| Author: | Wei, Sheng |
| Title: | Vibro-acoustic modelling and development of a lightweight frame structure for sound insulation |
| Advisors: | Choy, Yat Sze (ME) |
| Degree: | Ph.D. |
| Year: | 2026 |
| Department: | Department of Mechanical Engineering |
| Pages: | xxiii, 161 pages : color illustrations |
| Language: | English |
| Abstract: | Controlling low-frequency airborne noise in lightweight panels presents a significant challenge in the field of acoustics, primarily constrained by the mass law and mass-airmass resonance (MAMR) in conventional double-wall systems. This study introduces a novel lightweight frame structure that integrates an inverted U-shaped frame with a host panel to form an air cavity, while strategically tunning radiation efficiency through the utilization of antisymmetric-like mode to enhance sound transmission loss (STL). The research aims to conduct an in-depth theoretical and experimental investigation into the vibrational and acoustic radiation characteristics of this U-shaped frame structure and its coupled system with the host panel. As the foundation of this research, this study first independently investigates the dynamic and acoustic radiation behaviors of the U-shaped frame structure. An acoustic radiation theoretical model was established to systematically analyze its natural frequencies, mode shapes, and vibration response and radiation efficiency under uniformly distributed force excitation. The results indicate that when the primary vibration direction of the panel is parallel to its surface (i.e., sway vibration), both the transverse vibration level and the corresponding sound radiation efficiency are significantly reduced. The sway structure exhibited a 43.5% reduction in maximum transverse displacement compared to a simply supported beam, while the maximum longitudinal displacement was adjusted to align with the transverse displacement levels. Furthermore, sway modes demonstrate lower radiation efficiency than simply supported beams due to their dipole-like sound radiation patterns. Consequently, the maximum sound pressure level of the sway structure was 7 dB lower than that of the simply supported beam. Building on this foundation, the dissertation thoroughly investigates the complete system formed by coupling the U-shaped frame with the host panel. A developed vibroacoustic coupling model reveals that, under sound excitation, the coupled system promotes anti-symmetric modes and sway vibrations on the panel, suppressing sound radiation through acoustic cancellation on the panel surface and converting bending vibration energy into longitudinal vibrations to reduce the overall system response. Within the target frequency band, the structure's average STL exceeds the mass law prediction and that of a double-wall system of identical height by 23.7 dB and 8.2 dB, respectively. To more accurately simulate an infinitely extended periodic structure, periodic boundary conditions were applied to analyze the unit cell's sound insulation potential over a broad frequency range. A key finding is the anti-resonance phenomenon arising from the frame-plate coupling, which minimizes the radiator response, resulting in near-zero normal displacement and exceptionally high dynamic effective density at the first STL peak. Parametric studies identify the geometric dimensions of the air gap between the frame and the host plate as critical for STL performance; increasing these dimensions enhances low-frequency STL primarily by shifting the MAMR to lower frequencies. After optimization using a genetic algorithm targeting the 200-1000 Hz range, the structure achieved average STL improvements of 7.9 dB and 10.2 dB relative to the mass law and the double-wall system, respectively. Since the sound insulation performance is highly influenced by structural modes, a non-uniform sub-configuration was designed to replace the original flat sub-configuration to better excite anti-symmetric modes. Within the 400-1050 Hz range, the non-uniform frame structure achieves an average STL that is 15.8 dB higher than the mass law prediction. In contrast, the uniform frame structure exceeds its corresponding mass law prediction by only 1.4 dB in the same frequency band. Parametric analysis demonstrates the critical influence of the non-uniform segment's length on the STL peak frequency, while extending the non-uniform segment's length further shortens the effective working band. This trend confirms that the optimization of sound insulation performance for non-uniform structures is achieved not through adding weight but through precise tuning of modal frequencies and vibrational energy distribution. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/14671