Active constrained layer damping of clamped-clamped plate vibrations

Surface damping treatments are often effective at suppressing higher frequency vibrations in thin-walled structures such as beams, plates and shells. However. the effective suppression of lower frequency modes usually requires the addition of an active vibration control scheme to augment the passive treatment. Advances in the technologies associated with the so-called smart materials are dramatically reducing the cost, weight and complexity of active structural control and make it feasible to consider active schemes in an increasing number of applications. In this paper, the authors present a numerical and experimental study of the application of active constrained layer damping to a clamped-clamped plate. Specifically. a passive constrained viscoelastic damping layer is augmented with an active scheme employing a PZT patch as the actuator. In the opening sections of the paper, emphasis is placed upon establishing a suitable model of the plate. Starting with an established finite element formulation it is shown how model updating and model reduction are required to produce a low order state-space model which can be used as the basis For active control. The effectiveness of the formulation is then demonstrated in a numerical study. Finally, in the description of the experimental study, it is shown how modes in the frequency range From 0 to 600 Hz are effectively suppressed: the two lowest modes (bending and torsional) through active control using only a single sensor and single actuator in the feedback loop, the higher modes(around 10 in number) by the constrained passive damping layer. The paper's original contribution lies in the experimental demonstration that given a sufficiently accurate model of the plate and passive constrained damping layer, together with a suitable active feedback control algorithm, spillover effects are not significant even when using a single sensor and single actuator. The experimental traces show. in some instances, minor effects due to spillover. However, it can be concluded that the presence of the passive layer introduces sufficient damping into the residual modes to avoid any major problems when using only the minimum amount of active control hardware. (C) 2001 Academic Press.