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
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
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.
