An Electromagnetic Vibration Energy Harvester with a Tunable Mass Moment of Inertia

This paper presents a vibration-based electromagnetic energy harvester whose resonance frequency can be adjusted to match that of the excitation. Frequency adjustment is attained by controlling a rotatable arm, with tuning masses, at the tip of a cantilever-type energy harvester, thereby changing the effective mass moment of inertia of the system. The rotatable arm is mounted on a servomotor that is autonomously controlled through a microcontroller and a photo sensor to keep the device at resonance for maximum power generation. A mathematical model is developed to predict the system response for different design parameters and to estimate the generated power. The system is investigated analytically by a distributed-parameter model to study the natural frequency variation and dynamic response. The analytical model is verified experimentally where the frequency is tuned from 8 to 10.25 Hz. A parametric study is performed to study the effect of each parameter on the system behavior.

MODAL ANALYSIS OF MULTISTEP TIMOSHENKO BEAM WITH A NUMBER OF CRACKS

Modal analysis of cracked multistep Timoshenko beam is accomplished by the Transfer Matrix Method (TMM) based on a closed-form solution for Timoshenko uniform beam element. Using the solution allows significantly simplifying application of the conventional TMM for multistep beam with multiple cracks. Such simplified transfer matrix method is employed for investigating effect of beam slenderness and stepped change in cross section on sensitivity of natural frequencies to cracks. It is demonstrated that the transfer matrix method based on the Timoshenko beam theory is usefully applicable for beam of arbitrary slenderness while the Euler-Bernoulli beam theory is appropriate only for slender one. Moreover, stepwise change in cross-section leads to a jump in natural frequency variation due to crack at the steps. Both the theoretical development and numerical computation accomplished for the cracked multistep beam have been validated by an experimental study

Detection of Broken Strands of Transmission Line Conductors Using Fiber Bragg Grating Sensors

Transmission lines are affected by Aeolian vibration, which causes strands to break and eventually causes an entire line to break. In this paper, a method for monitoring strand breaking based on modal identification is proposed. First, the natural frequency variation of a conductor caused by strand breakage is analyzed, and a modal experiment of the LGJ-95/15 conductor is conducted. The measurement results show that the natural frequencies of the conductor decrease with an increasing number of broken strands. Next, a monitoring system incorporating a fiber Bragg grating (FBG)-based accelerometer is designed in detail. The FBG sensor is mounted on the conductor to measure the vibration signal. A wind speed sensor is used to measure the wind speed signal and is installed on the tower. An analyzer is also installed on the tower to calculate the natural frequencies, and the data are sent to the monitoring center via 3G. Finally, a monitoring system is tested on a 110 kV experimental transmission line, and the short-time Fourier transform (STFT) method and stochastic subspace identification (SSI) method are used to identify the natural frequencies of the conductor vibration. The experimental results show that SSI analysis provides a higher precision than does STFT and can extract the natural frequency under various wind speeds as an effective basis for discriminating between broken strands.

Inelastic Parametric Analysis of Seismic Responses of Multistorey Bidirectional Eccentric Structure

This paper conducts a parametric study on the seismic response of multistorey bidirectional eccentric structures from elastic stage to inelastic stage. Based on a simplified multistorey bidirectional eccentric model composed of bidirectional lateral load-resisting members, a general law is proposed for three-stage natural frequency variation behaviour from elastic stage to inelastic stage of eccentric frame structures with different layers. Different simplification treatments are conducted on each stage and the three stable parameter analysis stages are defined. The corresponding dynamic stiffness matrices and motion equations in different loading stages are derived. On this basis, a parametric analysis of seismic response of a three-storey bidirectional regular eccentric structure from elastic stage to inelastic stage is conducted. Effects of the uncoupled torsion to lateral frequency ratios (Ω) and bidirectional eccentricities on the seismic responses are investigated. The results reveal that as Ω increases, translational displacement in the load direction first decreases and then increases; meanwhile, the displacement perpendicular to load direction and torsion displacement first rise and then decrease sharply. When Ω=1.1, the coupling effect between the translation in the load direction and the torsion is at its strongest condition. Increasing the eccentricities leads to a decrease in the displacement in the load direction as well as an increase in the displacement perpendicular to load direction and torsion displacement. Variation regularity of inelastic seismic response is remarkably different from that in elastic stage. The lateral-torsional coupling effect of the bidirectional eccentric structure is closely related to both the period ratio and the bidirectional eccentricities.

Comparative study between positive position feedback and negative derivative feedback for vibration control of a flexible arm featuring piezoelectric actuator

Positive position feedback control is the most common resonant control technique that has been studied for last three decades. As a low-pass filter, positive position feedback is very sensitive to low-frequency disturbances. To overcome this shortcoming of positive position feedback controller, negative derivative feedback controller, which acts as a bandpass filter and can effectively control the lower and higher frequency disturbances, has been developed recently. So far, there is no comparison work between positive position feedback and negative derivative feedback on flexible manipulator system. Consequently, to fill this gap, in this article, both positive position feedback and negative derivative feedback controllers are applied experimentally and analysed in terms of settling time and vibration attenuation at different damping ratios on a single link flexible manipulator featuring piezoelectric actuator. Moreover, robustness with respect to natural frequency variation is studied for the first time on flexible manipulator system. Based on experimental study conducted on the particular system developed in this article, it has been observed that negative derivative feedback controller is more effective than positive position feedback controller based on evaluated performance measures.

Design Method to Achieve High Frequency Stability of Electrostatically Actuated Doubly-Clamped Nano-Oscillators

Frequency stability is a desirable property for micro- and nanoelectromechanical system oscillators used in reference and timing applications. In case of doubly-clamped oscillators, resonant frequencies are highly sensitive to the operating temperature because of development of internal stresses due to thermal expansion under the restraint of fixed boundary conditions. In this paper, we present a design procedure to reduce the variation of resonant frequency with respect to change in operating temperature, in other words improve the frequency stability, by exploiting the interaction between electrostatic and geometric nonlinearities in electrostatically actuated doubly-clamped nano-oscillators. We have modeled the nano-oscillators using Euler-Bernoulli beam theory and Galerkin based reduced order modeling technique. We have examined first natural frequency variation due to temperature change for different carbon nanotube oscillators and an optimization based design procedure has been devised for improving the frequency stability.

Effect on Vibroengineering of Material Deterioration in a Scale-Down Reinforced Concrete Containment Vessel Specimen

This study is aim to evaluate the natural frequency variation of the scale-down reinforced concrete containment vessel specimen under accelerated corrosion conditions. A plastic ring was sealed around the perimeter of the cylindrical vessel bottom with the 3.5 % NaCl solution to achieve the accelerated corrosion test. Concrete resistivity, open circuit potential, corrosion rate and natural frequencies were tested and discussed in this study. Test results presented that the accelerated corrosion method with a direct 60 voltage applied was a suitable method for estimating and accelerating the concrete vessel specimen. Therefore, the changes in natural frequencies were consistent with the material degradation of the concrete vessel specimen. The natural frequencies decreased with the increasing corrosion rate or decreasing resistivities for the specimen at higher mode, but would be no change for the specimen at the natural frequency of 1stmode.