Finite Element Harmonic Analysis Research Articles

A smoothly tunable shape memory metamaterial with adaptive bandgaps for ultra-wide frequency spectrum vibration control

This article presents a smoothly tunable shape memory elastic metamaterial with adaptive bandgaps enabling the broadband frequency vibration control. The underlying bandgap-tuning mechanism arises from the reversible large deformation induced by shape memory alloy (SMA) element under electro-thermal loads, through which, various microstructural shape morphing could be achieved. Via delicately designing the unit cell, the numerically obtained band structures and effective medium properties display a successful attainment of the vibration stop-passing band formation and smoothly controllable two-way tuning phenomenon for a series of transitional and intermediate status. The overall controllable frequency scope could be shifted over an ultra-wide band. Subsequently, a systematic parametric study is carried out to unfold the bandgap-adjusting patterns by altering the apparent structural stiffness and the SMA elastic modulus, individually. The finite element harmonic analysis of a metamaterial unit-cell-chain model is further investigated to verify the effectiveness of vibration suppression and the variability of the stopband region from the frequency spectra and the equivalent stresses images. Finally, the experimental demonstration is performed to validate the numerical predication from a practical perspective. The proposed design may possess enabling application potentials for future active vibration control and noise isolation in engineering facilities.

Selective guided wave mode transmission enabled by elastic metamaterials

This article presents the selective guided wave mode transmission enabled by elastic metamaterials. The metamaterial unit cells are comprised of Locally Resonant (LR) cylinders arranged in a periodic pattern bonded on an aluminum plate. Via a careful design, the band structure of the metamaterial system displays a complete bandgap for either symmetric wave modes or antisymmetric wave modes within different frequency ranges. A numerical-based effective medium approach is adopted to calculate the effective dynamic mass densities for in-plane and out-of-plane wave motions under the subwavelength requirement. The finite element harmonic analysis of a chain model further substantiates the selective mode transmission capability via the frequency spectrum of the transmitted wave modes. Finally, a coupled-field transient dynamic finite element simulation is carried out to acquire the dynamic response of the structure. The frequency-wavenumber analysis of the transmitted wave field illuminates the successful achievement of the selective mode transmission behavior. Experimental demonstrations are also presented to validate the numerical predictions. The proposed selective wave mode transmission control capability may possess great application potential in Nondestructive Evaluation (NDE) and Structural Health Monitoring (SHM). The paper finishes with summary, concluding remarks, and suggestions for future work.

Anchor Loss Calculation for Ring Shape Anchored Contour Mode Disk Resonators

Miniaturization is the most sophisticated method for achieving UHF and SHF resonance frequencies in RF MEMS resonators. However, by reducing the dimensions of the resonators, the size of their supports become more comparable with the size of the resonator and anchor loss becomes the dominant loss mechanism, thereby suppressing the quality factor. This study considers, Ring Shape Anchored Contour Mode Disk Resonator and calculates anchor loss effects using both energy loss and acoustic impedance ratio methods. Results of analytical calculations are verified using finite element harmonic analysis. Simulation results show that RSACMDRs have an acceptable quality factor in comparison with the other state-of-the-art resonators.

Generalized Finite Element-Harmonic Analysis for Nonlinear Heat Transfer

A numerical method is devised for the solution of nonlinear problems in bodies whose boundaries can be uniquely described in cylindrical coordinates. It provides a generalization of standard finite element (FE) Fourier analysis to nonlinear problems with asymmetric geometry and material properties. One class of problems in this category is that involving nonlinear steady-state heat transfer in a body with asymmetric geometry, thermal loading, and thermal properties. The proposed method combines FE discretization in a plane or interval and a symbolically implemented Fourier decomposition in the circumferential direction. Applications include space structures or structural members in space structures exposed to incoming solar heat flux and emitting thermal radiation