Study On P2 Resonance Characteristics Of Metro Vehicle And Track System

With the continuous expansion of urban scale,major cities are actively building metro and other urban rail transit to ease traffic pressure.The development of urban rail transit has brought great convenience to residents’ daily travel.However,the vibration and noise as well as safety problems caused by the operation of metro vehicles have also attracted widespread attention.Wheel polygon and rail corrugation can aggravate the vibration of vehicle and track structure,which lead to serious vibration,noise and safety problems.P2 resonance frequency is one of the natural frequencies of vehicle/track system.It is considered as the resonance of unsprung mass and track mass on track elastic system.It can not only cause the occurrence and development of wheel polygon and rail corrugation,but also cause fatigue damage of vehicle and track components when the resonance occers in accordance with the natural frequencies of vehicle and track structure components,it is important to understand the P2 resonance characteristics of metro vehicle/track system for solving the vibration,noise and safety problems caused by P2 resonance.Based on the field investigation and numerical simulation of two metro lines(Line A and Line B),the P2 resonance characteristics of metro vehicles and track system are analyzed.The main research work and conclusions are as follows:(1)Through the analysis of the vibration acceleration of vehicle axle box,it is found that the P2 resonance frequencies of the four types track structures of line A are about 64 Hz,53 Hz,58-75 Hz and 66 Hz,respectively,corresponding to the monolithic concrete bed track with short sleepers,the monolithic concrete bed track with vibration damping fasteners,steel spring floating heavy slab track,steel spring floating light slab track.The P2 resonance frequencies of the three types track structures of line B are about 60 Hz,38 Hz and 34 Hz,respectively,corresponding to the monolithic concrete bed track with short sleepers,elastic short sleeper monolithic concrete bed track with 12 mm elastic pad,elastic short sleeper monolithic concrete bed track with 18 mm elastic pad.(2)Field test and analysis show that the excitation frequency of 5-8 order polygonal wear commonly existed on the wheels of the vehicles running on line A is consistent with the P2 resonance frequency,and that the rail corrugation generation of the monolithic concrete bed track with short sleepers of line B and the breakage of the primary steel spring of the vehicles running on line B may also be related to its P2 resonance.(3)The finite element model of the monolithic concrete bed track with short sleepers is established and validated.The influence of fastener stiffness and foundation stiffness on the first-order vertical bending frequency of rail is analyzed.It is found that the fastener stiffness has a greater impact on the first-order vertical bending frequency of rail,while the foundation stiffness has a smaller impact on the first-order vertical bending frequency of rail.Therefore,the fastener stiffness can be deduced by using the first-order vertical bending frequency of rail measured by field hammer-impact excitation based on Winkler foundation beam theory.(4)The finite element model of the unsprung mass and the monolithic concrete bed track with short sleepers coupling system is established.The influence of unsprung mass,fastener stiffness,foundation stiffness and sleeper spacing on the P2 resonance frequency is analyzed.The results show that the foundation stiffness has little influence on the P2 resonance frequency.The unsprung mass,fastener stiffness and sleeper spacing has a great influence on the P2 resonance frequency.The P2 resonance frequency decreases with the increase of unsprung mass,increases with the increase of fastener stiffness and decreases with the increase of sleeper spacing.(5)The finite element models of unsprung mass and track coupling system for steel spring floating slab track,elastic short sleeper monolithic concrete bed track and ballast track are established respectively.The influence of wheel and rail parameters on the P2 resonance frequency is analyzed.The results show that the unsprung mass,fastener stiffness and stiffness under sleeper have great influence on the P2 resonance frequency.The P2 resonance frequency decreases with the increase of unsprung mass,and increases with the increase of fastener stiffness and stiffness under sleeper.