|A general design strategy of acoustic resonators for noise control within low-frequency band
|Cheng, Li (ME)
Hong Kong Polytechnic University -- Dissertations
|Faculty of Engineering
|ix, 92 leaves : color illustrations ; 30 cm
|This work systematically investigates the acoustic interaction between the enclosure and resonators, and establishes general design strategies to optimize resonators for the best interior noise control. A general theoretical model is first established to predict the acoustic performance of multiple resonators placed in an acoustic enclosure of arbitrary shape. An analytical solution to the sound pressure inside the enclosure is obtained when a single resonator is installed, providing insight into the physics of the acoustic interaction between the enclosure and resonators. Simulations are performed to illustrate the control performance at a specific or several resonances within a frequency band of interest. Using the validated acoustic interaction model and the analytical solutions, the internal resistance of a resonator is optimized to improve its performance in a frequency band enclosing acoustic resonances. An energy reduction index is defined as the objective function for optimization. The dual process of the energy dissipation and radiation of the resonator is quantified. The optimal resistance of the resonator and its physical effect on the enclosure-resonator interaction are numerically evaluated and categorized in terms of frequency bandwidths. Considering that a tonal noise might not fall on any resonance frequency of an enclosure, as well as the shortage in the comprehension of the resonator effect at off-resonance frequencies, research efforts are conducted to account for the off-resonance cases. The transition of the control mechanism, for resonator tuned to, from resonance frequencies to off-resonance frequencies, is clarified which provides engineers a general design strategy for control of low-frequency noise in an enclosure. As an application, the noise control performance of a resonator in a manned spacecraft structure is experimentally examined. To more accurately model the coupled sound field within the structure, the patch transfer function method is utilized. A test rig is manufactured, with which various arrangements of resonators have been tested.
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