| CRTS?double-block ballastless track has been widely applied to the high-speed railway in China. Due to the relatively short paving and service time, currently, the research about its vibration performance and deformation characteristics is inadequate. In order to further optimize the design of the double-block track structure, and promote the relative technologies about vibration and noise reduction as well as damage detection and recognition, it is necessary to systematically research on the vibration performance in frequency domain and wave characteristics of the double-block track. In this dissertation, the Green's function method was used to systematically research on the vibration performance in frequency domain of the double-block track at first, and then the waveguide finite element method was adopted to have a relatively systematic research on the wave characteristics of the track.1. Research on vibration performance in frequency domain of double-block trackAccording to the structural characteristics of the double-block track, using the Green's function and superposition principle, the analytical model of the vertical vibration of the double-block track in frequency domain was established to analyze the responses of the double-block track in frequency domain and the influences of fastener stiffness, bedplate thickness and subgrade supporting stiffness on it, and the corresponding computational analytical program was compiled. The results show that there are three obvious peaks for the rail mobility which are caused by bedplate resonance ?35 Hz?, rail resonance ?200 Hz? and pinned-pinned resonance ?1 kHz?. The rail decay rate ranges from about 8 dB/m to less than 1 dB/m. Referred to the rail roughness value of 1×10-6 m, the rail velocity level reaches to the maximum value of 138 dB at the pinned-pinned resonance frequency, while the bedplate velocity level reaches to the maximum value of 126 dB at the wheel-rail coupling resonance frequency. Within the frequency range of less than 35 Hz, the bedplate mobility is determined by the bedplate supporting stiffness. Also the bedplate vibration decay rate increases with the increasing frequency, and the maximum value reaches to 0.001 dB/m. The bedplate resonance and wheel-rail coupling resonance have the most significant effect on the bedplate displacement. The frequency range where the rail high vibration decay rate lies gets wider with the larger fastener stiffness. Increasing the bedplate mass cannot attenuate its vibration in the mid-high frequency range.2. Waveguide finite element method and the corresponding program compiling for double-block trackThe waveguide finite element model of double-block track was established. The mathematical expressions of the waveguide plate element for bedplate, the waveguide eight-node solid element for rail and the spring-damper element were deduced as well as the solution procedures of free wave response and forced response for both the plate element and the solid element. The computational analytical program about the wave characteristics of the waveguide structures based on the waveguide finite element method was compiled. The adaptability of the waveguide finite element types was analyzed. It is suggested that the eight-node solid element is preferred to simulate the double-block track structure while modeling. The bedplate was set as the example to verify the correctness of the compiled computational analytical program by comparison with the Kirchhoff thin plate analytical model in the frequency range.3. Research on wave characteristics of rail ?wave characteristics referring to the causes, cut-on frequencies, propagation speeds, attenuation features, disappearance or transformation frequencies and influencing factors for waves in rail, etc.?The wave characteristics including the dispersion relation, phase speed, group speed and attenuation features were analyzed for rail. Also the characteristics of the mobility distribution for the rail cross-section were researched. Through the researches mentioned above, it is proposed that there are eight kinds of wave modes in rail within the frequency range of 6 kHz including the lateral bending wave A, the torsional wave B, the vertical bending wave C, the lateral bending wave D, the longitudinal wave/lateral bending wave E, the lateral bending wave/longitudinal wave F, the vertical bending wave/longitudinal wave G and the vertical bending wave H. The lateral bending wave A, the torsional wave B, the vertical bending wave C and the longitudinal wave/lateral bending wave E cutting on at low frequencies propagate across the whole frequency range, resulting in the different kinds of rail modes. The fastener supports result in the rail noise radiation from all kinds of waves in rail. At the cut-on frequencies, the decay rates of rail waves start to decrease sharply, and then the decay rates change to increase with the increasing frequency. Through the comparison between the waveguide finite element model and the Timoshenko beam model of rail, it is suggested that the Timoshenko beam model cannot reflect the high-order bending waves and the wave mode transformation phenomenon, so it is not suitable for the analysis of rail wave characteristics at high frequencies. The waveguide finite element model shows the superiority due to the fact that it includes the deformation features of rail cross-section.4. Research on wave characteristics of bedplateThe wave characteristics of bedplate and the mobility distribution for the bedplate cross-section were analyzed. And the variation regularities of wave characteristics of the monolayer bedplate and the integrated bedplate were researched as well as the influence of interlamination damage on the wave characteristics of the integrated bedplate. Through the researches mentioned above, it is proposed that there are ten kinds of wave modes in the monolayer bedplate within the frequency range of 1 kHz as well as in the integrated bedplate within the frequency range of 500 Hz. Within the frequency range of 1 kHz, the ten kinds of wave modes in the monolayer bedplate includes the zero-order vertical bending wave A, the torsional wave B ?the first-order vertical bending wave?, the second-order vertical bending wave C, the three-order vertical bending wave D, the lateral bending wave E, the zero-order longitudinal wave and the second-order longitudinal wave/shear wave F, the first-order longitudinal wave/shear wave G, the forth-order vertical bending wave H, the second-order longitudinal wave/shear wave and the zero-order longitudinal wave I, the second-order longitudinal wave/shear wave J. The integrated bedplate has the same wave modes as the monolayer bedplate including the zero-order, first-order, second-order and third-order vertical bending wave, the zero-order longitudinal wave and the second-order longitudinal wave/shear wave, the first-order longitudinal wave/shear wave. The integrated bedplate has two more kinds of wave modes which are not in the monolayer bedplate including the second-order longitudinal wave/shear wave and the zero-order longitudinal wave, the second-order longitudinal wave/shear wave. The mobility distribution for the bedplate cross-section is mainly affected by the vertical bending wave, and is not relative to the longitudinal wave and shear wave in the bedplate. The decay rates of the high-order waves in bedplate are higher than those of the four main waves ?the zero-order vertical bending wave A, the torsional wave B ?the first-order vertical bending wave?, the lateral bending wave E and the zero-order longitudinal wave and the second-order longitudinal wave/shear wave F?. When there is a damage between bedplate and supporting layer, the zero-order vertical bending wave, the first-order longitudinal wave/shear wave, the second-order vertical bending wave, the torsional wave ?the first-order vertical bending wave?, the zero-order longitudinal wave are the same as those in the integrated bedplate, but there is a big difference for the high-order waves. |
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