Objective To reduce the risk of choosing API starting materials incorrectly since the rationality of its selection and the scientific justification of quality research have a significant impact on the quality control ...Objective To reduce the risk of choosing API starting materials incorrectly since the rationality of its selection and the scientific justification of quality research have a significant impact on the quality control of API.Methods Failure mode and effects analysis(FMEA)strategy was used to do the risk management of API starting materials of D company.Results and Conclusion The FMEA method can improve the risk management of the research of API starting materials for D company,which is still effective to apply the method to C company and R company.展开更多
When the vehicle is on a split-μramp and is restricted by the differential's torque-equalizing characteristic,a sig-nificant functional conflict may occur between the driving force limitation requirement of the a...When the vehicle is on a split-μramp and is restricted by the differential's torque-equalizing characteristic,a sig-nificant functional conflict may occur between the driving force limitation requirement of the acceleration slip regulation(ASR)control strategy for low-adhesion side wheels and the driving force enhancement demand of the entire vehicle during hill starting.Aiming at this problem,this paper proposes an ASR control strategy for the start-up of the electric vehicle on the split-μramp based on the combined control architecture of the service brake system and the parking brake system.First,the relationship between the driving force,braking force,and road adhesion at the slip moment is analyzed,and the ground adhesion estimation algorithm based on the dynamic equation of the driving wheel slip moment is proposed.Second,a service braking torque control model is constructed,and an ASR controller method based on the super-twisting sliding mode control(STSMC)algorithm is proposed to study the hill start assist(HSA)control strategy of electric vehicles on split-μroads.Finally,the proposed control strategy is si-mulated in this paper.The simulation results show that the proposed strategy can accurately estimate the ground adhesion of the driving wheel on the low-adhesion side effectively preventing the vehicle from slipping back,and improving the dynamic performance of the vehicle under harsh conditions.展开更多
The accurate establishment of a ferrite transformation start temperature model is crucial to design a reasonable controlled rolling process and ensure uniform microstructure in aluminum bearing dual-phase steel.The me...The accurate establishment of a ferrite transformation start temperature model is crucial to design a reasonable controlled rolling process and ensure uniform microstructure in aluminum bearing dual-phase steel.The measurements of the expansion-temperature curves of aluminum bearing dual-phase steel under continuous cooling and isothermal conditions are presented,utilizing a dynamic transformation dilatometer experiment.Based on these expansion-temperature curves,the start temperature and incubation time of ferrite transformation were determined,elucidating the influence of process parameters on both the incubation time and the start temperature of ferrite transformation.By integrating metallurgical principles with measured incubation time of ferrite transformation,and considering the effects of temperature and strain,a fitting model for the variation in volume free energy during ferrite nucleation was derived.Building upon this foundation,a high-precision incubation time of ferrite transformation mathematical model for the experimental steel was established.To more accurately calculate the start temperature of ferrite transformation under continuous cooling conditions,the Scheil’s additivity rule was modified to account for the effects of deformation and cooling rate.The results indicate that the modification coefficient decreases with increasing the cooling rate and strain,thereby significantly improving the accuracy of calculating the starting temperature of ferrite transformation using the modified additivity rule.展开更多
聚焦PEP新教材Start to read板块教学,针对传统阅读启蒙课存在的思维培养不足、教学活动单一等问题,提出“问题·活动·评价”三位一体的教学新范式。通过构建层级化问题体系引导思维进阶,设计梯度式活动促进语篇理解,实施全程...聚焦PEP新教材Start to read板块教学,针对传统阅读启蒙课存在的思维培养不足、教学活动单一等问题,提出“问题·活动·评价”三位一体的教学新范式。通过构建层级化问题体系引导思维进阶,设计梯度式活动促进语篇理解,实施全程化评价保障学习效果。研究表明,该范式能有效提升学生阅读兴趣与综合语言能力,为小学英语阅读启蒙教学提供可复制、可推广的创新路径。展开更多
The impulse and self starting characteristics of a mixed-compression hypersonic inlet designed at Mach number of 6.5 are studied by applying the unsteady computational fluid dynamics （CFD） method. The full Navier–S...The impulse and self starting characteristics of a mixed-compression hypersonic inlet designed at Mach number of 6.5 are studied by applying the unsteady computational fluid dynamics （CFD） method. The full Navier–Stokes equations are solved with the assumption of viscous perfect gas model, and the shear-stress transport （SST） k–x two-equation Reynolds averaged Navier– Stokes （RANS） model is used for turbulence modeling. Results indicate that during impulse starting, the flow field is divided into three zones with different aerodynamic parameters by primary shock and upstream-facing shock. The separation bubble on the shoulder of ramp undergoes a generating, growing, swallowing and disappearing process in sequence. But a separation bubble at the entrance of inlet exists until the freestream velocity is accelerated to the starting Mach number during self starting. The mass flux distribution of flow field is non-uniform because of the interaction between shock and boundary layer, so that the mass flow rate at throat is unsteady during impulse starting. The duration of impulse starting process increases almost linearly with the decrease of freestream Mach number but rises abruptly when the freestream Mach number approaches the starting Mach number. The accelerating performance of booster almost has no influence on the self starting ability of hypersonic inlet.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
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
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
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
The high-current pulsed electron beam(HCPEB) treatment with current density 6 J/cm^2 was applied on AZ91 Mg alloy to improve its corrosion resistance. Results showed that the net-like Mg_(17)Al_(12) disappeared on the...The high-current pulsed electron beam(HCPEB) treatment with current density 6 J/cm^2 was applied on AZ91 Mg alloy to improve its corrosion resistance. Results showed that the net-like Mg_(17)Al_(12) disappeared on the surface of AZ91 Mg alloy after irradiation by HCPEB, which was instead of supersaturated Al element on the surface. Nevertheless, the application of HCPEB also led to the formation of crater-like and groove-like structures as well as micro-cracks on the surface of AZ91 Mg alloy. After HCPEB treatment by 3, 5 and 10 pulses, the AZ91 Mg alloy exhibited better corrosion resistance.However, the increasing amount of micro-cracks reduced the anti-corrosive properties of AZ91 Mg alloy as the pulse increased to 20 and 30.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
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 gradual advances of offshore oil and gas exploitation and the development tendency of equipment integration have prompted the design of a new type of the high-current composite umbilical to meet development needs....The gradual advances of offshore oil and gas exploitation and the development tendency of equipment integration have prompted the design of a new type of the high-current composite umbilical to meet development needs.In order to study the mechanical behavior of the high-current composite umbilical(HCCU)and provide design suggestions,a theoretical analysis framework of the tension-torsion coupled behavior of the spirally wound structure is proposed,which focuses more on the radial mechanical behavior.Then,by considering the mechanical and thermal conditions during the operation of HCCU,a semi-analytical method of the tension and torsion stiffness of the high-current composite umbilical considering the temperature effect is established.Furthermore,a practical case of HCCU is given,and the thermal effect on the radial and axial mechanical behaviors are analyzed.It is found that the thermal effect has a significant influence on the radial stiffness,and shows non-linear variation characteristics.Finally,the sensitivity analysis is carried out to study the influence of the design parameter on the stiffness of tension and torsion.The results indicated that the equivalent radial stiffness and helical angle have obvious effect on the tension-torsion coupled stiffness,which can provide reasonable reference for the design of HCCU.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
文摘Objective To reduce the risk of choosing API starting materials incorrectly since the rationality of its selection and the scientific justification of quality research have a significant impact on the quality control of API.Methods Failure mode and effects analysis(FMEA)strategy was used to do the risk management of API starting materials of D company.Results and Conclusion The FMEA method can improve the risk management of the research of API starting materials for D company,which is still effective to apply the method to C company and R company.
基金Supported by the National Natural Science Foundation of China(Grant No.52172369).
文摘When the vehicle is on a split-μramp and is restricted by the differential's torque-equalizing characteristic,a sig-nificant functional conflict may occur between the driving force limitation requirement of the acceleration slip regulation(ASR)control strategy for low-adhesion side wheels and the driving force enhancement demand of the entire vehicle during hill starting.Aiming at this problem,this paper proposes an ASR control strategy for the start-up of the electric vehicle on the split-μramp based on the combined control architecture of the service brake system and the parking brake system.First,the relationship between the driving force,braking force,and road adhesion at the slip moment is analyzed,and the ground adhesion estimation algorithm based on the dynamic equation of the driving wheel slip moment is proposed.Second,a service braking torque control model is constructed,and an ASR controller method based on the super-twisting sliding mode control(STSMC)algorithm is proposed to study the hill start assist(HSA)control strategy of electric vehicles on split-μroads.Finally,the proposed control strategy is si-mulated in this paper.The simulation results show that the proposed strategy can accurately estimate the ground adhesion of the driving wheel on the low-adhesion side effectively preventing the vehicle from slipping back,and improving the dynamic performance of the vehicle under harsh conditions.
基金supported by the National Science and Technology Major Project-Intelligent Manufacturing Systems And Robots(2025ZD1602200)the National Key Research and Development Program of China(Grant No.2022YFB3304800).
文摘The accurate establishment of a ferrite transformation start temperature model is crucial to design a reasonable controlled rolling process and ensure uniform microstructure in aluminum bearing dual-phase steel.The measurements of the expansion-temperature curves of aluminum bearing dual-phase steel under continuous cooling and isothermal conditions are presented,utilizing a dynamic transformation dilatometer experiment.Based on these expansion-temperature curves,the start temperature and incubation time of ferrite transformation were determined,elucidating the influence of process parameters on both the incubation time and the start temperature of ferrite transformation.By integrating metallurgical principles with measured incubation time of ferrite transformation,and considering the effects of temperature and strain,a fitting model for the variation in volume free energy during ferrite nucleation was derived.Building upon this foundation,a high-precision incubation time of ferrite transformation mathematical model for the experimental steel was established.To more accurately calculate the start temperature of ferrite transformation under continuous cooling conditions,the Scheil’s additivity rule was modified to account for the effects of deformation and cooling rate.The results indicate that the modification coefficient decreases with increasing the cooling rate and strain,thereby significantly improving the accuracy of calculating the starting temperature of ferrite transformation using the modified additivity rule.
文摘聚焦PEP新教材Start to read板块教学,针对传统阅读启蒙课存在的思维培养不足、教学活动单一等问题,提出“问题·活动·评价”三位一体的教学新范式。通过构建层级化问题体系引导思维进阶,设计梯度式活动促进语篇理解,实施全程化评价保障学习效果。研究表明,该范式能有效提升学生阅读兴趣与综合语言能力,为小学英语阅读启蒙教学提供可复制、可推广的创新路径。
文摘The impulse and self starting characteristics of a mixed-compression hypersonic inlet designed at Mach number of 6.5 are studied by applying the unsteady computational fluid dynamics （CFD） method. The full Navier–Stokes equations are solved with the assumption of viscous perfect gas model, and the shear-stress transport （SST） k–x two-equation Reynolds averaged Navier– Stokes （RANS） model is used for turbulence modeling. Results indicate that during impulse starting, the flow field is divided into three zones with different aerodynamic parameters by primary shock and upstream-facing shock. The separation bubble on the shoulder of ramp undergoes a generating, growing, swallowing and disappearing process in sequence. But a separation bubble at the entrance of inlet exists until the freestream velocity is accelerated to the starting Mach number during self starting. The mass flux distribution of flow field is non-uniform because of the interaction between shock and boundary layer, so that the mass flow rate at throat is unsteady during impulse starting. The duration of impulse starting process increases almost linearly with the decrease of freestream Mach number but rises abruptly when the freestream Mach number approaches the starting Mach number. The accelerating performance of booster almost has no influence on the self starting ability of hypersonic inlet.
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.
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.
基金the finacial support from the National Natural Science Foundation of China(Nos.51771128 and 51771129)the Projects of International Cooperation in Shanxi(No.201703D421039)the Natural Science Foundation of Shanxi(No.201601D011034)
文摘The high-current pulsed electron beam(HCPEB) treatment with current density 6 J/cm^2 was applied on AZ91 Mg alloy to improve its corrosion resistance. Results showed that the net-like Mg_(17)Al_(12) disappeared on the surface of AZ91 Mg alloy after irradiation by HCPEB, which was instead of supersaturated Al element on the surface. Nevertheless, the application of HCPEB also led to the formation of crater-like and groove-like structures as well as micro-cracks on the surface of AZ91 Mg alloy. After HCPEB treatment by 3, 5 and 10 pulses, the AZ91 Mg alloy exhibited better corrosion resistance.However, the increasing amount of micro-cracks reduced the anti-corrosive properties of AZ91 Mg alloy as the pulse increased to 20 and 30.
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.
基金financially supported by the National Key R&D Program of China(Grant No.2021YFA1003501)the National Natural Science Foundation of China(Grant Nos.U1906233 and 52001088)+1 种基金the Key R&D Program of Shandong Province(Grant No.2019JZZY010801)the Fundamental Research Funds for the Central Universities(Grant Nos.DUT20ZD213 and DUT20LAB308)。
文摘The gradual advances of offshore oil and gas exploitation and the development tendency of equipment integration have prompted the design of a new type of the high-current composite umbilical to meet development needs.In order to study the mechanical behavior of the high-current composite umbilical(HCCU)and provide design suggestions,a theoretical analysis framework of the tension-torsion coupled behavior of the spirally wound structure is proposed,which focuses more on the radial mechanical behavior.Then,by considering the mechanical and thermal conditions during the operation of HCCU,a semi-analytical method of the tension and torsion stiffness of the high-current composite umbilical considering the temperature effect is established.Furthermore,a practical case of HCCU is given,and the thermal effect on the radial and axial mechanical behaviors are analyzed.It is found that the thermal effect has a significant influence on the radial stiffness,and shows non-linear variation characteristics.Finally,the sensitivity analysis is carried out to study the influence of the design parameter on the stiffness of tension and torsion.The results indicated that the equivalent radial stiffness and helical angle have obvious effect on the tension-torsion coupled stiffness,which can provide reasonable reference for the design of HCCU.
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.
