Dynamic analyses of PZT based active nonlinear vibration absorbers

Abstract

"There are many physical systems such as engineering structures or machines which undergo severe vibration and need a reduction in vibration by using passive or active vibration absorbers. In the passive vibration absorber, structural modification is carried out by attaching an additional spring-mass-damper system to the vibrating main or primary system to reduce its vibration. Whereas in the active vibration absorber (AVA) various sensors and actuators are integrated with the passive vibration absorber to suppress the vibration of the primary system. The vibration absorbers are generally designed based on the assumption that the absorber structure possesses linear characteristics. However, an effective vibration absorber vibrates with a large amplitude leading to the dominance of structural nonlinearity. Thus, the linearity assumption regarding the elastic properties of the absorber substructure does not hold good in reality. Also, nonlinearity is inherently present in the main vibrating primary systems due to prolonged use, certain applications, or being subjected to various forms of external excitations. The available passive and active vibration absorbers also come up short to suppress the vibration in nonlinear primary systems under varied resonance conditions. Since the existence of nonlinearity in the primary systems and the absorber system are inevitable. It is observed from the literature that with the available passive or active vibration absorbers the vibration reduction of the primary system under varied resonance conditions is still high or limited to a very narrow range of operating frequencies. Also, complete vibration suppression of the nonlinear vibrating primary system is not achieved under various resonance conditions. The investigations of AVA with acceleration or combination feedbacks (displacement, velocity and acceleration) and its effectiveness in vibration suppression are also not explored. So, in the present thesis, a modified designed piezoelectric stack actuator based active nonlinear vibration absorber (ANVA) with various feedbacks and time delay is considered, where the frequency of the absorber can be actively changed to suppress the vibration of the primary system. In the modified designed ANVA the PZT (lead zirconium titanate) stack actuator is connected in series connection with a spring in the absorber configuration for a fail-safe design."