多類型複合地震超結構之寬頻帶設計與分析

地震超材料（seismic metamaterial）或地震超結構（seismic metastructure）為一種使用在既有建物外部的隔減振方法，其概念最早起源於電磁波領域，目的在於利用超材料的特殊性質控制或影響電磁波，而隨著研究發展與超材料尺度的增大，使得超材料的應用範疇延伸到聲學以及彈性波等領域。雖然此概念仍舊處於理論階段，但不同於傳統的隔減振方法，地震超材料具有可以使用在既有的建物外部，還能保護一個較大的區域而非單一結構物等優點，所以在近幾年，這種用以衰減或導引地震波的方法成為諸多力學領域學者所研究的新興議題。在地震波低頻的特性下，許多研究利用同一種單元結構（unit cell）以週期性排列組成地震超材料，在地震波通過時，引發單元結構內部產生局部共振（local resonance）進而導致波傳的衰減，然而多數的研究成果只能阻擋部分頻段的地震波傳。本文以Krӧdel et al.[51]的理念為基礎，提出鋼材與橡膠組成的複合圓柱能夠藉由控制子材料的體積比改變地震超材料的帶隙範圍，經過多種帶有不同特定帶隙頻率的圓柱以六角結構排列後，其多類型的複合地震超結構能夠產生一般地震超材料無法達到的寬頻帶隙，根據彈簧質量體的離散（discrete）模型與連體模型的分析，數值模擬的結果確實驗證了位於帶隙範圍2～9.6 Hz的波傳能量能夠被有效的衰減。最後提出數個值得被探討與改進的方向，提高未來在實驗與實作上的可行性。

關鍵字

地震超材料；局部共振；帶隙

並列摘要

Metamaterial is a new type of composites made of artificially structured constituents, in which it exploits local resonances to attenuate or to block propagating waves well above the characteristic size of the material structure. The concept of metamaterials was first originated in the context of optics, and applied later to thermal conduction, to acoustic waves, and more recently to seismic wave. The underlying concept relies on the design of material structure, with suitable material constituents and geometric configuration, so that the coupling interference at frequencies near local resonances will result in attenuation of the propagating waves in ways not behaved normally. Seismic metamaterial, corresponding to long-wavelength and low frequency range, is challenging in that the band width needs to be sufficiently broad. In this work, following the concept of Krodel et al. [51], we propose to use a hexagonal array of composite cylinders, made of a stiff steel core surrounded with soft rubber. To obtain broadband attenuation characteristics, the volume fraction of each composite cylinder is suitably devised so that each individual layer of composite cylinders will correspond to a different bandgap. The array, constituted by multiple layers of metamaterial, will effectively behave as a medium with wave mitigation in the infrasound regime (2-9.6 Hz). Numerical simulations based on discrete model as well as full-scale continuum model will be studied. Our finite element simulations show that within the bandgap the wave energy can be attenuated substantially. Lastly we propose a few issues that could be further explored in the future. This will add to the feasibility of practical field test in the future.

並列關鍵字

seismic metamaterials ； local resonance ； band gap

國際替代計量

多類型複合地震超結構之寬頻帶設計與分析

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