In this study, the intrinsic mechanism of aerodynamic effects on the motion stability of a high-speed maglev system was investigated. The concept of a critical speed for maglev vehicles considering the aerodynamic eff...In this study, the intrinsic mechanism of aerodynamic effects on the motion stability of a high-speed maglev system was investigated. The concept of a critical speed for maglev vehicles considering the aerodynamic effect is proposed. The study was carried out based on a single magnetic suspension system, which is convenient for proposing relevant concepts and obtaining explicit expressions. This study shows that the motion stability of the suspension system is closely related to the vehicle speed when aerodynamic effects are considered. With increases of the vehicle speed, the stability behavior of the system changes. At a certain vehicle speed,the stability of the system reaches a critical state, followed by instability. The speed corresponding to the critical state is the critical speed. Analysis reveals that when the system reaches the critical state, it takes two forms, with two critical speeds, and thus two expressions for the critical speed are obtained. The conditions of the existence of the critical speed were determined, and the effects of the control parameters and the lift coefficient on the critical speed were analyzed by numerical analysis. The results show that the first critical speed appears when the aerodynamic force is upward,and the second critical speed appears when the aerodynamic force is downward. Moreover, both critical speeds decrease with the increase of the lift coefficient.展开更多
Vehicular speeds are of particular interest in areas with a high number of pedestrians due to the fact that 14-percent of all fatal crashes involve pedestrians. This study investigated the effect of a radar speed disp...Vehicular speeds are of particular interest in areas with a high number of pedestrians due to the fact that 14-percent of all fatal crashes involve pedestrians. This study investigated the effect of a radar speed display sign placed for an extended period of time, at a location frequented by law enforcement on a road segment entering a university campus with a high number of pedestrians and vehicle speed violations. The statistical analysis included a comparison between AM peak, PM peak, and midday speeds collected one year apart. The data suggested that radar speed display signs can remain effective over a long period of time;causing drivers to decelerate when warned of a speeding violation. While other studies have examined long-term impacts of similar technologies, none have included a road entering a University campus. Thus, these findings support that other similar locations entering university campuses could see long-term benefits to stationary radar speed display signs.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
The rapid development of high-speed rail（HSR） is influencing regional development, regional structure, commuting, and regional integration. East Asia is the region with the world＇s first and largest current operati...The rapid development of high-speed rail（HSR） is influencing regional development, regional structure, commuting, and regional integration. East Asia is the region with the world＇s first and largest current operating and planned HSR network. In this paper, we examine the evolutionary mechanism and impacts on the transport circle and accessibility of HSR in East Asia. The results indicate that the HSR network first follows a ＂core-core＂ model and then forms a corridor in Japan, South Korea, and China Taiwan, but then forms a complete network in China Mainland. The current operating HSR lines are mostly distributed in regions with developed economies and dense populations, and more than half of the population and GDP in China can be served by HSR within 1 hour＇s travel time. The planned HSR network will expand to the western region of China and Japan and the southern region of South Korea. The development of the current operating and planned HSR network considerably enlarges the transport circle of core cities, especially cities along trunk HSR lines. This 1 h transport circle of core cities has formed continuous regions in the Yangtze River Delta, the Pearl River Delta, Tokyo, Seoul, and along trunk HSR lines. The HSR network will bring about substantial improvement in accessiblity, but also increase the inequality of nodal accessibility in China Mainland. Spatially, the spatial patterns of the weighted shortest travel time of cities in China Mainland, Japan, and South Korea all present the ＂core-peripheral structure＂, taking Zhengzhou, Tokyo, and Seoul, respectively, as core cities, and cities located along the trunk HSR lines gain large improvement in accessibility.展开更多
为实现黏滞效应影响下的车速准确预测,以云南省典型山区公路穿村镇段为例,基于无人机拍摄视频提取的行车轨迹数据,引入流体力学定义黏滞效应的作用机制,并构建黏滞系数测度模型,将黏滞系数与基于注意力机制的门控循环单元(Gate Recurren...为实现黏滞效应影响下的车速准确预测,以云南省典型山区公路穿村镇段为例,基于无人机拍摄视频提取的行车轨迹数据,引入流体力学定义黏滞效应的作用机制,并构建黏滞系数测度模型,将黏滞系数与基于注意力机制的门控循环单元(Gate Recurrent Unit based on Attention Mechanism,GRU-AM)模型相结合,提出了考虑黏滞效应的山区公路穿村镇段车辆速度预测方法并验证其有效性。结果表明,黏滞效应导致车流呈现近似流体的黏滞性假设成立,山区公路穿村镇段车辆运行速度特性呈“低车速、高离散”现象,其速度25%、50%、85%分位值与普通路段的差值分别为-2.01 m/s、-1.68 m/s、-1.35 m/s,速度变异系数、速度离散系数的差值分别为0.058、0.218。此外,将黏滞系数作为关键输入特征提高了预测模型的准确性,构建的GRU-AM模型拟合优度(R2)提高了2.57百分点、平均绝对误差(Mean Absolute Error,MAE)减小了0.188,用于对比的单一模型门控循环单元(Gate Recurrent Unit,GRU)和Transformer的R2分别提高了3.88百分点和9.89百分点、MAE分别减小了0.1075和0.2344,其中GRU-AM模型表现最好,R2为95.23%,MAE为0.4352。研究表明,考虑黏滞效应的山区公路穿村镇段车速预测方法具有良好的预测性能。展开更多
Based on the pioneering work of Konishi et al., in consideration of the influence of drivers＇ steady desired speed ef/ect on the traffic flow, we develop a new coupled map car-following model in the real world. By us...Based on the pioneering work of Konishi et al., in consideration of the influence of drivers＇ steady desired speed ef/ect on the traffic flow, we develop a new coupled map car-following model in the real world. By use of the control theory, the stability condition of our model is derived. The validity of the present theoretical scheme is verified via numerical simulation, confirming the correctness of our theoretical analysis.展开更多
基金supported by the National Key Research and Development Program of China(Grant 2016YFB1200602)the National Natural Science Foundation of China (Grants 11672306, 51490673)+2 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant XDB22020101)the National Basic Research Program (973 Program) of China (Grant 2014CB046801)the State Key Laboratory of Hydraulic Engineering Simulation and Safety (Tianjin University)
文摘In this study, the intrinsic mechanism of aerodynamic effects on the motion stability of a high-speed maglev system was investigated. The concept of a critical speed for maglev vehicles considering the aerodynamic effect is proposed. The study was carried out based on a single magnetic suspension system, which is convenient for proposing relevant concepts and obtaining explicit expressions. This study shows that the motion stability of the suspension system is closely related to the vehicle speed when aerodynamic effects are considered. With increases of the vehicle speed, the stability behavior of the system changes. At a certain vehicle speed,the stability of the system reaches a critical state, followed by instability. The speed corresponding to the critical state is the critical speed. Analysis reveals that when the system reaches the critical state, it takes two forms, with two critical speeds, and thus two expressions for the critical speed are obtained. The conditions of the existence of the critical speed were determined, and the effects of the control parameters and the lift coefficient on the critical speed were analyzed by numerical analysis. The results show that the first critical speed appears when the aerodynamic force is upward,and the second critical speed appears when the aerodynamic force is downward. Moreover, both critical speeds decrease with the increase of the lift coefficient.
文摘Vehicular speeds are of particular interest in areas with a high number of pedestrians due to the fact that 14-percent of all fatal crashes involve pedestrians. This study investigated the effect of a radar speed display sign placed for an extended period of time, at a location frequented by law enforcement on a road segment entering a university campus with a high number of pedestrians and vehicle speed violations. The statistical analysis included a comparison between AM peak, PM peak, and midday speeds collected one year apart. The data suggested that radar speed display signs can remain effective over a long period of time;causing drivers to decelerate when warned of a speeding violation. While other studies have examined long-term impacts of similar technologies, none have included a road entering a University campus. Thus, these findings support that other similar locations entering university campuses could see long-term benefits to stationary radar speed display signs.
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National Natural Science Foundation of China,No.41171107,No.41371143,No.4401121
文摘The rapid development of high-speed rail（HSR） is influencing regional development, regional structure, commuting, and regional integration. East Asia is the region with the world＇s first and largest current operating and planned HSR network. In this paper, we examine the evolutionary mechanism and impacts on the transport circle and accessibility of HSR in East Asia. The results indicate that the HSR network first follows a ＂core-core＂ model and then forms a corridor in Japan, South Korea, and China Taiwan, but then forms a complete network in China Mainland. The current operating HSR lines are mostly distributed in regions with developed economies and dense populations, and more than half of the population and GDP in China can be served by HSR within 1 hour＇s travel time. The planned HSR network will expand to the western region of China and Japan and the southern region of South Korea. The development of the current operating and planned HSR network considerably enlarges the transport circle of core cities, especially cities along trunk HSR lines. This 1 h transport circle of core cities has formed continuous regions in the Yangtze River Delta, the Pearl River Delta, Tokyo, Seoul, and along trunk HSR lines. The HSR network will bring about substantial improvement in accessiblity, but also increase the inequality of nodal accessibility in China Mainland. Spatially, the spatial patterns of the weighted shortest travel time of cities in China Mainland, Japan, and South Korea all present the ＂core-peripheral structure＂, taking Zhengzhou, Tokyo, and Seoul, respectively, as core cities, and cities located along the trunk HSR lines gain large improvement in accessibility.
文摘为实现黏滞效应影响下的车速准确预测,以云南省典型山区公路穿村镇段为例,基于无人机拍摄视频提取的行车轨迹数据,引入流体力学定义黏滞效应的作用机制,并构建黏滞系数测度模型,将黏滞系数与基于注意力机制的门控循环单元(Gate Recurrent Unit based on Attention Mechanism,GRU-AM)模型相结合,提出了考虑黏滞效应的山区公路穿村镇段车辆速度预测方法并验证其有效性。结果表明,黏滞效应导致车流呈现近似流体的黏滞性假设成立,山区公路穿村镇段车辆运行速度特性呈“低车速、高离散”现象,其速度25%、50%、85%分位值与普通路段的差值分别为-2.01 m/s、-1.68 m/s、-1.35 m/s,速度变异系数、速度离散系数的差值分别为0.058、0.218。此外,将黏滞系数作为关键输入特征提高了预测模型的准确性,构建的GRU-AM模型拟合优度(R2)提高了2.57百分点、平均绝对误差(Mean Absolute Error,MAE)减小了0.188,用于对比的单一模型门控循环单元(Gate Recurrent Unit,GRU)和Transformer的R2分别提高了3.88百分点和9.89百分点、MAE分别减小了0.1075和0.2344,其中GRU-AM模型表现最好,R2为95.23%,MAE为0.4352。研究表明,考虑黏滞效应的山区公路穿村镇段车速预测方法具有良好的预测性能。
基金Project supported by the Major Consulting Project of Chinese Academy of Engineering(Grant No.2012-ZX-22)the National Natural Science Foundation of China(Grant No.71201178)+3 种基金the Natural Science Foundation of Chongqing City,China(Grant No.cstc2012jjB40002)the Research Fund for the Doctoral Program of Higher Education of China(Grant No.20120191110047)the Engineering Center Research Program of Chongqing City,China(Grant No.cstc2011pt-gc30005)the Key Technology R&D Project of Chongqing City,China(Grant Nos.cstc2011AB2052 and cstc2012gg-yyjsB30001)
文摘Based on the pioneering work of Konishi et al., in consideration of the influence of drivers＇ steady desired speed ef/ect on the traffic flow, we develop a new coupled map car-following model in the real world. By use of the control theory, the stability condition of our model is derived. The validity of the present theoretical scheme is verified via numerical simulation, confirming the correctness of our theoretical analysis.
