Vibration control of a flexible structure using electromagnetic dampers

Abstract

This thesis presents both theoretical and experimental studies aimed at reducing vibrations in flexible structures using an electromagnetic damper. In recent years, semiactive vibration control systems have gained importance due to their ability to balance between effective vibration control and energy consumption compared to active control systems. Consequently, this research begins by exploring semiactive control strategies for the vibration control of the flexible structures.

A comprehensive investigation is conducted on vibration control of a SDOF structure using passive, active and semiactive control strategies. The effectiveness of each method is evaluated and compared. The passive and active control methods are introduced and compared with semiactive time-varying on-off control strategies. Numerical simulation demonstrates that the semi-active control provides better damping compared to the passive damping, although less effective than active control. In addition, the reviews of various active dampers such as magneto-rheological (MR) piezoelectric and electromagnetic dampers based on their ability to alter mechanical properties in response to external stimuli. The electromagnetic (EM) damper is the primary focus of this work, and its dynamic characterisation experimentally determined, confirming its potential for both active and semiactive control application.

The thesis further investigates the passive vibration control capabilities of an electromagnetic damper shunted damper with various RLC network. An analytical approach is used to evaluate the damping effects of purely resistive, RL and RLC shunt configuration. The optimal resistance values are evaluated using root locus method. The study extended by integrating the electromagnetic damper into primary structure- a cantilever beam modelled as SDOF system, where the EM damper functions as passive tuned mass damper under open circuit condition. While the passive TMDs are effective at suppressing vibration at specific resonant frequency that are limited to narrow bandwidth. To overcome this limitation, an electromagnetic damper tuned to the structural frequency is designed and evaluated. The performance of the tuned EM-TMD is compared with that of the conventional TMD, demonstrating enhanced vibration attenuation and improved adaptability.

The final part of the thesis focuses on active vibration control using electromagnetic dampers. The commonly used direct velocity feedback (DVF) control is implemented and evaluated. While DVF is effective at the fundamental resonant frequency, it offer limited suppression at other frequencies. To over this limitation, proportional resonant (PR) control is proposed and investigated. The PR control effectively reduces the vibration at resonance and can be tuned to specific resonant frequencies.

For numerical investigation, the beam is modelled as an SDOF structure. The vibration reduction performance of the PR controller is assessed for the various values of proportional gain, resonant gain, and damping ratio. Both time domain and frequency domain analysis are carried out, and the result shoes that the PR controller outperforms the conventional DVF control at the target resonance frequency.

In addition to numerical analysis, experimental validation is carried out using a cantilever beam equipped with an EM damper. The continuous-time PR controller is implemented on the dSPACE controller using its discrete-time equivalent. The experimental confirms the trend observed in the numerical analysis. The DVF control is also implemented experimentally to benchmark the performance of both strategies. Finally, the multimodal vibration control is achieved by placing multiple PR controllers in parallel, each tuned to distinct resonant mode. The experimental result shows that the proposed PR control strategy provides superior vibration suppression compared to the traditional direct velocity feedback control, especially for multi-mode vibration scenarios.

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Identifiers

ORCID for Suleiman Sharkh: orcid.org/0000-0001-7335-8503

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