Ke-Xiang Wei

Time-Varying Frequency-Modulated Component Extraction Based on Parameterized Demodulation and Singular Value Decomposition

To analyze the valuable frequency component for time-varying frequency-modulated (FM) signals, component extraction is necessary in most applications. Considering the advantage of parameterized demodulation (PD) in transforming FM signals to be stationary, a novel component extraction method based on PD and singular value decomposition (PD-SVD) for both monocomponent and multicomponent signals is proposed. By extending the idea of PD, the time-varying term of the continuous phase function for the interested FM component can be removed, thus resulting in a highly self-correlated component with constant phase. Then, the extraction of the target component from noise or other components can be realized by SVD. Compared with the existing methods, the proposed algorithm is able to analyze the multicomponent signal with crossed instantaneous frequency trajectories and effectively improve the signal-to-noise ratio of the extracted component. The effectiveness of the proposed method is demonstrated by applying it on several numerical signals and the radial vibration signal of a hydroturbine rotor, indicating the potential of analyzing many practical FM signals.

Vibration Characteristics of Rotating Sandwich Beams Filled with Electrorheological Fluids

Dynamic modeling and vibration characteristics of a rotating sandwich beam filled with an electrorheological (ER) materials layer are investigated in this study. The stress—strain relationship for the ER fluids is described by a complex shear modulus using linear visco-elasticity theory. A dynamic equation of the rotating ER beam is derived based on Hamiltons principle. The coupling and nonlinear equation is discretized and solved by the finite element method (FEM). The influence of various electric field strengths and rotating speeds on the natural frequencies and damping loss factors of the rotating ER beam are presented. The amplitudes of vibration at different operation conditions are compared. The results obtained indicate that significant vibration attenuation is achieved as the electric field is increased at different rotating speeds, and demonstrate the feasibility of using the ER fluids to control the vibration of the rotating beam.

A broadband compressive-mode vibration energy harvester enhanced by magnetic force intervention approach

This letter presents a magnetic force intervention approach to enhance the performance of a broadband compressive-mode vibration energy harvester. The magnetic force intervention promotes a magnetic oscillator to vibrate within a desired work area. A magnetic stator drives the magnetic oscillator away by employing a repulsive magnetic force, while two magnetic stoppers (upper and lower magnets) limit the unwanted large displacement of the magnetic oscillator and drive it back toward the magnetic stator. Numerical and experimental results show that the performances of a compressive-mode bistable vibration energy harvester under low-frequency (<10 Hz) weak excitation can be significantly enhanced by using magnetic stoppers. Moreover, the magnetic force that acting against the magnetic stopper can also generate electricity.

Numerical Prediction of Surface Roughness Effect on Slip Flow in Gas-Lubricated Journal Microbearings

Development of micro rotating devices in microelectromechanical (MEMS) has introduced a kind of ultrashort self-acting gas-lubricated journal microbearing with small length-to-diameter ratios. A mathematical model for the slip flow in an ultra-thin-film gas-lubricated microbearing is developed with surface roughness effect. The random surface roughness characterized by fractal geometry and described with a Weierstrass-Mandelbrot (W-M) function is applied to represent the roughness of the bearing surface. A modified Reynolds equation considering a velocity slip boundary condition is derived. Numerical simulations are obtained for the microbearing under effects of rarefaction and roughness. The results indicate that roughness has a more significant effect on the properties of the gas-lubricated journal microbearings for MEMS applications.

Nonlinear Dynamics of an Electrorheological Sandwich Beam with Rotary Oscillation

The dynamic characteristics and parametric instability of a rotating electrorheological (ER) sandwich beam with rotary oscillation are numerically analyzed. Assuming that the angular velocity of an ER sandwich beam varies harmonically, the dynamic equation of the rotating beam is first derived based on Hamiltons principle. Then the coupling and nonlinear equation is discretized and solved by the finite element method. The multiple scales method is employed to determine the parametric instability of the structures. The effects of electric field on the natural frequencies, loss factor, and regions of parametric instability are presented. The results obtained indicate that the ER material layer has a significant effect on the vibration characteristics and parametric instability regions, and the ER material can be used to adjust the dynamic characteristics and stability of the rotating flexible beams.