Abstract
Based on the capability of controlling low-frequency elastic waves in solids with subwavelength size, locally resonant phononic crystals have potential applications in track vibration reduction. By periodically embedding 3D locally resonant unit cells (LRUCs) in a concrete matrix, a wave-resistance sleeper with a negative effective mass density is proposed, and the generation mechanism of the bandgap and parameter sensitivity are studied. Furthermore, the vibration mitigation performance of the wave-resistance sleeper applied to the ballastless track is analyzed. The results show that the local resonance of the LRUC results in negative responses in the wave-resistance sleeper to the vibration excitation, and a bandgap is generated in this frequency range. By changing the elastic modulus of the coating or the core density, the boundary frequencies of the bandgap of the wave-resistance sleeper can be effectively adjusted, and the bandwidth can be expanded by increasing the ratio of core radius to coating thickness, or by increasing the filling fraction, and adopting a thinner steel spherical shell. The bandgap of the wave-resistance sleeper was verified by test results. Based on the local resonance mechanism, the wave-resistance sleeper can effectively prohibit vibrations at multiple design frequencies from transmitting to the track bed.
Highlights
The establishment of urban rail transit can greatly improve the travel efficiency and comfort of citizens and create substantial economic and social benefits
As the elastic wave spreading in locally resonant phononic crystal (LRPC) belongs to Bloch wave,32 and considering locally resonant unit cells (LRUCs) are arranged in the wave-resistance sleeper periodically, the Floquet periodic boundary constraint is added to the finite element model of the LRUC
It can be noted that the elastic modulus of the coating and the core density are two sensitive parameters affecting the boundary frequencies of the bandgap
Summary
The establishment of urban rail transit can greatly improve the travel efficiency and comfort of citizens and create substantial economic and social benefits. Phononic crystals (PCs), a kind of artificial composite material with periodic structure, are able to prohibit the propagation of elastic waves located in specific bandgap ranges.. The local resonance mechanism, the other basic mechanism for the creation of bandgaps, was proposed by Liu et al in 2000,3 and the application scope of PCs in the field of vibration and noise control engineering was further expanded as the lattice constant of the locally resonant phononic crystal (LRPC) could be almost two orders of magnitude lower than the wavelength of the elastic wave. In contrast to traditional vibration isolation methods applied in tracks, LRPCs inhibit propagation of vibrations with their bandgap properties, which has minor effects on the initial stiffness of the track. Using a finite element model of a half-track, the vibration mitigation performance of the proposed wave-resistance sleeper applied to the track system is discussed
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