Kozek M., Gusenbauer M., Höftberger F.

Plates with small structural damping are prone to considerable radiation of noise when excited with broad band vibrations. In order to avoid complex structural reinforcements or the addition of passive damping layers active damping using piezo materials become increasingly attractive. In this work the active damping of a quadratic plate using two piezo patch actuators is described. The elastic deformation of the plate is described by a modal model, which is derived from the analytical description as well as from finite element analysis. The latter procedure allows for future incorporation of more complex shapes of the plate. A numerical evaluation of an optimality criterion for placement of sensors and actuators defines the location for the piezo patches. A state-space controller is designed to add additional damping to the existing modes. Since only two sensor patches are applied to the structure a state observer has to be implemented to estimate the unmeasured states. Specific attention was paid to suppress spill-over (amplification of modes due to neglected dynamics), and a frequency response mode was added to account for the effect of higher-order modes. Simulation studies confirmed, that the bandwidth of the active damping system using state-space control is directly dependent on the number of actuators used. This theoretic prediction is due to the fact that the disturbance is non-collocated with the actuators. With two actuators in optimal positions only a small band of maximal two eigenmodes could be efficiently damped. Nevertheless, a mode at 167Hz showed an attenuation of over 17dB. Additional problems of the experiments were posed by the eigenmodes of the quadratic plate, which are very sensitive to small irregularities in shape. The relation between plate and sensor thickness is also critical, since the sensor must not detect membrane stresses.