سيدهاشم مدحت صفوتي

The propagation of surface waves caused by earthquakes an‎d human-induced vibrations, especially those generated by railway transportation, is one of the major challenges in geotechnical earthquake engineering. Owing to their large amplitudes an‎d low-frequency content, these waves play a significant role in energy transmission an‎d can cause substantial damage to structures an‎d infrastructure systems. Conventional vibration mitigation measures implemented along the wave propagation path such as rigid barriers an‎d trenches are often costly an‎d show limited effectiveness in attenuating low-frequency surface waves. Therefore, seismic metamaterials, which can generate ban‎d gaps to suppress surface wave propagation within specific frequency ranges, have gained significant attention as a modern vibration control strategy. Motivated by the growing interest in seismic metamaterials, the present study introduces a one-dimensional seismic metamaterial for mitigating surface waves in soil media. The unit cell of the presented metamaterial consists of a New Jersey block an‎d a soil column. To investigate the effect of soil layering, both single- an‎d layered soil media are considered. The main advantages of this unit cell are its simple geometry, the availability of materials, an‎d feasibility for real-scale civil engineering applications. Numerical analyses are performed using the finite element method within a two-dimensional plane strain model in COMSOL Multiphysics. In the course of this study, the numerical modeling approach is first validated by reproducing an‎d comparing the results of two well-established seismic metamaterial structures. Subsequently, eigenfrequency analysis is conducted to obtain the dispersion curves of the unit cells, an‎d surface-wave ban‎d gaps are identified using two surface-wave separation methods: (i) a combination of the sound cone an‎d energy-based method, an‎d (ii) a combination of the sound cone an‎d the inverse participation ratio (IPR) method. Then, both frequency-domain an‎d time-domain analyses are conducted for cases with an‎d without a finite number of unit cells, an‎d the results are compared to verify the existence of ban‎d gaps an‎d eva‎luate the practical performance of the proposed metamaterial in mitigating surface waves. Finally, a series of parametric studies are carried out to assess the influence of the soil properties an‎d the geometrical dimensions of the New Jersey block on the position an‎d width of the ban‎d gaps. Two ban‎d gaps are observed at 8.63-11.26 Hz an‎d 12.72-15.61 Hz for the unit cell consisting of a surface New Jersey block an‎d a single-layer soil column, an‎d at 9.40-12.58 Hz an‎d 14.06-17.32 Hz for the unit cell consisting of a surface New Jersey block an‎d a layered soil column. In the frequency-domain analysis, the maximum reduction of vertical vibration amplitude reaches approximately 21 dB for the single-layer soil an‎d 17 dB for the layered soil. Additionally, in the time-domain analysis, reductions of 70% an‎d 55% in vertical displacements are observed for the single-layer an‎d layered soil profiles, respectively. Based on the obtained results, the proposed New Jersey-based seismic metamaterial offers an effective, feasible solution to surface wave attenuation in the low-frequency range (below 30 Hz) an‎d demonstrates high potential for implementation in real-world civil engineering projects.

فراماده‌ لرزه‌اي , امواج سطحي , دست‌كاري امواج , كاهش ارتعاشات

Seismic metamaterial , Surface waves , Wave manipulation , Vibration mitigation

Seyed Hashem Medhat Sefvati

Javad Sadeghi