Investigation of composite plate for ducted noise control

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Investigation of composite plate for ducted noise control

 

Author: Gan, Xin Nie
Title: Investigation of composite plate for ducted noise control
Degree: M.Sc.
Year: 2013
Subject: Noise control.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: 88 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2576823
URI: http://theses.lib.polyu.edu.hk/handle/200/6911
Abstract: Silencer is a device for reducing noise. Noise control can be easily tackled from medium to high frequency range. However low frequency noise control still remain a technical challenge for acoustical researchers. Active noise control seems to be the most effective way in controlling low frequency noise. However, it is difficult to be implemented in real life due to its reliability issue. On the other hand, passive noise control still seems to be more attractive and reliable in tackling such a problem. However, traditional absorption method by using porous material cannot work well at low frequency due to the requirement of about quarter wavelength. Recently, drumlike silencer which is composed of two tensioned membrane covered with two cavities is developed to reflect sound back to the sources side. It works effectively at the low frequency range. Practically, it is not easy to install the tensioned membranes on the duct so the plate with bending stiffness is adopted to replace the tensioned membrane. The new device is so-called plate silencer. Through the optimization of the structural property of the plate and configuration of the cavity, it can be designed in more compact size on condition that the structural property of the plate should achieve some criterion value. The structural properties of the plate have to be extremely light with high bending stiffness. Nevertheless, it is challenging and demanding to find a raw material that can fulfill such a tough requirement. Therefore, the use of composite plate is the possible way. However, the existing core material and reinforcement material are very heavy. The research group of Choy has developed an approach to manufacture a very light composite plate with high bending stiffness by using PMI foam which is reinforced by carbon fibre tows. The carbon fibre tows are used to strengthen the stiffness of the core material without adding extra weight. The performance of plate silencer by using such composite plate is impressive. However, the effect of the number carbon tows and its alignment or attachment method on the structural mechanics of the core plate was not extensively studied. Therefore, in this study, experiment and simulation of the variation of the structural property of the plate with different spacing between the carbon fibre tows on the plate have been done. Simulation by using software package of Abaqus was adopted to investigate the structural mechanics of the composite plate. For experiment, three point bending test were carried out to shows that the carbon fibre spacing has the noticeable effect on bending stiffness in axial and lateral direction. The result from simulation and bending test were in agreement. The results were also verified by acoustic performance test and another acoustics simulation.

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