Numerical and experimental study of a sandwich-like metamaterial plate for vibration suppression

This paper presents the experimental validation of a numerical model for the prediction of subway induced vibrations. The model fully accounts for the dynamic interaction between the train, the track, the tunnel and the soil. The periodicity or invariance of the tunnel and the soil in the longitudinal direction is exploited using the Floquet transformation, which allows for an efficient formulation in the frequency-wavenumber domain. A general analytical formulation is used to compute the response of three-dimensional invariant or periodic media that are excited by moving loads.

Experimental validation of a numerical model for subway induced vibrations

Wave propagation in the ordered and randomly disordered periodic track structure in high-speed railways are investigated theoretically and experimentally. Taking the CRTS-I double-block ballastless...

Elastic wave propagation characteristics of periodic track structure in high-speed railway:

Phononic crystals that prevent the propagation of waves in a band gap have been widely applied in wave propagation control. In this paper, we propose 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, thereby improving mitigation of ground-borne vibrations. The locally resonant band gap properties of the metabarrier were studied based on the finite element method, and the shielding performance was verified by the transmission spectrum. Simplified models for band gap boundary frequencies were built according to the wave modes. Furthermore, a 3D half-track model was built to investigate the overall vibration mitigation performance of the floating-slab track with the metabarrier. An optimization mechanism for the band gap boundary frequencies is proposed. As the low-frequency ground-borne vibrations induced by subways carry the most energy, multi-objective genetic algorithm optimization was conducted to obtain a lower and wider band gap for a better shielding performance. The results show that 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. The vertical static stiffness of the metabarrier was close to that of the existing bearing of the floating-slab track. An optimized locally resonant band gap from 50 to 113 Hz was generated using the optimization mechanism.

Engineered metabarrier as shield from longitudinal waves: band gap properties and optimization mechanisms

Computational analysis of phononic crystal vibration isolators via FEM coupled with the acoustic black hole effect to attenuate railway-induced vibration

This paper presents the results of a study concerning the band-gap behaviours and formation mechanisms of periodic track structures. Based on the band-gap theories introduced from phononic crystal which concentrates on the elastic wave propagation in periodic structures, the railway track can be regarded as a novel locally resonant phononic crystal. The band-gaps are found by using the transfer matrix method combined with Bloch theorem, and the attenuation factors in band-gaps are also obtained firstly. Then, band-gap behaviours of periodic track structures are investigated with various parameters such as stiffness of rail pad, fastening spacing and thermal force in rail. Bounding frequencies and width of band-gaps are closely related to the parameters of track structures, resulting from the various wave motion modes at the bounding frequencies. Moreover, it has been found that Bragg band-gaps and locally resonance band-gaps coexist in periodic track structures. And formation mechanisms of band-gaps in periodic track structures can be explained by the Bragg scattering mechanism and locally resonance mechanism. The theoretical analysis is verified by the frequency response functions calculated through the finite element models at last.

Wave propagation in periodic track structures: band-gap behaviours and formation mechanisms

Excessive vibration and noise radiation of the track structure can be caused by the operation of high speed trains. Though the track structure is characterized by obvious periodic properties and band gaps, the bandwidth is narrow and the elastic wave attenuation capability within the band gap is weak. In order to effectively control the vibration and noise of track structure, the local resonance mechanism is introduced to broaden the band gap and realize wave propagation control. The locally resonant units are attached periodically on the rail, forming a new locally resonant phononic crystal structure. Then the tuning of the elastic wave band gaps of track structure is discussed, and the formation mechanism of the band gap is explicated. The research results show that a new wide and adjustable locally resonant band gap is formed after the resonant units are introduced. The phenomenon of coupling and transition can be observed between the new locally resonant band gap and the original band gap of the periodic track structure with the band gap width reaching the maximum at the coupling position. The broader band gap can be applied for vibration and noise reduction in high speed railway track structure.

Wave propagation control in periodic track structure through local resonance mechanism

A two-step approach is used to establish a numerical prediction model to study the impact of typical rail corrugation on ground vibration from an underground subway. In the first step, a vehicle-track-tunnel rigid-flexible coupling subsystem is established based on a lumped mass model dynamics and finite element analysis cosimulation method to simulate the generation of vibration. In the second step, a track-tunnel-soil three-dimensional (3D) finite element subsystem is built to simulate the propagation of the vibration. The ground vibration response is obtained by applying the wheel-rail force calculated from the first step. A section of Chengdu Metro Line 3 is studied, and the accuracy of the numerical prediction model is then verified by comparison with in-situ measurement. Based on that, the impact of corrugation on wheel-rail interaction and ground vibration is investigated by taking rail corrugation in typical subway sections and track geometry irregularities as system input excitation. In addition, to further analyze the sensitivity between different wavelength components in the rail corrugation samples and ground vibration, the measured rail corrugation is decomposed into five kinds with different wavelength components by filtering. The results show that the typical rail corrugation has a large impact on ground vibration response, which increases significantly in the range 8–16 Hz and 50–80 Hz, and the impact decreases with the distance from the vibration source. For typical subway rail corrugation with the significant wavelength of 125 mm and the secondary significant wavelength of 63 mm, the ground vibration response is sensitive to two wavelength components at 40–60 mm and 60–100 mm. Rail corrugation with the short wavelength of 60–100 mm significantly affects ground vibration levels.

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Xing Mengting

Papers

Wave propagation in periodic track structures: band-gap behaviours and formation mechanisms

Elastic wave propagation characteristics of periodic track structure in high-speed railway:

Engineered metabarrier as shield from longitudinal waves: band gap properties and optimization mechanisms

Wave propagation control in periodic track structure through local resonance mechanism

A Numerical Analysis of Ground Vibration Induced by Typical Rail Corrugation of Underground Subway