Balachandran, B. | Search NASA

NASA NTRS1996

Active Interior Noise Control Studies

Analytical and experimental investigations into the control of noise in the interior of a three-dimensional enclosure with a flexible boundary are presented. The rigid boundaries are constructed from acrylic material, and in the different cases considered the flexible boundary is constructed from either aluminum or composite material. Noise generated by an external speaker is transmitted into the enclosure through the flexible boundary and active control is realized by using Lead Zirconate Titanate (PZT) piezoelectric actuators bonded to the flexible boundary. Condenser microphones are used for noise measurements inside and outside the enclosure. Minimization schemes for global and local noise control in the presence of a harmonic disturbance are developed and discussed. In the experiments, analog feedforward control is implemented by using the harmonic disturbance as a reference signal.

Park, J.↗

NASA NTRS1992

On identification of structures with internal resonances

Identification of structures which exhibit modal interactions is considered, and the difficulties experienced due to these interactions are examined. Free oscillations of quadratically and cubically coupled pairs of oscillators are analytically studied to illustrate nonlinear interactions between structural modes involved in two-to-one and one-to-one frequency relationships. In light of this study, results obtained from application of the eigensystem realization algorithm toward identification of a beam-mass structure with a two-to-one frequency relationship and quadratic coupling are presented and discussed.

Balachandran, B.↗