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Méthodes d'holographie numérique couleur pour la métrologie sans contact en acoustique et mécanique

Abstract : This study proposes methods of digital color holography for contactless measurement in the field of acoustics, solid mechanics and fluid mechanics. The developed methods could be used to solve many academic and industrial problems, such as flaw and the crack detection in composite structures, deformation analysis and 3-component vibration analysis, surface and shape control, or fluids analyses in the case of turbulent flows in subsonic and supersonic mach. This report is organized around 5 chapters which summarize the various working axes. Firstly we summed up some theoretical aspects of digital holography and completed the knowledge about the numerical process of image reconstructions in digital holography. We proposed a generalized analytical formulation which includes the curvatures of the reference and the reconstruction digital waves as well as the non-linear phenomena in the recording process. In particular we focused our interest on developing a theoretical formulation of image formation which takes into account the pixel saturation of the camera. We demonstrated that, although the saturation phenomenon is non-linear nevertheless, we can write the object-image relation with a linear analytical formulation using the convolution products. The theoretical analysis was completed with an experimental study which resulted in validating the suitability of the approach. Secondly the general formulation of the reconstruction leads to define strategies for the digital reconstruction of "extended" objects ("extended objects" means objects, whose size is larger than the camera) encoded in the color holograms. The proposed algorithm must preserve the reconstructed horizon independently from the recording wavelength. In this context we proposed the method of Fresnel transform with zero-padding depending on wavelength which helps to fulfill the previous condition. We also proposed two convolution algorithms whose concept is to adapt the spatial bandwidth of the convolution kernel to that of the object, the first one is based on the spectral scanning of the object spectrum and the second one is based on the adjustable magnification of the convolution kernel. Besides, the method of Fourier transforms filtering was adapted for transparent object in fluid mechanics. These algorithms were validated experimentally for monochromatic, two-wavelength and three-wavelength recordings, which validates their suitability. The two last parts of this study are focused on the development of digital holographic setups with two and three wavelengths for contactless metrology. We carried out the experimentations in the solid mechanical field, acoustic and fluid mechanical field. We developed three main architectures: the first one is based on bi-color and three-color architectures with spatial multiplexing of holograms whereas the second is based on bi-color and three-color holograms recordings with a stack of photodiodes, and the third is based on bi-color and three-color holograms recordings with TriCCD. The last two architectures turn out to be the simplest to operate. The bi-color experimental setup with spatial multiplexing was applied to industrial and academic problems. The first one concerns the investigation of the crack origin of capacitance on the hybrid industrial electronic components inside the automobile. We put in evidence the nonuniform deformations on the capacitance during the embedding of the PCB into the electronic box. This anisotropic of constraint could be the cause of the cracking of the capacitance. The second application constitutes a first attempt to reveal the whirlings modes inside the unconsolidated granular materials. Therefore we developed two strategies. We developed two strategies of determination of the 3D vibration motion of the granular materials using two-color holograms recording with spatial multiplexing. The experimental results of the in-plan displacements show the whirlings modes at some excitation frequencies of the field. These experimental results present some contradictions, whose causes have been identified. To solve this ambiguity we developed a three-color pseudo-pulsed digital holography resulting in the exclusive determination of each of the displacement components. In collaboration with the ONERA (Lille Center), we have developed a method of three-color digital holography for flow analysis. The proposed method leads to the determination of the field of the optical index or the flow density; after validation of the proposed method it was applied to several cases of flows in subsonic and supersonic mach. The obtained experimental results constitute a first demonstration of the potentialities of the method of color digital holography in the field of fluid mechanics.
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https://tel.archives-ouvertes.fr/tel-00647931
Contributor : Patrice Tankam <>
Submitted on : Saturday, December 3, 2011 - 4:41:50 PM
Last modification on : Tuesday, March 31, 2020 - 3:20:59 PM
Long-term archiving on: : Monday, December 5, 2016 - 11:40:47 AM

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  • HAL Id : tel-00647931, version 1

Citation

Patrice Tankam. Méthodes d'holographie numérique couleur pour la métrologie sans contact en acoustique et mécanique. Optique [physics.optics]. Université du Maine, 2010. Français. ⟨tel-00647931⟩

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