Schemes for Active Vibration Control of Plates

Abstract of Master's Thesis (December 1995)

In this thesis, which is motivated by recent developments in active structures, active schemes for controlling thin plate vibrations are investigated. Active structures, which find applications in aircraft, automobiles, rotorcraft, and other systems, can be realized using piezoelectric patches as distributed actuators to apply axial forces and bending moments. The mechanics of a plate-piezoelectric patch system is complicated by geometric discontinuities at the patch boundaries. The available approaches, all of which involve simplifying approximations, are examined and a suitable one is chosen to model a thin plate with symmetrically placed piezoelectric patches. Control studies are based on a finite-dimensional model obtained through a Galerkin projection. Velocity feedback, adaptive feedforward, and hybrid active control schemes are studied with the aid of numerical simulations. The choice of a suitable scheme depends on many factors including the disturbance profile. Here, a velocity feedback control scheme is used for transient disturbances, and an adaptive feedforward control scheme based on the conventional filtered-x LMS algorithm is used for persistent harmonic disturbances. A hybrid active control scheme, which combines the two schemes, is explored when both transient and persistent harmonic components are present. It is seen that the hybrid control approach is more effective than the other two approaches in handling a combined disturbance. Furthermore, the results indicate that when noise is present in the reference signal, hybrid control could offer an alternative to conventional feedforward control based on large filters, which are more expensive in terms of computational effort and time.