Sound Radiation Characteristics of Rectangular Duct: An Experimental Approach

P, Aswin (2014) Sound Radiation Characteristics of Rectangular Duct: An Experimental Approach. Masters thesis, Indian Institute of Technology, Hyderabad.

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Abstract

The sound radiation characteristics of rectangular duct depend on acoustical and structural subsystems response. The coupling of acoustic duct modes and structural duct wall modes plays a critical role in generating noise in transverse direction of the duct, and its called as break-out noise. For nding coupled behaviour of the sys- tem, uncoupled analysis of each subsystem is necessary. Experimental modal analysis (EMA) of a standard dimension rectangular duct specimen is the rst practical step. It helps to understand the coupling behavior between acoustic and structural modes in HVAC ducts. As an initial study of EMA, we found the Modal Assurance Cri- teria (MAC) for xed-free beam, free-free and xed-free conditions of rectangular steel plate and free-free conditions of rectangular duct. Finally, for simply supported rectangular duct, modal parameters have obtained using Experimental Modal Anal- ysis (EMA). Correlated EMA results with Finite-Element Analysis (FEA) results using MAC method. An acoustic source for providing plane waves to the rectangular duct have been set up and found the input sound power supplied to the duct cavity. Methodology to nd input sound power have been introduced. Using the assistance of various experimental techniques, we found the sound power radiated from the duct walls and compared. vi

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