在新兴的软件定义网络(Software Defined Networking,SDN)、OpenFlow交换机中,为满足OpenFlow协议宽匹配域的需求,SDN交换设备需要更大的查找表存储容量.当流表溢出时,将导致控制报文数目爆炸性增长、数据包传输时延增大等危害网络正常...在新兴的软件定义网络(Software Defined Networking,SDN)、OpenFlow交换机中,为满足OpenFlow协议宽匹配域的需求,SDN交换设备需要更大的查找表存储容量.当流表溢出时,将导致控制报文数目爆炸性增长、数据包传输时延增大等危害网络正常运行的后果.然而考虑成本因素,高速查找表容量不可能无限增加.即使单纯地增加流表容量,并不能使溢出的概率降低为零,且极不经济.本文分析了网络流量的特征,提出了一种流表共享方法(Flow Table Sharing,FTS),针对流表溢出现象带来的危害,完善了Table-Miss处理机制,有效遏制了由于流表溢出而引发的危害网络正常运行的情况.相比目前的Table-Miss处理方式,FTS对流表溢出情况下控制消息数量和RTT时间的优化都达到两个数量级.此外,该文针对流表扩散方法设计了简单高效的基于OpenFlow组表的随机路由选择算法,系统结构实施简单,可以方便地降级为现行的通用Table-Miss处理模式.展开更多
The take-over control(ToC)of human–machine interaction is a hotspot.From automatic driving to manual driving,some factors affecting driver response time have not been considered in existing models,and little attentio...The take-over control(ToC)of human–machine interaction is a hotspot.From automatic driving to manual driving,some factors affecting driver response time have not been considered in existing models,and little attention has been paid to its effects on mixed traffic flow.This study establishes a ToC model of response based on adaptive control of thought-rational cognitive architecture(CAR-ToC)to investigate the effects of driver response time on traffic flow.A quantification method of driver’s situation cognition uncertainty is also proposed.This method can directly describe the cognitive effect of drivers with different cognitive characteristics on vehicle cluster situations.The results show that when driver response time in ToC is 4.2 s,the traffic state is the best.The greater the response time is,the more obvious the stop-and-go waves exhibit.Besides,crashes happen when manual vehicles hit other types of vehicles in ToC.Effects of driver response time on traffic are illustrated and verified from various aspects.Experiments are designed to verify that road efficiency and safety are increased by using a dynamic take-over strategy.Further,internal causes of effects are revealed and suggestions are discussed for the safety and efficiency of autonomous vehicles.展开更多
When there are several bodies with relative motion in a flow field,such as the flow in the compression system of modern aero-engine,the flow field will have certain special features,one of which is that the time-space...When there are several bodies with relative motion in a flow field,such as the flow in the compression system of modern aero-engine,the flow field will have certain special features,one of which is that the time-space structure of such multi-bodies unsteady vorticity flow field would be either of unsteady natural flow(UNF)pattern or of unsteady cooperative flow(UCF)pattern.If we further examine the aerodynamic design system of aero-engine,there is no mechanism for the unsteady cooperative flow to occur,in other words the flow field must be of the unsteady natural flow type.If certain technical measures can be adopted to transform UNF into UCF,the aerodynamic performances will surely be improved.This is the main task the author and their colleague have been devoted to and the results are reviewed in the present paper with emphases laid on basic ideas,technical approaches and experimental verifications.展开更多
A novel method to measure the flow rate in a wet gas is presented.Due to the presence of liquid,there is a deviation in the measurement of the gas volume flow rate obtained with standard vortex flow-meters.The propose...A novel method to measure the flow rate in a wet gas is presented.Due to the presence of liquid,there is a deviation in the measurement of the gas volume flow rate obtained with standard vortex flow-meters.The proposed method is based on a correction factor determined through the application of an over-reading approach to a bluff body in mist flow.The correction factor is obtained from the slip velocity ratio,i.e.,the ratio of droplet velocity to gas velocity,based on the analysis of the fluid velocity distribution in the pipeline section.It also takes into account relevant theoretical arguments.It is shown that the predicted results fit the experimental results well.展开更多
The hydrothermal wave was investigated numerically for large-Prandtl-number fluid (Pr = 105.6) in a shallow cavity with different heated sidewalls. The traveling wave appears and propagates in the direction opposite t...The hydrothermal wave was investigated numerically for large-Prandtl-number fluid (Pr = 105.6) in a shallow cavity with different heated sidewalls. The traveling wave appears and propagates in the direction opposite to the surface flow (upstream) in the case of zero gravity when the applied temperature difference grows and over the critical value. The phase relationships of the disturbed velocity,temperature and pressure demonstrate that the traveling wave is driven by the disturbed tem-perature,which is named hydrothermal wave. The hydrothermal wave is so weak that the oscillatory flow field and temperature distribution can hardly be observed in the liquid layer. The exciting mechanism of hydrothermal wave is analyzed and discussed in the present paper.展开更多
文摘在新兴的软件定义网络(Software Defined Networking,SDN)、OpenFlow交换机中,为满足OpenFlow协议宽匹配域的需求,SDN交换设备需要更大的查找表存储容量.当流表溢出时,将导致控制报文数目爆炸性增长、数据包传输时延增大等危害网络正常运行的后果.然而考虑成本因素,高速查找表容量不可能无限增加.即使单纯地增加流表容量,并不能使溢出的概率降低为零,且极不经济.本文分析了网络流量的特征,提出了一种流表共享方法(Flow Table Sharing,FTS),针对流表溢出现象带来的危害,完善了Table-Miss处理机制,有效遏制了由于流表溢出而引发的危害网络正常运行的情况.相比目前的Table-Miss处理方式,FTS对流表溢出情况下控制消息数量和RTT时间的优化都达到两个数量级.此外,该文针对流表扩散方法设计了简单高效的基于OpenFlow组表的随机路由选择算法,系统结构实施简单,可以方便地降级为现行的通用Table-Miss处理模式.
基金thankful to National Key Research and Development Plan(Grant No.2018YFB1600500)。
文摘The take-over control(ToC)of human–machine interaction is a hotspot.From automatic driving to manual driving,some factors affecting driver response time have not been considered in existing models,and little attention has been paid to its effects on mixed traffic flow.This study establishes a ToC model of response based on adaptive control of thought-rational cognitive architecture(CAR-ToC)to investigate the effects of driver response time on traffic flow.A quantification method of driver’s situation cognition uncertainty is also proposed.This method can directly describe the cognitive effect of drivers with different cognitive characteristics on vehicle cluster situations.The results show that when driver response time in ToC is 4.2 s,the traffic state is the best.The greater the response time is,the more obvious the stop-and-go waves exhibit.Besides,crashes happen when manual vehicles hit other types of vehicles in ToC.Effects of driver response time on traffic are illustrated and verified from various aspects.Experiments are designed to verify that road efficiency and safety are increased by using a dynamic take-over strategy.Further,internal causes of effects are revealed and suggestions are discussed for the safety and efficiency of autonomous vehicles.
基金the financial support received from the National Natural Science Foundation of China(Grant no.10902008)for this project.
文摘When there are several bodies with relative motion in a flow field,such as the flow in the compression system of modern aero-engine,the flow field will have certain special features,one of which is that the time-space structure of such multi-bodies unsteady vorticity flow field would be either of unsteady natural flow(UNF)pattern or of unsteady cooperative flow(UCF)pattern.If we further examine the aerodynamic design system of aero-engine,there is no mechanism for the unsteady cooperative flow to occur,in other words the flow field must be of the unsteady natural flow type.If certain technical measures can be adopted to transform UNF into UCF,the aerodynamic performances will surely be improved.This is the main task the author and their colleague have been devoted to and the results are reviewed in the present paper with emphases laid on basic ideas,technical approaches and experimental verifications.
基金supported by the Leading Talent Training Project for Young and Middle-Aged Teacher(A2-0265-22-41).
文摘A novel method to measure the flow rate in a wet gas is presented.Due to the presence of liquid,there is a deviation in the measurement of the gas volume flow rate obtained with standard vortex flow-meters.The proposed method is based on a correction factor determined through the application of an over-reading approach to a bluff body in mist flow.The correction factor is obtained from the slip velocity ratio,i.e.,the ratio of droplet velocity to gas velocity,based on the analysis of the fluid velocity distribution in the pipeline section.It also takes into account relevant theoretical arguments.It is shown that the predicted results fit the experimental results well.
基金Supported by the National Natural Science Foundation of China (Grant No. 10432060)
文摘The hydrothermal wave was investigated numerically for large-Prandtl-number fluid (Pr = 105.6) in a shallow cavity with different heated sidewalls. The traveling wave appears and propagates in the direction opposite to the surface flow (upstream) in the case of zero gravity when the applied temperature difference grows and over the critical value. The phase relationships of the disturbed velocity,temperature and pressure demonstrate that the traveling wave is driven by the disturbed tem-perature,which is named hydrothermal wave. The hydrothermal wave is so weak that the oscillatory flow field and temperature distribution can hardly be observed in the liquid layer. The exciting mechanism of hydrothermal wave is analyzed and discussed in the present paper.
