Aerodynamic Characteristics Of Train-bridge Systems And Running Reliability Of Trains In Cross Winds

With the rapid development of high-speed railways in China,the proportion of bridges in the line is increasing,and the travelling environment of trains is becoming more and more complex.The train usually travels on the areas subjected to a strong wind,such as plains,deserts and Gobi,river-crossing and sea-crossing bridges,valleys and mountains,and it is common to occur the train overturning and delayed outage accidents caused by strong winds.To ensure the running safety of trains,the cross wind aerodynamic characteristics and operation reliability of high-speed trains where travel on the ground,box-girder bridge and long-span truss bridge are studied in this paper.The main works can be summarized as followed:(1)Based on the theory of Computational Fluid Dynamics(CFD),numerical models of cross-wind flow around a train on the ground,box-girder bridge and long-span truss bridge are established.Then,adopting the overset method which can be used to simulate the real movement of trains and considering the aerodynamic effect of a moving train,the aerodynamic characteristics of train-bridge systems in cross wind are studied and the aerodynamic coupling mechanism between the air and train-bridge systems is explored.Also,the CFD results are compared with those of the relevant literatures and scaled wind tunnel tests associated with a moving train to validate the accuracy of this numerical model.Finally,the cross-wind aerodynamic coefficients of the train and bridge are calculated and the fitting expression of the aerodynamic coefficient of trains at various resultant wind angles is given.(2)The interpolating approach from discrete fixed points and the single moving point simulation based on Taylor's "frozen" turbulence assumption are introduced to obtain the fluctuating wind velocity time history relative to a moving train,and the advantages and applicabilities between two approaches are discussed.Using the quasisteady theory and considering the aerodynamic weighting function effect,a calculation formula is developed to predict the unsteady aerodynamic forces on a moving vehicle in a complete turbulent field,which can present the effects of different turbulent components and various incoming wind directions.Through a numerical case,the effect of the aerodynamic weighting function on unsteady forces of a moving train in a crosswind is analyzed and also,the probability distribution of unsteady forces is discussed.(3)A vehicle model is established by the multi-body dynamics,and the bridge is modeled using the finite element method.Through the wheel-rail contact relation and taking the wind loads on the train and bridge into account,the wind-train-bridge coupled model is established.Considering the coupling effect between the moving train and cross wind,when a train travels on the box-girder bridge and long-span truss bridge respectively,the dynamic responses of the train and bridge are calculated.Moreover,the effects of various wind speeds and train speeds on the dynamic responses of the train and bridge are discussed,and finally,the running safety of trains on the bridge is analyzed.(4)With the use of the pseudo excitation method(PEM),the random vibration analysis model of the ground train is established to calculate the random dynamic response of trains under the wind turbulence and track irregularity,and through a numerical case,the effects of various wind speeds and train speeds on the power spectrum of vehicle response are investigated.Based on the first passage failure criterion,the cross wind stability evaluation model of high-speed trains is developed by means of the Possion crossing assumption,Markov crossing assumption and maximum response approach.Also,the failure probability curve of the train is calculated,and the effects of various wind speeds,train speeds and wind directions on the failure probability of a train are investigated.Furthermore,the probabilistic characteristic wind curve(PCWC)is given to ensure the running safety of the ground train in a crosswind,and finally,the probabilistic characteristic wind surface(PCWS)with a consideration of the wind direction effect is proposed.(5)The bridge deformation is considered as an additional track irregularity and an inter-system iteration method is applied to solve the wind-train-bridge coupled equation.The effects of wind loads,track irregularity and bridge deformation on the train vibration are investigated for typical cases where a train respectively travels on the box-girder bridge and long-span truss bridge.The extreme wheel-rail forces are estimated based on the Hermite moment model,and the failure probability curve of a train on the bridge is calculated through the dynamic reliability method.Also,the effects of various wind speeds and train speeds on the running reliability of a train on the bridge are investigated,and the PCWC is given to ensure the running safety of a train traveling on the bridge at different failure probabilities in cross wind.