时钟同步是保障地铁通信系统安全、稳定运行的关键基础。针对老旧地铁通信系统中普遍存在的同步精度不足、系统稳定性下降、设备兼容性差以及运维成本较高等问题,本文结合实际工程改造经验,对相关技术瓶颈进行了系统分析。在此基础上,...时钟同步是保障地铁通信系统安全、稳定运行的关键基础。针对老旧地铁通信系统中普遍存在的同步精度不足、系统稳定性下降、设备兼容性差以及运维成本较高等问题,本文结合实际工程改造经验,对相关技术瓶颈进行了系统分析。在此基础上,引入高精度PTP(Precision Time Protocol)时钟同步技术,从技术原理、系统架构及工程适配性等方面展开研究。优化及运行维护等关键环节进行了全面梳理,并总结了典型故障及对应的优化策略。研究结果表明,PTP时钟同步技术能够显著提升地铁通信系统的时间同步精度与运行可靠性,同时有效降低系统运维成本,对于推动地铁通信系统向智能化与高可靠方向升级具有重要工程价值。展开更多
With the continuous increase in performance requirements for power systems in the aerospace and low-altitude economy sectors,designing lightweight and highstrength blade structures with excellent dynamic characteristi...With the continuous increase in performance requirements for power systems in the aerospace and low-altitude economy sectors,designing lightweight and highstrength blade structures with excellent dynamic characteristics has become critical.This paper puts forward a dynamic model for a rotating functionally graded graphenereinforced(FG-GPR)sandwich metal porous cantilever pre-twisted plate(PTP),aiming to analyze its natural vibration characteristics.To this end,the mixture principle and the revised Halpin-Tsai model are used to determine the parameters of graphene and porosity distributions in the core layer.With the classical plate theory,the Rayleigh-Ritz method,and the polynomials,the dynamic equations are derived to solve for the free vibration mode shapes and frequencies of the rotating FG-GPR sandwich metal porous cantilever PTP.The comparison of natural frequencies and mode shapes with available literature results confirms the precision of the theoretical formulation and numerical computations.The bending stiffnesses are analyzed.Finally,the effects of different graphene/pore distributions,length-to-thickness/width ratios,layer thickness ratios,twist angles,and rotational speeds on the natural frequencies of the system are systematically investigated.展开更多
异地站点之间需要在广域范围实现时间同步。除了采用卫星授时外,希望借助SDH(Synchronous Digital Hierarchy)网络进行时间同步性能的在线监测。但是广域范围内的SDH网络结构复杂、跳数较多,且大量存在上下行线路不对称的现象,对传统网...异地站点之间需要在广域范围实现时间同步。除了采用卫星授时外,希望借助SDH(Synchronous Digital Hierarchy)网络进行时间同步性能的在线监测。但是广域范围内的SDH网络结构复杂、跳数较多,且大量存在上下行线路不对称的现象,对传统网络时间同步技术提出了挑战。因此,针对广域SDH网络,提出了基于WR PTP(White Rabbit Precision Timing Protocol)技术的链路模型。该模型考虑了SDH网络中存在的各个延时环节及其计算方法,并针对实际网络中存在的不对称链路时延,给出了修正方法,推导了时钟偏差的修正计算公式。同时对于SDH环网中存在的链路倒换问题,给出了工程化解决方法。所提各方法在实际的SDH网络上进行了测试,结果表明,能达到的时间同步误差不超过1μs,可满足广域时间同步及时钟同步性能在线监测的需要。展开更多
针对PTP(precise time protocol)协议在应用层获取软件时间戳导致时钟同步精度下降的问题,提出一种基于MAC(media access control)层获取硬件时间戳的PTP同步优化方案。设计了以STM32F407微处理器为核心的PTP时钟应用平台,在MAC层实现...针对PTP(precise time protocol)协议在应用层获取软件时间戳导致时钟同步精度下降的问题,提出一种基于MAC(media access control)层获取硬件时间戳的PTP同步优化方案。设计了以STM32F407微处理器为核心的PTP时钟应用平台,在MAC层实现了硬件时间戳获取,避免了由于协议栈软件处理延时产生的不确定性;针对PTP时钟晶振老化导致的时间同步偏差及网络延迟抖动问题,采用迭代方法优化了本地时钟频率调节算法,提高了频率校正精度。经实际测试,主从时钟偏差的RMS(root mean square)优于20 ns,提升了时钟同步精度。展开更多
文摘时钟同步是保障地铁通信系统安全、稳定运行的关键基础。针对老旧地铁通信系统中普遍存在的同步精度不足、系统稳定性下降、设备兼容性差以及运维成本较高等问题,本文结合实际工程改造经验,对相关技术瓶颈进行了系统分析。在此基础上,引入高精度PTP(Precision Time Protocol)时钟同步技术,从技术原理、系统架构及工程适配性等方面展开研究。优化及运行维护等关键环节进行了全面梳理,并总结了典型故障及对应的优化策略。研究结果表明,PTP时钟同步技术能够显著提升地铁通信系统的时间同步精度与运行可靠性,同时有效降低系统运维成本,对于推动地铁通信系统向智能化与高可靠方向升级具有重要工程价值。
基金Project supported by the National Natural Science Foundation of China(Nos.12272056 and 11832002)。
文摘With the continuous increase in performance requirements for power systems in the aerospace and low-altitude economy sectors,designing lightweight and highstrength blade structures with excellent dynamic characteristics has become critical.This paper puts forward a dynamic model for a rotating functionally graded graphenereinforced(FG-GPR)sandwich metal porous cantilever pre-twisted plate(PTP),aiming to analyze its natural vibration characteristics.To this end,the mixture principle and the revised Halpin-Tsai model are used to determine the parameters of graphene and porosity distributions in the core layer.With the classical plate theory,the Rayleigh-Ritz method,and the polynomials,the dynamic equations are derived to solve for the free vibration mode shapes and frequencies of the rotating FG-GPR sandwich metal porous cantilever PTP.The comparison of natural frequencies and mode shapes with available literature results confirms the precision of the theoretical formulation and numerical computations.The bending stiffnesses are analyzed.Finally,the effects of different graphene/pore distributions,length-to-thickness/width ratios,layer thickness ratios,twist angles,and rotational speeds on the natural frequencies of the system are systematically investigated.
文摘针对PTP(precise time protocol)协议在应用层获取软件时间戳导致时钟同步精度下降的问题,提出一种基于MAC(media access control)层获取硬件时间戳的PTP同步优化方案。设计了以STM32F407微处理器为核心的PTP时钟应用平台,在MAC层实现了硬件时间戳获取,避免了由于协议栈软件处理延时产生的不确定性;针对PTP时钟晶振老化导致的时间同步偏差及网络延迟抖动问题,采用迭代方法优化了本地时钟频率调节算法,提高了频率校正精度。经实际测试,主从时钟偏差的RMS(root mean square)优于20 ns,提升了时钟同步精度。
