Prévision du comportement dynamique d'une turbomachine supportée par des Paliers Magnétiques Actifs durant un évènement critique

Turbomachines are rotating machines enabling the conversion of the different types of energy. The latter are composed of a rotating mechanical part, called rotor, interacting with a fluid. Therefore, rotation play a key role in these machines and the mechanical link between the fixed and the rotating parts, called bearing, is essential for reliable and optimal operations. Turbomachines supported by active magnetic bearings (AMBs) are increasingly used by industrial companies, especially thanks to the absence of direct contact between fixed and rotating parts, enabling energy savings and reduction of CO2 emissions. Most of the time, these machines are "on-board" and are fixed on mobile supports. The motions generated by these supports must be considered in the prediction of the dynamic behaviour of turbomachinery in order to improve the designs accordingly. This PhD is a contribution to the study of turbomachines supported by AMBs subjected to strong external base motions. The approach is numerical and experimental. The use of an academic scale test rig comprising a rotor-AMB system, with the properties of an industrial turbomachine, allowed to test the developed models for cases of external solicitations such as earthquake and shock, thanks to the 6-axis shaker of the equipex PHARE. It is shown that the model provides good predictions of the behaviour of the machine for the tested cases. This tool can therefore be used for industrial designs.De manière générale, les turbomachines sont des machines tournantes permettant la conversion des différents types d’énergie. Ces dernières sont composées d’une partie mécanique en rotation, appelée rotor, interagissant avec un fluide. La rotation a donc un rôle clé pour ces machines et la liaison entre les parties fixes et les parties tournantes, appelée palier, est primordiale pour un fonctionnement fiable et optimal. Les turbomachines supportées par des paliers magnétiques actifs (PMAs) sont de plus en plus utilisées par les industriels notamment grâce à l’absence de contact direct entre parties fixes et parties tournantes, permettant un gain d’énergie et une réduction des émissions de CO2. La plupart du temps, ces machines sont « embarquées » et reposent sur des supports mobiles. Les mouvements générés par ces supports doivent être considérés dans la prévision du comportement dynamique des turbomachines afin d’améliorer les designs en conséquence. Cette thèse est une contribution à l’étude des turbomachines supportées par des PMAs sujettes à de fortes sollicitations extérieures. L’approche est numérique et expérimentale. L’utilisation d’un banc d’essais académique composé d’un système rotor-PMA, aux propriétés d’une turbomachine industrielle, a permis de tester les modèles développés pour des cas de sollicitations extérieures de type séisme et choc, générées grâce à l'excitateur 6-axes de l'equipex PHARE. Il est montré que le modèle permet la bonne prévision du comportement réel de la machine. Cet outil pourra donc être utilisé pour des designs de type industriel

Stability of Rotating Machinery Supported on Active Magnetic Bearings Subjected to Base Excitation

International audienceAbstract The stability of rotating machinery is a major challenge for the floating production storage and offloading (FPSO) units such as steam turbines or centrifugal compressors. The use of active magnetic bearings (AMBs) in turbomachines enables high operating speeds, active mechatronic system for the diagnostics, and the control and enables downsizing of the whole installation footprint. In case of strong base motions, the rotor can contact its touchdown bearings (TDBs) which are used as emergency and landing bearings. The aim of this study is to assess the stability of a rotating machine supported on AMBs during severe foundation excitation. The combined effect of unbalance forces, base motion excitation, and contact non-linearity on a rotor–AMB system response is analyzed focusing on the capacity of an augmented proportional-integral-derivative controller to maintain the system stable. An academic scale test rig was used for the experimental investigations. The controller was efficient and able to maintain the system stable during and after the application of the excitation, but the dynamic capacity of the AMBs was largely oversized with respect to the studied system. In order to check the capacity of the AMBs, when they are designed as a function of the rotor weight and expected excitation, numerical simulations were carried out (downsized). A finite element (FE) model was developed to model the on-board rotor–AMB system. Predicted and measured responses due to impulse excitation applied on the foundations were compared. The capacity of the controller to maintain the system stability is then discussed

Investigations on the dynamic behaviour of an on-board rotor-AMB system with touchdown bearing contacts: modelling and experimentation

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Touchdown bearing models for rotor-AMB systems

International audienceThis paper investigates numerically and experimentally the rotor drop dynamics when unexpected Active Magnetic Bearings (AMBs) shut down occurs. In such an event, the rotor behaviour drops on two touchdown bearings (TDBs) composed of a ball bearing and a ribbon damper providing stiffness and damping to the overall system. The aim of this paper is to establish and to validate the rotor-drop system model. A first experimental set up is used to identify the dynamic characteristics of the corrugated ribbon damper and to test the Kelvin-Voigt model and the generalized Dahl model. Then, three TDB models are proposed including either the first or the second ribbon damper models. The second experimental set-up is devoted to the rotor drop response of an industrial scale rotor-AMB system equipped with two TDBs. Rotor drop simulations in the time domain are carried out by using the Finite Element method and the three TDB models. Predicted and measured rotor drop responses are compared regarding the displacements as well as transmitted loads and permits evaluating the model efficiency

Templated polycondensation of aminopropyltrimethoxysilane on DNA

International audienceThe polycondensation of a silane derivative such asaminopropyltrimethoxysilane (ATMS) in the presence of DNA was investigated in an organicsolvent for the first time. Here, NMR observation showed that the hydrolysis step of ATMSbefore polycondensation was faster when the reaction was carried out in presence of doublestranded DNA (146 bp) in chloroform. In order to test the specificity of this enhancementeffect, the influence of the different components of DNA on ATMS hydrolysis and/orpolycondensation was then investigated using different bases, nucleosides and nucleotides.The results showed that the kinetics of ATMS hydrolysis was affected by the typeofnucleotide units used, the faster hydrolysis reaction rate being observed with moleculescontaining adenosine group, and that in the absence of water the amino group ofdeoxyadenosine units can react with ATMS methoxy groups

Catalysis and specificity of the polycondensation of aminopropyltrimethoxysilane on nucleic acids

International audienceThe polycondensation of a silane derivative such as aminopropyltrimethoxysilane (ATMS) in the presence of nucleic acids has never been investigated. Our group has previously demonstrated that in chloroform ATMS hydrolysis and polycondensation were faster when the reaction were carried out in the presence of double stranded DNA (146 bp). The results showed that the kinetics of ATMS hydrolysis was affected by the base type used, a fast hydrolysis reaction rate being observed with nucleotide molecules containing adenosine group, and that in the absence of water the amino group of deoxyadenosine units, and not the hydroxylic group of the sucrose residue, can react with ATMS methoxy groups. The present work was initiated aiming at providing a better understanding of this effect. It was observed that the polymerization degree of oligodeoxyadenylate has a clear impact on the kinetic of reaction this effect being as much important as the polymerization degree of the oligodeoxyadenylate was high. Structural investigation by molecular modeling showed that this enhanced reactivity can be explained by conformational effects. Altogether, these results are accounted for assuming that DNA can act as a specific template for ATMS polycondensation, in organic medium such as chloroform, opening the way to possible DNA encapsulation, and a new way for DNA chemical modification in organic solvent

L'excitateur 6-axes de l'Equipex PHARE pour analyser et maitriser la dynamique de systèmes embarqués

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The cellular activity of cucurbitacin I is inhibited by glycosylation

International audienceCucurbitacins are a class of natural compounds known for their numerous potential pharmacological effects. The purpose of this work was to compare the effects of cucurbitacin glucosides and their aglycone counterparts on the human epithelial carcinoma cell line (HeLa). Lipophilic or aqueous extracts were prepared from seeds of Citrullus colocynthis (Cucurbitaceae). Five types of cucurbitacin glucosides (E, I, L, J, K) and two aglycones (E, I) were then isolated by HPLC and the chemical structures were elucidated by their UV, NMR and mass spectrometry data. Cucurbitacins E and I were the most abundant compounds isolated from C. colocynthis. We found that, at nanomolar concentrations, the aglycones of cucurbitacines I and E lead to alterations in the morphology of HeLa cells, with the formation of sub-membrane inclusions. Several nuclei appeared in these cells after 24h of drug exposure suggesting that cucurbitacines E and I inhibit cytokinesis but not mitosis. They also cause changes in the distribution of F-actin but not in the microtubule network. In contrast to their aglycone forms, glucosylated cucurbitacins I and E, at the same nanomolar concentrations, do not have impact on HeLa cells. However, after 24h of treatment with cucurbitacin glucosides E and I, an aggregation of actin was observed at micromolar concentrations. The data suggest that the cell activities induced by the cucurbitacins studied result from the interaction of their aglycone forms with cell receptor(s) still to be discovered

Radical Coupling Allows a Fast and Tuned Synthesis of Densely Packed Polyrotaxanes Involving γ-Cyclodextrins and Polydimethylsiloxane

International audienceThe first radical end-coupling synthesis of polydimethylsiloxane (PDMS)-γ-cyclodextrins (γ-CDs) based polyrotaxane is reported. Conversely to usual chemical way, the radical process leads to fast both controlled size and structure with minimal side reaction while exhibiting very high conversion rate (w/w, 80%). Pure PDMS-γ-CDs molecular necklaces were successfully isolated by preparative size exclusion chromatography and finely characterized both by 1D/2D/STD 1H and 13C NMR and MALDI-TOF mass spectrometry. The observations give clear evidence of the supramolecular assembly synthesis where the filling ratio (γ-CD/monomer unit) of PDMS chains is as high as 40% of γ-CDs. Combination of such radical-based coupling supported by detailed analytical characterizations appears at the forefront of a fast, suitable, and easily amenable scaling-up CDs-based polyrotaxane synthesis process