Active control of sound radiation due to subsonic wave scattering from an infinite or
a finite fluid-loaded plate excited below the critical frequency is analytically studied.
The disturbance is caused by a flexural wave in an infinite plate, or by a point force on
a finite plate at subsonic frequencies. The wave scattering is caused by discontinuities
on the plate or by the boundary conditions.
A feed-forward control approach is applied by implementing either point/line forces
or piezoelectric actuators on the plate. The amplitude and phase of control forces are
determined by the optimal solution of a cost function which minimizes the far-field
radiated acoustic power over a prescribed surface in the half space of the fluid field.
The results show that for subsonic excitations, high global reduction in radiated pressure
is possible with properly located active control forces. The number and location
of control forces employed in order to obtain high control performance are related to
the excitation frequency. The far-field sound radiation directivity pattern, the modal
amplitudes of the plate vibration, the plate vibration autospectrum in the wave number domain, and the near-field intensity distribution are extensively studied in order
to uncover the mechanisms of control.
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