| Author: | Ma, Li |
| Title: | Acoustic black hole plates for vibration and sound radiation mitigation |
| Advisors: | Cheng, Li (ME) |
| Degree: | Ph.D. |
| Year: | 2020 |
| Subject: | Hong Kong Polytechnic University -- Dissertations Vibration Sound-waves Noise control |
| Department: | Department of Mechanical Engineering |
| Pages: | xxvii, 217 pages : color illustrations |
| Language: | English |
| Abstract: | This thesis proposes an efficient, flexible and versatile 2D semi-analytical model for the vibration and sound radiation analyses of Acoustic Black Hole (ABH) plates. The proposed model, along with the associated wavelet-based solution procedure, is intended to overcome major technical difficulties which are specific to ABH structures: the non-uniform wavelength distribution and ABH-induced wave compressions at the high frequency range in a realistic structure of finite size. Under the general Rayleigh-Ritz framework, Daubechies wavelet (DW) scaling functions are used for expressing the transverse displacement of the ABH plates. The accuracy of the propose model is thoroughly validated using Finite Element simulations and experiments. Results show that the model allows an accurate prediction of various vibration and sound radiation parameters and provides a truthful description of the typical ABH phenomena. Vibration analyses on the ABH plates show a drastic increase in structural damping, by using only a small amount of damping material. ABH local modes are shown to be dominant in the damping increase which leads to remarkably reduced vibration responses above the cut-on frequency. Meanwhile, ABH plates exhibit broadband sound power and sound radiation efficiency reduction, compared with uniform plates. Below the critical frequency, the reduced radiation efficiency is caused by the weakening of the structural stiffness due to the ABH indentation. Above the critical frequency, a subsonic region inside the ABH cell containing acoustically slow structural waves may appear. This region, confined within a transonic boundary, is due to the ABH-specific phase velocity reduction of the bending waves. Visualization of the supersonic acoustic intensity allows identifying the effective sound radiation regions of ABH plates and their relationship with the transonic boundaries at different frequencies. Sound radiation analyses show that damping layers also increase the sound radiation efficiency of ABH plates due to their additional stiffness. The conflicting effect of damping layers in the increase of both structural damping and sound radiation efficiency calls for a balanced and meticulous design of their deployment to draw the best possible vibration or acoustic benefit. To tackle the problem, by combining the proposed model with an optimizer, the sound radiation of an ABH plate into a free space is minimized through adjusting the damping layer layout. Finally, an alternative ABH profile that is different from the standard ABH profiles is proposed for structural damping enhancement. Results show that a plate with optimized ABH profile entails significantly increased structural damping compared with a standard ABH plate. Local (n, 1) and (n, 2) modes that have n half waves in the circumferential direction and 1 or 2 half waves in the radial direction of the indentation dominate the modal damping increase. The optimized plate exhibits larger energy density ratio between the ABH portion and the uniform portion, which entails better energy dissipation. Also, a reduction in the sound radiation is observed which is confirmed by reduced energy level of the supersonic vibration components in wavenumber domain. |
| Rights: | All rights reserved |
| Access: | open access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| 991022378658603411.pdf | For All Users | 9.71 MB | Adobe PDF | View/Open |
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/200/10401