Effects Of Sudden Change Of Wind Loads On Rail Vehicle Running Performance In Crosswind Conditions

When rail vehicles are operating in crosswind conditions, some artificial factors in the analysis may lead to sudden change of wind fluctuations on vehicles, or the local change of flow field around rail vehicles also may bring about the significant change of aerodynamic characteristics of rail vehicles. It will inevitably lead to sudden change of wind loads acting on running rail vehicles. Focusing on three types of sudden change of wind loads, the impacts of sudden change of wind loads on rail vehicle running performance in crosswind conditions are studied, and the turbulence characteristics relative to moving vehicles are investigated.Firstly, based on Hilbert-Huang Transform, the effects of simulation separations on time-frequency characteristics of wind field are discussed. And the probability density distribution of sudden change of wind fluctuations is displayed with probabilistic statistical method, addressing the effects of simulation separation, mean wind speed and vehicle speed on the sudden change of wind fluctuations. In addition, a three-dimensional rail vehicle model is set up with multibody dynamics theory. In order to demonstrate the influences of sudden change of wind fluctuations caused by artificial discrete simulation of wind field on rail vehicle dynamic performance, the kinetic simulation of high-speed rail vehicle under cross wind is performed. Furthermore, with Principal Component Analysis, the comprehensive evaluation of rail vehicle running performance in crosswind conditions at different simulation separations of wind field is investigated.Secondly, in order to avoid the sudden change of wind fluctuations or aerodynamic forces on moving vehicle caused by artificial discrete simulation of wind field, based on Taylor's frozen turbulence hypothesis and isotropic turbulence model, the auto-correlation coefficient function of lateral wind fluctuation and cross-correlation coefficient functions of lateral and longitudinal wind fluctuations at fixed points are derived from the longitudinal wind spectrum which specified in the wind-resistent design specification for Highway bridges. Furthermore, the correlation coefficient functions and power spectra of wind turbulence relative to moving vehicles are also deduced based on the same hypothesis. In addition, a closed-form expression is also proposed to approximately represent the square-root coherence function of wind turbulence relative to moving vehicles. The characteristics of wind turbulence relative to moving vehicles are investigated, addressing the effects of speed ratio of moving vehicle to mean wind velocity and the angle between vehicle direction and mean wind direction.Thirdly, focusing on the process of two trains passing each other on bridge deck in crosswind conditions, the side force coefficient and lift force coefficient of middle vehicle of leeward train are numerically fitted and the corresponding fitting equations are proposed to approximately represent the aerodynamic coefficients. The impacts of sudden change of wind loads on rail vehicle running performance in the process of two trains passing each other on bridge deck are investigated by the kinetic simulation. In addition, in order to investigate the influences of simplified aerodynamic forces on the dynamic responses of rail vehicle when two trains passing each other, the dynamic responses of rail vehicle are also obtained using simplified aerodynamic forces and the results are compared with those using the real aerodynamic forces.Finally, based on the test data of aerodynamic coefficients of rail vehicle obtained by the developed testing system of a wind tunnel test rig with moving train model, the impacts of sudden change of wind loads on rail vehicle running performance as the train passing through the wake of bridge tower in crosswind conditions are investigated by the kinetic simulation.The results of turbulence characteristics relative to moving vehicles indicate that, the spectrum shifts into higher frequencies and the energy in the range 0.2-4.0Hz increases with increasing speed ratio. It implies that the moving vehicle experiences higher wind energy at the frequency range of interest, thus leads to higher aerodynamic forces. The coherence function increased with increasing speed ratio of moving vehicle to wind velocity. That suggested that the wind fluctuations and thus the aerodynamic forces on moving vehicles were more correlated in space. Both the increases in coherence and the power spectrum contributed to larger aerodynamic forces and wind-induced vehicle vibration as the increasing speed ratio.The results of impacts of sudden change of wind loads on rail vehicle running performance indicate that, the sudden change of wind loads will threaten the running safety and comfort of rail vehicles in crosswind conditions. This is particularly true in cases when wind speed and/or vehicle speed are high. The adverse effects of sudden change of wind loads can not be ignored.