Publication: Cascaded cylindrical micro-perforated panel for noise broadband attenuation
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Date
2023-04-01
Authors
Mohamad Izudin Bin Alisah
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Abstract
This research presents an analysis of cascaded cylindrical micro-perforated panel (MPP) for absorbing the sound of a flow system in a circular duct application. This is important for the cases where the noise source comes from multi direction as actual application would not in single direction. Since the typical MPP has limited narrow band attenuation, it is necessary to have a specific MPP to radiate noise from circular direction and broadband attenuation. The aim of this study is to model using simplified transfer matrix method, optimized via genetic algorithm and demonstrate the effectiveness of cascaded cylindrical micro-perforated panel on vacuum cleaner. Cascaded cylindrical MPP is a special class of cylindrical MPP, where two cylindrical MPPs are arranged in series to improve sound attenuation. The manufacturing of MPP primarily involves the machining of micro perforations because the small holes are not readily made using injection moulding due to the complexity of the die, flow control of the molten polymer through the small orifices and dimensional stability, making it unsuitable for mass production. This limitation can be overcome with the use of additive manufacturing (AM) technology based fused deposition method (FDM), where the micro perforations can be designed and manufactured, with relatively larger tolerances. Moreover, parametric studies on basis of perforation diameter, perforation ratio, depth of air cavity on the diameter of the duct and length ratio are carried out. Result shows that the transmission loss performance of cascaded cylindrical MPP can be improved by reducing the perforation diameter and by correct selection of perforation ratio and air cavity depth value. Experimental validation ensures that the manufactured cascaded cylindrical MPP is performed according to design. The application of transfer TMM framework was aligned with similar trend with boundary element method (BEM) and measured result via two-load method measurement. Small shift of the transmission loss peak values attributed to perforations in printed structures that were not perfectly circular in shape. The average Root Mean Square Error (RMSE) obtained was 3.04 dB. A case study is demonstrated here in the design and additive manufacturing of cascaded cylindrical MPP to attenuate peak noise at 1650 Hz. The manufactured cascaded cylindrical MPP is installed on a vacuum cleaner duct, and the measurement of sound power level shows a reduction of 5.2 dB (A).