vehicle design.
基金supported by the National Natural Science Foundation of China(Nos.12464010,52462035)2022 Jiangxi Province High-Level and High-Skilled Leading Talent Training Project Selected(No.63)+1 种基金Jiujiang“Xuncheng Talents”(No.JJXC2023032)Jiujiang Basic Research Program Project(2025).
文摘This paper investigates the power generation characteristics of solar cells mounted on unmanned aerial vehicles(UAVs)under the coupled influence of flight conditions and the sur-rounding environment.Firstly,the study reveals that the voltage,current,and power output of the solar cells undergo consistent temporal variations throughout the day,primarily driven by voltage fluctuations,with a peak occurring around noon.Secondly,it is observed that the cells’performance is significantly more influenced by temporal variations in external light intensity than by temperature changes resulting from variations in flight speed.Finally,the study finds that the impact of flight altitude on the cells’performance is slightly more pronounced than the influence of temporal variations in external light intensity.
