Water-tank metabarrier for seismic Rayleigh wave attenuation.

An innovative concept of metabarrier is presented for seismic Rayleigh wave attenuation, which consists of a periodic array of cylindrical water tanks acting as resonant units above the soil surface. A pertinent theoretical framework is developed and implemented in COMSOL Multiphysics. The framework treats the dynamics of the water tank by a well-established three-dimensional linear, pressure-based model for fluid-structure interaction under earthquake excitation, accounting for the flexibility of the tank wall; furthermore, the soil is idealized as a homogeneous and isotropic medium. Floquet-Bloch dispersion analysis of the unit cell demonstrates the presence of relevant band gaps in the low-frequency range below 20 Hz and in the higher frequency range as well. The dispersion analysis is validated by comparison with the frequency-domain analysis of a soil domain with a finite array of water tanks. The band gaps are of interest to attenuate seismic Rayleigh waves and, more generally, Rayleigh waves caused by other ground vibration sources such as road or railway traffic. The water-tank resonant units are readily tunable by varying the water level, which allows changing opening frequencies/widths of the wave attenuation zones. This is a remarkable advantage over alternative seismic metamaterials that, in general, are not designed to be tunable.This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 2)'.

Current developments in elastic and acoustic metamaterials science.

The concept of metamaterial recently emerged as a new frontier of scientific research, encompassing physics, materials science and engineering. In a broad sense, a metamaterial indicates an engineered material with exotic properties not found in nature, obtained by appropriate architecture either at macro-scale or at micro-/nano-scales. The architecture of metamaterials can be tailored to open unforeseen opportunities for mechanical and acoustic applications, as demonstrated by an impressive and increasing number of studies. Building on this knowledge, this theme issue aims to gather cutting-edge theoretical, computational and experimental studies on elastic and acoustic metamaterials, with the purpose of offering a wide perspective on recent achievements and future challenges.This article is part of the theme issue, 'Current developments in elastic and acoustic metamaterials science (Part 2)'.

Current developments in elastic and acoustic metamaterials science.

The concept of metamaterial recently emerged as a new frontier of scientific research, encompassing physics, materials science and engineering. In a broad sense, a metamaterial indicates an engineered material with exotic properties not found in nature, obtained by appropriate architecture either at macro-scale or at micro-/nano-scales. The architecture of metamaterials can be tailored to open unforeseen opportunities for mechanical and acoustic applications, as demonstrated by an impressive and increasing number of studies. Building on this knowledge, this theme issue aims to gather cutting-edge theoretical, computational and experimental studies on elastic and acoustic metamaterials, with the purpose of offering a wide perspective on recent achievements and future challenges. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'.

On the Free Vibrations of Non-Classically Damped Locally Resonant Metamaterial Plates.

In this paper, the focus is on the free vibrations of locally resonant metamaterial plates with viscously damped resonators. Upon formulating a dynamic-stiffness model where the resonators are represented via pertinent reaction forces depending on the deflections of the attachment points, the complex eigenvalues are calculated by a contour-integral algorithm introduced in the literature for general nonlinear eigenvalue problems. The interest in the proposed approach is twofold. The dynamic-stiffness model involves a limited number of generalised coordinates compared to the nodal degrees of freedom of a standard finite-element model, and the contour-integral algorithm proves successful in evaluating all complex eigenvalues, without missing any one, with remarkable computational efficiency. Numerical results are presented for Lévy plates, but are readily extendible to other plate theories. Finally, an ad hoc dynamic-stiffness approach is formulated to calculate the frequency response of the plate under arbitrarily placed loads, which is of particular interest to investigate its elastic wave attenuation properties.