In this research, the passive damping and active control authority of several basic active-passive hybrid piezoelectric networks are analysed and compared. The comparison is performed in a nondimensionalized manner, throughout which the importance of the generalized electro-mechanical coupling coefficient is highlighted. It is concluded that these configurations yield very similar open-loop performance for the same electro-mechanical coupling. It is shown that larger electro-mechanical coupling leads to higher passive network damping and, depending on the design and configuration, could also derive better active authority and overall performance. A method of increasing the electro-mechanical coupling coefficient by using a negative capacitance circuit is proposed, analysed and experimentally verified.

In this paper, a new active constrained layer (ACL) configuration is proposed to improve the active action transmissibility of the current ACL treatment. Introducing edge elements, the active action from the piezoelectric cover sheet can be transmitted to the host structure more directly. Results from this study illustrate that, compared to the current ACL, the proposed new configuration can significantly improve the active action transmissibility while retaining a similar level of passive damping ability. In other words, it could be a more effective active-passive hybrid system. It is also shown that the new arrangement is more robust: it can outperform both the purely active and passive systems throughout a much broader design space than the current ACL.

Frequency-shift-based structural damage identification has been explored extensively in recent years. The performance of current practices, however, is still limited for several reasons, one of which is that the number of measurable modal frequencies is usually much smaller than the number of system parameters required to characterize the damage. In this study, the state of the art of frequency-shift-based damage identification is advanced by incorporating a tunable piezoelectric transducer circuitry into the structure to enrich the modal frequency measurements, meanwhile implementing a high-order identification algorithm to sufficiently utilize the enriched information. By integrating tunable piezoelectric transducer circuitry into the structure, we can introduce additional resonant peaks into the system frequency response function, and these additional peaks can be placed/adjusted over the frequency band by tuning the inductance. Clearly, a significantly increased amount of frequency shift information can be expected to reflect the damage effect. An iterative second-order perturbation-based algorithm in conjunction with an optimization scheme is then used to find the damaged-induced stiffness parameter reduction based on the system eigenvalue changes (frequency shift) before and after the structural damage occurrence. The major advantage of using this algorithm is that it takes into account the damage-induced mode shape changes without the actual measurement of the modes. In a benchmark example, a series of analyses using a cantilever beam integrated with a tunable piezoelectric transducer circuitry is carried out to demonstrate this proposed methodology and verify the performance. It is shown that the modal frequencies can be greatly enriched by inductance tuning, which, together with the high-order identification algorithm, leads to a fundamentally improved performance on the identification of single and multiple damages with the usage of only lower-order frequency measurements.

The objective of this research is to synthesize a simultaneous left and right eigenvector assignment (SLREA) method for active vibration isolation. It is a pioneering effort to utilize such an eigenvector assignment concept for active isolator design, where the approach can provide good physical insight into the problem. In this investigation, a new algorithm for the synthesis of the desired left eigenvectors is developed, which is an improvement over the classical methods. The purpose of the right eigenvector assignment method is to alter the closed-loop system modes such that the modal components corresponding to the concerned region (isolation area of the isolator) have relatively small vibration amplitude. Correspondingly, the design goal of the left eigenvector assignment is to alter the left eigenvectors of the closed-loop system so that they are as closely orthogonal to the system's forcing vectors as possible. With the proposed approach, one can achieve both disturbance rejection and modal confinement concurrently for the purpose of vibration isolation. In this research, a new formulation is developed so that the desired left eigenvectors of this integrated system are selected through solving a generalized eigenvalue problem, where the orthogonality indices between the forcing vectors and the left eigenvectors are minimized. The components of the right eigenvectors corresponding to the concerned region are minimized concurrently. It is shown that, with the SLREA technique, both disturbance rejection and modal confinement can be achieved, and thus vibration amplitude in the isolated region can be suppressed significantly.

This study explores the possible use of a magnetorheological (MR) damper with feedback linearization control law for helicopter lag damping applications. Since this control law is based on an assumed damper model, the helicopter may be susceptible to limit cycle instabilities in the presence of model errors due to uncertainties (even if the prescribed damping using feedback linearization control is greater than the system negative damping). For specified uncertainty bounds, a robust control law can be synthesized which will eliminate limit cycle instability by using a much larger value of prescribed damping ratio. The resulting periodic loads in forward flight, however, would be excessively high. To reduce these periodic loads a band-rejecting filter is introduced that eliminates the 1/rev component of velocity from the feedback control signal. By doing so, stability of perturbation motions can be ensured and periodic loads can be drastically reduced, even in the presence of MR damper model errors.