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Contribution à l'estimation de la vitesse acoustique par Vélocimétrie Laser Doppler & Application à l'étalonnage de microphones en champ libre

Abstract : Laser Doppler Velocimetry (LDV) is a non intrusive technique widely used in fluid mechanics, but still marginal in acoustics, for measuring the particle velocimetry. Accessing to the acoustic particle velocity allows to characterize complex acoustics fields to study phenomena close to vibrating surfaces or around geometrical discontinuities for example. Research works of LDV applications to audible acoustics levels going from 60 to 120 dBSPL in presence of weak flows (a few mm/s) has been investigated by the Laboratoire d'Acoustique de l'Université du Maine for the middle of the nineteens. Signal processing methods nowadays implement on the measurement bench belong to time-frequency methods allowing to get the instantaneous frequency (proportional to the velocity) of the particle during its crossing of the measuring probe. These methods have been developed and validated experimentally on one single burst for weak flow leading to a velocity variation of several acoustics periods.
The objective of this Ph.D thesis is dual. In a first time, this thesis develops a new signal processing to get an estimation of the acoustic velocity parameters thanks to a large number of bursts. In a second time, this works presents the use the LDV sensor to estimate the acoustic pressure thanks to the measurement of the acoustic velocities.
The first part of this study consists in developing and validating a signal parametric method, based on the use of a wavelet transform, able to detect, localize, classify (single or overlap) bursts present on the noisy Doppler signal and in processing an estimation method of acoustics parameters and flow velocities estimation with the help of a least mean square method on the instantaneous frequency after the detection process of bursts.
The second part of this thesis allows to initiate new works, in collaboration with the Acoustics and Fluid dynamics group of Edinburgh, on free field microphone calibration thanks to acoustic velocities measurements by LDV. A first study investigates the possibility of getting an accurate pressure estimation thanks to acoustic velocities measurement to calibrate at first pressure microphones. Then, in a second time, an analytic approach based on the Green integral formulation proposes a two dimensional model of the acoustic pressure field function of the velocity close to the microphone membrane to hope a future calibration of free-field microphone.
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Contributor : Anne Degroot <>
Submitted on : Friday, November 30, 2007 - 2:33:04 PM
Last modification on : Friday, October 23, 2020 - 4:37:12 PM
Long-term archiving on: : Thursday, September 27, 2012 - 10:35:16 AM


  • HAL Id : tel-00193066, version 1


Anne Degroot. Contribution à l'estimation de la vitesse acoustique par Vélocimétrie Laser Doppler & Application à l'étalonnage de microphones en champ libre. Acoustique [physics.class-ph]. Université du Maine, 2007. Français. ⟨tel-00193066⟩



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