考虑密封垫表面工作状态的盾构隧道接缝防水能力数值模拟研究

针对目前施工中盾构隧道防水密封垫经常出现粘贴不牢、沾水、不涂抹润滑剂等情况，构建了密封垫防水能力数值计算模型，将数值方法计算结果与常规计算结果进行对比，并对密封垫在底部与管片槽口粘贴、密封垫顶部涂抹润滑剂及沾水等多种工作状态下的防水能力进行研究。结果表明： 1）计算时是否考虑密封垫表面工作状态导致的闭合压缩力、平均接触应力结果差异分别为3.3%、23.9%，因此考虑表面工作状态的密封垫防水能力评估较为合理； 2）由于粘贴效应约束了密封垫底部的横向变形，其因此闭合压缩力及平均接触应力均大于不考虑底部粘贴效应的计算结果，影响值范围分别为31%~199%、0~245%； 3）密封垫顶部涂抹润滑剂能够减小闭合压缩力、增加接触面平均接触应力，影响值范围分别为4.7%~19.9%、6.5%~111%； 4）密封垫沾水时，闭合压缩力降低29.1%, 接触面平均接触应力降低8.7%； 5）在长期工作情况下，由于密封垫表面接触状态的变化，其平均接触应力整体呈下降趋势，最终下降约23.9%。     

The role of the contact geometry in wheel–rail impact due to wheel flats

A thorough investigation of wheel–rail impact due to wheel flats is presented, together with a quantitative characterization of the main mechanisms and parameters. A criterion for the speed with respect to contact loss between wheel and rail is derived. In the subcritical speed regime, the magnitude of the impact force is shown to be directly related to the geometry of the flat, whereas in the transcritical speed regime a fictitious or effective flat depth exists, which decreases with the second order of the speed. In this domain, the position of impact shifts towards the end of the flat with increasing speed. The impact force increases with the second order of the speed in the subcritical speed regime and approximately the first order of the speed in the transcritical speed regime. The magnitude of the impact force is inversely proportional to the minimum circumferential curvature of the wheel tread defect in the subcritical speed regime, and to the effective minimum curvature in the transcritical case. The variation with the flat depth is less; the impact varies with the square root of the flat depth. The presented theory is in accordance with measurements reported in the literature and explains characteristic features in them.     

A method for testing railway wheel sets on a full-scale roller rig

Full-scale roller rigs for tests on a single axle enable the investigation of several dynamics and durability problems related with the design and operation of the railway rolling stock. In order to exploit the best potential of this test equipment, appropriate test procedures need to be defined, particularly in terms of actuators’ references, to make sure that meaningful wheel –rail contact conditions can be reproduced. The aim of this paper is to propose a new methodology to define the forces to be generated by the actuators in the rig in order to best reproduce the behaviour of a wheel set and especially the wheel –rail contact forces in a running condition of interest as obtained either from multi-body system (MBS) simulation or from on-track measurements. The method is supported by the use of a mathematical model of the roller rig and uses an iterative correction scheme, comparing the time histories of the contact force components from the roller rig test as predicted by the mathematical model to a set of target contact force time histories. Two methods are introduced, the first one considering a standard arrangement of the roller rig, the second one assuming that a differential gear is introduced in the rig, allowing different rolling speeds of the two rollers. Results are presented showing that the deviation of the roller rig test results from the considered targets can be kept within low tolerances (1% approximately) as far as the vertical and lateral contact forces on both wheels are concerned. For the longitudinal forces, larger deviations are obtained except in the case where a differential gear is introduced.     

道岔区轮轨力转移与分配特性研究

道岔区复杂的轮轨接触状态决定了其轮轨力特性与一般线路相比存在较大的差异。利用空间轮轨接触几何关系理论和Hertz非线性弹性接触理论，研究道岔区车轮与同侧并列的2股钢轨同时接触的2点接触问题。依据2点接触时轮轨弹性压缩量计算每一接触点上的轮轨力，由此确定车辆侧向和直向通过时的轮轨2点接触范围以及轮轨力转移和分配特性。结果表明：2股钢轨上轮轨力转移和分配特性不仅与钢轨外形、轨顶高度和宽度有关，而且与车辆过岔方式有关；考虑轮轨2点接触后的计算方法，消除了单点接触轮轨力计算中轮轨接触点从一股钢轨转移到另一股钢轨上时引起的轮轨力突变，使得轮轨力变化更为平顺和真实。     

An investigation on wheel/rail impact dynamics with a three-dimensional flat model

Wheel flat is one kind of railway train wheelset defects. It has great influence on wheel/rail dynamics and damages. In most of the presented studies, wheel/rail impact velocity or rolling radius variation of the wheel because of flat spot was taken into account to study the wheel/rail impact dynamics. In this paper, a three-dimensional wheel flat model considering the length, width and depth of the flat spot is established. Including the wheel rotation and wheel/rail contact geometry, a high-speed vehicle–rail coupling system dynamics model is developed to investigate the effect of the wheel flat on the wheel/rail dynamics. With time integration method of the models, the impact dynamics of the wheel/rail system with three types of flat width and five kinds of flat length are obtained. The results show that the width, the length of the wheel flat and the width/length ratio have a great influence on the wheel/rail impact dynamics. The wheel/rail impact dynamics of the flat with large width is more severe than with small width as the flat length is fixed. When a flat spot occurs, the permissible length of the wheel defect, needless to action, is 25?mm in maximum. The speed safety domain with three kinds of flat width/length ratio of a vehicle is obtained according to the wheel/rail vertical force limitation.     

Simulation of dynamic interaction between train and railway turnout

Dynamic train-track interaction is more complex in railway turnouts (switches and crossings) than that in ordinary tangent or curved tracks. Multiple contacts between wheel and rail are common, and severe impact loads with broad frequency contents are induced, when nominal wheel-rail contact conditions are disturbed because of the continuous variation in rail profiles and the discontinuities in the crossing panel. The absence of transition curves at the entry and exit of the turnout, and the cant deficiency, leads to large wheel-rail contact forces and passenger discomfort when the train is switching into the turnout track. Two alternative multibody system (MBS) models of dynamic interaction between train and a standard turnout design are developed. The first model is derived using a commercial MBS software. The second model is based on a multibody dynamics formulation, which may account for the structural flexibility of train and track components (based on finite element models and coordinate reduction methods). The variation in rail profile is accounted for by sampling the cross-section of each rail at several positions along the turnout. Contact between the back of the wheel flange and the check rail, when the wheelset is steered through the crossing, is considered. Good agreement in results from the two models is observed when the track model is taken as rigid.     

预应力混凝土T梁在施工阶段的挠度和边界条件分析

为了研究预加力时的梁体变形,实施了预应力混凝土T梁桥试验,得到了梁体变形的实测数据;建立了与试验梁对应的有限元模型,并考虑梁体底面存在接触的实际情况,探讨了梁体张拉过程中的摩擦接触问题;通过有限元计算分析了梁体在张拉过程中的挠度变化规律,并提出了计算的基本假设.为了验证计算基本假设的合理性,运用静力法对施工梁体进行受力分析,推导了确定边界约束条件的表达式,并与实桥试验成果以及有限元计算结果相比较.通过理论计算确定的边界约束条件与实测结果基本吻合.在施工阶段,梁的挠度和边界条件主要与预应力钢筋线型、纵断面位置,预加力大小以及构件自重集度有关.通过分析推导,得到了直线配筋和曲线配筋情况下的边界条件.     

关于既有接触网大修中心锚结位置设置的探讨

通过对接触网大修施工中锚段长度及线路情况变化后，中心锚结位置如何重新设置进行了讨论，并得出了相关公式。     

粗集料接触参数对沥青混合料损伤演化的影响

为了揭示沥青混合料内部细观损伤对宏观性能的影响，基于DIC方法与四点弯曲疲劳试验，对不同粗集料接触状态的混合料细观损伤尺度效应进行研究。首先以颗粒堆积理论与粒子干涉理论为基础，提出可表征细观主骨架结构状态的颗粒接触主力链配位参数（n_pfc）计算方法。采用SAC设计方法，通过控制关键筛孔2.36~4.75 mm的分计筛余质量百分比，设计4组可反映不同粒径尺寸集料组合形式的SAC16级配（B60S00~B60S15），计算不同级配沥青混合料对应的npfc。其次，结合DIC方法与四点弯曲疲劳试验，分析疲劳荷载作用下沥青混合料小梁试件水平应变场演化特征，并提出混合料疲劳损伤因子定量分析方法。最后对不同粗集料接触参数的沥青混合料的细观损伤演化特征、疲劳损伤因子D_FD及表征宏观抗疲劳性能的K_m进行分析。研究结果表明：随着疲劳荷载作用次数的增加，4种不同n_pfc混合料的水平应变量逐渐增大，各D_FD也均显著增加；随着n_pfc的增大，D_FD明显减小，当n_pfc=7.73~9.55时，D_FD较小，混合料的疲劳细观尺度损伤叠加效应较小；同时，随着n_pfc增加，K_m呈先增大后略微减小的趋势；当n_pfc=7.73~9.55时，对应的宏观抗疲劳性能较好；因此，选取合理的n_pfc可优化沥青混合料内部主骨架细观结构状态，减少细观尺度损伤叠加效应影响，提高沥青混合料的宏观抗疲劳性能。     

遂渝线无碴轨道综合试验段低净空隧道接触悬挂方案与施工

对遂渝铁路无碴轨道综合试验段中出现的低净空隧道的接触悬挂方式进行探讨，采用方案优化比较选择的方法，对于类似的低净空隧道的处理提出了一些可靠，可行的方案，解决了遂渝线无碴轨道试验段的低净空隧道问题，取得了良好的效果。