Mechanism Of Vibration And Noise Reduction Of Additional Damping Treatment For Rail In High-speed Railway And Its Application

As the construction of high-speed railway developed rapidly in recent years,ballastless track has been widely applied on new-built high-speed railway in China with its advantages of better track regularity and less maintenance.However,due to the large stiffness of ballastless track slab,the huge vibration and noise caused by the runningtrain is hardly to be attenuated,which greatly reduces the ride comfort of passengers in the train and brings serious vibration and noise pollution to the environment along the route.At present sound-absorbing panel and noise barrier are generally applied in the noise reduction of high-speed railway during the transmission of noise.Those methods play a certain role in noise reduction,but could not reduce the vibration intensity and noise emission of wheel/rail fundamentally.Additional damping treatments for rail,such as constrained damped structure or dynamic vibration absorber(DVA),are effective measures for mitigating wheel/rail vibration and noise at the source with its advantages of excellent vibration and noise reduction properties,convenient installation and low cost.As the additional damping treatment has no influence on the clearance limitations,rail flaw detection,telecommunication system and train operation,they could be widely used in high-speed railway in a short term,which have great significance to the reduction of the vibration and noise pollution in high-speed railway and harmonious-sustainable development between high-speed railway and environment.However,so far the additional damping treatments for rail are only applied in some urban rail transit and normal-speed railway at home and abroad,whereas the application in high-speed railway is still blank.Aiming at controlling the wheel/rail vibration and noise in high-speed railway at the vibration(noise)source effectively,the mechanism,application and optimization design of additional damping treatment for rail in the vibration and noise reduction of high-speed railway are studied in this paper with the support from the National 863 Project of China(Grant No.2011AA11A103-3-1-2).The main contents and conclusions in this paper are summarized as follows:(1)Establishment of vibration and noise analysis model for rail-ballastless track on high-speed railwayBased on the Hamilton's principle,the rule of "set-in-right-position",theory of vehicle-track coupling dynamics and sequential FEM-BEM approach,the vibro-acoustic model for rail-ballastless track was established,including the damped rail and DVA.This model could simulate the real structure size and material characteristics of damped rail and DVA well,and take the influence of damped rail or DVA on the wheel/rail force into consideration during the calculation.Consistency of simulated results in this paper and measured or simulated results in existing research literature verified the correctness of the model established in this paper.(2)Study on the vibration and noise characteristics of rail-ballastless track in high-speed railway and sensitivity of its influence factorsWith the vibration and noise analysis model for rail-ballastless track,vibration transmission and acoustic radiation characteristics of rail and ballastless slab excitated by the high-speed wheel/rail force were analyzed,and the relationship between vibration and noise of ballastless track system were discussed through the hammer test.Based on the parameters sensitivity analysis method,the influence of those parameters of ballastless track system on its vibration and noise characteristics were analyzed.The simulations results show that the increase of rail mass can reduce the vibration and noise radiated by the ballastless track system.The stiffness and damping of fastener are all classified as insensitive parameters since they have little influence on the pinned-pinned resonance of rail,while the influence of fastener span and fastener failure is significant.The elastic modulus of slab has a great influence on its vibration and noise characteristics,and has a slight influence on the vibration and noise characteristics of rail in high frequency range.(3)Study on the mechanism of vibration and noise reduction of damped rail in high-speed railway and its parameters optimization design.With the vibration and noise analysis model for damped rail-ballastless track,the vibration and noise reduction properties of damped rail on ballastless track under high-speed wheel/rail force were analyzed.The influence of materials and structural design parameters of damped rail on its vibration and noise reduction properties was studied to provide suggestions for the optimization design of damped rail in high-speed railway.The research shows that when selecting or improving the damping layer material,the requirement on loss factor of damping material below 800Hz may be less stringent,and the loss factor corresponding to medium and high frequency can be further increased according to the demand of vibration and noise reduction.The improvement of performance of damped rail is reducing with the increase of the thickness of damping layer since it is thicker than that of constrained layer.Lighter weight and thinner alloy materials are recommend to be used as the constrained layer.Laying constrained damping on rail top flange,rail waist and rail bottom flange can obtain the best noise and vibration reduction efficiency,but it is also appropriate to lay the constrained damping only on rail waist and rail bottom flange when the requirement of vibration and noise reduction is lower.Ameliorating the structure type to increase the shear effect of damping layer caused by the vertical deformation of rail can improve the vibration and noise reduction property of damped rail effectively.(4)Study on the design methods and vibration reduction properties of DVA on rail in high-speed railwayBased on the fixed point theory and design principle of DVA on multiple degrees of freedom(MDOF)structure,two kinds of DVAs on rail were devised with the optimum design methods for minimizing displacement and minimizing acceleration respectively,and the vibration and noise reduction properties of the two kinds of DVAs were compared to provide a reasonable advice for the selection of design method for DVA on rail in high-speed railway.Through the analysis of the influence of mass ratio,stiffness coefficient and damping coefficient on the vibration and noise reduction properties of DVA,reasonable value of design parameters for DVA in high-speed railway were proposed.The results show that it is better to set the lowest limit for mass ratio of DVA as 0.15.The deviation between actual stiffness coefficient and its design value should be controlled within-20%?+20%,which could be broadened to-20%?+50%in some difficult conditions.The damping coefficient should not be less than 70%or more than 2 times of its design value.(5)Study on the vibration and noise reduction technology using damped rail and DVA simultaneously in high-speed railwayTo attenuate the vibration and noise of rail in a broad frequency band and mitigate the highest noise level of ballastless track effectively,the synthetical vibration and noise control method using damped rail and DVA simultaneously was proposed based on the optimum design principles of DVA for the MDOF damped main structure.And the adhesive safety between rail waist and damped structure was also analyzed.Simulation and in-suit test results show that with the train speed of 250?350km/h,the synthetical vibration and noise control method could reduce the sound pressure by more than 3.9dB(A)at a distance of 3m from track center and the same height with rail tread,and reduce the sound pressure by more than 3.0dB(A)at a distance of 7.5m from track center and a height of 1.2m above rail tread.The synthetical damping device can control the vibration and noise of the ballastless track system in the middle and high frequency range effectively,showing a satisfactory prospect of application in vibration and noise reduction of high-speed railway.