1.Railway Science and Technology Research and Development Center, China Academy of Railway Sciences Corporation Limited, Beijing 100081, China
2.Wheel-Rail System Laboratory, National Engineering Research Center of System Technology for High-Speed Railway and Urban Rail Transit, Beijing 100081, China
Under the disadvantage working conditions of wind load and cant deficiency, the running safety of high-speed trains displays complicated variation laws. Therefore, it is necessary to conduct in-depth research on the safety of curve negotiation of high-speed trains under wind load. Based on the combined analysis method of aerodynamics and vehicle dynamics, the transient wind load model, the aerodynamic model and the vehicle dynamics model of high-speed train under cross wind are established taking into account the changes in running speed, wind speed, the measured wheel rail profile, as well as the track irregularity. The variation laws of aerodynamic load of high-speed trains under different wind speed and running speed are analyzed. And the variation laws of key dynamics parameters of high-speed trains are studied when train negotiates large radius curves with different cant deficiency at different speeds, including derailment coefficient, wheel unloading ratio and wheelset lateral force. The influence of wind load and cant deficiency on the derailment and overturning of high-speed trains is studied. The results show that the change in lateral force coefficient caused by wind speed is greater than that of running speed; under the disadvantage working conditions of wind load and cant deficiency, the safety margin of vehicle dynamics performance will significantly decrease such as the wheel unloading ratio and wheelset lateral force. And the working condition of key suspension components of the high-speed train deteriorates, the displacement of secondary lateral stop increases rapidly and it is tightly compressed, the pressure difference between the left and right air springs also increases rapidly, and the safety margin of the vehicle’s dynamic performance significantly decreases.
在风致列车运行安全性研究方面,一方面研究较多的是列车在直线区段运行时通过桥梁、路堤、路堑以及隧道等不同线路条件时的运行安全性,常用方法有利用流体力学计算软件[6]、等效风载模型[7]等,计算得到风载作用下车辆的等效载荷,再将其作为外载荷作用于车辆的动力学模型上,基于此分析车辆动力学性能的变化规律;另一方面研究较多的是风载作用下列车的倾覆稳定性和脱轨安全性[8-9],根据脱轨及倾覆安全性限值,讨论列车在不同风速下的最高安全运行速度。除此以外,部分研究[10-12]发现:风载对高速列车临界速度有显著影响,风载作用下高速列车蛇行运动稳定性也逐渐得到关注。除直线区段以外,风载作用下列车通过曲线区段时的运行安全性也被作为一种典型工况进行专门研究[13-14],由于曲线半径、超高条件及通过速度等的不同,欠超高会与风载叠加对车辆的运行安全性产生综合影响,因此风载作用下高速列车的曲线通过性能较直线时表现出更为复杂的变化规律。德国针对汉诺威—柏林以及汉诺威—维尔茨堡间高速铁路上运行的ICE2型列车,在制定环境风限速条件时区分了直线和曲线2种工况,规定当风速在曲线区段不大于22 m · s-1、直线区段不大于29 m · s-1时,列车可以按运行图规定的速度(运营速度250 km · h-1)运行,可见在评估某条线路上车辆在风载作用下的运行安全性时,除考虑风速的影响外,还需要考虑曲线线型的影响。
为尽量降低网格密度对计算结果的影响,进行网格无关性分析。设置粗网格、中网格和细网格3组模型,网格数量分别为1 500万、3 500万和5 600万个,用于验证计算结果对网格密度的敏感性。选择车速400 km · h-1、风速10 m · s-1作为边界条件,得到不同网格模型的头车气动横向力系数计算结果对比见表1。由表1可知:以细网格为基准,粗网格和中网格横向力系数分别减小5.3%和4.4%,这2种网格模型均满足计算精度要求;但综合考虑计算效率和计算精度,中网格模型与细网格相比,偏差小于4.5%,可满足后续分析要求,因此选择中网格模型进行仿真分析。
对应表2中不同车速和风速组合工况下的横向帽子风计算结果如图8所示。由图8可知:350 km · h-1速度级条件下风速分别为10,12及15 m · s-1时,对应的横向气动力最大值分别为36.14,47.18及63.92 kN;400 km/h速度级条件下对应的横向气动力最大值分别为38.24,50.79及69.79 kN;420 km · h-1速度级条件下对应的横向气动力最大值分别为38.75,52.04及71.94 kN。
由表4可知:在10,12及15 m · s-1这3组风速条件下,随车速的增加侧向力系数呈减小趋势,减小的幅度相差很小。
由表5可知:在350,400及420 km · h-1这3组车速条件下,随风速的增加侧向力系数呈增大趋势,增幅基本一致。
综合表4和表5,对比分析9组车速和风速工况的结果,表明车速由350 km · h-1增大至420 km · h-1即增幅为20%时,引起的侧向力系数增幅为-21.00%~-20.90%;风速由10 m · s-1增大至12 m · s-1即增幅为20%时,引起的侧向力系数增幅为26.54%~26.58%。可见,在所分析的风速和车速对应的工况范围内,由风速变化引起的侧向力系数变化幅度大于车速,即风速的影响大于车速。
90°横风风速u、车速及矢量合成速度的关系如图9所示。图中:θ为合成侧滑角,,例如当风速为12 m · s-1、车速为350 km · h-1时,合成侧滑角为7.036°。
为评估各个工况下动车组的运行安全性和关键影响因素,首先按照GB 5599—2019《机车车辆动力学性能评定及试验鉴定规范》[17]规定的方法,对每个工况下头车的脱轨系数和轮重减载率2 m滑动平均值累计频次曲线对应99.85%的值进行统计,结果见表6。由表6可知:相比于脱轨系数,轮重减载率对风速和车速变化更加敏感;动车组以420 km · h-1速度通过7 000 m半径曲线时,欠超高达122.4 mm,当风速达15 m · s-1时轮重减载率高达0.740,接近减载率指标限值0.8;而动车组以相同速度通过8 000 m半径曲线时,欠超高达135.2 mm,当风速同为15 m · s-1时轮重减载率增大至0.782,安全裕量大幅下降;可见在曲线欠超高和风载的叠加作用下,动车组倾覆的危险大大增加。
3节编组动车组通过8 000 m半径曲线时,车速为350 km · h-1、风速为10 m · s-1和车速为420 km · h-1、风速为10 m · s-1及车速为420 km · h-1、风速为15 m · s-1这3组工况下的轮轴横向力经过2 m滑动平均后的对比结果如图12所示。由图12可知:当车速由350 km · h-1增大至420 km · h-1后,曲线欠超高由55.7 mm增大至135.2 mm,由曲线欠超高和车速增加共同引起的轮轴横向力2 m滑动平均最大值由19.97 kN增大至34.09 kN,增幅为70.7%;对应420 km · h-1速度级条件下,当风速由10 m · s-1增大为15 m · s-1后,由于风速增加引起的轮轴横向力2 m滑动平均最大值增幅为71.3%,且车速为420 km · h-1、风速为15 m/s条件下头车的轮轴横向力2 m滑动平均最大值为58.40 kN,接近轮轴横向力限值;可见,在曲线欠超高和风载的叠加影响下,除轮重减载率安全裕量降低,动车组倾覆风险增加外,轮轴横向力安全裕量降低也同样需要重点关注。
3节编组高速动车组以350 km · h-1速度通过半径为8 000 m曲线时,在无风载及不同风速情况下二系横向止档位移对比结果如图13所示。模型中,二系横向止档间隙设置为70 mm,其中弹性间隙为50 mm。由图13可知:在无风载仅有曲线欠超高和轨道不平顺激励影响的情况下,二系横向止档已发生弹性接触;叠加风载作用后,二系横向止档位移迅速增大,二系横向止档的工作状态接近压并,这也是图10中轮轴横向力较大的原因之一。
除了二系横向止档以外,对空气弹簧的工作状态也进行了监测,图14给出了3节编组列车以350 km · h-1速度通过半径为8 000 m曲线时,后转向架左右侧空簧压力差在无风载和不同风速情况下的对比结果。由图14可知:与图13中二系横向止档的工作状态一致的是,在有风载的情况下左、右侧空气弹簧压力差迅速增大;在风载和曲线欠超高叠加的不利情况下,车辆关键悬挂部件工作状态恶化。
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