|Title:||Acoustic resonators for noise control in enclosures : modelling, design and optimization|
|Subject:||Hong Kong Polytechnic University -- Dissertations.|
|Department:||Department of Mechanical Engineering|
|Pages:||xxii, 174 leaves : ill. ; 30 cm.|
|Abstract:||This work systematically investigates the acoustic interaction between an enclosure and resonators, and establishes systematic design tools based upon the interaction theory to optimize the physical characteristics and the locations of resonators. Both conventional Helmholtz resonators (HRs) and long T-shaped acoustic resonators (TARs) are considered. A general theoretical model is first established to predict the acoustic performance of multiple resonators placed in an acoustic enclosure of arbitrary shape. Analytical solutions for the sound pressure inside the enclosure are obtained when a single resonator is installed, which provide insight into the physics of the acoustic interaction between the enclosure and resonators. It is shown that, under the effect of the multi-modal coupling, the optimal location for the resonator installation is no longer an arbitrary point in the anti-nodal surfaces of the targeted enclosure mode. The theoretical model is experimentally validated using T-shaped acoustic resonators in a rectangular enclosure. Design examples are given to illustrate the control performance at a specific or at several resonances within a frequency band of interest. The measured reductions and variations of sound pressure levels inside the enclosure agree well with predictions, showing the effectiveness and reliability of the theoretical model. 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 to conduct the optimization. The dual process of the energy dissipation and radiation of the resonator is quantified. Optimal resistance of the resonator and its physical effect on the enclosure-resonator interaction are numerically evaluated and categorized in terms of frequency bandwidths. Predictions on the resonator performance are confirmed by experiments. Comparisons with existing models based on different optimization criteria are also performed. It is shown that the proposed model serves as an effective design tool to determine the optimal internal-resistance of the resonator in a chosen frequency band. Due to the multi-modal coupling, the resonator performance is also affected by its location besides its physical characteristics. When multiple resonators are used, the mutual interaction among resonators significantly impacts on the control performance and leads to the requirement of a systematic optimization tool to determine their locations. In the last part of the present work, different optimization methodologies are explored. These include a sequential design approach, the simulated annealing algorithm, and the genetic algorithm. Simulations show that three optimization approaches can all achieve good control performance to different extent. Simulated annealing algorithm and genetic algorithm outperform sequential design methodology since the sequential design procedure partially neglects the coupling effect between the newly inserted resonator and the existing ones. Optimization results reveal the existence of multiple optimal location-configurations of the resonator array. These optimal configurations are verified by experiments. Considering the plural nature of the solutions, engineering design criteria are also proposed. As an application, noise transmission control through a double-glazed window incorporating T-shaped acoustic resonators is experimentally examined. The large aspect ratio of T-shaped acoustic resonators makes it possible to integrate a TAR array into the spacer of the window, which relaxes the space requirement in implementation. Test results show a significant increase in the sound insulation capability of the window.|
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