Study On Transmission Characteristics And Control Measure Of Railway Track Vibration

A series of problems occurs in the operation process of the Chinese railway industry,including track component damage and environmental vibration and noise,affecting healthy development of the railway industry.These problems are essentially caused by the track structure vibrations.By sorting out and summarizing relevant domestic and overseas research achievements,this thesis further studies transmission characteristics and control measure of track structure vibration.Main research contents and conclusions are stated as follows:1.Models and analysis methods of track vibration transmission researchA three-dimensional solid time-domain rail model is built to numerically simulate the hammer impact test,and the vertical vibration transmission characteristic of the rail is comprehensively analyzed from the perspectives of time domain,frequency domain and time-frequency domain.By imposing the periodic boundary conditions on both ends of the rail,periodic rail-substructure waveguide model is built,and the frequency-domain analysis is used to reveal the waveguide characteristic of the rail.A three-dimensional solid frequency-domain model of the steel-spring floating slab track is built.By combining with modal analysis and frequency-domain analysis,the vibration transmission characteristic of the steel-spring floating slab track is elaborated.2.Study on vertical rail vibration transmission characteristicBased on the three-dimensional solid time-domain rail model,the frequency response characteristic of vertical vibration is studied.Using the wavelet analysis,the time-frequency analysis of vertical rail vibration is conducted.In the meantime,the internal relation between time-frequency spectrum and receptance amplitude is explored.The force transmission rate,linear decay rates of time-frequency spectrum and receptance amplitude,and decay rate based on the standard are respectively calculated to reveal vertical vibration transmission characteristic.The influences of vertical fastener stiffness,vertical fastener damping and fastener spacing on receptance amplitude,force transmission rate and decay rate are analyzed.The results show that the reason of the peak existing around the first-order vertical rail bending resonance frequency in the mid-span direct receptance amplitude curve is that the relevant rail vibration has a large amplitude and a long duration,while the reason of the peak existing around the first-order vertical rail pinned-pinned resonance frequency is that the relevant rail vibration has only a long duration.Force transmission rate and decay rate within the low-frequency range are higher than those within the high-frequency range.3.Study on rail waveguide characteristicsBased on the periodic rail-substructure waveguide model,the waveguide characteristics of free,continuously supported and discretely supported rails below 6000 Hz are respectively studied.The dispersion relation curves,phase speed and group speed on different support conditions are calculated,and the wave mode shapes at different frequencies are drawn.The band gap properties of discretely supported rail below 6000 Hz are systematically analyzed,and the influence of discrete fastener support on wave mode shape is studied.The results show that eight propagating waves(denoted by A~H waves)have band gap properties.Within the frequency range of the band gap,the dispersion relation curve does not exist.Below 6000 Hz,A~G waves respectively have six,five,four,two,three,two and one band gaps,while H wave has none.The modes corresponding to the starting frequency and cut-off frequency of the band gaps are all related to rail pinned-pinned resonance.The discrete fastener support has different influences on mode shapes of each wave.4.Study on vibration transmission characteristic of steel-spring floating slab trackThe modal analysis of the steel-spring floating slab track is conducted,and the modal characteristic differences between the rail,floating slab bed and whole track system are studied.Based on the three-dimensional solid frequency-domain model of the steel-spring floating slab track,the frequency response characteristics of vertical track vibration on the conditions of two-rail excitation,one-rail excitation and one-rail excitation for the half-track model are calculated,respectively.The displacement and force transmission rates are used to explore the vibration coupling effect between track components and the vertical vibration transmission characteristic.The influence mechanism of track system modal on the frequency response characteristics of track components and the vibration transmission characteristic is elaborated,and the effects of relevant track parameters are also analyzed.The results show that the vibration coupling effect will form system resonance modals.With the increase of the frequency,the number of the system resonance modals gets large,and the vibration coupling effect becomes strong.There are peaks in the curves of displacement and force transmission rates around the natural frequencies of bending modal and torsional modal of the floating-slab bed.Thus,the vibration isolation performance of the floating-slab track is weakened.The displacement and force transmission rates within the low-frequency range are higher than those within the high-frequency range.5.Study on track vibration transmission control based on phononic crystal theoryThe phononic crystal theory is applied to the subway vibration mitigation.This thesis proposes the use of a metabarrier,based on a locally resonant phononic crystal mechanism,as a floating-slab track bearing to shield the infrastructure in a floating-slab track system from longitudinal waves from the slab.The wave modes and the band gap properties of the metabarrier are studied based on the finite element method.Simplified models for band gap boundary frequencies are built according to the wave modes.The shielding performance is verified by the displacement transmission rate.Furthermore,a 3D half-track model is built to investigate the overall vibration mitigation performance of the floating-slab track with the metabarrier.Based on the simplified models for band gap boundary frequencies and the multi-objective genetic algorithm optimization,the Pareto optimal set of key parameters are obtained,and the optimal solution is selected according to the field test result.The results show that the vertical static stiffness of the metabarrier is close to that of the existing bearing of the floating-slab track.The retained vibration isolation performance of the low natural frequency,the shielding performance of the band gap,and the controllability of band gap boundary frequencies all contribute to an improvement in overall vibration mitigation performance.An optimized band gap from 50 to 113 Hz is generated using the optimization mechanism.