Reproduction de : Thèse de doctorat : Dynamique des fluides : Toulouse, INPT : 2007. / Titre provenant de l'écran-titre. Bibliogr. 71 réf.

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A one-dimensional, quasi-steady ablation model with finite rate surface chemistry and frozen equilibrium pyrolysis gases is developed and discussed. This material response model is then coupled to a film-transfer boundary layer model to enable the computation of heat and mass transfer to and from the ablating surface. A shock model is outlined, as well, and all three components are then coupled together to form a stand-alone ablation code. The coupled models in the code are validated with respect to arcjet experiments, and comparisons are drawn between the ablation code and the unsteady ablation code Chaleur, as well as other computations for a graphite ablator in an arcjet. The coupled code is found to compare very well to both the experimental results and the other calculations. It is also found to have unique computational capabilities due to the use of finite-rate surface chemistry. Finally, uncertainty propagation using the quadrature method of moments (QMOM) is discussed. The method is applied to a number of simplified sample problems, for both univariate and multivariate scenarios. QMOM is then used to compute the uncertainty in an application of the coupled ablation code using a graphite ablator. The results of this study are discussed, and conclusions about the utility of the method as well as the properties of the ablation code are drawn. / text

published_or_final_version / abstract / Chemistry / Master / Master of Philosophy

Laser machining is a commonly used method for materials processing. Focusing laser energy onto a sample can lead to material modifications and achieve feature sizes on the order of micrometres. However, designing a machining platform capable of producing high quality, repeatable, and accurate results is a key challenge because the final outcome can be variable, even when using fixed laser parameters. Therefore, in order to understand and monitor the process, real-time in situ metrology is required. In this work, a coherent imaging technique analogous to spectral domain optical coherence tomography (SD-OCT) was applied inline with a machining laser in order to monitor the cut development of various materials for industrial and biomedical applications. Such inline coherent imaging (ICI) provides axial resolution on the order of ones to tens of micrometers as well as temporal resolution on the order of microseconds. In stainless steel, the machining front was observed to have very different responses to pulsed lasers operating in different ablation regimes. Applying shorter pulse duration with higher peak intensity led to more deterministic material removal with little relaxation between pulses, while longer pulses revealed periodic melting and refilling behaviour. In addition, improvement of depth sensitivity to nanometre scales was explored by accessing phase information for Doppler processing techniques. For poorly absorbing materials, ICI provides the ability to observe structures below the surface. This is a very important characteristic for biomedical applications, such as guiding ablation in biological tissue. By monitoring the ablation of bone tissue in real-time using ICI, the operator was able to terminate exposure from the machining laser 50 μm before perforation into a natural inclusion in the tissue. ICI was able to anticipate the inclusion 176 ± 8 μm below the ablation front with signal intensity 9 ± 2 dB above the noise floor. With added real-time depth control, many applications will benefit whether it is achieving higher precision cuts in industrial materials, or limiting the possibility of damaging organs at risk below the cutting surface in surgical intervention. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2010-10-29 16:01:38.048

Thesis (M.S.) -- Worcester Polytechnic Institute. / Keywords: Teflon ablation; pulsed plasma thrusters; numerical analysis; PPT; depolymerization. Includes bibliographical references (p.102-105).

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis(M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographic references.

Thesis (M.Phil.)--University of Hong Kong, 2000. / Includes bibliographical references. Also available in print.