Study on the operational safety of high-speed trains exposed to stochastic winds

The characteristic wind curve （CWC） was com- monly used in the previous work to evaluate the operational safety of the high-speed trains exposed to crosswinds. How- ever, the CWC only provide the dividing line between safety state and failure state of high-speed trains, which can not evaluate the risk of derailment of high-speed trains when ex- posed to natural winds. In the present paper, a more realistic approach taking into account the stochastic characteristics of natural winds is proposed, which can give a reasonable and effective assessment of the operational safety of high-speed trains under stochastic winds. In this approach, the longitudi- nal and lateral components of stochastic winds are simulated based on the Cooper theory and harmonic superposition. An algorithm is set up for calculating the unsteady aerody- namic forces （moments） of the high-speed trains exposed to stochastic winds. A multi-body dynamic model of the rail vehicle is established to compute the vehicle system dynamic response subjected to the unsteady aerodynamic forces （mo- ments） input. Then the statistical method is used to get the mean characteristic wind curve （MCWC） and spread range of the high-speed trains exposed to stochastic winds. It is found that the CWC provided by the previous analyticalmethod produces over-conservative limits. The methodol- ogy proposed in the present paper can provide more signif- icant reference for the safety operation of high-speed trains exposed to stochastic winds.

Bifurcation\instability forms of high speed railway vehicles

The China high speed railway vehicles of type CRH2 and type CRH3, modeled on Japanese high speed Electric Multiple Units (EMU) E2 series and Euro high speed EMU ICE3 series possess different stability behaviors due to the different matching re-lations between bogie parameters and wheel profiles. It is known from the field tests and roller rig tests that, the former has a higher critical speed while large limit cycle oscillation appears if instability occurs, and the latter has lower critical speed while small limit cycle appears if instability occurs. The dynamic model of the vehicle system including a semi-carbody and a bogie is established in this paper. The bifurcation diagrams of the two types of high speed vehicles are extensively studied. By using the method of normal form of Hopf bifurcation, it is found that the subcritical and supercritical bifurcations exist in the two types of vehicle systems. The influence of parameter variation on the exported function Rec1(0) in Hopf normal form is studied and numerical shooting method is also used for mutual verification. Furthermore, the bifurcation situation, subcritical or supercritical, is also discussed. The study shows that the sign of Re(λ) determinates the stability of linear system, and the sign of Rec1(0) determines the property of Hopf bifurcation with Rec1(0)>0 for supercritical and Rec1(0)<0 for subcritical.

Development and validation of a model for predicting wheel wear in high-speed trains

目的:高速列车车轮磨耗过程非常复杂,涉及因素较多。本文旨在发展及验证一个高速列车车轮磨耗预测模型,对高速铁路轮轨型面设计、车辆悬挂参数设计、车轮镟修计划的制订及降低运营维护成本等具有非常重要的意义。创新点:1.建立一个包含车辆轨道动力学仿真、轮轨局部接触求解、车轮磨耗计算和型面平滑与更新策略的高速列车车轮磨耗预测模型;2.利用跟踪测试的高速列车车轮磨耗结果对预测模型进行验证;3.修正USFD磨耗函数,使得预测结果与实测结果更为吻合。方法:1.在SIMPACK多体动力学软件中建立CRH3型动车组拖车的动力学模型,对武广高铁的实际线路进行统计,采用统计的虚拟线路代替实际线路;2.利用Fa Strip进行轮轨局部接触求解;3.采用修正后的USFD磨耗函数进行车轮磨耗计算;4.利用现场实测数据验证模型的可靠性。结论:轮轨界面状态对车轮磨耗具有较大的影响;直接采用已有的磨耗模型进行车轮磨耗预测可能会导致一定的偏差,需要对其进行适当的修正才能获得较好的预测结果。