| Available from UMI in association with The British Library. Requires signed TDF.; This project considers the vibratory response of a thin steel annular disc, and utilises the piezoelectric polymer polyvinylidine fluoride (PVDF) as an active control agent to attenuate this response. PVDF is a material widely used in the field of acoustics, but has only recently been considered for applications in active vibration control. Assessment of PVDF film, in this respect, represents an attempt to adopt the material as an alternative to conventional forms of active control, such as membrane stress techniques and electromagnets, and passive control devices such as viscous dashpots.; Modelling of the disc behaviour is achieved using Galerkin's method, with the effects of in-plane stress, shear stress, rotary inertia, passive layering and active layering being considered. The disc used in this project had become distorted during its manufacture; consequently, models are considered for determining the effect of this distortion. From a free decay response, the modal parameters are experimentally determined using the Sparse Time Domain method; reduction in the required analysis is achieved with identification of the disc modes from Fast Fourier Transform spectra of the response.; Modal control, a method which avoids the spillover effects associated with flexible structures, produces a control system, the complexity of which increases with the number of modes being controlled; consequently, this project utilises the actuator influence function to determine the feedback signal. In order to employ a time delay for phase shifting, the modal co-ordinates of the higher frequency modes are subtracted from the feedback signal. In this manner, eight modes can be subject to a control force, with only one feedback loop being required. The substantial reductions in vibratory amplitude, and corresponding increases in damping obtained, demonstrate that there is potential for the use of PVDF in active vibration control of lightly damped, flexible structures. |
