An investigation of low frequency noise and airflow effects due to wind past a duct

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An investigation of low frequency noise and airflow effects due to wind past a duct

 

Author: Shen, Yunlu
Title: An investigation of low frequency noise and airflow effects due to wind past a duct
Degree: M.Sc.
Year: 2012
Subject: Air ducts -- Noise.
Fluid dynamics.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Civil and Structural Engineering
Pages: xiv, 81 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2551504
URI: http://theses.lib.polyu.edu.hk/handle/200/6855
Abstract: Low frequency sound or infrasound is the sound below 20 Hz, which is often inaudible by human; somehow, it may be annoying and causing discomfort to exposed persons depending on the duration. In general, for sound pressure levels that present in our everyday life, the low-frequency effects are not shown to be significant in terms of causing long-term physiological damage. However, the sound pressure level over 120 dB will cause discomfort, mainly nausea due to periodic movement of the stomach and other organs of the body. In the progress of the study, I have started to work on measuring the noise levels for different types of ducts and further discussed the effects of ventilation for each duct as well. The cavity resonance is the most important factor that generates the low frequency noise, and its frequency is dependent on the length of duct and opening area of that. I attempt to alleviate the noise generation and increase the wind velocity inside and outside of chamber by reducing the resistance of wind flowing to the duct near the opening area. During the experiment, the airflow path is been proved as the key to deal with the problem of wind resistance. Inspired by Dr. Ng, I have designed a new shape of duct to guide the wind flow into the room in a smooth way, and the air flow path is expected to be streamlined with less resistance force. Based on the experiment data, it indicates that the sound press levels of new duct are slightly lower than that of current duct at low frequency range, and the wind velocity of inside room is increased as well.

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