Narrow Results

This paper presents a comprehensive study and it concludes that the resonance of forest trees with properly aligned conditions precisely working as naturally available locally resonant metamaterials that are equipped with wonderful capability of generating low frequency extremely wide bandgaps in the earthquake frequency range of interest. At the geophysical scale, the propagation of Rayleigh wave in the soft sedimentary soil basin experiences strong wave attenuation when the longitudinal resonant modes of trees are coupled with vertical component of the Rayleigh wave that mimic wave hybridization phenomena. A finite element-based numerical technique is adopted and we considered a total of 10 cases where spacing, height, thickness and mechanical properties of resonant trees are varied to study the Rayleigh wave propagation and attenuation mechanism. The trapping and/or mode conversion of Rayleigh wave by resonant trees is observed as dominant phenomena for wave attenuation. A time history analysis is conducted based on an actual earthquake record to validate the performance and efficiency of the bandgaps. The effects of ground stiffness, resonant tree mechanical and geometric properties on the bandgaps are also discussed. The study explores another peculiar characteristic of the forest trees that controls the propagation of seismic wave to protect a region from earthquake hazards. Our study may motivate the relevant organizations, authorities and global communities on the needs of forestation to reduce the earthquake catastrophe.

Functionally graded material (FGM) beams are widely used in engineering as moving components. Nevertheless, their generated vibrations usually become annoying. To realize multi-broadband vibration reduction of FGM beams, an enhanced multiple dynamic vibration absorber (EMDVA), which utilizes an amplification mechanism, is proposed in this study. The devices are periodically arranged on the FGM beams. The dispersion and vibration transmission characteristics of the structure are investigated using the energy method and nullspace technique. The accuracy of the model is verified using the finite element method. The effects of parameter on its vibration damping performance are also analyzed. Finally, the relationship between the amplification coefficient and the operating performance of the EMDVA is revealed in terms of both the impedance principle and the energy method. The results show that the amplification mechanism can amplify the stiffness, damping, and mass of the MDVA by a factor of square of the amplification coefficient. Therefore, the proposed EMDVA has a wider damping band and stronger attenuation performance compared to the conventional MDVA. This study provides a simple and easy-to-implement solution for multi-band vibration reduction in FGM beams, which is useful for the engineering application of FGM beams in vibration and noise reduction.

Two novel seismic metamaterials models, trophy and apple core, inspired by an ancient Chinese puzzle are proposed in this study. Bandgaps below 15Hz are achieved by exclusively using concrete as the base material in the designs. Vibration modes are investigated to clarify the bandgap formation. Through comparison, we found that under the same volume, the apple core model can provide a lower frequency bandgap than the trophy model. Results from transient simulations and band structures are in good agreement, validating the accuracy of the simulation results. To broaden the bandwidth, the radii of the apple core models are varied and arranged in a gradient pattern. Transient analyses using a Gaussian wave packet and Taiwan’s Chi-Chi earthquake dataset are conducted to verify the effectiveness of the gradient apple core seismic metamaterial.

Train vibrations are the primary concern in environmental engineering and civil engineering. It is significantly imperative to find new methods for reducing and isolating vibrations. The locally resonant metamaterials (LRMs) propose a novel method and concept for reducing train vibration. However, the accurate and quick design structures of LRMs based on vibration characteristics are still an issue. Thus, this study presents a novel inverse design model of three-component locally resonant metamaterial barriers (LRMBs) for vibration reduction based on deep learning. The bandgap characteristics and vibration modes of the LRMB are investigated by using the improved plane wave expansion (IPWE) and finite element method (FEM). Besides, the gradient-combined LRMBs are proposed based on time–frequency features of measured vibration caused by trains and the novel inverse design model, and a two-dimensional finite element model coupling with infinite element boundaries is established to study the reduction efficiency of the gradient-combined LRMBs. And the performances of different LRMBs are fully analyzed in time and frequency domains. The results show that the novel inverse design model can be successfully used to design the LRMB based on vibration features. Moreover, the gradient-combined LRMBs have better isolation performance.