雙質量共振地震超材料之實驗與數值研究

Abstract

地震超材料是一種源自光子晶體的週期性結構，透過其帶隙特性來衰減入射的地震波。帶隙是頻散曲線中的特殊特徵，在特定頻率範圍內不存在實數傳播模態。透過週期性排列單元晶格，入射波在這些單元晶格中會發生布拉格散射，導致波的破壞性干涉，從而形成帶隙。然而，地震超材料面臨的一個挑戰是，引入布拉格散射機制需要晶格常數與入射波長相近，導致其帶隙頻率對於減震應用而言通常過高。因此，學者偏向於引入局部共振機制，以設計單元結構的共振頻率來控制頻率帶隙。

大量研究已證實，共振地震超材料能有效產生低頻且寬帶的帶隙，並在此範圍內顯示出顯著的波傳衰減效果。利用彩虹效應或慣性放大等先進技術，可以進一步加寬這些帶隙。然而，在實驗部分，對於其實際應用的可行性和表現的研究仍然較少。因此，本研究旨在使用最近發展的雙質量共振筒型地震超材料來填補這一領域的空白。此超材料由泡綿包覆的木殼內插入混凝土內核，並以泡綿連接。所產生的帶隙對於地震應用足夠低，並且可以透過結構單元的材料性質進行調整。有限元素分析顯示，在該帶隙內具有良好的衰減效果，實驗研究也證實了這個結果。進一步的有限元素分析驗證了實驗中觀察到的機制和物理現象。

Stemming from photonic crystals, seismic metamaterials are periodic structures that attenuate incoming seismic waves through their band gap properties. The band gap is a unique feature in the dispersion curve, where no real (propagating) modes exist within a certain frequency range. By arranging periodic arrays of unit cells, the band gap can be created through destructive interference induced by the Bragg scattering mechanism. However, a challenge in developing seismic metamaterials is that the frequency band gap is often too high for seismic applications. Inducing this Bragg mechanism requires unit cell with periodicity length comparable to the wavelength. Therefore, researchers favor inducing local resonance mechanisms, where the frequency band gap is controlled by the resonance frequency of the designed unit cell.

Numerous studies have demonstrated the effectiveness of resonant seismic metamaterials in creating low and wide frequency band gaps with strong attenuation capabilities. Advanced techniques such as utilizing the rainbow trapping effect or applying inertial amplification can further widen these band gaps. However, not much research is developed in the experimental part to check the feasibility and capability in practice. Hence, this study aims to provide those aspects through the recently-developed dual-mass tube-type resonant seismic metamaterials containing a concrete inner core inserted inside a foam-enveloped wooden shell, connected by foams. The generated band gap is sufficiently low for seismic applications and can be adjusted through the material properties of the unit cell. Finite element analysis shows good attenuation within the band gap, and the experimental study corroborates these results. Further finite element analysis is conducted to verify the mechanisms and physics observed in the experiments.