Through introducing a generalized optimal speed function to consider spatial position, slope grade and variable safe headway, the effect of slope in a single-lane highway on the traffic flow is investigated with the e...Through introducing a generalized optimal speed function to consider spatial position, slope grade and variable safe headway, the effect of slope in a single-lane highway on the traffic flow is investigated with the extended optimal speed model. The theoretical analysis and simulation results show that the flux of the whole road with the upgrade （or downgrade） increases linearly with density, saturates at a critical density, then maintains this saturated value in a certain density range and finally decreases with density. The value of saturated flux is equal to the maximum flux of the upgrade （or downgrade） without considering the slight influence of the driver＇s sensitivity. And the fundamental diagrams also depend on sensitivity, slope grade and slope length. The spatiotemporal pattern gives the segregation of different traffic phases caused by the rarefaction wave and the shock wave under a certain initial vehicle number. A comparison between the upgrade and the downgrade indicates that the value of saturated flux of the downgrade is larger than that of the upgrade under the same condition. This result is in accordance with the real traffic.展开更多
The temperature distributions of different parts of a subgrade were analyzed based on the results of three years of moni- toring data from the Harbin-Qiqihaer Passenger Dedicated Line, a high-speed railway, including ...The temperature distributions of different parts of a subgrade were analyzed based on the results of three years of moni- toring data from the Harbin-Qiqihaer Passenger Dedicated Line, a high-speed railway, including the slope toes, shoulders, and natural ground. The temperature variation with time and the maximum frozen depths showed that an obvious sun- ny-shady effect exists in the railway subgrade, which spans a seasonal frozen region. Development of frost heave is af- fected by the asymmetric temperature distribution. The temperature field and the maximum frozen depths 50 years after the subgrade was built were simulated with a mathematical model of the unsteady phase transition of the geothermal field.展开更多
Semi-solid casting of M2 high speed steel ingots was investigated by inclined slope pre-crystallization method. Effects of casting temperature and slope length on the microstructure of M2 HSS ingots were investigated....Semi-solid casting of M2 high speed steel ingots was investigated by inclined slope pre-crystallization method. Effects of casting temperature and slope length on the microstructure of M2 HSS ingots were investigated. M2 cast ingots of non-dendritic primary austenite and fine eutectic ledeburite network carbide structure were obtained, with the casting temperature, slope length and angle of 1480 ℃, 500 mm and 60° respectively. Meanwhile, the microstructure of cast samples was quantitatively assessed by Image tool software. Results show that optimum mean equivalent diameter of primary austenite crystal grain is 50.8 μm, shape factor is 0.83, and mean thickness of network carbide is 5.21 μm.展开更多
Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafros...Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafrost embankment design in frozen ground regions. The prediction may be further complicated due to the inherent uncertainties of material properties. Hence, stochastic analyses should be conducted. Firstly, Karhunen-Loeve expansion is applied to attain the random fields for hydraulic and thermal conductions. Next, the mixed-form modified Richards equation for mass transfer （i.e., mass equation） and the heat transport equation for heat transient flow in a variably saturated frozen soil are combined into one equation with temperature unknown. Furthermore, the finite element formulation for the coupled thermal-hydraulic fields is derived. Based on the random fields, the stochastic finite element analyses on stability of embankment are carried out. Numerical results show that stochastic analyses of embankment stability may provide a more rational picture for the distribution of factors of safety （FOS）, which is definitely useful for embankment design in frozen ground regions.展开更多
若风电机组参与调频时采用步进惯量控制(stepwise inertial control,SIC)策略,其退出调频时有功快速下降可能会引发系统频率二次跌落(frequency second drop,FSD)问题。已有文献中一类改进的SIC策略通过减小风电机组退出调频后有功下降...若风电机组参与调频时采用步进惯量控制(stepwise inertial control,SIC)策略,其退出调频时有功快速下降可能会引发系统频率二次跌落(frequency second drop,FSD)问题。已有文献中一类改进的SIC策略通过减小风电机组退出调频后有功下降阶段的斜率来应对FSD问题,然而该类改进的SIC策略使得风电机组在退出调频后其有功需要一段时间才会小于风能捕获,在此期间转子转速会继续下降并有可能低于转速下限,危及风电机组运行安全。文章对这一类改进的SIC策略做了进一步完善,提出了一种风电机组自适应SIC策略,根据风电机组退出调频时的转子转速自适应设置风电机组退出调频后有功下降阶段的斜率,在确保风电机组退出调频后转子转速不会低于转速下限的前提下,最小化FSD的幅度。展开更多
In order to analyze the characteristics of wheel-rail vibration of the vertical section in a high-speed railway, a vehicle-line dynamics model is established using the dynamics software SIMPACK. Through this model, th...In order to analyze the characteristics of wheel-rail vibration of the vertical section in a high-speed railway, a vehicle-line dynamics model is established using the dynamics software SIMPACK. Through this model, the paper analyzes the influence of vertical section parameters, including vertical section slope and vertical curve radius, on wheel-rail dynamics interaction and the acting region of wheel-rail vibration. In addition, the characteristics of wheel- rail vibration of the vertical section under different velocities are investigated. The results show that the variation of wheel load is not sensitive to the vertical section slope but is greatly affected by the vertical curve radius. It was also observed that the smaller the vertical curve radius is, the more severe the interaction between the wheel and rail be- comes. Furthermore, the acting region of wheel-rail vibration expands with the vertical curve radius increasing. On another note, it is necessary to match the slope and vertical curve radius reasonably, on account of the influence of operation speed on the characteristics of wheel-rail vibration. This is especially important at the design stage of vertical sec- tions for lines of different grades.展开更多
基金Project supported by the National Basic Research Program of China (Grant No 2006CB705500)the National Natural Science Foundation of China (Grant Nos 10532060 and 10562001) the Shanghai Leading Academic Discipline Project, China (Grant No Y0103)
文摘Through introducing a generalized optimal speed function to consider spatial position, slope grade and variable safe headway, the effect of slope in a single-lane highway on the traffic flow is investigated with the extended optimal speed model. The theoretical analysis and simulation results show that the flux of the whole road with the upgrade （or downgrade） increases linearly with density, saturates at a critical density, then maintains this saturated value in a certain density range and finally decreases with density. The value of saturated flux is equal to the maximum flux of the upgrade （or downgrade） without considering the slight influence of the driver＇s sensitivity. And the fundamental diagrams also depend on sensitivity, slope grade and slope length. The spatiotemporal pattern gives the segregation of different traffic phases caused by the rarefaction wave and the shock wave under a certain initial vehicle number. A comparison between the upgrade and the downgrade indicates that the value of saturated flux of the downgrade is larger than that of the upgrade under the same condition. This result is in accordance with the real traffic.
基金supported by the National Natural Science Foundation of China(Nos.51378057 and 41371081)Scientific and Technological Research and Development Plan of Chinese Railway Corporation(2014G003-A)
文摘The temperature distributions of different parts of a subgrade were analyzed based on the results of three years of moni- toring data from the Harbin-Qiqihaer Passenger Dedicated Line, a high-speed railway, including the slope toes, shoulders, and natural ground. The temperature variation with time and the maximum frozen depths showed that an obvious sun- ny-shady effect exists in the railway subgrade, which spans a seasonal frozen region. Development of frost heave is af- fected by the asymmetric temperature distribution. The temperature field and the maximum frozen depths 50 years after the subgrade was built were simulated with a mathematical model of the unsteady phase transition of the geothermal field.
基金Funded by the Science Foundation of Beijing Jiaotong University (No.230-12)
文摘Semi-solid casting of M2 high speed steel ingots was investigated by inclined slope pre-crystallization method. Effects of casting temperature and slope length on the microstructure of M2 HSS ingots were investigated. M2 cast ingots of non-dendritic primary austenite and fine eutectic ledeburite network carbide structure were obtained, with the casting temperature, slope length and angle of 1480 ℃, 500 mm and 60° respectively. Meanwhile, the microstructure of cast samples was quantitatively assessed by Image tool software. Results show that optimum mean equivalent diameter of primary austenite crystal grain is 50.8 μm, shape factor is 0.83, and mean thickness of network carbide is 5.21 μm.
基金supported by the National 973 Project of China (No. 2012CB026104)the National Natural Science Foundation of China (No. 51378057)
文摘Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafrost embankment design in frozen ground regions. The prediction may be further complicated due to the inherent uncertainties of material properties. Hence, stochastic analyses should be conducted. Firstly, Karhunen-Loeve expansion is applied to attain the random fields for hydraulic and thermal conductions. Next, the mixed-form modified Richards equation for mass transfer （i.e., mass equation） and the heat transport equation for heat transient flow in a variably saturated frozen soil are combined into one equation with temperature unknown. Furthermore, the finite element formulation for the coupled thermal-hydraulic fields is derived. Based on the random fields, the stochastic finite element analyses on stability of embankment are carried out. Numerical results show that stochastic analyses of embankment stability may provide a more rational picture for the distribution of factors of safety （FOS）, which is definitely useful for embankment design in frozen ground regions.
文摘若风电机组参与调频时采用步进惯量控制(stepwise inertial control,SIC)策略,其退出调频时有功快速下降可能会引发系统频率二次跌落(frequency second drop,FSD)问题。已有文献中一类改进的SIC策略通过减小风电机组退出调频后有功下降阶段的斜率来应对FSD问题,然而该类改进的SIC策略使得风电机组在退出调频后其有功需要一段时间才会小于风能捕获,在此期间转子转速会继续下降并有可能低于转速下限,危及风电机组运行安全。文章对这一类改进的SIC策略做了进一步完善,提出了一种风电机组自适应SIC策略,根据风电机组退出调频时的转子转速自适应设置风电机组退出调频后有功下降阶段的斜率,在确保风电机组退出调频后转子转速不会低于转速下限的前提下,最小化FSD的幅度。
基金support and motivation provided by the National Natural Science Foundation of China (No. 51075340)the Fok YingTong Education Foundation for Young Teachers in the Higher Education Institutions of China (No. 121075)the Program for Innovation Research Team in University in China (No. IRT1178)
文摘In order to analyze the characteristics of wheel-rail vibration of the vertical section in a high-speed railway, a vehicle-line dynamics model is established using the dynamics software SIMPACK. Through this model, the paper analyzes the influence of vertical section parameters, including vertical section slope and vertical curve radius, on wheel-rail dynamics interaction and the acting region of wheel-rail vibration. In addition, the characteristics of wheel- rail vibration of the vertical section under different velocities are investigated. The results show that the variation of wheel load is not sensitive to the vertical section slope but is greatly affected by the vertical curve radius. It was also observed that the smaller the vertical curve radius is, the more severe the interaction between the wheel and rail be- comes. Furthermore, the acting region of wheel-rail vibration expands with the vertical curve radius increasing. On another note, it is necessary to match the slope and vertical curve radius reasonably, on account of the influence of operation speed on the characteristics of wheel-rail vibration. This is especially important at the design stage of vertical sec- tions for lines of different grades.
