Browsing by Author "Azni Nabela Wahid"

Vibration control using piezoelectric (PZT) material has gained significant attention for its ability to behave as a sensor or actuator due to PZT direct and inverse effect. For control or excitation purposes, PZT patch actuator is embedded or attached on engineering built-up structures. Engineering systems such as aircraft, ships and automotive are considered built-up structures and dynamically they are thought of as being fabricated from many components that are classified as deterministic structure (DS) and non-deterministic structure (Non-DS). Adding a PZT actuator on a structure is equivalent to adding an external moment to the dynamics of the structure. However, the influence of adding input moment to a Non-DS is not fully understood due the complexity of the resulting wave; no mathematical representation has been established. In order to apply SEA method for input moments, a mathematical representation for moment generated by PZT patch in the form of average power is needed; so that a control system can be implemented. In this research, a simply-supported plate attached with a PZT patch is taken as a benchmark model. Ensemble average of power given by the PZT patch actuator to the plate when subjected to structural uncertainties is simulated using Lagrangian method and Monte-Carlo simulation. In addition, it is found out that the mathematical solution to estimate average power delivered to a structure can also be represented by mobility function. The findings of the research discovered that using moment mobility equation for a thin plate excited by a force couple, the power delivered by PZT actuator to a non-deterministic plate can be well-represented, particularly at high frequency range, therefore drastically cut computation time and cost. Parametric studies show that changing the patch location on the structure will not affect the ensemble average power supplied at high frequency. On the contrary, changing the patch size will change the power magnitude proportionally. In the second part of the thesis, the optimal gain values for a PZT patch controller in order to achieve maximum energy reduction for a non-deterministic thin plate is obtained using the Hybrid modelling method and mobility function. It is theoretically shown that by using larger numbers of point controllers on a Non-DS, better control effect can be achieved. A concluding remark can be made that findings from this research can be applied in SEA and the hybrid method used for analysing and vibration control of complex built-up structures.

Engineering systems such as aircrafts, ships and automotive are built-up structures fabricated from many components that can be classified as deterministic substructure (DS) and non-deterministic substructure (Non-DS). Non-DSs are subjected to short wavelength deformation, producing response that cannot be described mathematically using deterministic method. This makes vibration control effort difficult due to the combined modal response which produce no visible distinct peaks, with addition of the response being very sensitive to structural uncertainties. Piezoelectric (PZT) transducer connected to a shunt circuit is an attractive choice to attempt vibration attenuation of a Non-DS due to its ability to be fully passive thus ensuring stability, in addition of having high-strength and small-volume properties. Using Hybrid modelling equation (a method commonly used to model and analyse high-frequency vibration response), it is determined that to achieve maximum power dissipation from a Non-DS using PZT shunt damper, the shunt circuit needs to be designed such that the impedance is complex conjugate of its inherent capacitance parallel with impedance faced by the host structure at the connection area. In the first part of this research, the impedance faced by the Non-DS at the connection area is estimated using effective line mobility of an infinite thin plate under moment excitation by a square PZT patch using double integration of the infinite mobility which resulted to a hypergeometric function. The analytical model is compared with the average response of a randomized finite thin plate via Monte Carlo simulation which managed to significantly cut computational time to ~40 times shorter compared to using the finite method. Using findings from this part, the implementation of the designed shunt circuit using physical electronic components is carried out. One possible circuit configuration that closely resembles the theoretical impedance derived is realized by application of two negative impedance converters (NICs) utilizing op-amps, in order to replicate the circuit components with negative impedance values. Through parametric studies, it is shown that that the more PZT shunt dampers are attached to its non-deterministic host structure, the more energy can be dissipated from the system. By using different patch size for the shunt damper, it is shown that patch with larger size resulted to better energy reduction of the Non-DS; bearing in mind that cut-off frequency will occur earlier for bigger patch due to the bending wavelength limitation. Parametric study using different patch configuration shows that no conclusive difference can be seen for energy reduction of the plate when the patch is connected in series, parallel or independent. However, considering the complexity of the circuit needed to be designed when more patches are used for series and parallel arrangements, this work will focus on independent PZT shunt damper design where each patch is connected to its own shunt circuit. Experiments are conducted via real lab measurements or virtually using finite element software to validate the findings. From this research, the analytical solution for the optimal shunt circuit of a PZT shunt damper to attenuate the highest energy from a structure vibrating at high frequency range has been derived and shown. Findings from this research can serve as a guide for future researches in high-frequency structural vibration control.