Le générateur de vapeur a un rôle d’échangeur thermique et de sûreté nucléaire. L’énergie du fluide primaire est transférée au circuit secondaire via un faisceau de tubes en U soutenus par des plaques entretoise. Un dépôt modifie les conditions de liaison et l’écoulement du fluide secondaire. Le tube peut alors entrer en instabilité fluide-élastique, qui aboutit à une ruine rapide. Cette thèse vise à mieux comprendre l’effet de la non-linéarité de contact sur la dynamique d’un tube en air rentrant en contact intermittent avec les entretoises et ses conséquences en présence d’une instabilité. La discrétisation des conditions de contact entre le tube et les plaques, par des obstacles circulaires répartis sur l’épaisseur, ainsi que l’utilisation de bases de réductions enrichies permettent des résolutions numériques non-linéaires fiables et rapides, numériquement valides pour de fortes non-linéarités et des amortissements modaux négatifs, et bien corrélées avec les mesures correspondantes. On analyse les évolutions du contenu spectral (DSP) en fonction de l’amplitude d’excitation : remplissage des anti-résonances, décalage et étalement des pics ; puis on met en évidence la pertinence d’une notion de raideur apparente d’un contact bilatéral permanent qui permet de décrire ces transitions. En présence d’un système libre instable, on montre enfin que la non-linéarité conduit à des réponses bornées ou stabilisées ouvrant ainsi la voie vers une extension des travaux réalisés vers des applications avec fluide réel ou simulé. / The steam generator is a heat exchanger and participates to the nuclear safety. Energy is transferred from the primary to the secondary fluid through many U-tubes maintained vertically by support plates. A sludge deposit tends to modify the boundary conditions and the secondary fluid flow. A fluid-elastic instability can then occur and lead to quick tube ruin. This thesis seeks a better understanding of the effect of contact nonlinearity on the dynamics of a tube in-air intermittently impacting the support plates and its consequences in regards with instability. The use of discretized contact conditions with circular obstacles distributed over the thickness of the plates and the use of enriched reduction bases allow quick and relevant nonlinear numerical simulations. These simulations are well correlated with experimental measurements and valid even with strong nonlinearity or negative modal damping. The evolution of power spectral densities (PSD) with growing excitation amplitude is analyzed: padding of the anti-resonances, peak shift and spread. It is then shown that an apparent stiffness associated with a permanent bilateral contact is pertinent to describe these transitions. In the case of an unstable linear system, one demonstrates that the nonlinearity keeps the responses bounded or stabilised, thus paving the way for future work with real or simulated fluid flows.

No description available.

New NMR Tools for Impurity Analysis was written by Jane Power and submitted for the degree of Doctor of Philosophy in the Faculty of Engineering and Physical Sciences at the University of Manchester, on 31st March 2016.NMR spectroscopy is rich in structural information and is a widely used technique for structure elucidation and characterization of organic molecules; however, for impurity analysis it is not generally the tool of choice. While 1H NMR is quite sensitive, due to its narrow chemical shift range (0 - 10 ppm) and the high abundance of hydrogen atoms in most drugs, its resolution is often poor, with much signal overlap. Therefore, impurity signals, especially for chemically cognate species, are frequently obscured. 19F NMR on the other hand offers extremely high resolution for pharmaceutical applications. It exhibits far wider chemical shift ranges (± 300 ppm) than 1H NMR, and typical fluorinated drugs, of which there are many on the market, have only one or two fluorine atoms. In view of this, 19F NMR is being considered as an alternative for low-level impurity analysis and quantification, using a chosen example drug, rosuvastatin. Before 19F NMR can be effectively used for such analysis, the significant technical problem of pulse imperfections, such as sensitivity to B1 inhomogeneity and resonance-offset effects, has to be overcome. At present, due to the limited power of the radiofrequency amplifiers, only a fraction of the very wide frequency ranges encountered with nuclei such as fluorine can be excited uniformly at any one time. In this thesis, some of the limitations imposed by pulse imperfections are addressed and overcome. Two new pulse sequences are developed and presented, CHORUS and CHORUS Oneshot, which use tailored, ultra-broadband swept-frequency chirp pulses to achieve uniform constant amplitude and constant phase excitation and refocusing over very wide bandwidths (approximately 250 kHz), with no undue B1 sensitivity and no significant loss in sensitivity. CHORUS, for use in quantitative NMR, is demonstrated to give accuracies better than 0.1%. CHORUS Oneshot, a diffusion-ordered spectroscopic technique, exploits the exquisite sensitivity of the 19F chemical shift to its local environment, giving excellent resolution, which allows for accurate discrimination between diffusion coefficients with high dynamic range and over very wide bandwidths. Sulfur hexafluoride (SF6) is investigated and shown to be a suitable reference material for use in 19F NMR. The bandshape of the fluorine signal and its satellites is simple, without complex splitting patterns, and therefore good for reference deconvolution; in addition, it is sufficiently soluble in the solvent of choice, DMSO-d6.To demonstrate the functionality of the CHORUS sequences for low-level impurity analysis, 470 MHz 1H decoupled 19F spectra were acquired on a 500 MHz Bruker system, using a degraded sample of rosuvastatin, to reveal two low-level impurities. Using a standard Varian probe with a single high frequency channel, simultaneous 1H irradiation and 19F acquisition was made possible by time-sharing. Simultaneous 19F{1H} and 19F{13C} double decoupling was then performed using degraded and fresh samples of rosuvastatin, to reveal three low-level impurities (in the degraded sample) and low-level 1H and 13C modulation artefacts.