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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

Contribution à la suppression du phénomène stick slip et à la construction d'un observateur de dimension infinie en forage pétrolier / Control of torsional vibrations in an oil platform

Toumi, Samir 15 December 2017 (has links)
Les différents types de vibrations des garnitures de forage jouent un rôle important dans le dysfonctionnement des opérations de forage car celles-ci conduisent à la rupture prématurée des trains de tiges, par conséquent, à la perte de l'outil au fond du trou et aussi à l'endommagement de la machine. En s'intéressant au forage de type rotary, cette thèse étudie le phénomène des vibrations de torsion de point de vu, modélisation par une EDP (modèle distribué) dont on établi les conditions aux limites adéquats. Une large partie de notre analyse dans ce mémoire concerne la commande du phénomène de vibration de torsion conduisant à une vitesse de rotation contrôlée sur le bord. La modélisation du phénomène de torsion affectant le train de tiges lors d'un forage pétrolier a été représentée par une équation aux dérivées partielles (1D) d'ordre deux: type linéaire intégrant le phénomène de frottement. Deux entrées apparaissent dans les conditions aux limites en termes de vitesse de rotation du train et de la réaction avec le sol. Il s'agit donc de designer la commande en vitesse qui assure la rotation adéquate pour le forage et qui n'excite pas le phénomène du torsion en tenant en compte l'interaction de la formation avec le sol. La stabilité de la garniture de forage dépend d'un système de boue du fluide qui doit injecté. Nous traitons une connexion entre le système de forage rotary et le système du fluide. Nous obtenons un système couplé sous la forme EDP-EDO. Egalement, nous avons transformé le système couplé à un système neutre avec retard. Nos achevons ce mémoire par la construction d'une loi de contrôle pour l'observateur du système de forage rotary avec une seule mesure aux limites dans le haut de la colonne pour estimer les paramètres de l'outil de forage qui sont accessibles à mesurer. / The different types of drilling vibrations play an important role in the malfunctioning of the drilling operations because the lead to the premature rupture of the trains, consequently, to the Loss of the tool at the bottom hole and also damage to the machine. Much of our analysis in this specification relates to the control of the phenomenon of vibration of twisting leading to a controlled rotational speed on the edge. The mathematical aspects and simulation results will be detailed. The modeling of the torsion phenomenon affecting the drill string during was represented by a second order partial differential equation : linear type integrating the phenomenon of friction. Two entries appear in the boundary conditions in terms of the speed of the train and the reaction with the soil. It is therefore a matter of designating the speed which ensures adequate rotation for drilling and which avoid the torsional phenomenon of twist taking into account the interaction of formation with the soil. The dynamic of the drill string stability depends on a system of fluid which should be injected to bring cuttings out of the well bore and amplify the torsional vibrations phenomena. To suppress fracturing collapse or influx of fluids surrounding the well, it is important to integrate the dynamic of the pressure in this study : PDE-ODE control problem. Finally, we are concerned with the problem of boundary observer stabilization for a system of hyperbolic PDEs which describes the drilling systems. The design relies on the top boundary measurements only.
2

The search for stability through stabilisation: case studies from Afghanistan and Nepal

Dennys, C 25 September 2013 (has links)
© Cranfield University / This thesis focuses on what stability is, and what interventions have supported stability in four communities in Afghanistan and Nepal. It is the author’s view that this is the first in-depth village level assessment of how populations conceive of stability and stabilisation and thus presents a challenge to existing analysis and research about how to foster stability in contexts in extreme tension and often violent conflict. The thesis argues that international, particularly Western, notions of stability and stabilisation processes have failed to grasp the importance of local political legitimacy formation, which is a vital aspect of contemporary statebuilding of a ‘non-Westphalian’ nature. The interventions, across defence, diplomatic and defence lines, have also at times undermined one another and in some cases contributed to instability. This is particularly acute when the interventions have been motivated by the conflicting demands of statebuilding, counter-insurgency (COIN) and development theories. The thesis argues that the nature of the interventions, their conception of stability and exogenously-driven goals limit the ability to promote stability. Research findings indicate that that local processes of stabilisation have, at times, proven to be more enduring but only in circumstances where a combination of local and national political processes have allowed political legitimacy to be formed and maintained. Research findings also suggest that the more successful stability interventions have been critically supported by humanitarian and security activities which have provided for the immediate needs of the population. Longer term stability has only been embedded in contexts which have also been able to exploit economic opportunities.
3

The search for stability through stabilisation : case studies from Afghanistan and Nepal

Dennys, C. January 2013 (has links)
This thesis focuses on what stability is, and what interventions have supported stability in four communities in Afghanistan and Nepal. It is the author’s view that this is the first in-depth village level assessment of how populations conceive of stability and stabilisation and thus presents a challenge to existing analysis and research about how to foster stability in contexts in extreme tension and often violent conflict. The thesis argues that international, particularly Western, notions of stability and stabilisation processes have failed to grasp the importance of local political legitimacy formation, which is a vital aspect of contemporary statebuilding of a ‘non-Westphalian’ nature. The interventions, across defence, diplomatic and defence lines, have also at times undermined one another and in some cases contributed to instability. This is particularly acute when the interventions have been motivated by the conflicting demands of statebuilding, counter-insurgency (COIN) and development theories. The thesis argues that the nature of the interventions, their conception of stability and exogenously-driven goals limit the ability to promote stability. Research findings indicate that that local processes of stabilisation have, at times, proven to be more enduring but only in circumstances where a combination of local and national political processes have allowed political legitimacy to be formed and maintained. Research findings also suggest that the more successful stability interventions have been critically supported by humanitarian and security activities which have provided for the immediate needs of the population. Longer term stability has only been embedded in contexts which have also been able to exploit economic opportunities.
4

Regulation of the homeostasis of cytochrome C oxidase

Chrzanowska-Lightowlers, Zofia Maria Alexandra January 1995 (has links)
No description available.
5

Eco-engineering practices in Malaysia

Abdul Rahman, Nordin January 1995 (has links)
No description available.
6

Competitive adsorption of milk proteins at oil-water interfaces

Euston, Susan Elizabeth January 1989 (has links)
No description available.
7

Centrifuge modelling of soil nailing : an investigation of lifetime performance

Jones, Alun M. C. January 1999 (has links)
No description available.
8

Transformation durch Partizipation : die Bedeutung alternativer Privatisierungsmethoden für den Erfolg der Reformen in Osteuropa /

Albrecht, Barthold. January 1900 (has links)
Diss.--Wirtschaft--München--Ludwig-Maximilians-Universität, 1995. / Bibliogr. p. 225-237. Index.
9

Phase behavior, structure and stability of surfactant organised assemblies

Dunn, Carolyn M. January 1990 (has links)
No description available.
10

Looking with the head and eyes : a developmental study

Daniel, Brigid January 1987 (has links)
No description available.

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