浮置板轨道周期结构弹性波传播特性及异常多普勒效应

Characteristics of elastic wave propagation and anomalous Doppler effect in the periodic structure of floating slab track

浮置板轨道因其良好的减振性能被广泛应用于城市轨道交通中。为研究浮置板结构的弹性波传播模式,本文基于广义平面波展开法,对其特征方程进行程序求解,得到了无限周期结构的复频散曲线。发现在0至300 Hz范围内存在八个带隙,并提出了相应的理论分析。力锤激励试验也验证了带隙对弹性波的阻碍作用。根据波模式特性,发现双周期轨道结构的带隙形成机制与单周期轨道结构不同,即在双周期情况下,局部布拉格散射或局部共振无法阻止耦合弹性波的传播。频率-波数域的计算结果表明,异常多普勒效应发生在带隙范围,而常规多普勒效应发生在通带范围。

Floating slab track is widely used in urban rail transit because of its proven vibration attenuation and isolation performance.To investigate the elastic wave propagation in floating slab structure,the characteristic equation for wave dispersion is obtained using generalized plane wave expansion.Double periodicities from unit slab and fastener spacing are considered simultaneously.The complex dispersion curve of the infinite periodic floating slab track is obtained.Eight band-gaps are found to exist in the range from 0 to 300 Hz,and the corresponding theoretical analysis on wave dispersion is provided.An impact test was conducted,which verifies the band-gaps blocking effect on elastic wave propagation.Based on the wave-mode properties,it is found that the band-gap formation mechanism of track structure with double periodicities is different from track structure with a single periodicity,i.e.,the localized Bragg scattering or localized resonance modes cannot prevent the propagation of coupled elastic waves in the case of double periodicities.The results in the frequency-wave number domain demonstrate that anomalous Doppler effect occurs in the stopband range and the normal Doppler effect occurs in the passband range.