高弹扣件轨道车轮间振动波的反射对钢轨短波长波磨的影响

地铁线路使用高弹扣件的直、曲线段均出现严重的短波长钢轨波磨(25 mm^30 mm)。针对该问题,在时域建立多车轮板式轨道系统模型研究了车轮间钢轨振动波反射而引起的垂向动态轮轨作用力。轮轨之间非线性的滚动接触等效为二维接触模型,其中纵向滑移区内的磨损与切应力引起的摩擦功成比例。综合瞬时轮轨动力学、接触力学和轮轨的长期磨损,对单、多轮轨作用下高弹扣件地铁线路以及普通扣件线路中钢轨波磨的进化过程分别进行仿真,通过对比结果表明使用高弹扣件地铁线路钢轨短波长波磨异常增长主要原因是钢轨振动波在临近车轮间的反射使得垂向动态接触力剧烈波动而加速轮轨间的不均匀磨损。最后,调频钢轨吸振器(TRD)引入系统模型并分析了其对这类短波长波磨的抑制作用,仿真结果表明TRD可以有效缓解车轮间的振动波反射以及相关的短波长波磨的异常增长。     

螺旋波纹波导中的返波

从螺旋波纹波导的一般性耦合波传输方程出发,根据螺旋波纹波导的模式耦合规则给出该波导内返波的耦合波方程和色散方程并分析其色散特性,由此分析螺旋波纹波导返波管的工作机理,并通过耦合波理论计算出本征模式中场的分布情况.     

单面瓦楞机高速瓦楞辊齿形参数的优化设计

以瓦楞辊的运动学性能参数为目标函数,以齿形参数（ｒ１,ｒ２,Ｒ１,Ｒ２）设计变量,以ＭＡＴＬＡＢ语言工具箱为工具进行优化,得出在满足原纸最大张力、进纸速度、折楞率、齿形角、楞高等约束条件下的最优齿形参数。此结果对进一步研究瓦楞机的运动特性,优化工作性能提供了依据。     

山地城市地铁牵引与制动工况下钢轨波磨成因对比研究

目的 探究山地城市地铁牵引与制动工况下的钢轨波磨成因。方法 基于摩擦自激振动理论,结合山地城市地铁长大坡道区段现场调研,分别构建上坡牵引和下坡制动工况下车辆−轨道系统的动力学模型,对比研究长大坡道区段牵引与制动工况下车辆−轨道系统的动力学特性。分别构建对应区段的轮对−钢轨−牵引系统和轮对−钢轨−制动系统的有限元模型,并采用复特征值法对比研究山地城市地铁牵引与制动工况下的钢轨波磨成因。采用最小二乘法和粒子群算法提出抑制长大坡道区段钢轨波磨的车辆−轨道参数的最优解。结果 在轮对−钢轨−牵引系统中存在不稳定振动频率369.93 Hz,其复特征值实部为19.36。在轮对−钢轨−制动系统中存在不稳定振动频率443.92 Hz,其复特征值实部为4.970 5。结论 在牵引摩擦副与轮轨摩擦副的共同作用下产生的摩擦自激振动,在制动摩擦副与轮轨摩擦副的共同作用下产生的摩擦自激振动,分别是长大坡道牵引与制动区段钢轨波磨的主要诱因,且牵引区段发生的可能性高于制动区段。在制动工况下设置制动压力为5 kN,在牵引工况下设置牵引运行速度为80 km/h,并结合优化后的扣件参数,能有效抑制长大坡道区段钢轨波磨。     

如何减少铝锭表面波纹

铝锭表面的波纹,影响品质和价格,根据实验观察,波纹有同心圆状、泡状、两端波纹状三种形态,是振动引起的液态铝晃动而形成的。减轻波纹应从铸机本身和引起振动的外部因素着手,效果是明显的。     

THERMOHYDRAULICS OF LAMINAR FLOW THROUGH A CIRCULAR TUBE HAVING INTEGRAL HELICAL CORRUGATIONS AND FITTED WITH HELICAL SCREW-TAPE INSERT

The experimental friction factor and Nusselt number data for laminar flow through a circular duct having integral helical corrugations and fitted with a helical screw-tape insert are presented. Predictive friction factor and Nusselt number correlations are also presented. The thermohydraulic performance was evaluated. The major findings of this experimental investigation are that the helical screw-tape insert in combination with integral helical corrugations performs significantly better than the individual enhancement technique acting alone for laminar flow through a circular duct up to a certain value of the fin parameter. This research finding is useful in designing tubes carrying solar thermal mass of viscous oil in a parabolic trough solar collector used in environmentally sound and increasingly cost-effective solar thermal electric power plants. The result is also useful in designing heat exchangers used in process industries.     

偏振激光诱导的薄膜表面周期性自组织结构

本文研究了激光诱导的周期性表面结构(LIPSS)在聚甲基丙烯酸甲酯(PMMA)薄膜表面的形成过程。在导电玻璃衬底上制备得到PMMA薄膜,经p偏振的XeCl准分子激光照射后形成周期性的褶皱结构。用原子力显微镜(AFM)观察发现,形成的褶皱结构周期具有纳米量级,且当引入外加电场时,褶皱形成所需的激光脉冲数减少到2。当外加电压增加到30V时,褶皱的周期间隔明显减小,LIPSS变得不可控,出现了柱状的自组织结构。与直接用准分子激光照射的薄膜样品相比,外加辅助电压的引入改变了PMMA样品表面褶皱结构形成的时间和周期大小,褶皱形成的内部驱动力也发生了变化。     

EFFECT OF DISCRETE SUPPORTS OF RAIL ON INITIATION AND EVOLUTION OF RAIL CORRUGATION

The effect of discrete support of rail on the formation and evolution of rail corrugation is primarily investigated with numerical method in the situation of wheelset curving steadily and repeatedly. In the numerical analysis of corrugation it is considered that a combination of Kalker's rolling contact theory with non-Hertzian to be modified, a linear frictional work model and a vertical dynamics model of railway vehicle coupled with a curved track. And the uneven support stiffness of rail in the vertical direction due to discrete sleeper support and the different running speed of the wheelset are taken into consideration. The damage on the running surface of rail, concerning rail corrugation formation, is restricted to wear mechanism of rail material. The numerical results obtained indicate that the discrete supports of rail by sleepers have a great influence on the formation of the corrugation under the condition of non-zero and stable creepages of wheelset and track.