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Simulation and optimization of smart structures

Marakakis Konstantinos

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Summary

The scope of this thesis is to study the piezoelectric shunt circuits for the control of vibration and noise in various applications. Piezoelectric shunt systems consist of an electrical impedance, which in turn consists of a resistor, inductance (coil) or capacitance (capacitor) in any possible combination. Various types of such systems have been proposed in the literature for noise or vibration control for both single and multiple mode systems.The basic application concept of these systems is based on the ability to convert the dynamic energy of deformation of the structure (for example, a smart beam or plate) into electrical energy. Using the properties of the direct piezoelectric effect, this energy is fed into the electrical circuits of the shunt (for example in a resistor) where it can be partially consumed and converted into heat. For this purpose, transducers are used which are made of piezoelectric materials, as such materials exhibit excellent electromechanical coupling properties, as well as good frequency response.A detailed study has been done in the recent literature where several studies have been published on beams and plates coupled with shunt circuits. The tuning and optimization of such systems is carried out either during the design and placement of piezoelectric transducers or by improving and refining the electrical characteristics of the system, namely the values of resistance, inductance and capacitance. There are various applications of shunt systems in the literature, including structural noise control, oscillation control, application to hard disk drives, smart panels, etc.For the analysis and comparison of different techniques, an efficient and accurate finite element model for beam and plate with embedded piezoelectric patches was developed. A general methodology for modelling passive piezoelectric shunt circuits using the state-space method was also developed, with the possibility of extension to any type of structure with embedded or surface piezoelectric patches.Particle swarm optimization (PSO) and genetic (GA) optimization algorithms were applied to the theoretical models developed for the shunt parameters of the passive circuits. The design variables for single-mode control were resistor R and inductor L. While for the optimization of multi-mode circuits, besides resistor R and inductor L, capacitance C is introduced as a new design variable in multi-mode "current flow" circuits. The originality of using the capacitor as a new design variable had a significant contribution to the performance of multi-mode shunt damping.The computational results obtained from the proposed method were compared with published experimental results and with models from commercial simulation software packages.A study of the contribution of the quadratic electromechanical coupling coefficient on the performance of the application of shunted plate control was also carried out, where together with circuit optimization significantly increased the damping performance.The shunt circuits can also be used for energy harvesting in order to capture the small amount of energy necessary to make the system energy autonomous.Finally, in addition to the theoretical models developed, an experimental investigation of shunted piezoelectric circuits was carried out, where resonant circuits are connected through piezoelectric patches in a smart beam to control mechanical vibrations.

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