Wave Propagation And Control In Periodic Railway Track Structure

Rail transit has played a key role in the economic development and social progress,however,with the substantial increase of the speed and operating density of railway lines,the dynamics of the vehicle/track interaction become more intense,causing structural vibration and noise radiation.The physical essence of structural vibration and noise is the propagation and coupling of elastic waves in the medium.The vibration properties of railway track structure can be further explained and new measures for the vibration and noise control can be proposed from the perspective of wave motion.In this dissertation,the periodic railway track structure is chosen as the research object,wave propagation properties and wave propagation control of periodic track structure are studied.The main research contents are as follows:1.Band gaps properties of periodic track structure.Based on the transfer matrix method,the periodic railway track structure models are established.The band gaps of different types of waves in track structure are obtained,and the influences of the parameters on the elastic band gaps are discussed.Combining with the band gaps theory of phononic crystal and the modal analysis of finite structure,the band gaps formation mechanisms of periodic track structures are revealed.In order to verify the pass band/ band gap properties,vibration transmission and power flow properties of the track structure are studied.It is found that the band gap is closely related to the rail axial force,thus,the rail axial force estimation is studied according to the standing wave modes are discussed theoretically and experimentally.The filed test and indoor experiment of the fastening are conducted to explain the different behaviors of the vertical and lateral wave modes with the change of temperatures.2.Wave propagation in three-dimensional periodic track structureAccording to the wave finite element method,the wave propagation in three-dimensional periodic track structure is studied.The modal confidence criterion is used for the separation of different types of elastic waves,and the coupling and transition behaviors of different waves are explained based on the wave modes.After determining the frequency at which the wave mode transition occurs according to the group velocity mutation of the dispersion curves,the band gaps of three-dimensional track structure can be obtained.Besides,the local resonant unit of the track structure is only coupled with a single type of wave in the rail,thus single coupling relation is formed.At last,the frequency response function can be calculated efficiently using the wave finite element method.The coupling and transition properties are verified according to the frequency response functions and the vibration transmissions properties under symmetric and asymmetric excitation are also clarified.3.Wave propagation in disordered or defected track structure.The localization factor is used to analyze the wave attenuation in disordered track structure.The wave propagation properties of vertical bending wave,lateral bending wave and torsion wave are studied and verified according to the vibration transmission coefficients obtained in the field experiment.Then,the Floquet transformation and supercell technique are used to established the model which consider the defects of periodic track structure.The common defect modes are extracted and formation mechanisms are discussed.Meanwhile,the periodic slab track model is also studied using the Floquet transformation which overcomes the numerical problem of the transfer matrix method.The band gap properties,formation mechanisms and the defect modes are also studied for the periodic slab track.4.Wave motion of track structure under moving train loadIn order to discuss the relations between the moving source frequency,response frequency and the wavenumber,the response of periodic track structure under moving source is derived in the frequency wavenumber domain.Combining with the dispersion curves and frequency response function of periodic track structure under moving harmonic load,the wave propagation in periodic track structure is discussed and the anomalous Doppler effect is found.Afterwards,the structural response and wave motion is analyzed when the excitation frequency is located in the band gap or the passband frequency range,and the conditions for the anomalous Doppler effect are obtained.Then,the transfer functions of track structure are obtained by wave finite element method and the train-infinite periodic track coupling model is established in the time domain,subsequently.Based on the model,the dynamic properties of wheel-rail force and parametric excitation under moving train load are studied.5.Wave propagation control in periodic track structureIn order to effectively suppress the wave propagation in periodic track structure,the local resonance mechanism is introduced to broaden the band gap and realize wave propagation control.The tuning of the elastic wave band gaps of track structure by local resonators is discussed,and the phenomenon of coupling and transition between the new locally resonant band gap and the original band gap of the periodic track structure is explicated.To further extend the bandgap range,the disordered parameters of local resonators and multi-frequency local resonators are introduced,and the effects of different band gap broadening methods on the elastic band gap of track structure are analyzed.