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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

High temperature deformation modelling and finite element implementation for single crystal turbine blade materials

Han, Songlin January 2000 (has links)
No description available.
2

Elastic wave modelling in anisotropic media using the spectral-element method.

Sinclair, Catherine Ellen January 2010 (has links)
Forward modelling of seismic waves is an essential tool in the determination of the underlying structure of the Earth using inversion techniques. Despite recent advances in computer power and memory resources, full 3-D elastic wave modelling continues to place a heavy burden on a typical personal computer. 2.5-D modelling reduces the computational burden while maintaining 3-D wavefield characteristics. In this thesis I present 2.5-D frequency-domain equations of motion for elastic wave modelling in anisotropic media. The reduced set of equations for vertical transversely isotropic media and tilted transversely isotropic media are presented separately. Using the spectral-element method, I develop the equations of motion into readily implemented sub-equations by identifying simple 1-D and 2-D patterns. Some aspects of my computational implementation are unique, in particular the use of a system of dynamically growing binary trees to serve as a system matrix. Using this system, the matrix is automatically stored in compressed row format. I investigate the use of both distributed memory and shared memory super-computers for 3-D modelling and compare the resource use of various matrix solvers. In this thesis I adapt recently developed Perfectly Matched Layer formulations to the 2.5-D elastic case, and find them to be adequate in most situations. I investigate the possiblity of instability in the absorbing layers. Observation of 2.5-D modelling results in the frequency wavenumber domain uncovers polelike behaviour at critical wavenumbers within the spectrum. I demonstrate how this behaviour threatens the accuracy of the inverse Fourier transformed frequency-domain solution. However for inhomogeneous media, under certain conditions the only medium that exhibits pole-like behaviour is the medium containing the source. Further study of the phenomenon shows that in homogeneous, transversely isotropic media, the critical wavenumber values are not dependent on the receiver position, but rather can be predicted using the maximum phase velocities of the media. The recommended strategy for wavenumber sampling is to use dense even spacing of values, to adequately capture the behaviour close to the critical wavenumbers. A further recommendation it to introduce slight attenuation through the use of complex velocities (or elastic constants) to eliminate any pole-like behaviour at the critical values. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1385923 / Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2010
3

Total variational optical flow for robust and accurate bladder image mosaicing / Calcul du flot optique dans une approche variationnelle totale pour le mosaïquage robuste et précis d’images de la vessie

Ali, Sharib 04 January 2016 (has links)
La cystoscopie est l’examen de référence pour le diagnostic et le traitement du cancer de la vessie. Le champ de vue (CdV) réduit des endoscopes complique le diagnostic et le suivi des lésions. Les mosaïques d’images sont une solution à ce problème car elles visualisent des CdV étendus. Toutefois, pour la vessie, le mosaïque d’images est un véritable défi à cause du faible contraste dans les images, des textures peu prononcées, de la variabilité intra- et inter-patient et des changements d’illumination dans les séquences. Ce défi est également à relever dans d’autres modalités endoscopiques ou dans des scènes non médicales comme les vidéos sous-marines. Dans cette thèse, une énergie variationnelle totale a d’abord été minimisée à l’aide d’un algorithme primal-dual du premier ordre pour obtenir un flot optique fournissant une correspondance dense et précise entre les points homologues des paires d’images. Les correspondances sont ensuite utilisées pour déterminer les paramètres des transformations requises pour le placement des images dans le repère global de la mosaïque. Les méthodes proposées pour l’estimation du flot optique dense incluent un terme d’attache aux données qui minimise le nombre des vecteurs aberrants et un terme de régularisation conçu pour préserver les discontinuités du champ devecteurs. Un algorithme de flot optique qui est robuste vis-à-vis de changements d’illumination importants (et utilisable pour différentes modalités) a également été développé dans ce contexte. La précision et la robustesse des méthodes de recalage proposées ont été testées sur des jeux de données (de flot optique) publiquement accessibles et sur des fantômes de vessies et de la peau. Des résultats sur des données patients acquises avec des cystoscopes rigides et flexibles, en lumière blanche ou en fluorescence, montrent la robustesse des algorithmes proposés. Ces résultats sont complétés par ceux obtenus pour d’autres séquences endoscopiques réelles de dermatoscopie, de scène sous-marine et de données d’exploration spatiale. / Cystoscopy is the reference procedure for the diagnosis and treatment of bladder cancer. The small field of view (FOV) of endoscopes makes both the diagnosis and follow-up of lesions difficult. Image mosaics are a solution to this problem since they visualize large FOVs of the bladder scene. However, due to low contrast, weak texture, inter- and intra-patient texture variability and illumination changes in these image sequences, the task of image mosaicing becomes challenging. This is also a major concern in other endoscopic data and non-medical scenes like underwater videos. In this thesis, a total variational energy has been first minimized using a first-order primal-dual algorithm in convex optimization to obtain optical flow vector fields giving a dense and accurate correspondence between homologous points of the image pairs. The correspondences are then used to obtain transformation parameters for registering the images to one global mosaic coordinate system. The proposed methods for dense optical flow estimation include a data-term which is modeled to minimize at most the outliers and a regularizer which is designed to preserve at their best the flow field discontinuities. An optical flow algorithm, which is robust to strong illumination changes (and which suits to different modalities), has also been developed in this framework. The registration accuracy and robustness of the proposed methods are tested on both publicly available datasets for optical flow estimation and on simulated bladder and skin phantoms. Results on patient data acquired with rigid and flexible cystoscopes under the white light and the fluorescence modality show the robustness of the proposed approaches. These results are also complemented with those of other real endoscopic data, dermoscopic sequences, underwater scenes and space exploration data.

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