Дисертації з теми "Instability and transition"
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Zhao, Yongling. "Instability and Transition of Natural Convection Boundary Layers." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/13126.
Повний текст джерелаPicella, Francesco. "Retarder la transition vers la turbulence en imitant les feuilles de lotus." Thesis, Paris, ENSAM, 2019. http://www.theses.fr/2019ENAM0014/document.
Повний текст джерелаMany passive control strategies have been recently proposed for reducing drag in wall-bounded shearflows. Among them, underwater SuperHydrophobic Surfaces (SHS) have proven to be capable of dramaticallyreducing the skin friction of a liquid flowing on top of them, due to the presence of gas bubbles trapped within thesurface nano-sculptures. In specific geometrical and thermodynamical conditions for which wetting transition isavoided (in particular, when the roughness elements characterizing the SHS are several orders of magnitude smallerthan the overlying flow), the so-called ’Lotus effect’ is achieved, for which the flow appears to slip on the surfacewith a non zero velocity. In this framework, we propose to study, by means of numerical simulations, the influence ofSHS on laminar-turbulent transition in a channel flow. To do so we have performed a series of direct numericalsimulations (DNS), from the laminar to the fully turbulent state, covering the majority of transition scenarios knownin the literature, as well as local and global stability analysis so to determine the influence of SHS onto the initialstages of the process. While the conditions for observing controlled K-type transition in a temporal channel flow arewell defined, this is not the case for uncontrolled ones. To this end, a novel theoretical numerical framework has beendeveloped so to enable the observation of natural transition in wall-bounded flows. This method, similarly to theFree-Stream-Turbulence framework available for the boundary layer flow, is capable of triggering uncontrolledtransition t hrough flow receptivity to a purpose-built forcing. Different surface modellings for the superhydrophobicsurfaces are tested. First, homogeneous slip conditions are used. Then, the spatial heterogeneity of the SHS has beenconsidered by modelling it as a flat surface with alternating slip no-slip boundary conditions. Finally, the dynamics ofeach microscopic liquid-gas free-surface has been taken into account by means of a fully coupled fluid-structuresolver, using an Arbitrary Lagrangian Eulerian formulation. We show that while SHS are ineffective in controllingtransition in noisy environment , they can strongly delay transition to turbulence for the K-type scenario . Thisbehaviour results from the balance of two opposing effects. On one hand slippery surfaces inhibit the development ofcharacteristic hairpin vortices by altering the vortex stretching-tilting process. On the other hand, the movement ofthe gas-liquid free-surfaces interacts with the overlying coherent structures, producing wall-normal velocities thatenhance the sweep-ejection process, leading to a rapid formation of hairpin-like head vortices. Thus, whenconsidering flat interfaces transition time is strongly increased, while taking into account the interface dynamicsinduces smaller changes with respect to the no-slip case, indicating the need for an appropriate modelling of SHS fortransition delay purposes
Patel, Sanjay. "Computational modelling of instability and transition using high-resolution methods." Thesis, Cranfield University, 2007. http://hdl.handle.net/1826/3235.
Повний текст джерелаYoshimura, Kazuyuki. "Mode instability and chaoticity transition in one-dimensional anharmonic lattices." Kyoto University, 1997. http://hdl.handle.net/2433/202314.
Повний текст джерелаRobey, H. F. Liepmann H. W. Liepmann H. W. "The nature of oblique instability waves in boundary layer transition /." Diss., Pasadena, Calif. : California Institute of Technology, 1986. http://resolver.caltech.edu/CaltechETD:etd-05242007-150746.
Повний текст джерелаSavin, Deborah Jane. "Linear and nonlinear aspects of interactive boundary layer transition." Thesis, University College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243306.
Повний текст джерелаHagan, J. "Nonlinear instabilities and transition to turbulence in magnetohydrodynamic channel flow." Thesis, Coventry University, 2013. http://curve.coventry.ac.uk/open/items/cc5976b0-419c-4944-a2ff-3af446a03d05/1.
Повний текст джерелаHosseini, Seyed Mohammad. "Stability and transition of three-dimensional boundary layers." Licentiate thesis, KTH, Stabilitet, Transition, Kontroll, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-123175.
Повний текст джерелаQC 20130604
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Appelquist, Ellinor. "The rotating-disk boundary-layer flow studied through numerical simulations." Doctoral thesis, KTH, Mekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-200827.
Повний текст джерелаQC 20170203
Schmidt, Oliver [Verfasser]. "Numerical investigations of instability and transition in streamwise corner-flows / Oliver Schmidt." München : Verlag Dr. Hut, 2014. http://d-nb.info/1052375626/34.
Повний текст джерелаWang, Yaxing. "Instability and transition of boundary layer flows disturbed by steps and bumps." Thesis, Queen Mary, University of London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404889.
Повний текст джерелаJouravleva, Karina. "Telomere-driven chromosome instability impacts the genetic program through genome-wide epigenetic reprogramming." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066286.
Повний текст джерелаTelomere shortening is a major source of chromosome instability (CIN) at early stages during carcinogenesis. However, the mechanisms through which telomere-driven CIN (T-CIN) contributes to the acquisition of tumor phenotypes remain uncharacterized. We have shown that human epithelial kidney (HEK) cells undergo massive microRNA deregulation upon CIN, in particular a miR-200-dependent epithelial-mesenchymal transition (EMT), which is thought to enable epithelial cancer cells to migrate and invade other tissues to form metastases. Our work also indicated that CIN+ cells that underwent EMT were able to form tumors in a senescent microenvironment. Notably, this progression in tumor capacity was associated with further microRNA deregulation and the manifestation of enhanced stem-like properties. To investigate how stem-like properties are acquired in CIN+ cells in the contact with senescent microenvironment we adapted knockdown and overexpression approaches to modulate miR-145 expression, and demonstrated that enhanced stem-like properties depended on miR-145 repression. To fully apprehend the impact of CIN on the genetic program of epithelial cells, we used an unbiased approach to characterize the chromatin state of HEK CIN+ cells and uncover genome wide redistributions that were in direct correlation with gene expression changes. Our results reveal for the first time that T-CIN profoundly modifies the chromatin landscape genome-wide thereby fueling the transformation process of pre-tumor epithelial cells
Nicholls, Ursula Joy. "An investigation of a structural phase transition : the R-point instability in KMnF₃." Thesis, University of Edinburgh, 1987. http://hdl.handle.net/1842/15519.
Повний текст джерелаValiev, Damir. "Flame Dynamics and Deflagration-to-Detonation Transition." Doctoral thesis, Stockholm : Industriell teknik och management, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4875.
Повний текст джерелаLiu, Chonghui. "A numerical investigation of instability and transition in adverse pressure gradient boundary layers." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0010/NQ36999.pdf.
Повний текст джерелаImayama, Shintaro. "Studies of the rotating-disk boundary-layer flow." Doctoral thesis, KTH, Strömningsfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-158973.
Повний текст джерелаQC 20150119
Hosseini, Seyed Mohammd. "On stability, transition and turbulence in three-dimensional boundary-layer flows." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-177617.
Повний текст джерелаQC 20151125
Valiev, Damir. "The role of Landau-Darrieus instability in flame dynamics and deflagration-to-detonation transition." Licentiate thesis, Stockholm : Materialvetenskap, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4334.
Повний текст джерелаMoradi, Nour Zeinab. "Simulation and modal analysis of instability and transition in a steady eccentric stenotic flow." Thesis, KTH, Mekanik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118945.
Повний текст джерелаTrajkova, Natasha. "Instability and volatility of economic growth under transition : an application of exogenous growth theory." Thesis, Staffordshire University, 2013. http://eprints.staffs.ac.uk/2031/.
Повний текст джерелаPlogmann, Benjamin [Verfasser]. "Experimental investigations on roughness initiated instability and transition in airfoil boundary layers / Benjamin Plogmann." München : Verlag Dr. Hut, 2015. http://d-nb.info/1079768254/34.
Повний текст джерелаRowley, Craig Emlyn. "Transient behaviour in boundary layers close to the transition from convective to absolute instability." Thesis, Keele University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398909.
Повний текст джерелаLefort, Eric. "Caractérisation des bifurcations et de la dynamique d'une lentille thermique par analyse spectrale." Rouen, 1987. http://www.theses.fr/1987ROUES019.
Повний текст джерелаImayama, Shintaro. "Experimental study of the rotating-disk boundary-layer flow." Licentiate thesis, KTH, Mekanik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95147.
Повний текст джерелаQC 20120529
Marais, Anthony. "Influence du vieillissement statique sur la transition ductile-fragile des aciers au C-Mn." Phd thesis, École Nationale Supérieure des Mines de Paris, 2012. http://pastel.archives-ouvertes.fr/pastel-00820120.
Повний текст джерелаMicchi, Gianluca. "Mechanical signatures of the current-blockade instability in suspended carbon nanotubes." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0337/document.
Повний текст джерелаThe strong coupling between electronic transport in a single-level quantum dot and a capacitively coupled nano-mechanical oscillator may lead to a transition towards a mechanically-bistable and blocked-current state. Its observation is at reach in carbonnanotube state-of-art experiments. Therefore, we investigate the mechanical response of the system, namely the displacement spectral function, the linear response to a driving, and the ring-down behavior, and the electric response, namely the electric current and current spectral function. We show that a close relation between electric and mechanical quantities exists. We find that, by increasing the lectromechanical coupling, the peak in both spectral functions broadens and shifts at low frequencies while the oscillator dephasing time shortens. These effects are maximum at the transition where nonlinearities dominate the dynamics, and are robust towards the effect of external uctuations and dissipation. These strong signatures open the way to detect the blockade transition in devices currently studied by several groups
Lu, Meichen. "Transition between flow regimes in porous media using magnetic resonance velocimetry : from laminar to turbulent." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288744.
Повний текст джерелаWeirauch, Daniel R. "A high-resolution record of climate instability spanning ~1.0 million years across the mid-Pleistocene transition." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 131 p, 2007. http://proquest.umi.com/pqdweb?did=1472642111&sid=21&Fmt=2&clientId=8331&RQT=309&VName=PQD.
Повний текст джерелаBrandt, Luca. "Numerical studies of bypass transition in the Blasius boundary layer." Doctoral thesis, KTH, Mechanics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3517.
Повний текст джерелаExperimental findings show that transition from laminar toturbulent ow may occur also if the exponentially growingperturbations, eigensolutions to the linearised disturbanceequations, are damped. An alternative non-modal growthmechanism has been recently identi fied, also based on thelinear approximation. This consists of the transient growth ofstreamwise elongated disturbances, with regions of positive andnegative streamwise velocity alternating in the spanwisedirection, called streaks. These perturbation are seen toappear in boundary layers exposed to signi ficant levels offree-stream turbulence. The effect of the streaks on thestability and transition of the Blasius boundary layer isinvestigated in this thesis. The analysis considers the steadyspanwise-periodic streaks arising from the nonlinear evolutionof the initial disturbances leading to the maximum transientenergy growth. In the absence of streaks, the Blasius pro filesupports the viscous exponential growth of theTollmien-Schlichting waves. It is found that increasing thestreak amplitude these two-dimensional unstable waves evolveinto three-dimensional spanwiseperiodic waves which are lessunstable. The latter can be completely stabilised above athreshold amplitude. Further increasing the streak amplitude,the boundary layer is again unstable. The new instability is ofdifferent character, being driven by the inectional pro filesassociated with the spanwise modulated ow. In particular, it isshown that, for the particular class of steady streaksconsidered, the most ampli fied modes are antisymmetric andlead to spanwise oscillations of the low-speed streak (sinuousscenario). The transition of the streak is then characterisedby the appearance of quasi-streamwise vorticesfollowing themeandering of the streak.
Simulations of a boundary layer subjected to high levels offree-stream turbulence have been performed. The receptivity ofthe boundary layer to the external perturbation is studied indetail. It is shown that two mechanisms are active, a linearand a nonlinear one, and their relative importance isdiscussed. The breakdown of the unsteady asymmetric streaksforming in the boundary layer under free-stream turbulence isshown to be characterised by structures similar to thoseobserved both in the sinuous breakdown of steady streaks and inthe varicose scenario, with the former being the mostfrequently observed.
Keywords:Fluid mechanics, laminar-turbulent transition,boundary layer ow, transient growth, streamwise streaks,lift-up effect, receptivity, free-stream turbulence, secondaryinstability, Direct Numerical Simulation.
Chiu, Hsin-Yao. "Family Structure and Family Instability: Evaluating Their Influence on Adult Outcomes." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3398.
Повний текст джерелаGazanion, Bertrand. "Transition laminaire-turbulent dans un conduit à paroi débitante." Thesis, Toulouse, ISAE, 2014. http://www.theses.fr/2014ESAE0053/document.
Повний текст джерелаThe present work is related to the prediction of oscillations in solid rocket motors inner flow. It consists in a study of the laminar-turbulent transition of the motor’s inner flow, which is represented by a cylindrical injection-driven flow, and the relation between this phenomenon and the natural instability named Parietal Vortex Shedding (PVS). Three aspects have been analyzed.First of all, previous cold-gas experiments – reproducing the injection driven flow – are analyzed in order to highlight the transition laminar-turbulent transition. This transition is then imposedin URANS simulations to enable a study of its influence on the PVS modes. Finally, Large Eddy Simulations are performed to simulate the laminar-turbulent process. A strategy based on spatial steady disturbances is used to ease this process. The mains conclusions of this work are the following ones. The laminar-turbulent transition is a consequence of the spatial amplification of PVS modes. Simulations of this process highlight a strong influence of the injected numerical disturbances. The URANS simulations show that this transition reduces the amplification of PVSmodes, and the resulting pressure oscillations levels. These results confirm the role of the transitionin the absence of pressure oscillations when the motor cavity is long. A distinctive feature ofthis transition is its dependence on the radial position, which leads to the coexistence of a laminar region in the channel core and a turbulent region near the injecting wall at a given axial position
Farano, Mirko. "Using nonlinear optimization to understand coherent structures in turbulence and transition." Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0047/document.
Повний текст джерелаThis thesis aims at unraveling the main mechanisms involved in transitional and turbulent flows. The central idea is that of using a nonlinear optimization technique to investigate the origin and role of coherent structures usually observed in these flows. This method has been used in three different contexts. First, a linearly stable laminar flow has been considered and the optimization has been used to compute the most amplified perturbations among all disturbances able to trigger transition to turbulence. Once turbulence is well established, a fully 3D nonlinear optimization maximizing the turbulent kinetic energy is used to study coherent structures populating turbulent shear flow as well as investigate the mechanisms responsible for the energy (optimally) growth and exchange. Then, a dynamical system approach is applied to fluid flow equations. The geometry of the state space is investigated by using transient growth theory to reveal the importance of the stable and unstable manifold. In the same framework, a nonlinear minimization algorithm is used to compute heteroclinic connections among invariant solutions of the Navier-Stokes equations
Puckert, Dominik [Verfasser]. "Experimental Investigation on Global Instability and Critical Reynolds Number in Roughness-Induced Laminar-to-Turbulent Transition / Dominik Puckert." München : Verlag Dr. Hut, 2019. http://d-nb.info/1181515130/34.
Повний текст джерелаAppelquist, Ellinor. "Direct numerical simulations of the rotating-disk boundary-layer flow." Licentiate thesis, KTH, Mekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-146087.
Повний текст джерелаQC 20140708
Samad, Abdul. "The convective instability of the boundary-layer flow over families of rotating spheroids." Thesis, University of Leicester, 2011. http://hdl.handle.net/2381/27576.
Повний текст джерелаHögberg, Markus. "Optimal Control of Boundary Layer Transition." Doctoral thesis, KTH, Mechanics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3245.
Повний текст джерелаTyagi, P. K. "Linear Instability Of Laterally Strained Constant Pressure Boundary Layer Flows." Thesis, Indian Institute of Science, 2001. https://etd.iisc.ac.in/handle/2005/265.
Повний текст джерелаTyagi, P. K. "Linear Instability Of Laterally Strained Constant Pressure Boundary Layer Flows." Thesis, Indian Institute of Science, 2001. http://hdl.handle.net/2005/265.
Повний текст джерелаChiffaudel, Arnaud. "Dynamique spatio-temporelle de la convection a bas nombre de prandtl." Paris 7, 1988. http://www.theses.fr/1988PA077037.
Повний текст джерелаKhapko, Taras. "Transition to turbulence in the asymptotic suction boundary layer." Licentiate thesis, KTH, Stabilitet, Transition, Kontroll, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-141344.
Повний текст джерелаQC 20140213
Chrust, Marcin. "Etude numérique de la chute libre d'objets axisymétriques dans un fluide newtonien." Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00749659.
Повний текст джерелаStewart, I. J. "A model for transition by attachment line contamination and an examination of cross-flow instability in three-dimensional boundary layers." Thesis, Cranfield University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380625.
Повний текст джерелаGurun, Akif Murat. "Interactions of Tollmien-Schlichting Waves and Stationary Transient Disturbances." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1133374397.
Повний текст джерелаMartínez, Germán Andrés Gaviria. "Towards natural transition in compressible boundary layers." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-24052017-114027/.
Повний текст джерелаNo presente trabalho, um código DNS (Direct Numerical Simulation) foi desenvolvido para abordar problemas de transição para turbulência em camada limite subsônica compressível em uma placa plana. Foram realizados testes de validação de código , nos regimes linear e não linear do processo de transição, nos regimes incompressível e compressível. O foco do presente trabalho é estudar transição natural modelada por meio de pacotes de onda em camada limite compressível subsônica, e realizar uma análise preliminar da transição induzida por ruído branco. Três assuntos principais foram considerados: uma simulação DNS e uma análise comparativa com o experimento (MEDEIROS; GASTER, 1999b) sobre a evolução de um pacote de ondas em camada limite incompressível, a influência da compressibilidade na evolução de pacotes de ondas no regime subsônico, e por último, um estudo preliminar da transição induzida por ruído branco em Mach 0.2 e Mach 0.9. As comparações realizadas entre a solução numérica e os dados experimentais mostram uma boa concordância, nos regimes linear e não linear, tanto no espaço físico quanto no espaço de Fourier. A simulação numérica deste experimento e a análise realizada neste trabalho, não são encontradas na literatura para o regime incompressível. A análise modal não linear aplicada aos resultados, permitiu identificar a presença das ressonâncias tipo H e tipo K no pacote de ondas. A influência da compressibilidade na evolução dos pacotes de onda foi estudada em Mach 0.7 e Mach 0.9. Na literatura não há trabalhos sobre pacotes de ondas no regime sub- sônico. No regime linear da transição, os modos oblíquos resultam ser os mais instáveis para Mach > 0.7, como era de esperar, de acordo com os resultados da literatura. No regime não linear, foram observadas estrias de moderada amplitude, associadas com modos de baixa frequência que acabam decaindo. O pacote de ondas em Mach 0.9 apresentou amplificação não linear somente na banda subharmônica, que pode ser associada com transição tipo H ou ressonância dessintonizada. No entanto, o comportamento geral neste regime é estabilizante. Por sua vez, a interação entre pacotes de ondas em Mach 0.9 mostrou um comportamento desestabilizante, pois a interação acaba gerando amplificação não linear em modos que decaem no pacote isolado. Os modos amplificados sugerem a presença do mecanismo de transição oblíqua. Finalmente, a evolução da mesma perturbação constituída por ruído branco em Mach 0.2 e Mach 0.9, resultaram ser completamente diferentes. Na camada limite incompressível foram observados vórtices tipo lambda, que poderiam ser gerados pela presença localizada das ressonâncias tipo H e/ou tipo K. No regime compressível foram observados vórtices distribuidos em todo o domínio, o que sugere a presença da transição oblíqua. Na transição gerada por ruído branco a compressibilidade teve uma influência maior que no pacote de ondas. Nas condições estudadas, a interação entre pacotes de ondas parece ser uma melhor representação do ruído branco no regime compressível.
She, Zhen-Su. "Instabilites et dynamique a grande echelle en turbulence." Paris 7, 1987. http://www.theses.fr/1987PA077241.
Повний текст джерелаBrandt, Luca. "Study of generation, growth and breakdown of streamwise streaks in a Blasius boundary layer." Licentiate thesis, KTH, Mechanics, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1256.
Повний текст джерелаTransition from laminar to turbulent flow has beentraditionally studied in terms of exponentially growingeigensolutions to the linearized disturbance equations.However, experimental findings show that transition may occuralso for parameters combinations such that these eigensolutionsare damped. An alternative non-modal growth mechanism has beenrecently identified, also based on the linear approximation.This consists of the transient growth of streamwise elongateddisturbances, mainly in the streamwise velocity component,called streaks. If the streak amplitude reaches a thresholdvalue, secondary instabilities can take place and provoketransition. This scenario is most likely to occur in boundarylayer flows subject to high levels of free-stream turbulenceand is the object of this thesis. Different stages of theprocess are isolated and studied with different approaches,considering the boundary layer flow over a flat plate. Thereceptivity to free-stream disturbances has been studiedthrough a weakly non-linear model which allows to disentanglethe features involved in the generation of streaks. It is shownthat the non-linear interaction of oblique waves in thefree-stream is able to induce strong streamwise vortices insidethe boundary layer, which, in turn, generate streaks by thelift-up effect. The growth of steady streaks is followed bymeans of Direct Numerical Simulation. After the streaks havereached a finite amplitude, they saturate and a new laminarflow, characterized by a strong spanwise modulation isestablished. Using Floquet theory, the instability of thesestreaks is studied to determine the features of theirbreakdown. The streak critical amplitude, beyond which unstablewaves are excited, is 26% of the free-stream velocity. Theinstability appears as spanwise (sinuous-type) oscillations ofthe streak. The late stages of the transition, originating fromthis type of secondary instability, are also studied. We foundthat the main structures observed during the transition processconsist of elongated quasi-streamwise vortices located on theflanks of the low speed streak. Vortices of alternating signare overlapping in the streamwise direction in a staggeredpattern.
Descriptors:Fluid mechanics, laminar-turbulenttransition, boundary layer flow, transient growth, streamwisestreaks, lift-up effect, receptivity, free-stream turbulence,nonlinear mechanism, streak instability, secondary instability,Direct Numerical Simulation.
QC 20100518
Boulfelfel, Salah Eddine. "Atomic Scale Investigation of Pressure Induced Phase Transitions in the solid State." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-25283.
Повний текст джерелаLe, Quéré Patrick. "Etude de la transition à l'instationnarité des écoulements de convection naturelle en cavité verticale différentiellement chauffée par méthodes spectrales chebyshev." Poitiers, 1987. http://www.theses.fr/1987POIT2003.
Повний текст джерелаZhou, Wei. "Instabilités de trajectoires de sphères, ellipsoïdes et bulles." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAD038/document.
Повний текст джерелаThe thesis presents a numerical study of path instabilities for spheres, oblate spheroids and bubbles moving freely under the effect of the gravity, buoyancy and hydrodynamic forces. For spheres, the parametric study of Jenny et al. (2004) is revisited, improved end extended with a special focus on the chaotic states. The results reveal that the effect of density ratio responsible for different oblique oscillating states of low and high frequencies has a significant impact both on the onset of chaos and on the behavior of fully chaotic states. Several quantitative statistical quantities are proposed and shown to be relevant for establishing the relation between chaotic and ordered states and for an objective comparison of random data of numerical or experimental origin. The extensive study on freely moving spheroids establishes the link between disks and spheres by varying the aspect ratio of spheroids from infinitely flat to almost spherical. The state diagrams provided for eight different aspect ratios of spheroid show in detail how the transition scenario varies depending of the body shape. The investigation of almost spherical spheroids reveals the specificities of the dynamics of light imperfect spheres.For the deformable gas bubble in the limit of zero gas/liquid density and viscosity ratio, a marginal stability curve is given in the two-parameter plane of the Galileo and the Bond number indicating the critical Galileo numbers for the loss of stability of vertical trajectories. The numerical investigation covers more than two decades of Bond number going from 0.1 to 20. The results clearly show the crucial role of the surface deformation
Graumer, Pierre. "Etude du mélange gazeux produit par instabilité de Richtmyer-Meshkov en régime initial périodique faiblement diffus." Thesis, Toulouse, ISAE, 2019. http://www.theses.fr/2019ESAE0015/document.
Повний текст джерелаThis work proposes an experimental analysis of the spatio-temporal development of an air/heliummixing zone promoted by the Richtmyer-Meshkov instability (RMI). This study relies on the useof a vertical shock tube and on the development of a new experimental protocol associated with aninnovative device for the generation of an initial interface between two gazeous species. This deviceconsists a rigid retractable curtain and of a series of rotating shutters. The characterization ofthis initial interface and the spatio-temporal evolution of the RMI-induced mixing zone is carriedout by exploiting the results of various experimental methods such as time resolved Schlierenvisualizations, planar laser mie scattering and Particle Image Velocimetry (PIV). In a first step,various measurement campaigns have made it possible to quantify the repeatability of the newdevice and to demonstrate its ability to generate a periodic, weakly diffused interface. In a secondstep, a study of the gaseous mixing for a given set of experimental parameters is proposed. Theanalysis focuses on the understanding of the underlying mechanisms driving the gaseous interfaceformation and the transition to turbulence of the RMI-induced mixing. The interaction betweenthis mixing zone and the reflected shock from the upper end of the tube (re-shock phenomenon)is also studied in order to confirm the turbulent transition of the mixing zone