NASA Langley Res. Ctr., MS 463, Hampton, VA 23681-0001
Experimental results show that one can convert the nonlinear periodic motion of a panel structure to a linear one by controlling the system about the fundamental orbit through a time-dependent, phase-shift forced perturbation. An aircraft fuselage panel structure is forced at resonance by plane acoustic waves. Once the nonlinear response is triggered, the oscillation evolves through a sequence of subharmonic and harmonic bifurcations. The radiated acoustic pressure also contains harmonics whose level increases with distance relative to the fundamental. Control is achieved by actively forcing the panel either with a piezoceramic element or with an electrical shaker. Results show that the energy is transferred from the fundamental to the harmonics and vice versa as the response changes from linear to nonlinear and back to the linear state. An analytical model using a control linearization technique of Duffing's equation with periodic forcing is discussed.