The research of acoustic waves is a long-time striving that lasts over centuries. The aspects of research, on the whole, consist of generation, propagation, detection, and perception. Acoustics offers challenges that are fundamental in nature and also broad in application. The thesis aims to find the proper design for the acoustic structures and devices based on optimization methods. Two independent works construct the whole content of the thesis: The first part aims to build an efficient way to realize acoustic invisibility in turbulence. The second part intends to construct a level-set-based topology optimization scheme for acoustic designs.

In the first part of the thesis, a refine acoustic invisibility theory was constructed. Most acoustic cloak designs are based on the stationary m...[ Read more ]

The research of acoustic waves is a long-time striving that lasts over centuries. The aspects of research, on the whole, consist of generation, propagation, detection, and perception. Acoustics offers challenges that are fundamental in nature and also broad in application. The thesis aims to find the proper design for the acoustic structures and devices based on optimization methods. Two independent works construct the whole content of the thesis: The first part aims to build an efficient way to realize acoustic invisibility in turbulence. The second part intends to construct a level-set-based topology optimization scheme for acoustic designs.

In the first part of the thesis, a refine acoustic invisibility theory was constructed. Most acoustic cloak designs are based on the stationary medium, which may be inaccurate in many practical applications with non-uniform flows. By using the constructed theoretical framework, the study describes the optimization of the acoustic cloaking performance as an active noise control problem. Then the optimized cloaking strategy is applied to airfoils in turbulent flows to demonstrate the capability of the proposed modeling for cases of practical importance. Also, it is found that the performance of the optimized cloak is insensitive to the frequency of the incident wave. The promising results suggest that an optimized cloaking design can effectively suppress the sound scattering, providing confidence with the mathematical framework for the potential aeronautics and marine applications.

The second part of the thesis aims to build a solid topology optimization scheme for acoustic design problems. The design targets include eigenfrequency, noise control, and sound transmission control. The optimized design's eigenfrequency exceeds 20,000 Hz for the acoustic guide channel study, ensuring good sound characteristics during the human hearing range. The second case is the balcony optimization design to enhance noise mitigation at the high building. Balconies can provide noise shielding for residents who live in high-rise apartment buildings by changing how noise propagates to the residential accommodation. The design of the shape of the balcony ceiling affects the performance of noise reduction significantly. Noise sources at both single and multi-frequency optimization are considered. The positive results in both the single and multi-frequency cases prove that the proposed design strategy can be widely used in various noise reduction applications in buildings and the environment. In addition, for the hornspeaker design, this thesis proposes an SPL-based objective function for the optimization. The transmission efficiency and directivity requirements can be realized simultaneously in the optimization.