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Nackley, Brittany B. "Temporal Dynamics of the Defense Cascade." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/99987.
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Understanding physiological responses to threat can inform therapeutic interventions for phobias, anxieties, and PTSD. The defense cascade is reviewed as a theoretical model that predicts behavioral and physiological responses to threats. Nineteen undergraduates (five male), average age 19.4 experienced a novel virtual reality (VR) threat scenario while their physiology was measured. The Subjective Units of Distress Scale (SUDS) was used as a self-report indicator of distress in the research setting. Averaged SUDS reports suggested that the VR stimulus was experienced as threatening for most participants, but their autonomic response patterns did not fit those predicted by the defense cascade. Participants who had scored high on adaptive response questionnaires tended to show uncoupled ANS activation during baseline, but varied across the stimulus condition. Nearly all participants showed either coactivation or reciprocal activation during the stimulus period except those reporting the most dissociative trauma experiences, who mostly showed uncoupled ANS activation.M.S.
The more we understand about how people’s bodies and their energies act when they feel threatened, the better we can find help for folks who struggle with anxiety, trauma or other challenging conditions. This research uses a theoretical model called the defense cascade to explore how people respond mentally and physically to threatening situations. Nineteen undergraduates went through a virtual reality (VR) experience that was designed to feel threatening while their body and its energy systems were measured. A scale was introduced called the Subjective Units of Distress Scale (SUDS) and was used to help the researchers understand how distressed people felt while they were in the VR experience. Averaged SUDS reports suggested that the VR stimulus was experienced as threatening for most participants, but their body response patterns did not fit those predicted by the defense cascade. Participants whose questionnaire responses suggested they were not anxiety-prone or traumatized, tended to show bodily activation that uncoupled their two autonomic bodily systems during a baseline period before the threatening stimulus. However, their autonomic responses during the stimulus period varied. Nearly all participants showed either both autonomic systems acting together or only one system acting in a mutually exclusive way to the other system during the stimulus period. This was the case for most participants except those reporting the most trauma involving dissociative experiences. This latter group mostly showed uncoupled autonomic bodily patterns.
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Monaco, Jeffrey Francis. "Supersonic flows of Bethe-Zel'dovich-Thompson fluids in cascade configurations." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06112009-063024/.
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Zambonini, Gherardo. "Unsteady dynamics of corner separation in a linear compressor cascade." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC049/document.
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Le présent travail concerne l'étude du décollement de coin de compresseurs par des investigations expérimentaux sur le banc d'essai subsonique grille d'aubes situé au LMFA (Re = 3.8 x 105, M = 0,12, profil NACA 65-009). Habituellement, cette particulière séparation tridimensionnelle a lieu dans le coin entre l'aubage et la paroi du moyeu des rangées d'aubes, également dans les stators et les rotors.Les performances de l’étage sont ainsi dégradées à cause des pertes de charge et du blocage conséquent à la séparation de l’écoulement. Bien que les caractéristiques stationnaires sont bien connues par la littérature, uniquement des récentes études expérimentales avancées combinées aux améliorations de simulations numériques, telles que URANS et LES, ont permis de découvrir le comportement très instable du décollement de coin. Des études préalables sur le même banc d'essai ont rapporté un comportement intermittent du décollement, appelé comportement bimodal. Dans la présente thèse de doctorat, il est montré que le comportement bimodal correspond à deux états spécifiques du champ fluide: une séparation fermée, presque supprimée, et une séparation ouverte caractérisée par un blocage massif. Il est clair que cette commutation bimodale du décollement de coin apparaissant dans une machine réelle pourrait avoir un impact fortement déstabilisant. En utilisant la méthode de mesure PIV haute vitesse couplée à des mesures de pression résolues en temps sur la surface de l'aubage, l'écoulement d'un canal inter-aube a été étudié pour deux différentes incidences. Les mesures PIV fournissent pour la première fois des visualisations résolues en temps et étendues à toute la section de l'aubage de la variation bimodale du décollement. L'interaction des grandes structures aléatoires de la couche limite à l'amont avec le bord d'attaque de l'aubage déstabilise le front du décollement et agrandit la région de recirculation. Une séparation ainsi massive persiste jusqu'à ce que le blocage dans le canal inter-aube provoque la rupture des plus grandes structures constituant la zone de recirculation. Successivement le débit recommence à accélérer et la séparation est presque supprimée. Cette dynamique coïncide avec le régime d'écoulement hautement instationnaire et apériodique des diffuseurs, appelé large transitory stall, caractérisé par des grandes amplitudes d'énergie dans la gamme des basses fréquences du spectre. Des moyennes conditionnelles de pression et la décomposition orthogonale modale (POD) des champs de vitesse ont été appliquées pour montrer l'effet rétroactif du blocage induit par la séparation ouverte sur l'angle local au bord d'attaque. Ces résultats supportent l’hypothèse d'une instabilité auto-entretenue causée par la diffusion imposée dans le stator. En fin, des mesures de pression totale résolues en temps ont été effectuées en utilisant des capteurs à haute réponse en fréquence, situés à la même position dans les différents canaux adjacents. La cohérence et la linéarité de l'angle de phase trouvée entre les capteurs confirment que l'instabilité du décollement peut se propager d'un canal a l'autre, en analogie avec les perturbations tournantes (rotating instabilities) apparaissant dans les bancs d'essai annulaires. Ceci montre pour la première fois que, même dans une grille d'aubes linéaire de compresseur, l'instabilité intrinsèque du décollement de coin peut déclencher la propagation d'instabilitésThe present work focuses on the study of the corner separation phenomenon in compressors carried out by experimental investigations on a subsonic linear cascade test rig (Re=3.8x105, M=0.12, blade profile NACA 65-009). Usually, this particular three-dimensional separation takes place in the corner between the blade and the endwall of compressor rows, mostly at hub, both in stators and rotors.Its main features are high total pressure losses and blockage of the flow, with consequent impacts on the efficiency. Whereas time averaged characteristics are well known from the past, only recent advanced experimental studies and improvements of numerical simulations, such as URANS and LES, have permitted to uncover the highly unsteady behavior of corner separation in compressors. Precedent studies on the same test rig have reported an intermittent unsteady behavior of corner separation, called bimodal behavior. In the present thesis it is shown that the bimodal behavior corresponds to two specific states of the flow: a closed separation, almost suppressed, and an open separation characterized by massive blockage and losses. Clearly hub-separation bimodal switches appearing in a real machine could have a first order detrimental effect on the stability of the flow in the compressor. By using high speed PIV coupled with unsteady pressure measurements on the surface of the blade the flow in a single blade passage has been investigated for different incidences. The PIV measurements provide, for the first time, time-resolved flow visualizations of the size switch of the separation with an extended field of view covering the entire blade section. The interaction of random large structures of the incoming boundary layer with the blade is found to be a predominant element that destabilizes the separation boundary and enlarges the recirculation region. Such a massive separation persists until the blockage in the passage causes the breakdown of the largest structures in the aft part of the blade, reestablishing the closed separation state. Such dynamics coincide with the aperiodic intermittent flow regime of diffusers, called transitory stall regime, and the associated Fourier spectra show the largest energy amplitudes in the low frequency range. Conditional ensemble averages of pressure and proper orthogonal decomposition (POD) of velocity fields have been applied to show the feedback effect of the blockage of the separation on the flow angle around the blade leading edge. These results draw the picture of a self-sustained instability caused by the diffusion imposed by the inter-blade passage. To answer the question about the interaction between adjacent corner separations, time-resolved total pressure measurements have been carried out by using high frequency response sensors positioned in bimodal points of multiple passages. The coherent propagation velocity and the linearity of the phase angle found between the signals confirm that the unsteadiness of the separation can propagate in pitch-wise direction. It is interesting to underline that equivalent elements characterize rotating disturbances appearing in annular test rigs. This finally shows that, even in an isolated stator blade row, the intrinsic unsteadiness of corner separation can start the propagation of instabilities. It is the first time that such a propagation effect is observed in a linear compressor cascade
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Kiss, Tibor. "Experimental and numerical investigation of transonic turbine cascade flow." Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-02022007-133636/.
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Zaccaria, Michael A. "Development of a transonic turbine cascade facility." Thesis, Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53201.
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This thesis describes the design and initial testing of a transonic turbine cascade facility. It is specifically concerned with the best way to obtain flow periodicity and repeatability through the cascade by the use of tailboards at the cascade exit. The problem of how to achieve flow periodicity and repeatability has not been completely resolved. An examination of the literature available on transonic turbine cascade testing indicates some researchers use no tailboards, some use a solid tailboard, and still others use a porous tailboard. In this thesis, the flow through the turbine cascade is tested for three different cascade exit configurations; no tailboard, a solid tailboard, and a porous tailboard. The cascade is also tested with the tailboard at different angles, to see what effect the angle of the tailboard has on the flow through the cascade. The data acquisition and flow visualization systems are discussed and some preliminary results are given.Master of Science
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Rodger, Philippe (Philippe William) Carleton University Dissertation Engineering Aerospace. "Establishing two-dimensional flow in the large-scale planar turbine cascade." Ottawa, 1992.
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Carneal, James P. "Experimental investigation of reversed flow in a compressor cascade." Thesis, Virginia Tech, 1990. http://hdl.handle.net/10919/42096.
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Moore, H. "Experiments in a turbine cascade for the validation of turbulence and transition models." Thesis, Durham University, 1995. http://etheses.dur.ac.uk/5356/.
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This thesis presents a detailed investigation of the secondary flow and boundary layers in a large scale, linear cascade of high pressure turbine rotor blades. The puropose of the data is to provide a suitable test case to aid the design and validation of the turbulence and transition models used in computational fluid dynamics. Hot-wire measurements have been made on a number of axial planes upstream, within and downstream of the blades to give both the mean flow conditions and all six components of Reynolds stress. Suitable inlet conditions have been defined at one axial chord upstream of the blade leading edge where the velocity and turbulence have been measured in both the freestream and endwall boundary layer. The turbulence dissipation rate has also been measured in order to define fully the inlet flow, a quantity that is usually missing in other data. Measurements through the blade show that the turbulence generation associated with the secondary flows is considerable and that all three shear stress components are significant. Intermittency measurements close to the endwall and blade surfaces show that the boundary layers are mostly laminar or transitional. The new endwall boundary layer, that forms behind the separation line, was found to be initially laminar. On the suction surface transition occurs over the latter part of the blade and on the pressure surface the accelerating flow causes relaminarisation. A number of calculations using a mixing length and high and low Reynolds number k-ϵ calculations show that reasonable overall results may be obtained. The lack, or failure, of transition modelling caused profile losses to be generally overpredicted and there was little evidence that the more sophisticated models produced better results. No model accurately predicted the individual turbulence quantities largely due to the inadequacy of the Boussinesq assumption for this type of flow. Good transition modelling appears to be more important than turbulence modelling in terms of the overall results.
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Menzel, Stefan. "Intraband Electron Dynamics in new materials and designs for quantum cascade lasers." Thesis, University of Sheffield, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500220.
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Friart, Gaetan. "Semiconductor laser dynamics: two polarization feedback, quantum cascade lasers, and ring lasers." Doctoral thesis, Universite Libre de Bruxelles, 2017. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/248835.
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Semiconductor lasers (Sls) are very sensitive to external perturbations which may destabilize their steady output. This is particularly striking when the SL is subject to optical feedback, i.e. when part of the light coming out of the laser is reinjected in the cavity after reflection from a distant mirror. For some applications, this is a nuisance that we wish to avoid. But optical feedback may also drive the laser into dynamical regimes which are useful for new applications. In this thesis, we study different problems where an SL is subject to a delayed feedback or to an injected signal. These problems are motivated by recent experiments, technological issues, or particular dynamical phenomena. Specifically, we combine analytical techniques, numerical simulations, and experiments to investigate the bifurcation mechanisms leading to a large variety of oscillatory outputs. The systems that we discuss are an edge-emitting laser with polarization-rotated optical feedback, a two-mode laser with optical injection, a quantum cascade laser with optical feedback, and a semiconductor ring laser with optical feedback. We show that the bifurcations from the steady-states are of primary importance. They not only delimit the stability boundaries of the laser output but they also form the backbone structure of many pulsating waveforms. We investigate these bifurcations in detail in order to find the best operating conditions to observe specific dynamical regimes. Our results highlight laser key parameters that allow their efficient control.Les lasers à semi-conducteur sont sensibles aux perturbations externes et celles-ci peuvent déstabiliser leur faisceau de sortie d’intensité constante. Ceci est particulièrement marquant quand le laser à semi-conducteur est sujet à un feedback optique, c’est-à-dire quand une partie de la lumière sortant du laser est réinjectée dans sa cavité après réflexion par un miroir distant. Pour certaines applications, cela représente une nuisance que l’on souhaite éviter. Mais le feedback optique peut aussi engendrer des régimes dynamiques utiles pour de nouvelles applications. Dans cette thèse, nous étudions différents problèmes où un laser à semi-conducteur est soumis à un feedback retardé ou à un signal injecté. Nos travaux sont motivés par de récentes expériences, des questions technologiques ou des phénomènes dynamiques particuliers. Nous combinons des techniques analytiques, des simulations numériques ainsi que des expériences afin d’analyser les mécanismes de bifurcation menant à une large variété de régimes oscillants.Nous étudions en premier lieu la dynamique d’un laser à semi-conducteur soumis à un feedback avec rotation de la polarisation. Nous examinons, à la fois théoriquement et expérimentalement, la séquence de bifurcations menant à des oscillations sous forme d’ondes carrées. Nous mettons en évidence une multistabilité entre différentes ondes carrées de périodes spécifiques. Nous introduisons alors un mécanisme de contrôle qui nous permet de sélectionner l’onde carrée désirée. Nous analysons ensuite les frontières de stabilité d’un laser à semi-conducteur à deux polarisations soumis à une injection optique. Nous montrons que si les gains des deux modes de polarisation sont suffisamment proches, un état stationnaire mixte stable peut exister. Nous explorons également les conditions permettant une bistabilité entre un état stationnaire pur et un état stationnaire mixte. Les lasers à cascade quantique sont de nouveaux lasers à semi-conducteur prometteurs qui possèdent une forte tolérance au feedback optique. Nous examinons de façon systématique leur stabilité dans la limite des grands retards. Nous montrons que des instabilités oscillantes sont cependant possibles pour de faibles valeurs du courant de pompe. Le dernier dispositif que nous étudions dans cette thèse est le laser à semi-conducteur en anneau soumis à un feedback optique. Nous identifions le mécanisme de bifurcation, appelé pont de bifurcation, responsable des instabilités oscillantes dans le faisceau de sortie du laser. Ces oscillations sont indésirables pour la plupart des applications impliquant de tels lasers. Nous montrons qu’elles peuvent être évitées en contrôlant la phase du feedback.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Wang, Cheng. "Modulation dynamics of InP-based quantum dot lasers and quantum cascade lasers." Thesis, Rennes, INSA, 2015. http://www.theses.fr/2015ISAR0009/document.
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Le besoin incessant de débits toujours plus élevés dans les systèmes de télécommunications a un impact sur tous les éléments composant la chaine de transmission. Ainsi, pour faire face à l’augmentation croissante du volume de données échangées à travers le monde, le développement de nouvelles sources optiques semi-conductrices est absolument nécessaire. La modulation directe de lasers nanostructurés constitue une alternative bas coût et à faible consommation énergétique qui permettra de remplacer progressivement les diodes lasers à puits quantiques actuelles. De nombreux efforts en recherche ont été consacrés au cours des dernières années en vue d’améliorer les performances dynamiques des lasers nanostructurés notamment en terme de bande passante, de facteur de couplage phase-amplitude (facteur α) et de dérive de fréquence (chirp). Pour les applications aux très grands réseaux et systèmes de communication, la croissance d’îlots ou de fils quantiques déposés sur substrat InP permet de réaliser des dispositifs nanostructurés émettant dans le proche infra-rouge autours de 1550 nm. Dans ce mémoire, la dynamique de modulation des lasers nanostructuré est étudiée en régime de modulation directe. Les caractéristiques analysées comprennent: la modulation en amplitude (AM) et en fréquence (FM), le chirp, et les réponses en régime grandsignal. Grâce à une approche semi-analytique, il est démontré que la bande passante et l’amortissement sont fortement limités par les phénomènes de capture et de relaxation des porteurs de charge dans les nanostructures. Afin d’étudier les propriétés du facteur α et du chirp, un nouveau modèle dynamique a été proposé, prenant en compte la contribution à l’indice optique des porteurs de charge dans des états hors résonance. Il est ainsi montré que, contrairement au cas des lasers à puits quantiques, le facteur α dépend fortement du courant de pompe et de la fréquence de modulation. Le facteur α reste constant à basses fréquences (<0,1 GHz) et supérieur aux valeurs obtenues à hautes fréquences (au-delà de quelques GHz) à partir de la technique FM/AM. Ces caractéristiques sont essentiellement attribuées aux contributions des porteurs dans les états hors résonance. Les simulations montrent que le facteur α peut être réduit en augmentant la séparation énergétique entre l’état fondamental résonant (GS) et les états hors résonance. En particulier, un effet laser sur 1’état excité des nanostructures (ES) constitue une solution prometteuse pour améliorer les performances dynamiques, en accroissant notamment la bande passante de modulation et en réduisant le facteur α d’environ 40%. Les techniques d’injection optique sont également intéressantes pour régénérer les performances dynamiques des lasers. Le couplage phase-amplitude et le gain optique y sont substantiellement modifiés via le contrôle de l’amplitude et du désaccord en fréquence du faisceau injecté. Dans ce cadre, ce travail propose une nouvelle technique dérivée de la méthode Hakki-Paoli, permettant de mesurer, sous injection optique, le facteur α à la fois en dessous et au-dessus du seuil. Les lasers à cascade quantique (QCL) sont basés sur des transitions électroniques inter-sous-bandes dans des hétérostructures à puits quantiques. Ces lasers présentent une bande passante (AM) relativement de quelques dizaines de GHz et sans résonance ce qui est prometteur pour les transmissions en espace libre. De manière surprenante, les calculs montrent que les QCL présentent une largeur de bande FM extrêmement large de l’ordre quelques dizaines de THz, environ trois ordres de grandeur supérieure à la largeur de bande AM. L’injection optique dans ces lasers présente les mêmes avantages que ceux procurés dans les lasers à transitions interbandes. Des désaccords positifs ou négatifs en fréquence augmentent notamment la largeur de la bande passanteHigh performance semiconductor lasers are strongly demanded in the rapidly increasing optical communication networks. Low dimensional nanostructure lasers are expected to be substitutes of their quantum well (Qwell) counterparts in the next-generation of energy-saving and high-bandwidth telecommunication optical links. Many efforts have been devoted during the past years to achieve nanostructure lasers with broad modulation bandwidth, low frequency chirp, and reduced linewidth enhancement factor. Particularly, 1.55-μm InP-based quantum dash (Qdash)/dot (Qdot) lasers are preferable for long-haul transmissions in contrast to the 1.3-μm laser sources. In this dissertation, we investigate the dynamic characteristics of InPbased nanostructure semiconductor lasers operating under direct current modulation, including the amplitude (AM) and frequency (FM) modulation responses, the linewidth enhancement factor (also known as α-factor), as well as large-signal modulation responses. Using a semi-analytical analysis of the rate equation model, it is found that the modulation bandwidth of the quantum dot laser is strongly limited by the finite carrier capture and relaxation rates. In order to study the α- factor and chirp properties of the quantum dot laser, we develop an improved rate equation model, which takes into account the contribution of carrier populations in off-resonant states to the refractive index change. It is demonstrated that the α-factor of quantum dot lasers is strongly dependent on the pump current as well as the modulation frequency, in comparison to the case of Qwell lasers. The α-factor remains constant at low modulation frequencies (<0.1 GHz) and higher than the value derived at high modulation frequencies (beyond several GHz) from the FM/AM technique. These unique features are mostly attributed to the carrier populations in off-resonant states. Further simulations show that the α-factor can be reduced by enlarging the energy separation between the resonant ground state (GS) and off-resonant states. Lasing from the excited state (ES) can be a promising alternative to enhance the laser’s dynamic performance. The laser exhibits a broader modulation response and the α-factor can be reduced by as much as 40%. The optical injection technique is attractive to improve the laser’s dynamical performance, including bandwidth enhancement and chirp reduction. These are demonstrated both theoretically and experimentally. The phase-amplitude coupling property is altered as well in comparison with the free-running laser and the optical gain depends on the injection strength and the frequency detuning. This work proposes a new method derived from the Hakki-Paoli method, enabling to measure the α-factor of semiconductor lasers under optical injection both below and above threshold. In addition, it is demonstrated theoretically that the α-factor in nanostructure lasers exhibits a threshold discontinuity, which is mainly attributed to the unclamped carrier populations in the off-resonant states. It is a fundamental limitation, preventing the reduction of the α-factor towards zero. Quantum cascade (QC) lasers rely on intersubband electronic transitions in multi-quantum well heterostructures. QC lasers show flat broadband AM response (tens of GHz) without resonance, which constitutes promising features for free-space communications. Surprisingly, calculations show that the QC laser exhibits an ultrabroad FM bandwidth on the order of tens of THz, about three orders of magnitude larger than the AM bandwidth. Optically injection-locked QC lasers also exhibit specific characteristics by comparison to interband semiconductor lasers. Both positive and negative frequency detunings enhance the modulation bandwidth
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Grove, Darren V. "Experimental and numerical investigation of second-generation, controlled-diffusion, compressor blades in cascade." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1997. http://handle.dtic.mil/100.2/ADA333407.
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Shaffer, Damon M. "Reynolds stress measurements downstream of a turbine cascade." Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/45735.
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An experimental investigation was performed to measure Reynolds stresses in the turbulent flow downstream of a large-scale linear turbine cascade. A rotatable X-wire hot-wire probe that allows redundant data to be taken with solution for mean velocities and turbulence quantities by least-squares fitting procedures was developed. This measurement technique was verified in a fully-developed turbulent pipe flow; the results show the accuracy of the probe when used in an end-flow orientation at various incidence angles and with a multiple number of angular settings.
Traverses with a single hot-wire at mid-span near the blade row exit show very high levels of turbulence locally in the blade wake near the trailing edge which quickly lessen in magnitude downstream. The rotatable X-wire was used to obtain the Reynolds stresses on a measurement plane located 10% of an axial chord downstream of the trailing edge. Here the turbulence kinetic energy exhibits a distribution resembling the contours of total pressure loss obtained previously, but is highest in the blade wake where losses are relatively low. The turbulent shear stresses obtained are consistent in sign and magnitude with the gradients of mean velocity. The mass-averaged turbulence kinetic energy accounts for 21% of the total pressure loss at this measurement plane.Master of Science
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Mezynski, Alexis. "Measurements of pressure and thermal wakes in a transonic turbine cascade." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06112009-063252/.
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Chesnakas, Christopher J. "Experimental studies in a supersonic through-flow fan blade cascade." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39790.
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An investigation has been performed of the flow in a supersonic through-flow fan blade
cascade. The blade shapes are those of the baseline supersonic through-flow fan (STFF) under
investigation at the NASA Lewis Research Center. Measurements were made at an inlet Mach
number of 2.36 over a 15° range of incidence. Flowfield wave patterns were recorded using spark
shadowgraph photography and steady-state instrumentation was used to measure blade surface
pressure distributions and downstream total and static pressure distributions. A two-dimensional
LDV system was used to map the downstream flowfield. From these measurements, the integrated
loss coefficients are presented as a function of incidence angle along with analysis indicating the
source of losses in the STFF cascade. The results are compared with calculations made using a
two-dimensional, cell-centered, finite-volume, Navier-Stokes code with upwind options. Good
general agreement is found at design conditions, with lesser agreement at off-design conditions.
Analysis of the leading edge shock shows that the leading edge radius is a major source of losses
in STFF blades. Losses from the leading edge bluntness are convected downstream into the blade
wake, and are difficult to distinguish from viscous losses. Shock losses are estimated to account
for 70% to 80% of the losses in the STFF cascade.Ph. D.
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Eickemeyer, Felix. "Ultrafast dynamics of coherent intersubband polarizations in quantum wells and quantum cascade laser structures." Doctoral thesis, [S.l.] : [s.n.], 2002. http://dochost.rz.hu-berlin.de/dissertationen/eickemeyer-felix-2002-07-03.
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Glova, Michael A. "Experimental verification of the flow around compressor blades in cascade at stall with initial numerical simulations." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Mar%5FGlova.pdf.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, March 2006.Thesis Advisor(s): Garth V. Hobson. "March 2006." Includes bibliographical references (p. 69-70). Also available online.
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Horne, Kyle S. "Nano-scale Thermal Property Prediction by Molecular Dynamics Simulation with Experimental Validation." DigitalCommons@USU, 2014. https://digitalcommons.usu.edu/etd/3089.
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Quantum cascade laser (QCL) diodes have potential applications in many areas including emissions analysis and explosives detection, but like many solid-state devices they suer from degraded performance at higher temperatures. To alleviate this drawback, the thermal properties of the QCL diodes must be better understood. Using molecular dynamics (MD) and photothermal radiometry (PTR), the thermal conductivity of a representative QCL diode is computed and measured respectively.
The MD results demonstrate that size eects are present in the simulated systems, but if these are accounted for by normalization to experimental results the thermal conductivity of the QCL can be reasonably obtained. The cross-plane conductivity is found to be in the range of 1.8 to 4.3 W=m K, while the in-plane results are in the range of 3.7 to 4.0 W=m K. These values compare well with experimental results from the literature for both QCL materials and for AlInAs and GaInAs, which the QCL is composed of. The cross-plane conductivity results are lower than those of either AlInAs or GaInAs, which demonstrates the phonon scattering at the interfaces. The in-plane results are between AlInAs and GaInAs, which is to be expected.
The PTR results are less concrete, as there seem to be heat transfer eects active in the samples which are not included in the models used to t the frequency scans. These effects are not 2D heat transfer artifacts nor are they the result of volumetric absorption. It is possible that they are the results of plasmon induction, but this is only supposition. As the data stand, the PTR and MD results are within an order of magnitude of each other and follow reasonable trends, which suggests that both results are not too far o from reality. While the experimental results are not entirely conclusive, the simulations and experiments corroborate each other suciently to warrant further investigation using these techniques. Additionally, the simulations present sucient internal consistency so as to be useful for thermal property investigation independent of the PTR results.
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Spitz, Olivier. "Mid-infrared quantum cascade lasers for chaos secure communications." Electronic Thesis or Diss., Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLT054.
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Les lasers à cascades quantiques (LCQs) sont des lasers semiconducteurs émettant dans le moyen-infrarouge. Ce domaine optique est bien connu pour ses propriétés d'absorption pour de nombreuses molécules et les lasers à cascades quantiques ont déjà fait leurs preuves en spectroscopie. Des expériences de communication en espace libre ont également vu le jour à ces longueurs d'onde et l'objectif de cette thèse était d'explorer plus en détail ce champ d'applications en réalisant une communication sécurisée reposant sur le chaos optique. La thèse avait pour but de préciser de manière expérimentale les conditions optimales (température, courant de pompe, longueur de cavité externe...) pour obtenir du chaos optique afin de l'utiliser dans des applications futures. Durant cette thèse, une transmission sécurisée a été réalisée avec deux LCQs grâce au principe de synchronisation du chaos, ce qui est une première. Cela permet d'entrevoir tout le potentiel offert par ces lasers en terme de communication au moyen-infrarouge, où la transparence de l'atmosphère donne un net avantage aux LCQs comparés aux diodes laser conventionnelles émettant dans le proche infrarouge. En parallèle de ces expériences sur les communications sécurisées, d'autres phénomènes non-linéaires ont également été observés en fonction des conditions d'opération. Ainsi, le phénomène d'entrainement, connu pour les diodes laser, a pu être démontré expérimentalement. Lors d'une réinjection avec rotation de polarisation, il a été possible de voir que le LCQ était capable d'émettre une onde carrée dont la période et le rapport cyclique pouvaient être modifiés en fonction des paramètres du montage. Enfin, la présence d'événements extrêmes, commune à d'autres systèmes optiques et même d'autres systèmes physiques, a également pu être observée, ce qui pourrait être un frein à un système de communication utilisant des LCQs car les événements extrêmes ont tendance à perturber le signal du laser et ainsi à brouiller le message envoyé. L'ensemble de ces résultats expérimentaux a permis une meilleure compréhension des dynamiques non-linéaires présentes dans un LCQ et contribueront à étendre les champs d'application pour ce type de laser moyen-infrarouge qui reste pour le moment restreint à la spectroscopie et aux contre-mesures optiques mais dont le potentiel est très élevéThe mid-infrared domain is a promising optical domain because it holds two transparency atmospheric windows, as well as the fingerprint of many chemical compounds. Quantum cascade lasers (QCLs) are one of the available sources in this domain and have already been proven useful for spectroscopic applications and free-space communications. The purpose of that dissertation is to go one step further by implementing a secure free-space communication relying on optical chaos and consequently, to give an accurate cartography of non-linear phenomena in quantum cascade lasers. Initial efforts about free-space secure chaotic transmission have been carried out during this Ph.D. thesis with two chaos-synchronized QCLs, which is a pioneer result paving the way for mid-infrared private communications. In order to have a global picture about the non-linear dynamics in QCLs under external optical feedback, we tuned many experimental parameters and this allowed us studying new phenomena in QCLs. We thus found similarities between QCLs and laser diodes when the chaotic dropouts are synchronized with an external modulation, known as the entrainment phenomenon. A cross-polarization reinjection technique led to square-wave emission in the output of the QCL. Eventually, we studied the triggering of rogue waves in QCLs. Rogue waves are a quite common phenomenon in optics (among other domains in science) but they have never been triggered on-demand in semiconductor lasers under external optical feedback before. Further studies will try to avoid such phenomenon in the output of a QCL under external optical feedback since it can disturb the message to be transmitted in a secure communication. All these experimental results allowed a better understanding of the non-linear dynamics of QCLs and will extend the potential applications of this kind of semiconductor lasers, which have currently been restricted to molecular spectroscopy and optical countermeasure systems
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Rogers, Daniel R. "Design of a Three-Passage Low Reynolds Number Turbine Cascade with Periodic Flow Conditions." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2684.pdf.
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Ainslie, Walter E. "The effect of solidity on the pre- and post-stall flow in a linear compressor cascade." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43579.
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An experimental investigation of the performance characteristics of a solid wall linear compressor cascade was conducted. The purpose of the experiments was to determine the effects of the blade row configuration parameters stagger and solidity on the pre-and post-stall behavior of the flow in the cascade. Tests were conducted at a solidity of 1.5, and for two stagger angles, 36.4 degrees and 25 degrees.
The investigation included the use of high speed motion pictures with smoke flow visualization in the cascade, measurements of the total pressure and velocity of the flow upstream and downstream of the cascade, and measurements of the blade surface pressures. The experiments were conducted for a range of angle of attack from 0 degrees to 45 degrees.
To determine the effects of solidity on the pre- and post-stall behavior of the flow in the cascade, the results obtained for the present 1.5 solidity cascade were compared to previous results from the same cascade tested at a solidity of 1.0. The flow in the two cascades was observed to be similar in nature, but the influence of the reduced blade loading in the high solidity cascade was apparent. For the higher solidity cascade, flow losses at low angle of attack were found to be larger, but stalling behavior was delayed.
Master of Science
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Jumpertz, Louise. "Photonique non-linéaire dans les lasers à cascade quantique moyen infrarouges." Electronic Thesis or Diss., Paris, ENST, 2016. https://pastel.hal.science/tel-03689516.
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Les lasers à cascade quantique émettant dans le moyen-infrarouge sont des lasers semi-conducteurs unipolaires qui sont devenus des sources couramment utilisées pour des applications telles que la spectroscopie de gaz, les communications en espace libre ou les contre-mesures optiques. Appliquer une perturbation externe, typiquement une contre-réaction optique ou de l’injection optique, entraîne une forte modification des propriétés d’émission du laser à cascade quantique. La contre-réaction optique influe sur les propriétés statiques du laser Fabry-Perot ou à contre-réaction répartie, conduisant à une augmentation de la puissance, à une diminution du seuil, à une modification du spectre optique qui peut devenir monomode ou multimode, et à une amélioration de la qualité de faisceau dans les lasers à ruban large fortement multimode transverses. Cela induit également un comportement dynamique différent, et un laser à cascade quantique soumis à de la contre-réaction peut osciller périodiquement ou même devenir chaotique : ce travail présente la toute première observation d'instabilités optiques dans le moyen-infrarouge. De plus, une étude numérique de l’injection optique montre que les lasers à cascade quantique peuvent se verrouiller optiquement sur une plage de plusieurs gigahertz, sur laquelle leur stabilité devrait être accrue et leur bande passante de modulation significativement augmentée. Une dynamique prometteuse apparaît également en dehors de la zone de verrouillage, avec l’apparition d’oscillations périodiques à une fréquence accordable ainsi que des événements isolés de forte intensité. Un laser à cascade quantique soumis à un contrôle externe peut donc être une source très performante pour les applications moyen-infrarouges usuelles, mais pourrait aussi en adresser de nouvelles, telles que des oscillateurs photoniques accordables, des générateurs d’événements rares, des LIDAR chaotiques, des communications sécurisées par chaos ou des contre-mesures imprévisiblesMid-infrared quantum cascade lasers are unipolar semiconductor lasers, which have become widely used sources for applications such as gas spectroscopy, free-space communications or optical countermeasures. Applying external per-turbations such as optical feedback or optical injection leads to a strong modification of the quantum cascade laser prop-erties. Optical feedback impacts the static properties of mid-infrared Fabry-Perot and distributed feedback quantum cas-cade lasers, inducing power increase, threshold reduction, modification of the optical spectrum, which can become either single- or multimode, and enhanced beam quality of broad-area transverse multimode lasers. It also leads to a different dynamical behavior, and a quantum cascade laser subject to optical feedback can oscillate periodically or even become chaotic: this work provides the very first analysis of optical instabilities in the mid-infrared range. A numerical study of optical injection furthermore proves that quantum cascade lasers can injection-lock over a few gigahertz, where they should experience enhanced stability and especially improved modulation bandwidth. Furthermore, some promising dynamics appear outside the locking range with periodic oscillations at a tunable frequency or high-intensity events. A quantum cascade laser under external control could therefore be a source with enhanced properties for the usual mid-infrared applications, but could also address new applications such as tunable photonic oscillators, extreme events gen-erators, chaotic LIDAR, chaos-based secured communications or unpredictable countermeasures
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Walker, Richard James. "Quantum cascade laser spectroscopy : developments and applications." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:5021ac50-c69d-4a1d-8071-e59ffed9fcb8.
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This thesis presents work examining the characteristics and applicability of quantum cascade lasers. An introduction is given explaining both the desire for a widely tunable, narrow bandwidth device working in the midinfrared, as well as detailing the ways in which quantum cascade lasers (QCLs) fulfill these requirements. The development and manufacture of QCLs are then discussed. The experimental section of this thesis is then split into three parts. Chapter 2 concerns the characterisation and application of several pulsed QCLs. The intrapulse mode of operation is employed and the effect of the resulting rapid frequency chirp upon molecular spectra is investigated in the form of rapid passage signals. The evolution of said rapid passage signals is then investigated as a function of chromophore pressure and identity, with different QCLs, chirp rates, and optical path lengths. The prospect of producing population transfer with chirped lasers is discussed. Chapters 3, 4, and 5 are then concerned with the application and characterisation of continuous wave QCLs. In these chapters a widely tunable commercially produced EC-QCL is utilised as well as two DFB QCLs, one of which is used in tandem with a home-made mount and temperature controller. In Chapter 3 a number of sensitive detection techniques are compared with the employment of wavelength modulation spectroscopy, long path cells and optical cavities, and the narrow bandwidth of QCLs utilised to determine a previously unknown spectral constant of DBr. Chapters 4 and 5 then utilise the high power of an external cavity quantum cascade laser in sub-Doppler Lamb-dip and polarisation spectroscopy measurements and then a pump-probe experiment. The laser linewidth is investigated on a millisecond timescale returning a current noise limited value of c.a. 2 MHz and the fundamental linewidth of the device investigated by altering the injection current. Chapter 5 is concerned with the pump-probe experiment, directly measuring the hot band absorption in a ladder like transition (R(6.5)$_\frac{1}{2}$ $v=1\leftarrow0$ and P(7.5)$_\frac{1}{2}$ $v=1\leftarrow0$). The Bennett peak in the hot band is observed with a DFB-QCL swept at $\sim 0.15$ MHz ns$^{-1}$ and is seen not just as a pump bandwidth limited lineshape, but as a highly velocity selected rapid passage signal. The effect of pressure, pump and probe scan rate and power upon this rapid passage signal is also studied. It is further noted that rapid thermalisation occurs within $v=1$ such that at pressures above c.a. 30 mTorr a broad NO doublet absorption is observed beneath the Bennett peak from which a total population transfer of c.a. $16 \%$ can be estimated. Finally an experiment is discussed in which this population transfer could be increased for use in secondary applications. Chapter 6 then presents initial measurements with two prototype pulsed 3.3 \si{\micro\metre} QCLs considering the prospects of such devices. A Fabry-P\'rot device is first studied using a Fourier transform spectrometer and temperature tuning used to produce a spectrum of the Q-branch of CH$_4$ around 3025 cm$^$. Experiments are then performed using a DFB QCL investigating the chirp rate of the system as an indicator of the rate of heat accumulation within the system. Heat management is of particular consideration when the sea-change is made from pulsed to continuous devices. For this device absorption spectra of two CH$_4$ transitions at 2971 cm$^$ are used to determine the chirp rate, which is found to be c.a. 1.8 GHz ns$^$, at least an order of magnitude higher than that of the longer wavelength pulsed devices considered in Chapter 2.
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McDonald, William J. "Design and computational analysis of aerodynamics in an annular cascade." Honors in the Major Thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1112.
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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.Bachelors
Engineering and Computer Science
Aerospace Engineering
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Le, Roy Pascal. "Cascade inverse et dispersion turbulente en turbulence bidimensionnelle." Phd thesis, Ecole Nationale des Ponts et Chaussées, 1988. http://tel.archives-ouvertes.fr/tel-00529772.
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Cette thèse étudie la turbulence bidimensionnelle au moyen de simulations numériques. La turbulence bidimensionnelle intéresse surtout les météorologues et les océanographes car elle constitue une première approximation de leurs écoulements. Mon travail sur le modèle de turbulence bidimensionnelle du Laboratoire de Météorologie Dynamique a consisté à la fois en l'amélioration du modèle et la réalisation de diverses expériences sur ce modèle. La principale amélioration apportée au modèle est la mise au point d'une bonne modélisation de la cascade inverse d'énergie, i.e. une simulation plus réaliste des plus grandes échelles de l'écoulement. Les expériences réalisées sur ce modèle amélioré concernent la dispersion (absolue ou relative), i.e. nous simulons l'advection de flotteurs lagrangiens par l'écoulement. Les résultats obtenus diffèrent sensiblement des conjectures théoriques et nous obligent à envisager une approche différente de la dispersion turbulente. J'ai ajouté le travail d'une année, réalisé comme scientifique du contingent à l'Institut de Mécanique de Grenoble, sur les instabilités qui se développent dans une couche de mélange bidimensionnelle.
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Fitzgerald, Kevin D. "Examination of flow around second-generation controlled diffusion compressor blades in cascade at stall." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FFitzgerald.pdf.
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Dubos, Thomas. "Cascade bidimensionnelle d'un traceur : diagnostic dans l'espace physique et modélisation." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2001. http://tel.archives-ouvertes.fr/tel-00007421.
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Nous présentons des résultats numériques et théoriques concernant les cascades en turbulence bidimensionnelle, et plus spécialement la cascade d'un traceur, en développant une approche dans l'espace physique. Une telle approche permet de mettre en évidence l'absence d'intermittence dans la cascade inverse d'énergie, y compris dans des situations dominées par les structures cohérentes. Le coeur de la thèse est consacré à l'analyse et à la modélisation de la cascade d'un traceur. Nous proposons une méthode de diagnostic de la cascade d'un traceur : considérant l'évolution d'un incrément de traceur, nous définissons dans l'espace physique le flux entre échelles de la variance de traceur. Nous nous intéressons ensuite au problème de la paramétrisation du mélange turbulent. Nous justifions l'emploi une paramétrisation anisotrope, que nous baptisons diffusivité de déformation (strain diffusivity, SD)[Dubos01]. Nous relions ses propriétés diffusives aux propriétés géométriques de l'écoulement. La vorticité est en deux dimensions un traceur actif, et la paramétrisation sous-maille pour la vorticité agit sur la vitesse. La cascade inverse d'énergie impose aux paramétrisations admissibles de conserver l'énergie. Nous montrons que la SD conserve l'énergie, et qu'elle est la seule d'une classe de modèles simples. Nous étudions numériquement les propriétés des outils introduits. Nous montrons que, contrairement à une diffusivité/hyperdiffusivité isotrope, la SD induit une diffusion bien corrélée au flux local de variance de traceur. Le filtre effectif qu'elle impose correspond au filtre gaussien à partir duquel elle est calculée. Cependant la réduction de l'erreur commise en cas d'utilisation d'une méthode spectrale et d'un filtre raide n'est pas évidente. Appliquée à la vorticité dans une situation où le forçage est à très petite échelle, la SD démontre en revanche une bien meilleure représentation des grandes échelles qu'une hyperdiffusivité. Enfin, nous analysons comparativement les propriétés de cascade de la vorticité et d'un traceur passif. Les critères de comparaison reposent sur des moyennes conditionnelles des dérivées lagrangiennes du carré du gradient du traceur. Nous mettons en évidence pour un champ aléatoire une différence cinématique entre traceur passif et vorticité, dont il subsiste une trace dans des champs turbulents.
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Arisi, Allan Nyairo. "Heat Transfer and Flow Characteristics on the Rotor Tip and Endwall Platform Regions in a Transonic Turbine Cascade." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/64501.
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This dissertation presents a detailed experimental and numerical analysis of the aerothermal characteristics of the turbine extremity regions i.e. the blade tip and endwall regions. The heat transfer and secondary flow characteristics were analyzed for different engine relevant configurations and exit Mach/Reynolds number conditions. The experiments were conducted in a linear blowdown cascade at transonic high turbulence conditions of Mexit ~ 0.85, 0.60 and 1.0, with an inlet turbulence intensity of 16% and 12% for the vane and blade cascade respectively. Transient infrared (IR) thermography technique and surface pressure measurement were used to map out the surface heat transfer coefficient and aerodynamic characteristics. The experiments were complemented with computational modeling using the commercial RANS equation solver ANSYS Fluent. The CFD results provided further insight into the local flow characteristics in order to elucidate the flow physics which govern the measured heat transfer characteristics. The results reveal that the highest heat transfer exists in regions with local flow reattachment and new-boundary layer formation. Conversely, the lowest heat transfer occurs in regions with boundary layer thickening and separation/lift-off flow. However, boundary layer separation results in additional secondary flow vortices, such as the squealer cavity vortices and endwall auxiliary vortex system, which significantly increase the stage aerodynamic losses. Furthermore, these vortices result in a low film-cooling effectiveness as was observed on a squealer tip cavity with purge flow. Finally, the importance of transonic experiments in analyzing the turbine section heat transfer and flow characteristics was underlined by the significant shock-boundary layer interactions that occur at high exit Mach number conditions.Ph. D.
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Russ, Thomas William. "A surface flow visualization study of boundary layer behavior on the blades of a solid-wall compressor cascade at high angles of attack." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53161.
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The oil-film surface flow visualization technique was applied to circular arc compressor blades in a solid wall, high aspect ratio cascade for the purpose of describing the transition from corner stall to full blade stall, and the blade surface flow under fully stalled conditions. Photos of the visualizations for three stagger angles are presented and analyzed. A map quantitatively describing the observed boundary layer development at midspan is presented.
The most interesting discovery of the work showed the suction surface flow to be essentially two-dimensional, in the geometric sense, preceding and following the transition to a fully separated flow at the leading edge. Corner stall was the observed three-dimensional mechanism prior to full stall. For fully-stalled conditions, the three-dimensional mechanism took the form of recirculating flow regions at the blade ends. Complete separation at the leading edge occurred at lower angles of attack for the higher stagger angles. Special blade oil-flow tests were conducted to evaluate Reynolds number and tip clearance effects on boundary layer development.
The experimental work was done as part of a larger research program aimed at measuring and predicting the stalled performance of a compressor cascade.Master of Science
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Nessler, Chase A. "Characterization of Internal Wake Generator at Low Reynolds Number with a Linear Cascade of Low Pressure Turbine Blades." Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1270749309.
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Hayward, Erin M. G. "Atomistic studies on irradiation damage in iron." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34004.
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Two topics involving irradiation damage in alpha-iron have been considered. First, damage cascades representative of those that would be induced by radiation have been simulated using molecular dynamics (MD). The number and type of defects produced are compared for pure iron and iron with a small hydrogen concentration. Second, the inter- action energy between point defects and line dislocations has been calculated for a number of configurations, using both molecular statics methods and calculations based on linear elastic continuum theory and the dipole force tensor. Results from both methods are com- pared. Results from these two topics are relevant for predicting macroscopic behaviors such as creep and plasticity in reactor structural materials.
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Nunes, Bonaventure R. "Numerical Loss Prediction of high Pressure Steam Turbine airfoils." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/51742.
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Steam turbines are widely used in various industrial applications, primarily for power extraction. However, deviation for operating design conditions is a frequent occurrence for such machines, and therefore, understanding their performance at off design conditions is critical to ensure that the needs of the power demanding systems are met as well as ensuring safe operation of the steam turbines. In this thesis, the aerodynamic performance of three different turbine airfoil sections ( baseline, mid radius and tip profile) as a function of angle of incidence and exit Mach numbers, is numerically computed at 0.3 axial chords downstream of the trailing edge. It was found that the average loss coefficient was low, owing to the fact that the flow over the airfoils was well behaved. The loss coefficient also showed a slight decrease with exit Mach number for all three profiles. The mid radius and tip profiles showed near identical performance due to similarity in their geometries. It was also found out that the baseline profile showed a trend of substantial increase in losses at positive incidences, due to the development of an adverse pressure zone on the blade suction side surface. The mid radius profile showed high insensitivity to angle of incidence as well as low exit flow angle deviation in comparison to the baseline blade.Master of Science
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Gompertz, Kyle Adler. "Separation Flow Control with Vortex Generator Jets Employed in an Aft-Loaded Low-Pressure Turbine Cascade with Simulated Upstream Wakes." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243990496.
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Severin, Timm Steffen [Verfasser], Dirk [Akademischer Betreuer] Weuster-Botz, Dirk [Gutachter] Weuster-Botz, and Harald [Gutachter] Klein. "Computational Fluid Dynamics Assisted Design of Thin-Layer Cascade Photobioreactor Components / Timm Steffen Severin ; Gutachter: Dirk Weuster-Botz, Harald Klein ; Betreuer: Dirk Weuster-Botz." München : Universitätsbibliothek der TU München, 2017. http://d-nb.info/1152006517/34.
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Severin, Timm Steffen Verfasser], Dirk [Akademischer Betreuer] [Weuster-Botz, Dirk [Gutachter] Weuster-Botz, and Harald [Gutachter] Klein. "Computational Fluid Dynamics Assisted Design of Thin-Layer Cascade Photobioreactor Components / Timm Steffen Severin ; Gutachter: Dirk Weuster-Botz, Harald Klein ; Betreuer: Dirk Weuster-Botz." München : Universitätsbibliothek der TU München, 2017. http://nbn-resolving.de/urn:nbn:de:bvb:91-diss-20171206-1363208-1-0.
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Vallgren, Andreas. "Dynamic properties of two-dimensional and quasi-geostrophic turbulence." Doctoral thesis, KTH, Mekanik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25712.
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Two codes have been developed and implemented for use on massively parallelsuper computers to simulate two-dimensional and quasi-geostrophic turbulence.The codes have been found to scale well with increasing resolution and width ofthe simulations. This has allowed for the highest resolution simulations of twodimensionaland quasi-geostrophic turbulence so far reported in the literature.The direct numerical simulations have focused on the statistical characteristicsof turbulent cascades of energy and enstrophy, the role of coherent vorticesand departures from universal scaling laws, theoretized more than 40 yearsago. In particular, the investigations have concerned the enstrophy and energycascades in forced and decaying two-dimensional turbulence. Furthermore, theapplicability of Charney’s hypotheses on quasi-geostrophic turbulence has beentested. The results have shed light on the flow evolution at very large Reynoldsnumbers. The most important results are the robustness of the enstrophycascade in forced and decaying two-dimensional turbulence, the sensitivity toan infrared Reynolds number in the spectral scaling of the energy spectrumin the inverse energy cascade range, and the validation of Charney’s predictionson the dynamics of quasi-geostrophic turbulence. It has also been shownthat the scaling of the energy spectrum in the enstrophy cascade is insensitiveto intermittency in higher order statistics, but that corrections apply to the”universal” Batchelor-Kraichnan constant, as a consequence of large-scale dissipationanomalies following a classical remark by Landau (Landau & Lifshitz1987). Another finding is that the inverse energy cascade is maintained bynonlocal triad interactions, which is in contradiction with the classical localityassumption.QC 20101029
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Gorbach, Kathleen R. "Benthic Community Structure Response to Flow Dynamics in Tropical Island and Temperate Continental Streams." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1354226302.
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Blackbourn, Luke A. K. "An analytical, phenomenological and numerical study of geophysical and magnetohydrodynamic turbulence in two dimensions." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/4291.
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In this thesis I study a variety of two-dimensional turbulent systems using a mixed analytical, phenomenological and numerical approach. The systems under consideration are governed by the two-dimensional Navier-Stokes (2DNS), surface quasigeostrophic (SQG), alpha-turbulence and magnetohydrodynamic (MHD) equations. The main analytical focus is on the number of degrees of freedom of a given system, defined as the least value $N$ such that all $n$-dimensional ($n$ ≥ $N$) volume elements along a given trajectory contract during the course of evolution. By equating $N$ with the number of active Fourier-space modes, that is the number of modes in the inertial range, and assuming power-law spectra in the inertial range, the scaling of $N$ with the Reynolds number $Re$ allows bounds to be put on the exponent of the spectrum. This allows the recovery of analytic results that have until now only been derived phenomenologically, such as the $k$[superscript(-5/3)] energy spectrum in the energy inertial range in SQG turbulence. Phenomenologically I study the modal interactions that control the transfer of various conserved quantities. Among other results I show that in MHD dynamo triads (those converting kinetic into magnetic energy) are associated with a direct magnetic energy flux while anti-dynamo triads (those converting magnetic into kinetic energy) are associated with an inverse magnetic energy flux. As both dynamo and anti-dynamo interacting triads are integral parts of the direct energy transfer, the anti-dynamo inverse flux partially neutralises the dynamo direct flux, arguably resulting in relatively weak direct energy transfer and giving rise to dynamo saturation. These theoretical results are backed up by high resolution numerical simulations, out of which have emerged some new results such as the suggestion that for alpha turbulence the generalised enstrophy spectra are not closely approximated by those that have been derived phenomenologically, and new theories may be needed in order to explain them.
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Ljungbäck, Jacob. "Characterization of Cascade gearbox for wave energy converter." Thesis, KTH, Maskinkonstruktion (Inst.), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-182811.
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This Master Thesis, written in collaboration with CorPower Ocean, serves as the finalization of the author’s master degree education at KTH (Royal Institute of Technology) Stockholm. The purpose has been to characterize the Cascade gearbox which is used to convert vertical motion induced by waves to rotational motion which powers generators in the company’s future wave energy power plant. The purpose was also to suggest future improvements and shed light on any problems discovered. The method for characterizing the Cascade gearbox was to conduct physical measurements of the load sharing in the inherently overdetermined geometrical design. These data were then used to calibrate a static as well as a dynamic model also developed for this thesis. Focus has been on determining that the novel load sharing method is sufficient and that no gear takes more than the 2,5% overload during max load the gearbox is dimensioned for at any time. Also included in the thesis is an analysis of the tolerances effect on the performance of the Cascade gearbox. Results showed that the current design perform within the expected dimensioning limits. However some unexpected characteristics were discovered after analysis of the results. Because of deliberate geometric decisions half of the gears trail behind initially in one direction causing uneven load sharing and unwanted lateral forces on the rack. Also discovered was the importance of equal stiffness of the flex units, used to divide the load evenly between the gears, since the load sharing factor converges towards values directly proportional to the stiffness ratios in between them. As a conclusion it can be said that although the current design is sufficient, there is still room for improvements which could enhance life expectancy as well as load sharing performance of the Cascade gearbox.Detta examensarbete utfört i samarbete med CorPower Ocean, är det slutgiltiga steget i författarens utbildning på masternivå på KTH (Kungliga Tekniska Högskolan) Stockholm. Syftet med arbetet är att karakterisera en kaskadväxellåda som används för att omvandla vertikal rörelse från vågor till rotation som driver generatorer i företagets framtida vågkraftverk samt att utifrån resultat föreslå möjliga förbättringar och belysa eventuella problem. Den metod som använts för att karakterisera kaskadväxellådan var att via fysiska mätningar, på den testrigg placerad på KTH (Kungliga Tekniska Högskolan) i Stockholm, erhålla data för lastfördelningen i den geometriskt överbestämda konstruktionen. Dessa data användes sedan för att kalibrera en statisk och en dynamisk modell som också utvecklades för det här projektet. Huvudfokus för arbetet har legat i att ta reda på om den konstruktion som används för att fördela lasten mellan kugghjulen fungerar tillfredställande samt att säkerställa att inget kugghjul tar mer än de 2,5% överlast vid fullast växellådan är dimensionerad för vid något tillfälle. Examensarbetet inkluderar även feltoleransers inverkan på lastfördelningen i kaskadväxeln. Resultaten visade att den nuvarande konstruktionen presterar inom de specificerade dimensioneringsintervallen. Några oväntade karaktärsdrag upptäckdes dock vid analys av resultaten. På grund av en avsiktlig geometrisk oregelbundenhet släpade hälften av kugghjulen efter åt ena hållet vilket i sin tur resulterade i en ojämn lastfördelning och oönskade sidokrafter på kuggracken. Flexenheterna som används för att fördela lasten likvärdigt mellan kugghjulen skilde sig åt i styvhet. Den inverkan spridningen av dessa har på lastfördelningen belystes också eftersom lastfördelningen konvergerar mot värden direkt proportionella mot styvhetsförhållandet mellan dem. Slutsatsen från examensarbetet är att den nuvarande konstruktionen, även om den fungerar tillfredställande, lämnar utrymme för förbättringar som potentiellt kan förbättra både livslängd och lastfördelningsprestanda.
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Raven, Hans Rafael. "Flow Control Optimization for Improvement of Fan Noise Reduction." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/30847.
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The study of the flow of a fan blade was conducted to improve tonal fan noise reduction by optimizing an existing flow control configuration. The current configuration consisted of a trailing edge Slot with a flow control area of 0.045 in² per inch span with an exit angle of -3.3° with respect to the blade exit angle. Two other flow control configurations containing discrete jets were investigated. For the first configuration, the trailing edge jets (TEJ), the fan blade was modified with discrete jets spaced 0.3 inches apart with a flow control area of 0.01 in² per inch span positioned on the trailing edge aimed at -3.3° with respect to the blade exit angle. Similarly, discrete jets were also placed on the suction surface at 95.5% chord aimed at 15° with respect to the local blade surface. This configuration is referred to as the suction surface jet (SSJ). The discrete jets for both configurations were designed to be choked while injecting a mass flow rate of 1.00% of the fan through-flow. Computational Fluid Dynamics (CFD) was used to model new configurations and study subsequent changes in total pressure deficit using a blade design inlet Mach number of 0.73, Reynolds number based on chord length of 1.67 à 106, and design incidence angle of 0°. Experimental testing was later conducted in a 2D cascade tunnel. The TEJ and SSJ were tested at design blowing of 1.00% and at off-design conditions of 0.50%, 0.75%, and 1.25% fan through-flow. Results between the different flow control configurations were compared using a blowing coefficient. CFD showed the TEJ and SSJ offered aerodynamic improvement over the Slot configuration. Testing showed the SSJ outperformed the TEJ, as validated in CFD, producing wider and shallower wakes. SSJ area-averaged pressure losses were 25% less than TEJ at design. Noise predictions based on CFD findings showed that both TEJ and SSJ provided additional tonal sound power level attenuation over the Slot configuration at similar blowing coefficients, with the SSJ providing the most attenuation. Noise prediction based on experimental results concurred that the SSJ provided more total attenuation than the TEJ. Experimental results showed that the SSJ performed better aerodynamically and, based on analytical prediction, provided 2 dB more total attenuation than the TEJ.Master of Science
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Gelwick, Katrina D. "Full of Hot Air: Heat Flow at the Medicine Lake Volcano Hot Spot, Modoc County, California." Oberlin College Honors Theses / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1398936533.
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Mukherji, Shankar 1982. "The dynamics of enzymatic switch cascades." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/32747.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics; and, (S.B.)--Massachusetts Institute of Technology, Dept. of Mathematics, 2004.Includes bibliographical references (leaf 67).
We examine the dynamics of the mitogen-activated protein kinase (MAPK) multi-step enzymatic switching cascade, a highly conserved architecture utilised in cellular signal transduction. In treating the equations of motion, we replace the usual deterministic differential equation formalism with stochastic equations to accurately model the 'effective collisions' picture of the biochemical reactions that constitute the network. Furthermore we measure the fidelity of the signaling process through the mutual information content between the output of a given switch and the original environmental input to the system. We find that the enzymatic switches act as low-pass filters, with each switch in the cascade able to average over high frequency stochastic fluctuations in the network and throughput cleaner signals to downstream switches. We find optimal regions of mutual information transfer with respect to reaction velocity and species number parameters, and observe the dynamical memory-gain and memory-loss as well as decay in mutual information in quadruple-linked switch systems.
by Shankar Mukherji.
S.B.
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Vallgren, Andreas. "Statistical characteristics of two-dimensional and quasigeostrophic turbulence." Licentiate thesis, KTH, Linné Flow Center, FLOW, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-13128.
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Two codes have been developed and implemented for use on massively parallelsuper computers to simulate two-dimensional and quasigeostrophic turbulence.The codes have been found to scale well with increasing resolution and width ofthe simulations. This has allowed for the highest resolution simulations of two-dimensional and quasigeostrophic turbulence so far reported in the literature.The direct numerical simulations have focused on the statistical characteristicsof turbulent cascades of energy and enstrophy, the role of coherent vorticesand departures from universal scaling laws, theoretized more than 40 yearsago. In particular, the investigations have concerned the enstrophy and energycascade in forced and decaying two-dimensional turbulence. Furthermore, theapplicability of Charney’s hypotheses on quasigeostrophic turbulence has beentested. The results have shed light on the flow evolution at very large Reynoldsnumbers. The most important results are the robustness of the enstrophycascade in forced and decaying two-dimensional turbulence, the unexpecteddependency on an infrared Reynolds number in the spectral scaling of theenergy spectrum in the inverse energy cascade, and the validation of Charney’spredictions on the dynamics of quasigeostrophic turbulence. It has also beenshown that the scaling of the energy spectrum in the enstrophy cascade isinsensitive to intermittency in higher order statistics, but that corrections mightapply to the ”universal” Batchelor-Kraichnan constant.
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Listén, Hedlin Embla. "Enzymatic cascade for dynamic kinetic resolution of amines." Thesis, KTH, Skolan för bioteknologi (BIO), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-215018.
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Toombes, Luke. "Experimental study of air-water flow properties on low-gradient stepped cascades /." St. Lucia, Qld, 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16746.pdf.
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McBean, Ivan William 1974. "Simulation of 3-dimensional aeroelastic effects in turbomachinery cascades." Monash University, Dept. of Mechanical Engineering, 2002. http://arrow.monash.edu.au/hdl/1959.1/7690.
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Fletcher, Nathan James. "Design and Implementation of Periodic Unsteadiness Generator for Turbine Secondary Flow Studies." Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1560810428267352.
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Iima, Makoto. "Dynamical Aspects of Cascade Process in Fully Developed Turbulence." 京都大学 (Kyoto University), 1998. http://hdl.handle.net/2433/182439.
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LIN, PENG. "Enzyme cascade reactions on 3D DNA scaffold with dynamic shape transformation." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/265209.
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京都大学新制・課程博士
博士(エネルギー科学)
甲第23437号
エネ博第424号
新制||エネ||81(附属図書館)
京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻
(主査)教授 森井 孝, 教授 佐川 尚, 教授 片平 正人
学位規則第4条第1項該当
Doctor of Energy Science
Kyoto University
DFAM
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Roux, Louis. "Modélisation dynamique du départ d'une pale et de la tenue des pales suiveuses dans une turbomachine." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI056.
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Lors de la phase de certification d’un turbomoteur, le motoriste doit démontrer que la perte d’une pale de rotor ne conduit pas au "Knocking-Off", c’est à dire à la rupture en cascade des pales suiveuses. Cette démonstration est faite en général par un essai au banc coûteux car partiellement destructif. Grâce à l’amélioration des moyens de calcul, il devient possible de simuler la réponse transitoire de la structure soumise à ce type de chargement très complexe. En tant que point d’entrée sur la simulation, la connaissance du comportement des matériaux est primordiale. Or, peu d’études sont publiées sur le comportement dynamique des superalliages à base nickel monocristallins et, de surcroît, à des températures élevées de l’ordre de 1000°C. Pour prédire efficacement les conséquences d’impacts sur des pales de turbines, des travaux expérimentaux et numériques ont été réalisés sur un monocristal couramment utilisé par Turbomeca. Des essais de compression dynamique à haute température sur barres de Hopkinson permettent d’estimer le seuil de plasticité et l’écrouissage du matériau en fonction de l’orientation du cristal, de la vitesse de déformation et de la température. Les paramètres d’une loi visco-plastique anisotrope sont identifiés pour modéliser efficacement le comportement macroscopique du MC2 sous des chargements intenses et fortement multi-axiaux. Une campagne d’essais balistiques au banc de Safran Snecma a été réalisée sur des plaques et des pales monocristallines à hautes températures. Afin de prendre en compte la fragmentation des profils dans les calculs de perte de pale, un critère en déformation plastique dépendante du taux de triaxialité des contraintes est calibré puis validé par confrontation aux essais de tirs sur plaques. Des mesures de stéréo-corrélation postmortem et des enregistrements à la caméra rapide permettent de valider les simulations. Une pratique de modélisation de la perte d’une pale avec l’outil LS-Dyna a été établie et appliquée à un cas industriel de perte de pale en service. Enfin, en vue de justifier le découplage temporel entre les dommages primaires, liés aux impacts directs sur les premières pales suiveuses, et secondaires, liés aux effets de l’excentration, une approche de dynamique d’ensemble de ligne d’arbre a été développée puis validéeDuring the certification process of a turbo engine, the engine manufacturer has to demonstrate that the loss of a rotor blade does not lead to the "knocking-off" phenomenon, in other words to the cascading failure of the successive blades. Generally, this demonstration is carried out through a costly rig test driving to the partial destruction of the engine. Thanks to the improvement of computational resources, it is now possible to simulate the transient response of the structure subjected to this complex loading. The knowledge of material behavior turns out to be the essential starting point for the simulation. However, only a few studies have been published on the dynamic behavior of nickel-based single crystal superalloys at high temperature reaching 1000°C. With a view to efficiently predicting the consequences of impacts on turbine blades, experimental and numerical works have been conducted on a single crystal frequently used by Turbomeca. High-temperature dynamic compressive tests on Split Hopkinson Pressure Bars (SHPB) have enabled to estimate the material plasticity level and hardening, depending on the crystal orientation, strain rate and temperature. The parameters of a viscoplastic anisotropic law have been identified to effectively model the MC2 macroscopic behavior under highly intense and multiaxial loading. At Safran Snecma Villaroche, ballistic tests have been undertaken on both single crystal plates and blades under high temperatures. In order to consider the fragmentation of profiles in blade-off simulations, a plastic strain criterion depending on stress triaxiality has been calibrated and validated by comparison with the impacts on blades. Post-mortem digital images correlation measurements and high-speed camera recordings have confirmed these simulations. Using LS-Dyna solver, a blade-off modeling strategy has been created and applied to an actual blade-off industrial case. Finally, a rotordynamics approach has been developed and validated with the aim of separately analyzing the primary damage, caused by direct impacts on the first following blades, and the secondary damage due to the effects of unbalance on a flexible rotor