### ASA 125th Meeting Ottawa 1993 May

## 3pSA4. Active control of nonlinear vibration of a panel structure.

**Lucio Maestrello
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*NASA Langley Res. Ctr., MS 463, Hampton, VA 23681-0001
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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.