### Hybrid methodology for the identification of incoherent noise sources

#### Abstract

The Nearfield Acoustical Holography (NAH) is generalized for the identification of multiple, incoherent noise sources on complex geometry. Transfer functions are generated using boundary element methods and relates the sound field in the acoustic domain to the surface velocity on source geometry. Matrix equations are solved to identify the noise sources. The equations are solved using a Singular Value Decomposition (SVD) technique. A Tikhonov regularization scheme is utilized in the present study. The reconstruction of the normal velocity for the aircraft blades passage frequency (BPF) is presented. The analysis was done on Beechcraft 1900D airplane. Signal averaging could be used at each microphone position to increase the signal to noise ratio.

#### Keywords

Acoustic holography; Acoustic noise measurement; Acoustooptical effects; Aircraft propellers; Boundary element method; Fuselages; Matrix algebra; Microphones; Pressure measurement; Signal to noise ratio; Transfer functions; Vibration measurement; Blade passage frequency (BPF); Complex geometry; Hermitian matrices; Nearfield acoustical holography (NAH); Planar structures; Singular value decomposition (SVD); Synchrophaser signals; Tikhonov regularization

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