Active control of structural intensity and acoustic radiation of an infinite mindlin plate in an acoustic medium

by 1967- Won, Jungyun

In this thesis, the active control of the structural intensity and the radiated acoustic power is modeled by the use of an infinite Mindlin plate theory in contact with a heavy acoustic medium. Unlike the conventional Bernoulli-Euler plate theory, the Mindlin theory can predict the vibrational behavior accurately in the high frequency range. In the low frequency range, most of the mechanical power injected into the plate is confined to and travels in the plate. In the high frequency range, i.e., above the coincidence frequency, the mechanical power in the plate transfers to the acoustic medium. The plate is excited by either an infinite line force or a point force, and the corresponding expressions of the structural intensity are derived. One or several controllers on the plate control the structural intensity or the radiated acoustic power following the Steepest Gradient Algorithm. While controlling the structural intensity at a reference point in a line-excited plate, a line-force controller located at multiples of a half fluid-loaded structural wavelength from the source reduces the structural intensity in the far-field and at the reference point. The radiated acoustic power below the coincidence frequency is reduced when the controller is located within a quarter fluid-loaded structural wavelength of the source. Above the coincidence frequency, a controller located at a distance of multiples of a half fluid-loaded structural wavelength achieves larger reduction of the radiated acoustic power than controllers placed at other locations. The number of controllers becomes important when controlling the structural intensity or the radiated acoustic iv power from a point-excited plate. In order to achieve global reduction of the structural intensity, a system of four synchronous controllers should be located within a quarter fluid-loaded structural wavelength from the source. With the controller(s) at multiples of a half fluid-loaded structural wavelength, larger reductions of structural intensity are observed than when the controllers are placed at other locations. Significant radiated power reduction is achieved only with the controllers located within a quarter fluidloaded structural wavelength. v