Active Control of Sound Transmission Into Three-Dimensional Enclosures
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The aim of this dissertation work is to understand active control of sound fields inside a three-dimensional rectangular enclosure into which noise is transmitted through a flexible boundary. To this end, analytical and numerical studies have been conducted. In the modeling efforts, a spherical wave excitation, which is generated by a noise source located in the near field of the flexible panel, is considered. Piezoelectric patches, which are bonded symmetrically to the top and bottom surfaces of the panel, are used as actuators. Microphones located inside and outside the enclosure serve as pressure sensors. The efforts account for panel interactions with both the external sound field and the enclosed sound field, and this feature makes it appealing for model-based active control schemes. The feasibility of implementing two zero spillover schemes for active structural-acoustic control systems has been studied through analysis and experiments. These schemes have been developed to ensure that spillover does not occur outside the control bandwidth. The numerical results are found to be in good agreement with the corresponding experimental observations; attenuations ranging up to 18.1 dB are experimentally obtained for narrowband disturbances and an attenuation of 8.3 dB is obtained for broadband excitation in the frequency range of 40 Hz £ f £ 230 Hz. The following contributions have resulted from this work: i) an analytical model capable of predicting the external pressure fields due to both the noise source and structural?acoustic interactions and that accounts for the general case of spherical wave propagation, ii) development of zero spillover, active structural-acoustic control schemes for controlling three?dimensional sound fields, and iii) a new relaxed zero spillover control scheme to ensure that the controlled response is bounded over the entire frequency range.