The Bypass Dual Throat Nozzle(BDTN)is a novel fluidic Thrust Vectoring(TV)nozzle,it switches to TV state by opening the valve in the bypass.To greatly manipulate the BDTN,the dynamic characteristics in the TV starting...The Bypass Dual Throat Nozzle(BDTN)is a novel fluidic Thrust Vectoring(TV)nozzle,it switches to TV state by opening the valve in the bypass.To greatly manipulate the BDTN,the dynamic characteristics in the TV starting process should be analyzed.This paper conducts numerical simulations to grasp the variation processes of performances and the flow field evolution of BDTN and Dual Throat Nozzle(DTN).The dynamic responses of TV starting in typical DTN models are investigated at first.Then,the TV starting processes of BDTN in different Nozzle Pressure Ratio(NPR)conditions are simulated,and the valve opening durations(T)are also considered.Before the expected TV direction is achieved in the DTN,the jet is deflected to the opposite direction at the beginning of the dynamic process,which is called the reverse TV phenomenon.However,this phenomenon disappears in the BDTN.The larger injection width of DTN intensifies unsteady oscillations,and the reverse TV phenomenon is strengthened.In the BDTN,T determines the delay degree of performance variations compared to the static results,which is called hysteresis effect.At NPR=10,the hysteresis affects the final stable performance of BDTN.This study analyses the dynamic characteristics in DTN and BDTN,laying a foundation for further design of nozzles and control strategies.展开更多
Compressible starting flow at small angle of attack （AoA） involves small amplitude waves and time-dependent lift coefficient and has been extensively studied before. In this paper we consider hypersonic starting flo...Compressible starting flow at small angle of attack （AoA） involves small amplitude waves and time-dependent lift coefficient and has been extensively studied before. In this paper we consider hypersonic starting flow of a two-dimensional flat wing or airfoil at large angle of attack involving strong shock waves. The flow field in some typical regions near the wing is solved analytically. Simple expressions of time-dependent lift evolutions at the initial and final stages are given. Numerical simulations by compuational fluid dynamics are used to verify and complement the theoretical results. It is shown that below the wing there is a straight oblique shock （OSW） wave, a curved shock wave （CSW） and an unsteady horizontal shock wave （USW）, and the latter moves perpendicularlly to the wing. The length of these three parts of waves changes with time. The pres- sure above OSW is larger than that above USW, while across CSW there is a significant drop of the pressure, making the force nearly constant during the initial period of time. When, however, the Mach number is very large, the force coefficient tends to a time-independent constant, proportional to the square of the sine of the angle of attack.展开更多
The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment sy...The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment system of gas-water-sand three-phase flow was used to test the conversion law of flow pattern based upon the different gas void fraction.Secondly,the influence of slug bubbles on sand migration was investigated according to distinctive hole deviation angles,gas void fraction and sand concentration.Finally,the critical sand starting velocity was tested based on dissimilar hole deviation angles,gas void fraction,sand concentration and sand particle size,and then the influence of the abovementioned key parameters on the sand starting velocity was debated based on the force analysis of the sand particles.The experimental results illustrated that when the gas void fraction was less than 5%,it was bubbly flow.When it increased from 5%to 30%,the bubbly flow and slug flow coexisted.When it was between 30%and 50%,the slug flow and agitated flow coexisted.When it reached 50%,it was agitated flow.Providing that the hole deviation angle was 90°,the phenomenon of overall migration and wavelike migration on the surface of sand bed was observed.On the contrary,the phenomenon of rolling and jumping migration was recognized.The critical sand starting velocity was positively correlated with the hole deviation angle and sand particle size,but negatively associated with the gas void fraction and sand concentration.This research can provide a certain reference for sand-starting production in the field of petroleum engineering.展开更多
According to the textual research into the historical documents dominated by archives yearly, as well as the verification with several other kinds of data, the later or earlier starting time of the rainy seasons in Yu...According to the textual research into the historical documents dominated by archives yearly, as well as the verification with several other kinds of data, the later or earlier starting time of the rainy seasons in Yunnan during 1711-1982 has been reconstructed. The analysis indicates that there are obvious fluctuations in the starting date of the rainy seasons in Yunnan in a year or years, and long fluctuation on the decadal scale. The rainy season comes earlier in the early 18th century, later in the 19th century and earlier again in the 20th century. This reflects to a certain degree the gradual change of the summer monsoon in Yunnan. There exists an obvious quasi-3 years cycle, which is related to EI-Nino＇s quasi-3 years cycle, and a 11.3-year cycle which is notably related to the 11-year cycle of the solar activity of starting date of the rainy seasons in Yunnan. Meanwhile, the dissertation finds that the EI-Nino is very important to the starting date of the rainy seasons in Yunnan. The starting date of the rainy seasons in Yunnan often comes later or normally in the year of EI-Nino. However, there is an obvious imperfect period in such influence, which in turn may mean that there is a certain fluctuation in the effect of ENSO on Asian summer monsoon.展开更多
The typical behavior of unsteady flow and force evolution in a number of applications,such as aero-elastics, gust-wing interaction, flapping flight and flight maneuvering, can be understood using the starting flow mod...The typical behavior of unsteady flow and force evolution in a number of applications,such as aero-elastics, gust-wing interaction, flapping flight and flight maneuvering, can be understood using the starting flow model. Starting flow model is obtained either by setting rapidly an angle of attack for a wing moving at constant speed, or by accelerating a wing to a constant speed while gaining an angle of attack. In the limiting case of impulsively starting flow, the wing is assumed to gain suddenly an angle of attack in an initially uniform flow. Theories have been developed for impulsively starting flow at small angle of attack long before and at large angle of attack only recently, especially for incompressible and supersonic flow. This paper intends to provide a state-of-art overview of the typical flow phenomena, force evolution characteristics and developed theories for impulsively starting flow at any angle of attack and for both lower speed flow(vortex dominated) and high speed flow(compressible wave dominated). This review also provides some new topics that deserve further studies.展开更多
The starting dates of the pre-summer rainy season during historical times （1736- 1911） in Fuzhou and Guangzhou of South China, were determined and reconstructed on the basis of historical documents in the Yu-Xue-Fen...The starting dates of the pre-summer rainy season during historical times （1736- 1911） in Fuzhou and Guangzhou of South China, were determined and reconstructed on the basis of historical documents in the Yu-Xue-Fen-Cun archive, together with observed features of precipitation during the pre-summer rainy season. In addition, starting dates of the pre-summer rainy season from 1953 in Fuzhou and from 1952 in Guangzhou were reconstructed for the instrumental period. These data allowed for analyses of inter-annual and inter-decadal changes in the starting dates of the pre-summer rainy season in South China over the past 300 years. Results show that the mean starting date of the pre-summer rainy season in South China was the first pentad of May; in addition, periodicities in the starting dates of 2-3 years, 10 years, and 40 years were detected during the period 1736-1911, and of 2-3 years, 10 years, and 22 years during the instrumental period. From 1736 to 1911, the earliest starting dates at Fuzhou and Guangzhou both occurred at the fourth pentad of April, while the latest starting dates were at the sixth pentad of May in Fuzhou and the first pentad of June in Guangzhou. During the instrumental period, the earliest and latest starting dates were at the fourth pentad of April and the first pentad of June, respectively, in both Fuzhou during 1953-2010 and Guangzhou during 1952-2010. The maximum difference between neighboring decades during 1736-1911 was 2.2 and 1.6 pentads in Fuzhou and Guangzhou, respectively, and during the instrumental period it was 2.5 and 2.4 pentads in Fuzhou and Guangzhou, respectively.展开更多
Warm deformation was investigated for steels containing carbon of 0. 45%,0. 79%, and 1. 26% respeetively with martensite starting structure, using Gleeble 3500 thermomechanical simulator at the temperature ranging fro...Warm deformation was investigated for steels containing carbon of 0. 45%,0. 79%, and 1. 26% respeetively with martensite starting structure, using Gleeble 3500 thermomechanical simulator at the temperature ranging from 873 K to 973 K and the strain rate ranging from 0.1 s^-1 to 0. 001 s^-1. The effect of carbon content on the deformation activation energy, Z value and the deformation resistance was analyzed, The results showed that the deformation resistance decreased with increasing carbon content. The peak stress of the steel containing earbon of 1.26% was decreased by 16.2% compared to the steel containing carbon of 0.45% under the same condition. This may be attributed to the weakening effect of solid solution strengthening which outweighs the precipitation strengthening of cementite.展开更多
Impulsively starting flow, by a sudden attainment of a large angle of attack, has been well studied for incompressible and supersonic flows, but less studied for subsonic flow. Recently,a preliminary numerical study f...Impulsively starting flow, by a sudden attainment of a large angle of attack, has been well studied for incompressible and supersonic flows, but less studied for subsonic flow. Recently,a preliminary numerical study for subsonic starting flow at a high angle of attack displays an advance of stall around a Mach number of 0.5, when compared to other Mach numbers. To see what happens in this special case, we conduct here in this paper a further study for this case, to display and analyze the full flow structures. We find that for a Mach number around 0.5, a local supersonic flow region repeatedly splits and merges, and a pair of left-going and right-going unsteady shock waves are embedded inside the leading edge vortex once it is sufficiently grown up and detached from the leading edge. The flow evolution during the formation of shock waves is displayed in detail. The reason for the formation of these shock waves is explained here using the Laval nozzle flow theory. The existence of this shock pair inside the vortex, for a Mach number only close to 0.5, may help the growing of the trailing edge vortex responsible for the advance of stall observed previously.展开更多
In order to study the application of dual clutch transmission （DCT） on tracked vehicles, a simulation moclel and two control methods were performed for starting analysis. Based on a certain transmission of an existi...In order to study the application of dual clutch transmission （DCT） on tracked vehicles, a simulation moclel and two control methods were performed for starting analysis. Based on a certain transmission of an existing tracked vehicle, a DCT structure was proposed. Matlab/Simulink was a dopted as a platform to develop the simulation model. The engine speed was controlled to follow the target speed as a launch strategy. Two control methods, a proportional integral derivative （ PID ） control method and a fuzzy control method, were proposed to control the engine throttle and oil pressure in order to track the target engine speed. Simulation results show that either the PID control or fuzzy control method can improve the starting performance compared with no loop control meth od. Fuzzy control method can lead a better starting quality compared with PID control method.展开更多
The starting flow due to a suddenly applied pressure gradient in a parallel plate channel which is rotating as a system is studied. Exact analytic series solutions to the unsteady Navier-Stokes equations are found by ...The starting flow due to a suddenly applied pressure gradient in a parallel plate channel which is rotating as a system is studied. Exact analytic series solutions to the unsteady Navier-Stokes equations are found by both the Laplace transform method and the separation of parameters method, the latter is shown to be superior. Rotation not only induces a secondary transverse flow but also alters the character of the transient flow rate and velocity profiles. Back flow and inertial oscillations occur, especially at higher rota- tion rates.展开更多
Synthesizing the mechanical models of the belt, the driver and the take-up device, the dynamics model was established on the longitudinal vibration of the overall belt conveyor system with finite elemental method, and...Synthesizing the mechanical models of the belt, the driver and the take-up device, the dynamics model was established on the longitudinal vibration of the overall belt conveyor system with finite elemental method, and S-function simulation block of asynchronous motor owing feedback function was built in Matlab/Simulink software, the simulation block indicates that motor rotation speed and its output moment vary with load and time, and the motor is a dynamic feedback system in working process. The state space block was adopted to express model of the belt. Thus it created simulation model of established dynamic model of overall belt conveyor system with Mat- lab/Simulink software, and simulates the course of starting by properly setting simulation parameters, and processes data for visualization.展开更多
When the induction motor is fed from the PWM VSI inverter, with and without torque enhancing function, the variations of the starting torque and the starting current versus the starting frequency are analyzed, base...When the induction motor is fed from the PWM VSI inverter, with and without torque enhancing function, the variations of the starting torque and the starting current versus the starting frequency are analyzed, based on the steady state equivalent circuit of the induction motor.The corresponding expressions are derived, and the corresponding curves are also drawn, from which the initial starting frequency range can be determined properly and easily. The initial starting frequency range is the common range, in which the starting torque should be high enough and the starting current low enough.Some other useful formulas are also derived.These results are significant for electrical drive designers to make the starting schemes. The effects of the increase of the stator and the rotor resistances on the starting torque and the initial starting frequency range are also discussed, which is caused by the skin effects of the high order harmonics present in the PWM inverter output voltage.展开更多
With the rapid development of urbanization,the industrial parks originally located in the suburbs are gradually incorporated into the urban center.Industries that fail to follow the transformation of urban economic de...With the rapid development of urbanization,the industrial parks originally located in the suburbs are gradually incorporated into the urban center.Industries that fail to follow the transformation of urban economic development and are forced to close,or enterprises that move out without conforming to the environment,become a gray area within the city.Most of the existing assessments are conducting single assessment of some indicators,but than their actual benefits.Through the field investigation on the starting area of Handan Economic Development Zone,and the evaluation on the nature of land use,development intensity,investment and output,and idle land,inefficient land use in the park is identified.According to different evaluation results,different update and promotion methods are put forward.The research could provide a new evaluation method and idea for subsequent renewal and development of urban industrial parks.展开更多
<正>In a recent paper,Donaldson et al.~1 argued that lower extremity injuries can be prevented.Evidence-based sports injury preventive exercise programs usually have limited impact on public health because they ...<正>In a recent paper,Donaldson et al.~1 argued that lower extremity injuries can be prevented.Evidence-based sports injury preventive exercise programs usually have limited impact on public health because they are not widely adopted or sustained into regular training routines.One reason for this is that the intervention program may not seem relevant for the展开更多
Starting of combustion engines is a typical transient operating mode that has sigrdficant influence to the engine performance.Due to the distinct variations in the pathes of air intake and fuel injection,the model of ...Starting of combustion engines is a typical transient operating mode that has sigrdficant influence to the engine performance.Due to the distinct variations in the pathes of air intake and fuel injection,the model of the engine system contains considerable uncertain parameters.To search effective control schemes that guarantee desired performance,engine starting control is proposed as a benchmark challenge problem.As a challenging result,a model-based control scheme is developed perviously.In this work,the benchmark problem is revisited and a modification for the fuel injection path control of the previous work is proposed by integrating a time sequence regressive based parameter tuning strategy.Validation by the benchmark problem simulator shows that although the new strategy has simple structure,similar control performance is obtained.Especially,the new strategy has potential extensibility with learning based methods to further improve the performance of the benchmark problem on engine starting control.展开更多
Flow visualization was used to investigate experimentally the evolution process from symmetrical shedding to staggered shedding of the starting vortex and the phenomenon of secondary separation on an elliptic cylinder...Flow visualization was used to investigate experimentally the evolution process from symmetrical shedding to staggered shedding of the starting vortex and the phenomenon of secondary separation on an elliptic cylinder at moderate Reynolds numbers.The vortex structure of the flow separation was studied.The temporal variation of separation angle and length of wake vortex were given. The photographs and experimental results provided basis for further investigation of the complicated feature of the starting process of unsteady separated flows around an elliptic cylinder.展开更多
Unstart is an unwanted flow phenomenon in a hypersonic inlet. When an unstart occurs, the captured airflow flowing through the engine significantly decreases with strong unsteady characteristics, which may lead to thr...Unstart is an unwanted flow phenomenon in a hypersonic inlet. When an unstart occurs, the captured airflow flowing through the engine significantly decreases with strong unsteady characteristics, which may lead to thrust loss or even combustor flameout. In this study, various bump configurations were designed to be integrated with a hypersonic inlet to improve its starting ability. A bump was defined as an integrated 3D compression surface installed upstream of the inlet entrance. The starting processes of these bump inlets were numerically simulated to investigate the effect laws and flow mechanisms of the bump parameters. Tests on bump height revealed that the starting performance could be significantly improved by increasing bump height, with the starting Mach number decreasing by 0.55 for the inlet with the highest bump. The high bump facilitates the side movement of the subsonic flow in the separation zone, which leads to a small separation bubble, thus accelerating the starting process. Further, the starting ability can be improved by designing a relatively wide bump, which results in a decline in the starting Mach number by 0.44. When the bump has the same or greater width compared with the airflow capture range, a growing spillage along the transverse direction can be formed so that the airflow in the separation bubble can be easily excluded, improving the starting ability.展开更多
From relativistic linear Vlasov-Maxwell equations,the expressions of the startingcurrent and frequency deviation of a electrostatic gyromonotron with a field distribution sin k‖zare derived and the numerical calculat...From relativistic linear Vlasov-Maxwell equations,the expressions of the startingcurrent and frequency deviation of a electrostatic gyromonotron with a field distribution sin k‖zare derived and the numerical calculation is carried out.展开更多
An automatic procedure for building a protein polyalanine backbone from guiding alpha-carbon positions is presented here,which is different from a previously developed'spare parts'approach(Jones and Thirup,198...An automatic procedure for building a protein polyalanine backbone from guiding alpha-carbon positions is presented here,which is different from a previously developed'spare parts'approach(Jones and Thirup,1986;Claessens et al.,1989). In our procedure,the geometric restraint of angle N-CA-C is used to generate a list of polypeptide chains,and several filters are used later to select the best conformer.The most important filter is based upon the Ramachandran scatter plot of mainchain dihedral angles PHI and PSI.Results for all test cases are satisfactory,with more than 95%of peptide planes correctly reconstructed and the overall root-mean-square deviation less than 0.5 angstrom compared with the refined X-ray coordinates.展开更多
基金the continued support of Key Laboratory of Inlet and Exhaust system Technology (Nanjing University of Aeronautics and Astronautics), ChinaMinistry of Education, National Science and Technology Major Project of China (Nos. 2017-V-0004-0054, 2019-II-0007-0027, Y2022II-0005-0008)+6 种基金Defense Industrial Technology Development Program of China (No. JCKY2019605D001)Advanced Jet Propulsion Creativity Center of AEAC of China (No. HKCX2020-02-011)China Postdoctoral Science Foundation (No. 2022M721598)Jiangsu Funding Program for Excellent Postdoctoral Talent of China (No. 2022ZB214)the Youth Fund Project of Natural Science Foundation of Jiangsu Province of China (No. BK20230891)the National Natural Science Foundation of China (No. 12332018)Science Center for Gas Turbine Project, China (P2022-B-I-006-001) and some other related foundations
文摘The Bypass Dual Throat Nozzle(BDTN)is a novel fluidic Thrust Vectoring(TV)nozzle,it switches to TV state by opening the valve in the bypass.To greatly manipulate the BDTN,the dynamic characteristics in the TV starting process should be analyzed.This paper conducts numerical simulations to grasp the variation processes of performances and the flow field evolution of BDTN and Dual Throat Nozzle(DTN).The dynamic responses of TV starting in typical DTN models are investigated at first.Then,the TV starting processes of BDTN in different Nozzle Pressure Ratio(NPR)conditions are simulated,and the valve opening durations(T)are also considered.Before the expected TV direction is achieved in the DTN,the jet is deflected to the opposite direction at the beginning of the dynamic process,which is called the reverse TV phenomenon.However,this phenomenon disappears in the BDTN.The larger injection width of DTN intensifies unsteady oscillations,and the reverse TV phenomenon is strengthened.In the BDTN,T determines the delay degree of performance variations compared to the static results,which is called hysteresis effect.At NPR=10,the hysteresis affects the final stable performance of BDTN.This study analyses the dynamic characteristics in DTN and BDTN,laying a foundation for further design of nozzles and control strategies.
基金supported by the Natural National Science Foundation of China(No.11472157)
文摘Compressible starting flow at small angle of attack （AoA） involves small amplitude waves and time-dependent lift coefficient and has been extensively studied before. In this paper we consider hypersonic starting flow of a two-dimensional flat wing or airfoil at large angle of attack involving strong shock waves. The flow field in some typical regions near the wing is solved analytically. Simple expressions of time-dependent lift evolutions at the initial and final stages are given. Numerical simulations by compuational fluid dynamics are used to verify and complement the theoretical results. It is shown that below the wing there is a straight oblique shock （OSW） wave, a curved shock wave （CSW） and an unsteady horizontal shock wave （USW）, and the latter moves perpendicularlly to the wing. The length of these three parts of waves changes with time. The pres- sure above OSW is larger than that above USW, while across CSW there is a significant drop of the pressure, making the force nearly constant during the initial period of time. When, however, the Mach number is very large, the force coefficient tends to a time-independent constant, proportional to the square of the sine of the angle of attack.
基金supporting by the Youth Program of National Natural Science Foundation of China(52104012)the China Postdoctoral Science Foundation(2021M693494)+2 种基金the Key Program of the National Natural Science Foundation of China(51734010)the Key Natural Science Projects of Scientific Research Plan in Colleges and Universities of Xinjiang Uygur Autonomous Region(XJEDU2021I028)the Strategic Cooperation Technology Projects of CNPC and CUPB(ZLZX2020-01-01)
文摘The purpose of this paper is to study the critical sand starting velocity and transformation law of flow pattern based on gas-water-sand three-phase flow in an inclined pipe.Firstly,the indoor simulation experiment system of gas-water-sand three-phase flow was used to test the conversion law of flow pattern based upon the different gas void fraction.Secondly,the influence of slug bubbles on sand migration was investigated according to distinctive hole deviation angles,gas void fraction and sand concentration.Finally,the critical sand starting velocity was tested based on dissimilar hole deviation angles,gas void fraction,sand concentration and sand particle size,and then the influence of the abovementioned key parameters on the sand starting velocity was debated based on the force analysis of the sand particles.The experimental results illustrated that when the gas void fraction was less than 5%,it was bubbly flow.When it increased from 5%to 30%,the bubbly flow and slug flow coexisted.When it was between 30%and 50%,the slug flow and agitated flow coexisted.When it reached 50%,it was agitated flow.Providing that the hole deviation angle was 90°,the phenomenon of overall migration and wavelike migration on the surface of sand bed was observed.On the contrary,the phenomenon of rolling and jumping migration was recognized.The critical sand starting velocity was positively correlated with the hole deviation angle and sand particle size,but negatively associated with the gas void fraction and sand concentration.This research can provide a certain reference for sand-starting production in the field of petroleum engineering.
基金Knowledge Innovation Program of CAS, No.KZCX3-SW-321-3Key Project of the Ministry of Education of China, No.01JAZJD770008
文摘According to the textual research into the historical documents dominated by archives yearly, as well as the verification with several other kinds of data, the later or earlier starting time of the rainy seasons in Yunnan during 1711-1982 has been reconstructed. The analysis indicates that there are obvious fluctuations in the starting date of the rainy seasons in Yunnan in a year or years, and long fluctuation on the decadal scale. The rainy season comes earlier in the early 18th century, later in the 19th century and earlier again in the 20th century. This reflects to a certain degree the gradual change of the summer monsoon in Yunnan. There exists an obvious quasi-3 years cycle, which is related to EI-Nino＇s quasi-3 years cycle, and a 11.3-year cycle which is notably related to the 11-year cycle of the solar activity of starting date of the rainy seasons in Yunnan. Meanwhile, the dissertation finds that the EI-Nino is very important to the starting date of the rainy seasons in Yunnan. The starting date of the rainy seasons in Yunnan often comes later or normally in the year of EI-Nino. However, there is an obvious imperfect period in such influence, which in turn may mean that there is a certain fluctuation in the effect of ENSO on Asian summer monsoon.
基金supported by the Natural National Science Foundation of China (No. 11802157)
文摘The typical behavior of unsteady flow and force evolution in a number of applications,such as aero-elastics, gust-wing interaction, flapping flight and flight maneuvering, can be understood using the starting flow model. Starting flow model is obtained either by setting rapidly an angle of attack for a wing moving at constant speed, or by accelerating a wing to a constant speed while gaining an angle of attack. In the limiting case of impulsively starting flow, the wing is assumed to gain suddenly an angle of attack in an initially uniform flow. Theories have been developed for impulsively starting flow at small angle of attack long before and at large angle of attack only recently, especially for incompressible and supersonic flow. This paper intends to provide a state-of-art overview of the typical flow phenomena, force evolution characteristics and developed theories for impulsively starting flow at any angle of attack and for both lower speed flow(vortex dominated) and high speed flow(compressible wave dominated). This review also provides some new topics that deserve further studies.
基金Strategic Priority Research Program of the Chinese Academy of Sciences,No.XDA05080100"135"strategic Research Project of IGSNRR,CAS,No.2012ZD001Basic Research Project of the Ministry of Science and Technology,No.2011FY120300
文摘The starting dates of the pre-summer rainy season during historical times （1736- 1911） in Fuzhou and Guangzhou of South China, were determined and reconstructed on the basis of historical documents in the Yu-Xue-Fen-Cun archive, together with observed features of precipitation during the pre-summer rainy season. In addition, starting dates of the pre-summer rainy season from 1953 in Fuzhou and from 1952 in Guangzhou were reconstructed for the instrumental period. These data allowed for analyses of inter-annual and inter-decadal changes in the starting dates of the pre-summer rainy season in South China over the past 300 years. Results show that the mean starting date of the pre-summer rainy season in South China was the first pentad of May; in addition, periodicities in the starting dates of 2-3 years, 10 years, and 40 years were detected during the period 1736-1911, and of 2-3 years, 10 years, and 22 years during the instrumental period. From 1736 to 1911, the earliest starting dates at Fuzhou and Guangzhou both occurred at the fourth pentad of April, while the latest starting dates were at the sixth pentad of May in Fuzhou and the first pentad of June in Guangzhou. During the instrumental period, the earliest and latest starting dates were at the fourth pentad of April and the first pentad of June, respectively, in both Fuzhou during 1953-2010 and Guangzhou during 1952-2010. The maximum difference between neighboring decades during 1736-1911 was 2.2 and 1.6 pentads in Fuzhou and Guangzhou, respectively, and during the instrumental period it was 2.5 and 2.4 pentads in Fuzhou and Guangzhou, respectively.
基金Item Sponsored by National Natural Science Foundation of China (50821001 ,50371074,50271060)Natural Science Foundation of Hebei Province of China (E2008000784)
文摘Warm deformation was investigated for steels containing carbon of 0. 45%,0. 79%, and 1. 26% respeetively with martensite starting structure, using Gleeble 3500 thermomechanical simulator at the temperature ranging from 873 K to 973 K and the strain rate ranging from 0.1 s^-1 to 0. 001 s^-1. The effect of carbon content on the deformation activation energy, Z value and the deformation resistance was analyzed, The results showed that the deformation resistance decreased with increasing carbon content. The peak stress of the steel containing earbon of 1.26% was decreased by 16.2% compared to the steel containing carbon of 0.45% under the same condition. This may be attributed to the weakening effect of solid solution strengthening which outweighs the precipitation strengthening of cementite.
基金supported by the National Natural Science Foundation of China(No.11472157)
文摘Impulsively starting flow, by a sudden attainment of a large angle of attack, has been well studied for incompressible and supersonic flows, but less studied for subsonic flow. Recently,a preliminary numerical study for subsonic starting flow at a high angle of attack displays an advance of stall around a Mach number of 0.5, when compared to other Mach numbers. To see what happens in this special case, we conduct here in this paper a further study for this case, to display and analyze the full flow structures. We find that for a Mach number around 0.5, a local supersonic flow region repeatedly splits and merges, and a pair of left-going and right-going unsteady shock waves are embedded inside the leading edge vortex once it is sufficiently grown up and detached from the leading edge. The flow evolution during the formation of shock waves is displayed in detail. The reason for the formation of these shock waves is explained here using the Laval nozzle flow theory. The existence of this shock pair inside the vortex, for a Mach number only close to 0.5, may help the growing of the trailing edge vortex responsible for the advance of stall observed previously.
基金Supported by Defense Advanced Research Support Project(62301030303)111 Project(B08043)
文摘In order to study the application of dual clutch transmission （DCT） on tracked vehicles, a simulation moclel and two control methods were performed for starting analysis. Based on a certain transmission of an existing tracked vehicle, a DCT structure was proposed. Matlab/Simulink was a dopted as a platform to develop the simulation model. The engine speed was controlled to follow the target speed as a launch strategy. Two control methods, a proportional integral derivative （ PID ） control method and a fuzzy control method, were proposed to control the engine throttle and oil pressure in order to track the target engine speed. Simulation results show that either the PID control or fuzzy control method can improve the starting performance compared with no loop control meth od. Fuzzy control method can lead a better starting quality compared with PID control method.
文摘The starting flow due to a suddenly applied pressure gradient in a parallel plate channel which is rotating as a system is studied. Exact analytic series solutions to the unsteady Navier-Stokes equations are found by both the Laplace transform method and the separation of parameters method, the latter is shown to be superior. Rotation not only induces a secondary transverse flow but also alters the character of the transient flow rate and velocity profiles. Back flow and inertial oscillations occur, especially at higher rota- tion rates.
文摘Synthesizing the mechanical models of the belt, the driver and the take-up device, the dynamics model was established on the longitudinal vibration of the overall belt conveyor system with finite elemental method, and S-function simulation block of asynchronous motor owing feedback function was built in Matlab/Simulink software, the simulation block indicates that motor rotation speed and its output moment vary with load and time, and the motor is a dynamic feedback system in working process. The state space block was adopted to express model of the belt. Thus it created simulation model of established dynamic model of overall belt conveyor system with Mat- lab/Simulink software, and simulates the course of starting by properly setting simulation parameters, and processes data for visualization.
文摘When the induction motor is fed from the PWM VSI inverter, with and without torque enhancing function, the variations of the starting torque and the starting current versus the starting frequency are analyzed, based on the steady state equivalent circuit of the induction motor.The corresponding expressions are derived, and the corresponding curves are also drawn, from which the initial starting frequency range can be determined properly and easily. The initial starting frequency range is the common range, in which the starting torque should be high enough and the starting current low enough.Some other useful formulas are also derived.These results are significant for electrical drive designers to make the starting schemes. The effects of the increase of the stator and the rotor resistances on the starting torque and the initial starting frequency range are also discussed, which is caused by the skin effects of the high order harmonics present in the PWM inverter output voltage.
文摘With the rapid development of urbanization,the industrial parks originally located in the suburbs are gradually incorporated into the urban center.Industries that fail to follow the transformation of urban economic development and are forced to close,or enterprises that move out without conforming to the environment,become a gray area within the city.Most of the existing assessments are conducting single assessment of some indicators,but than their actual benefits.Through the field investigation on the starting area of Handan Economic Development Zone,and the evaluation on the nature of land use,development intensity,investment and output,and idle land,inefficient land use in the park is identified.According to different evaluation results,different update and promotion methods are put forward.The research could provide a new evaluation method and idea for subsequent renewal and development of urban industrial parks.
文摘<正>In a recent paper,Donaldson et al.~1 argued that lower extremity injuries can be prevented.Evidence-based sports injury preventive exercise programs usually have limited impact on public health because they are not widely adopted or sustained into regular training routines.One reason for this is that the intervention program may not seem relevant for the
基金Foundation of State Key Laboratory of Automotive Simulation and Control(No.20161101)the National Natural Science Foundation of China(No.61703179).
文摘Starting of combustion engines is a typical transient operating mode that has sigrdficant influence to the engine performance.Due to the distinct variations in the pathes of air intake and fuel injection,the model of the engine system contains considerable uncertain parameters.To search effective control schemes that guarantee desired performance,engine starting control is proposed as a benchmark challenge problem.As a challenging result,a model-based control scheme is developed perviously.In this work,the benchmark problem is revisited and a modification for the fuel injection path control of the previous work is proposed by integrating a time sequence regressive based parameter tuning strategy.Validation by the benchmark problem simulator shows that although the new strategy has simple structure,similar control performance is obtained.Especially,the new strategy has potential extensibility with learning based methods to further improve the performance of the benchmark problem on engine starting control.
基金The project supported by the National Natural Science Foundation of China.
文摘Flow visualization was used to investigate experimentally the evolution process from symmetrical shedding to staggered shedding of the starting vortex and the phenomenon of secondary separation on an elliptic cylinder at moderate Reynolds numbers.The vortex structure of the flow separation was studied.The temporal variation of separation angle and length of wake vortex were given. The photographs and experimental results provided basis for further investigation of the complicated feature of the starting process of unsteady separated flows around an elliptic cylinder.
基金supported by the National Natural Science Foundation of China (No. 12102470)the Hunan Provincial Innovation Foundation for Postgraduate (No. CX20200082), China。
文摘Unstart is an unwanted flow phenomenon in a hypersonic inlet. When an unstart occurs, the captured airflow flowing through the engine significantly decreases with strong unsteady characteristics, which may lead to thrust loss or even combustor flameout. In this study, various bump configurations were designed to be integrated with a hypersonic inlet to improve its starting ability. A bump was defined as an integrated 3D compression surface installed upstream of the inlet entrance. The starting processes of these bump inlets were numerically simulated to investigate the effect laws and flow mechanisms of the bump parameters. Tests on bump height revealed that the starting performance could be significantly improved by increasing bump height, with the starting Mach number decreasing by 0.55 for the inlet with the highest bump. The high bump facilitates the side movement of the subsonic flow in the separation zone, which leads to a small separation bubble, thus accelerating the starting process. Further, the starting ability can be improved by designing a relatively wide bump, which results in a decline in the starting Mach number by 0.44. When the bump has the same or greater width compared with the airflow capture range, a growing spillage along the transverse direction can be formed so that the airflow in the separation bubble can be easily excluded, improving the starting ability.
文摘From relativistic linear Vlasov-Maxwell equations,the expressions of the startingcurrent and frequency deviation of a electrostatic gyromonotron with a field distribution sin k‖zare derived and the numerical calculation is carried out.
文摘An automatic procedure for building a protein polyalanine backbone from guiding alpha-carbon positions is presented here,which is different from a previously developed'spare parts'approach(Jones and Thirup,1986;Claessens et al.,1989). In our procedure,the geometric restraint of angle N-CA-C is used to generate a list of polypeptide chains,and several filters are used later to select the best conformer.The most important filter is based upon the Ramachandran scatter plot of mainchain dihedral angles PHI and PSI.Results for all test cases are satisfactory,with more than 95%of peptide planes correctly reconstructed and the overall root-mean-square deviation less than 0.5 angstrom compared with the refined X-ray coordinates.
