密封环挠性安装形式对干气密封动态追随性的影响

基于气体润滑理论,并通过小扰动法建立了螺旋槽干气密封微扰膜压控制方程,在高速高压条件下获得了气膜动态特性系数;基于动力学相关知识,在考虑转轴轴向振动的情况下,利用气膜轴向动态刚度和阻尼系数分别求解了静环挠性安装、动环挠性安装和两环均挠性安装的干气密封挠性环运动方程.在不同轴向激励振幅、激励频率、挠性环质量、弹簧刚度和辅助密封圈阻尼下分别研究了三种典型结构干气密封动态追随性并进行了对比分析.结果表明:当轴向激励频率较高或挠性环质量较大时,静环挠性安装干气密封在刚受到外界激励时膜厚突变相对严重,动态追随性较差;在轴向激励频率较低且挠性环质量较小时,静环挠性安装干气密封相比动环挠性安装干气密封表现出更好的动态追随性;在三种密封环挠性安装形式中,两环均挠性安装干气密封动态追随性最好,且具有绝对优势.     

Flow topology and unsteady features of the wake of a generic high-speed train

The unsteady wake of a high-speed train is investigated experimentally. From a practical point of view, the wake region is of considerable importance as it is where slipstream velocities—velocities induced by the vehicles movement through air—are largest. In turn, this can create a considerable risk for passengers and track-side workers as the train passes. The flow is quantified in a 1:10 scale wind-tunnel experiment using high-frequency 4-hole dynamic pressure cobra probes, surface-pressure measurements and flow visualisation. The dominant feature of the time-average wake topology consists of a clearly identifiable counter-rotating streamwise vortex pair. Although the wake structure and evolution should perhaps be considered as a whole, the near wake exhibits periodic unsteadiness, at a Strouhal number of 0.2, that could be attributed to periodic shedding from the sides and to a lesser extent the top surface. This periodicity feeds into the trailing vortices, consistent with lateral and vertical displacement of the cores as they advect downstream and thus affecting maximum slipstream velocities.     

强脉冲电磁力驱动的冲击载荷

冲击载荷在材料科学与工程领域具有一定的应用。随着研究的深入, 对冲击速度、冲击能量提出了更高的需求, 是落锤所无法达到的。强脉冲磁场可由脉冲大电流产生, 通过合适的装置可产生强脉冲电磁力, 进而可转换为冲击载荷。通过数值模拟, 给出了强脉冲磁场、电磁力及冲头运动过程的数值模拟结果。采用高速摄像对该压缩冲击装置的运动过程进行记录, 通过对影像数据处理获得了冲击速度及冲击能量, 验证了模拟结果。     

弹体高速侵彻效率的实验和量纲分析

为了研究高速侵彻时弹体撞击速度、材料强度等对质量侵蚀特性和侵彻效率的影响规律,开展了不同材料强度和长径比的弹体高速侵彻半无限厚素混凝土靶实验,弹体撞击速度为880~1 900 m/s,弹头形状为尖卵型(半径口径比为3),口径为30 mm。由实验发现:弹体撞击速度对侵彻效率的影响呈抛物线分布,最大侵彻效率时的弹体特征撞击速度约1 400 m/s;高速侵彻时弹体的质量侵蚀主要发生在卵形头部,弹身及尾部损伤极少;速度超过特征撞击速度时,弹体侵蚀严重,甚至弯曲变形或解体;弹体强度提高至约2倍时,质量侵蚀率降低约80%。基于实验,利用量纲分析原则建立了量纲一侵彻效率和量纲一弹体撞击速度的函数关系式,可估算出最大侵彻效率对应的弹体撞靶速度,为高速侵彻效应模拟实验提供理论指导。     

铁路货车纵向载荷的试验测量和统计推断研究

通过线路测试得到我国通用线路C70货车车钩纵向载荷时间历程,利用雨流计数法得到车钩纵向载荷均值-频次谱。分别对我国通用线路C70货车车钩纵向载荷谱、大秦线C80B货车车钩纵向载荷谱、AAR90.7t漏斗车车钩纵向载荷谱及FMG矿石车车钩纵向载荷谱的分布特征进行分析,并对最大纵向载荷进行统计推断研究。研究结果表明:铁路货车最大纵向载荷随着轴重、牵引吨位的增大而增大。经纵向动力学仿真分析发现,单车轴重、牵引吨位、编组方式的不同是导致上述变化的原因。     

列车荷载作用下黏弹性半空间体的随机动力响应Dynamic response of viscoelastic half-space subjected to train loads

针对列车荷载作用下黏弹性半空间体响应的问题,利用虚拟激励法将系统的随机分析转化为确定性分析。根据列车荷载构造了相应的虚拟激励形式,通过傅里叶积分变换法把半空间体控制方程转入波数‐频率域,并推导获得了系统虚拟响应的积分形式解。当相速度接近或大于瑞利波速时,积分形式解中被积函数往往具有奇异性和高振荡性,使得数值计算相当困难。对此,将被积函数图形化以确定函数的积分限,并通过自适应数值积分算法解决被积函数的振荡性。数值算例中,进行了随机列车荷载作用下半空间体的响应分析,讨论了荷载移动速度及频率等参数变化对响应的影响,给出了响应的时间和空间分布规律。本文方法可进一步推广至移动矩形荷载等载荷模型,对移动荷载作用下环境振动行为预测具有很好的借鉴意义。     

Time-resolved measurement technique for pulsed electron beam envelope basing on framing and streaking principle

The time-resolved electron beam envelope parameters, including cross sectional distribution and beam centroid position, are very important for the study of beam transmission characteristics in a magnetic field and for verifying the rationality of the magnetic field parameters employed. One kind of high time-resolved beam envelope measurement system has recently been developed, constituted of a high-speed framing camera and a streak camera.It can obtain three panoramic images of the beam and time continuous information along the given beam profile simultaneously. Recently obtained data has proved that several fast vibrations of the beam envelope along the diameter direction occur during the front and the tail parts of the electron beam. The vibration period is several nanoseconds. The effect of magnetic field on the electron beam is also observed and verified. Beam debugging experiments have proved that the existing beam transmission design is reasonable and viable. This beam envelope measurement system will establish a good foundation for beam physics research.     

工艺参数对高铁轴承外圈端面成形质量的影响

为了实现高铁轴承外圈的精确成形, 应用ABAQUS有限元软件, 对不同工艺参数下的冷辗扩轧制过程进行了有限元模拟, 得到了工艺参数对高铁轴承外圈成形质量的影响规律为: 较大的驱动辊转速和芯辊直线进给速度有利于坯料上端面的成形, 较小的轧制比获得的坯料上端面成形质量较好.     

Discrete event model-based simulation for train movement on a single-line railway

The aim of this paper is to present a discrete event model-based approach to simulate train movement with the considered energy-saving factor. We conduct extensive case studies to show the dynamic characteristics of the traffic flow and demonstrate the effectiveness of the proposed approach. The simulation results indicate that the proposed discrete event model-based simulation approach is suitable for characterizing the movements of a group of trains on a single railway line with less iterations and CPU time. Additionally, some other qualitative and quantitative characteristics are investigated. In particular, because of the cumulative influence from the previous trains, the following trains should be accelerated or braked frequently to control the headway distance, leading to more energy consumption.     

Selective creation of maximum coherence in multi-level Λ system

We consider the creation of the maximum Raman coherence in the six-level Λ system using optimal control theory. Optimal fields are designed for different initial conditions, resonant, and off-resonant, using the Krotov method including a reference field into the cost functional. Suppression of the population transfer to the intermediate level is achieved via an additional functional constraint which depends on the system dynamics. We demonstrate that the spectrum of the optimised fields has major contribution from the corresponding resonant frequencies independently of the choice of carrier frequency of the initial guess field. We also indicate that the pulse train emerges as a solution of the control problem of coherence optimisation in multi-level quantum systems.