On Quality Factor Improvement in a NEMS Resonator With Nonlinear Damping

Nonlinear damping effects have been reported in experiments on nanoelectromechanical (NEMS) resonators and suggested as a pathway to improve the quality (Q) factors of the resonators. In particular, in a nonlinearly damped Duffing NEMS resonator operating in the hardening regime, it has been shown that white noise excitation can shrink the hysteresis region resulting in higher Q factors. In this paper the authors: (1) find that an analytical expression they previously derived using the method of harmonic balance for the frequency-amplitude relationship of a weakly-excited, nonlinearly damped Duffing NEMS resonator is valid for strong excitation, (2) show analytically and verify numerically that for constant values of the nonlinear damping coefficient, higher amplitude of forcing leads to increase in the resonant frequency, (3) find that white-noise induced stochastic parametric excitation can lead to enhanced Q factors and (4) show that decreasing the nonlinear damping coefficient leads to higher Q-factor. The results, in addition to being theoretically significant, are expected to be important in sensing applications using NEMS resonators.

Nonlinear Analysis of Shape Memory Devices With Duffing and Quadratic Oscillators

In this paper, we investigate the linear and nonlinear response of shape memory alloy (SMA)-based Duffing and quadratic oscillator under large deflection conditions. In this study, we first present thermomechanical constitutive modeling of SMA with a single degree-of-freedom system. Subsequently, we solve equation to obtain linear frequency and nonlinear frequency response using the method of harmonic balance and validate it with numerical solution as well as averaging method under the isothermal condition. However, for nonisothermal condition, we analyze the influence of cubic and quadratic nonlinearity on nonlinear response based on method of harmonic balance. Analysis of results leads to various ways of controlling the nature and extent of nonlinear response of SMA-based oscillators. Such findings can be effectively used to control external vibration of different systems.

Frictional Damping of Flutter: Microslip Versus Macroslip

Friction dampers are utilized in turbomachinery to reduce blade vibrations resulting from aeroelastic interactions. In this paper, the microslip friction model is applied to a blade with blade to ground damper and subjected to negative damping. Analysis using the describing function method, also known as the method of harmonic balance, is used to identify the behavior of the system and the maximum negative damping that can be stabilized by such a damper. These results are compared to those for the macroslip friction model.

Frictional Damping of Flutter: Microslip Versus Macroslip

Friction dampers are utilized in turbomachinery to reduce blade vibrations resulting from aeroelastic interactions. In this paper, the microslip friction model is applied to a blade with blade to ground damper and subjected to negative damping. Analysis using the describing function method, also known as the method of harmonic balance, is used to identify the behavior of the system and the maximum negative damping that can be stabilized by such a damper. These results are compared to those for the macroslip friction model.

Estimation of Local Delamination Buckling in Orthotropic Composite Plates Using Kirchhoff Plate Finite Elements

We analyse the buckling process of composite plates with through-the-width delamination and straight crack front applying uniaxial compression. We are focusing on the mixed mode buckling case, where the non-uniform distribution of the in-plane forces controls the occurence of the buckling of the delaminated layers. For the analysis, semi-discrete finite elements will be derived based on the Lèvy-type method. The method of harmonic balance is used for taking into account the force distribution that is generally non uniform in-plane.

Excitation-Induced Stability in a Bistable Duffing Oscillator: Analysis and Experiments

The excitation-induced stability (EIS) phenomenon in a harmonically excited bistable Duffing oscillator is studied in this paper. Criteria to predict system and excitation conditions necessary to maintain EIS are derived through a combination of the method of harmonic balance, perturbation theory, and stability theory for Mathieu's equation. Accuracy of the criteria is verified by analytical and numerical studies. We demonstrate that damping primarily determines the likelihood of attaining EIS response when several dynamics coexist while excitation level governs both the existence and frequency range of the EIS region, providing comprehensive guidance for realizing or avoiding EIS dynamics. Experimental results are in good agreement regarding the comprehensive influence of excitation conditions on the inducement of EIS.

Stability Analysis of Drill Rods as Shells in the Gas Stream

In the paper steadiness of the compressed and twisted drill rod is examined. The rod is presented in the form of a circular cylindrical shell, which is circulated from the outer side by a supersonic stream of gas. The rod is affected by the uniformly distributed on its length axial force and the torque. The problem of stability is solved by means of reviewing of a small deviation from the periodic solution of the problem. Boundaries of instability zones of the mechanical system are defined with application of the method of harmonic balance.