Carra S., Amabili M., Ohayon R.

The active vibration control on a thin-walled rectangular plate representing a flexible wall of a Plexiglas container is experimentally investigated in the case of both empty and water-filled tank. The use of active control techniques in suppressing vibrations of very light structures is in fact of great interest in several practical applications. In particular, aeronautical and space structures often present thin walls containing fuel, where effects of fluid-structure interactions cannot be neglected. In this study, active control is tested in presence of broadband excitation between 0 Hz and 400 Hz, for both empty and completely water-filled tank. The studied plate has boundary conditions close to those of clamped edges. Five piezoelectric PZT actuators are glued on its surface in order to apply the secondary control input. In the past, after some preliminary modal analyses which were realized in presence of different water levels in the container, several control algorithms were experimentally applied by some of the authors on the studied system in presence of broadband or sinusoidal disturbance, using Single Input Single Output (SISO) or MultiSISO approach. In this work, the filtered-x Least Mean Square adaptive feedforward algorithm and the Direct Velocity Feedback technique are experimentally tested and their effectiveness is compared while using different kinds of error sensors and different conditions of collocation. In case of feedforward control, five accelerometers are firstly adopted as sensors in a nearly-collocated configuration; a laser Doppler vibrometer has then been used in order to measure velocities or displacements even in a perfectly-collocated position. In case of feedback control, a digitally implemented pseudo-integrator produces the required velocity signals from the measured accelerations. A laser Doppler vibrometer is also used in order to directly measure such velocities and to evaluate the variation of the stability properties of the control system in case of perfect collocation.