Dissertations / Theses on the topic 'Hydrodynamics instabilities'
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Barber, Jacqueline Claire. "Hydrodynamics, heat transfer and flow boiling instabilities in microchannels." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/4000.
Full textCai, Kai. "Three-dimensional hydrodynamics simulations of gravitational instabilities in embedded protoplanetary disks." [Bloomington, Ind.] : Indiana University, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3229601.
Full text"Title from dissertation home page (viewed July 11, 2007)." Source: Dissertation Abstracts International, Volume: 67-08, Section: B, page: 4472. Adviser: Richard H. Durisen.
Murphy, Jeremiah Wayne. "Multi-dimensional Hydrodynamics of Core-collapse Supernovae." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/194155.
Full textHadley, Kathryn Z. 1955. "Linear stability analysis of nonaxisymmetric instabilities in self-gravitating polytropic disks." Thesis, University of Oregon, 2011. http://hdl.handle.net/1794/11253.
Full textAn important problem in astrophysics involves understanding the formation of planetary systems. When a star-forming cloud collapses under gravity its rotation causes it to flatten into a disk. Only a small percentage of the matter near the rotation axis falls inward to create the central object, yet our Sun contains over 99% of the matter of our Solar System. We examine how global hydrodynamic instabilities transport angular momentum through the disk causing material to accrete onto the central star. We analyze the stability of polytropic disks in the linear regime. A power law angular velocity of power q is imposed, and the equilibrium disk structure is found through solution of the time-independent hydrodynamic equations via the Hachisu self-consistent field method. The disk is perturbed, and the time-dependent linearized hydrodynamic equations are used to evolve it. If the system is unstable, the characteristic growth rate and frequency of the perturbation are calculated. We consider modes with azimuthal e im[varphi] dependence, where m is an integer and [varphi] is the azimuthal angle. We map trends across a wide parameter space by varying m , q and the ratios of the star-to-disk mass M * /M d and inner-to-outer disk radius r - /r + . We find that low m modes dominate for small r - /r + , increasing to higher r - /r + as M * /M d increases, independent of q . Three main realms of behavior are identified, for M * << M d , M * [approximate] M d and M * >> M d , and analyzed with respect to the I, J and P mode types as discussed in the literature. Analysis shows that for M * << M d , small r - /r + disks are dominated by low m I modes, which give way to high m J modes at high r - /r + . Low m J modes dominate M * [approximate] M d disks for small r - /r + , while higher m I modes dominate for high r - /r + . Behavior diverges with q for M * >> M d systems with high q models approximating M * [approximate] M d characteristics, while low q models exhibit m = 2 I modes dominating where r - /r + < 0.60.
Committee in charge: Raymond Frey, Chairperson; James Imamura, Advisor; Robert Zimmerman, Member; Paul Csonka, Member; Alan Rempel, Outside Member
Simon, Jacob B., Philip J. Armitage, Andrew N. Youdin, and Rixin Li. "Evidence for Universality in the Initial Planetesimal Mass Function." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626045.
Full textNuruzzaman, Shelly. "Study of parametric and hydrodynamic instabilities in laser produced plasmas." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391443.
Full textKazeroni, Rémi. "Explosion asymétrique des supernovae gravitationnelles." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS315/document.
Full textA core-collapse supernova represents the ultimate stage of the evolution of massive stars.The iron core contraction may be followed by a gigantic explosion which gives birth to a neutron star.The multidimensional dynamics of the innermost region, during the first hundreds milliseconds, plays a decisive role on the explosion success because hydrodynamical instabilities are able to break the spherical symmetry of the collapse.Large scale transverse motions generated by two instabilities, the neutrino-driven convection and the Standing Accretion Shock Instability (SASI),increase the heating efficiency up to the point of launching an asymmetric explosion and influencing the birth properties of the neutron star.In this thesis, hydrodynamical instabilities are studied using numerical simulations of simplified models.These models enable a wide exploration of the parameter space and a better physical understanding of the instabilities, generally inaccessible to realistic models.The non-linear regime of SASI is analysed to characterize the conditions under which a spiral mode prevails and to assess its ability to redistribute angular momentum radially.The influence of rotation on the shock dynamics is also addressed.For fast enough rotation rates, a corotation instability overlaps with SASI and greatly impacts the dynamics.The simulations enable to better constrain the effect of non-axisymmetric modes on the angular momentum budget of the iron core collapsing into a neutron star.SASI may under specific conditions spin up or down the pulsar born during the explosion.Finally, an idealised model of the heating region is studied to characterize the non-linear onsetof convection by perturbations such as those produced by SASI or pre-collapse combustion inhomogeneities. The dimensionality issue is examined to stress the beneficial consequences of the three-dimensional dynamics on the onset of the explosion
Simon, Jacob B., Philip J. Armitage, Rixin Li, and Andrew N. Youdin. "THE MASS AND SIZE DISTRIBUTION OF PLANETESIMALS FORMED BY THE STREAMING INSTABILITY. I. THE ROLE OF SELF-GRAVITY." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621219.
Full textMeyer, Christophe. "Experimental study of imprinting and hydrodynamic instabilities in laser and soft X-ray driven targets." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298814.
Full textRiolfo, Luis Atilio. "Fingering instabilities in reactive and non ideal systems: an experimental approach." Doctoral thesis, Universite Libre de Bruxelles, 2013. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209515.
Full textNous étudions tout d’abord l’évolution de la zone de mélange non idéal entre deux fluides purs lorsque le fluide le moins dense est placé au dessus du fluide le plus dense dans le champ de gravité. Nous montrons que le fait que la densité du mélange évolue de manière non monotone en fonction de sa composition peut être la source de digitation de densité. Nous étudions ensuite l'influence de réactions chimiques simples sur la digitation de densité à l'interface entre fluides miscibles et partiellement miscibles, en clarifiant l’impact de la diffusion différentielle entre divers solutés de solutions réactives et du taux de miscibilité sur le phénomène de digitation. Dans le cas de la digitation de viscosité, nous analysons tout d'abord dans quelle mesure une réaction chimique, en induisant des profils de viscosité non monotones, peut accroître ou limiter le développement de la digitation visqueuse. Nous démontrons de plus que, dans le déplacement stable d'un fluide moins visqueux par un fluide plus visqueux, une réaction chimique peut générer de la digitation visqueuse en induisant des profils de viscosité non monotones. Enfin, nous explorons expérimentalement l’étalement de films minces réactifs sur des substrats solides. Nous démontrons que, dans certaines conditions, des réactions chimiques peuvent induire des flux convectifs de Marangoni liés à des gradients de tension superficielle qui déstabilisent le bord du film par digitation, produisant un motif fractal.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Klee, J., T. F. Illenseer, M. Jung, and W. J. Duschl. "The impact of numerical oversteepening on the fragmentation boundary in self-gravitating disks." EDP SCIENCES S A, 2017. http://hdl.handle.net/10150/625972.
Full textHammer, Michael, Kaitlin M. Kratter, and Min-Kai Lin. "Slowly-growing gap-opening planets trigger weaker vortices." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/623939.
Full textLehmann, M. (Marius). "Waves in planetary rings:hydrodynamic modeling of resonantly forced density waves and viscous overstability in Saturn’s rings." Doctoral thesis, Oulun yliopisto, 2018. http://urn.fi/urn:isbn:9789526221168.
Full textLin, Min-Kai, and Andrew N. Youdin. "A Thermodynamic View of Dusty Protoplanetary Disks." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626177.
Full textLin, Min-Kai, and Kaitlin M. Kratter. "ON THE GRAVITATIONAL STABILITY OF GRAVITO-TURBULENT ACCRETION DISKS." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621384.
Full textMamatsashvili, George. "Dynamics of perturbation modes in protoplanetary discs : new effects of self-gravity and velocity shear." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/5283.
Full textBaehr, Hans, Hubert Klahr, and Kaitlin M. Kratter. "The Fragmentation Criteria in Local Vertically Stratified Self-gravitating Disk Simulations." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626182.
Full textGérard, Thomas. "Theoretical study of spatiotemporal dynamics resulting from reaction-diffusion-convection processes." Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209861.
Full textDans ce contexte, le but de notre thèse a été d'étudier de manière théorique et sur des modèles réaction-diffusion-convection simples les propriétés de dynamiques spatio-temporelles résultant du couplage chimie-hydrodynamique.
Nous nous sommes focalisés sur les instabilités hydrodynamiques de digitation visqueuse et de densité qui apparaissent respectivement lorsqu'un fluide dense est placé au-dessus d'un fluide moins dense dans le champ de gravité et lorsqu'un fluide visqueux est déplacé par un fluide moins visqueux dans un milieu poreux.
En particulier, nous avons étudié les problèmes suivants:
- L'influence d'une réaction chimique de type A + B → C sur la digitation visqueuse. Nous avons montré que les structures formées lors de cette instabilité varient selon que le réactif A est injecté dans le réactif B ou vice-versa si ces réactifs n'ont pas un coefficient de diffusion ou une concentration initiale identiques.
- Le rôle de pertes de chaleur par les parois du réacteur dans le cadre de la digitation de densité de fronts autocatalytiques exothermiques. Nous avons caractérisé les conditions de stabilité de fronts en fonction des pertes de chaleur et expliqué l'apparition de zones anormalement chaudes lors de cette instabilité.
- L'influence de l'inhomogénéité du milieu sur la digitation de densité de solutions réactives ou non. Nous avons montré que les variations spatiales de perméabilité d'un milieu poreux peuvent figer ou faire osciller la structure de digitation dans certaines conditions.
- L'influence d'un champ électrique transverse sur l'instabilité diffusive et la digitation de densité de fronts autocatalytiques. Il a été montré que cette interaction peut donner lieu à des nouvelles structures et changer les propriétés du front.
En conclusion, nous avons montré que le couplage entre réactions chimiques et mouvements hydrodynamiques est capable de générer de nouvelles structures spatio-temporelles dont les propriétés dépendent entre autres des conditions imposées au système.
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In industrial reactors or in nature, fluid flows can be coupled to chemical reactions. In many cases, the result is the emergence of complex structures whose properties depend among others on the geometry of the system.
In this context, the purpose of our thesis was to study theoretically using simple models of reaction-diffusion-convection, the properties of dynamics resulting from the coupling between chemistry and hydrodynamics.
We focused on the hydrodynamic instabilities of viscous and density fingering that occur respectively when a dense fluid is placed above a less dense one in the gravity field and when a viscous fluid is displaced by a less viscous fluid in a porous medium.
In particular, we studied the following issues:
- The influence of a chemical reaction type A + B → C on viscous fingering. We have shown that the fingering patterns observed during this instability depends on whether the reactant A is injected into the reactant B or vice versa if they do not have identical diffusion coefficients or initial concentrations.
- The role of heat losses through the reactor walls on the density fingering of exothermic autocatalytic fronts. We have characterized the conditions of stability of fronts depending on heat losses and explained the appearance of unusually hot areas during this instability.
- The influence of the inhomogeneity of the medium on the density fingering of reactive solutions or not. We have shown that spatial variations of permeability of a porous medium may freeze or generate oscillating fingering pattern under certain conditions.
- The influence of a transverse electric field on the Rayleigh-Taylor and diffusive instabilities of autocatalytic fronts. It was shown that this interaction may lead to new structures and may change the properties of the front.
In conclusion, we showed that the coupling between chemical reactions and hydrodynamic motions can generate new space-time structures whose properties depend among others, on the conditions imposed on the system.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Hasan, Haider. "Nearshore hydrodynamical instabilities." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438557.
Full textMarant, Mathieu. "Contrôle en boucle ouverte d'un écoulement tridimensionnel décollé par perturbations optimales." Phd thesis, Toulouse, INPT, 2017. http://oatao.univ-toulouse.fr/19494/1/MARANT_Mathieu.pdf.
Full textLi, Rui-Qing. "Hydrodynamic instabilities of cylindrical interfaces." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39521.
Full textExperiments were carried out to measure the dominant unstable wavelength during the breakup of a liquid film around a cylindrical body. It was found that the dominant wavelength decreased with a decrease in the radius of the cylindrical body in agreement with the present theory and in contradiction to previously published work.
In another application of the present theory, the breakup of a cylindrical liquid-in-gas jet and a cylindrical gas-in-liquid jet was analyzed based on the Kelvin-Helmholtz instability. It was predicted that the dominant wavelength decreased rapidly with an increase in the jet velocity.
In the second part of the thesis, gas injection through a very narrow slot into a liquid is examined extensively. A modified bubble formation model is proposed taking into consideration the surface tension force and the inertial force.
When gas was injected into liquid through a very narrow slot (50-250$ mu$m), three different bubbling regimes were found as the flow rate of gas was increased. They were: regular bubble regime at low flow rates, coalescence bubble regime at medium flow rates, and gas globe regime at high flow rates. The gas-dispersion characteristics of each of the regimes were discussed and mathematically analyzed. In the regular bubble regime, the bubble formation was dominated by both surface tension force and inertial force. In the coalescence bubble regime, the formation of bubbles was dominated by inertial forces only. In the gas globe regime, due to the Rayleigh-Taylor instability, multiple bubbles were formed at separate nodes of a continuous gas blanket extending the length of the slot. The critical transition condition between the regular bubble formation regime and the coalescence bubble regime is given.
Lebranchu, Yannick. "Étude d'ondes non linéaires hydrodynamiques : approches théorique et expérimentale." Thesis, Vandoeuvre-les-Nancy, INPL, 2008. http://www.theses.fr/2008INPL005N/document.
Full textA first part is devoted to the study of the Rossby waves that appear in a rotating spherical shell representing the core of a terrestrial planet by thermal instabilities for two heating types. Internal heating is driven by radioactive sources and differential heating is driven by a difference of temperature between the internal and external frontiers. According to the Proudman-Taylor theorem, the flow depends only weakly on the axial coordinate because of the high rotation rate. Thus the 3D models can be simplified into quasi-geostrophic 2D models \textit{via} an axial integration. I present the first systematic comparison between 2D and 3D models (Simitev, U-Glasgow) for weakly nonlinear Rossby waves. In 2D the Landau equation that controls the amplitude of the critical wave is calculated. Predicted convection' amplitude and zonal flows agree rather well with the 3D results. The existence of a subcritical bifurcation is established at very low Ekman numbers with internal and differential heating; in this latter case, the Prandtl number also has to be small for the bifurcation to be subcritical. The second part is an experimental study of water flows and its first instabilities in an annular channel digged in a plate which may rotate, and which is sheared by a rotating lid. Three cases are studied: a pure shear where only the lid turns, a rapid corotation and a pure contrarotation. The onset of instability is studied with global measurements (using a video camera) and local ones (Laser Doppler Anemometry) and is characterized by spiralling waves. In the case of contrarotation, patterns localized in space and time may coexist with the waves. The comparison of these results with numerical ones (Serre, CNRS-Marseille) is done and shows a rather good agreement for the basic azimutal flow and the first instability (critical Reynolds number, wavenumber and angular frequency)
Roland, Caroline. "Formation de micro-jets depuis des défauts de surface dans des échantillons métalliques soumis à des chocs laser." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2017. http://www.theses.fr/2017ESMA0025/document.
Full textWhen a dense material is subjected to a dynamic load (such as projectile impact, explosive detonation or irradiation by a high energy laser beam), a shock wave propagates from the loaded surface. If this shock wave interacts with a free surface with geometrical defects such as grooves, scratches or cavities, it can lead to the ejection of micrometric debris with typical velocities of a few km/s. Understanding this microjetting process is a key issue for many applications, including shielding design, pyrotechnics, high-speed machining and Inertial Confinement Fusion experiments.In this work in collaboration with the CEA-DIF at Bruyères-le-Châtel, this phenomenon is studied under laser-driven shock loading in four materials (Aluminum, Tin, Copper and Lead) with calibrated grooves of two types: isolated triangular profile with controlled aperture half-angles (20°, 30° and 45°) or periodic sinusoidal shape. The influences of the material, of the geometry of the defects, of the shock pressure and of the state of matter (solid or melted under shock or release wave) on the ballistic properties of the ejecta (jet velocity, size distribution and areal mass of the debris constituting the jet) are investigated with three complementary approaches: experimental, theoretical and numerical.The experimental study involves several campaigns performed at the LULI2000 facility of the Laboratoire pour l’Utilisation des Lasers Intenses (Ecole Polytechnique, Palaiseau) and complementary diagnostic techniques: Transverse Shadowgraphy, Heterodyne Velocimetry, fast in situ X-ray radiography, recovery of the ejecta in a gel followed by microtomography. The results are compared with theoretical predictions (2D shocks and shaped charges hydrodynamics for the triangular grooves, Richtmyer-Meshkov Instabilities for the sinusoidal grooves). Then, numerical simulations are performed with the Radioss code with two complementary approaches: the Lagrangian Finite Elements and the SPH (Smoothed Particles Hydrodynamics) formulation, still very scarcely applied to microjetting, more empirical than the first approach but more suitable to the high strains in the jets and allowing access to size distributions of the debris
Lyra, Wladimir. "Turbulence-Assisted Planetary Growth : Hydrodynamical Simulations of Accretion Disks and Planet Formation." Doctoral thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9537.
Full textGuha, Anirban. "Two dimensional hydrodynamic instabilities in shear flows." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44571.
Full textMackerrell, O. S. "Some hydrodynamic instabilities of boundary layer flows." Thesis, University of Exeter, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381355.
Full textKaiser, Thomas. "Impact of Flow Rotation on Flame Dynamics and Hydrodynamic Stability." Thesis, Toulouse, INPT, 2019. http://oatao.univ-toulouse.fr/24115/1/Kaiser_Thomas.pdf.
Full textKifonidis, Konstantinos. "Nucleosynthesis and hydrodynamic instabilities in core collapse supernovae." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=962128457.
Full textForth, Shaun Anthony. "Morphological and hydrodynamic instabilities in undirectional alloy solidification." Thesis, University of Bristol, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292481.
Full textD'Hernoncourt, Jessica. "Influence of thermal effects and electric fields on fingering of chemical fronts: a theoretical study." Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210607.
Full textIn this context our work aims to understand theoretically in which way a chemical reaction can induce and influence such instabilities in a fluid initially at rest.
To understand the dynamics resulting from the coupling between chemical reactions and hydrodynamical instabilities we use chemical fronts as model systems. These fronts result from the coupling between autocatalytical chemical reactions and diffusion and they allow to create a self-organized interface between the products and the reactants. As during a chemical reaction the density may vary due to solutal and thermal effects, the products and the reactants can have different densities which may trigger convection movements leading to the destabilization of the fronts.
We have in particular studied the influence of the exothermicity of the reaction on the fingering of chemical fronts, focusing first on the influence of heat losses through the walls of the set-up.
These leaks have a marked influence on the dynamics because they affect the temperature profiles and hence the density profiles too. We have also classified the various types of instabilities that may appear dues to solutal and thermal effects. We have found a new type of hydrodynamic instability of statically stable fronts induced by the chemical reaction.
We have furthermore analyzed an isothermal model with two chemical species. If they diffuse at different rates the front can be subject to diffusive instabilities as well. We have shown that the coupling between such a diffusive instability and fingering can trigger complex dynamics. We have eventually studied the influence of an external electric field on the diffusive instabilities and on fingering underlying the possibility to destabilize otherwise stable fronts./
Différents types d'instabilités hydrodynamiques peuvent affecter les interfaces entre deux fluides comme par exemple, une instabilité de Rayleigh-Taylor (ou digitation de densité) quand un fluide plus dense se trouve placé au-dessus d'un fluide moins dense dans le champ de gravité ou des instabilités de double diffusion induites par des différences entre les diffusivités d'un soluté et de la chaleur contenus dans les fluides. Dans ce contexte, notre thèse s'attache à comprendre de manière théorique comment une réaction chimique peut influencer ces instabilités voire les générer dans un fluide initialement au repos. Pour étudier les dynamiques résultant du couplage entre réactions chimiques et instabilités hydrodynamiques, nous utilisons des systèmes modèles: les fronts chimiques de conversion résultant de la compétition entre réactions chimiques autocatalytiques et diffusion créant une interface auto-organisée entre les réactifs et les produits. Comme au cours d'une réaction chimique la densité peut varier par des effets solutaux et thermiques, les produits et les réactifs de densités différentes peuvent générer des mouvements de convection qui conduisent à la déstabilisation des fronts.
Nous avons en particulier étudié l'influence de l'exothermicité de la réaction sur les instabilités de digitation de fronts chimiques, en nous focalisant dans un premier temps sur l'influence des pertes de chaleur par les parois du réacteur.
Ces fuites ont un effet marqué sur les instabilitités car elles affectent les profils de température et donc les profils de densité dans le système. Nous avons également classifié les différentes instabilités qui peuvent apparaître via des changements de densité dûs à des effets thermiques et solutaux et mis en évidence un nouveau type de déstabilisation hydrodynamique de fronts statiquement stables induit par une réaction chimique.
Nous avons ensuite analysé un modèle isotherme impliquant deux espèces chimiques. Si ces dernières diffusent a des vitesses différentes le front peut être sujet à une instabilité diffusive. Nous avons montré qu'un couplage entre une telle instabilité diffusive et de la digitation peut être à l'origine de dynamiques complexes. Nous avons ensuite considéré l'influence d'un champ électrique sur les instabilité diffusives et de digitation en soulignant la possibilié de déstabiliser via ce champ des fronts initialement stables.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Sandin, Christer. "A Study of Grain Drift in C Stars : Theoretical Modeling of Dust-Driven Winds in Carbon-Rich Pulsating Giant Stars." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3397.
Full textMarston, Jeremy Oliver. "Hydrodynamic assist, hysteresis and non-uniqueness of instabilities in curtain coating." Thesis, University of Birmingham, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502201.
Full textBridel-Bertomeu, Thibault. "Investigation of unsteady phenomena in rotor/stator cavities using Large Eddy Simulation." Thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/17867/1/BRIDEL_BERTOMEU.pdf.
Full textNegretti, Maria Eletta. "Hydrodynamic instabilities and entrainment in two-layer stratified flows down a slope." Karlsruhe : Univ.-Verl. Karlsruhe, 2007. http://d-nb.info/985610263/34.
Full textJones, Samuel Edward. "Symmetries in the kinematic dynamos and hydrodynamic instabilities of the ABC flows." Thesis, University of Exeter, 2013. http://hdl.handle.net/10871/14689.
Full textJunk, Veronika. "Hydrodynamical instabilities and the trace of dark energy within the CMB." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-133349.
Full textParé, Gounséti Nimonoka. "Création et éjection des gouttes de l'atomisation." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066318/document.
Full textThis thesis deals with the hydrodynamic instabilities which occur in a liquid ligament in presence of axial flow. We investigate the formation of drops during the atomization process. Previous studies highlighted a common step to all types of atomization processes: the initial formation of the ligament which later evolves into droplets. The ligaments fragmentation process is governed by two possible instabilities: the “Rayleigh-Plateau” instability which is characteristic of an infinite ligament and the “end-pinching” phenomenon, which occurs in semi-infinite ligaments. In both cases, capillarity is the driving mechanism underlying the ligament segmentation. In this thesis we show that, under certain conditions, the liquid ligament can surprisingly escape from pinch-off through creation of a vortex ring (“escape phenomenon”). A detailed analysis of the constriction zone (neck of the ligament) during the “escape phenomenon” suggested that nonlinear effects associated to fluid viscosity might play an important role in the escape process. Both our experimental observations and numerical results confirmed the occurrence of the detachment of the viscous layer into a jet downstream of the neck through creation of a vortex ring, when fluid viscosity exceeds a threshold. Accordingly, the fluid in the constriction zone undergoes an axial acceleration associated to a decrease in the pressure: this is the so-called “Venturi effect”. This type of flow is characteristic of the instability which emerges at the capillary bridge between two tubes subjected to axial flow. Part of the results obtained were the subject of a publication or article submission
Pagani, Bruno. "Explosion asymétrique des supernovæ gravitationnelles." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS244.
Full textThe observational history of supernovæ dates back to several millennia, but it has been less than one hundred years since we know that some of them mark the death of massive stars. The gravitational collapse of the iron core at the centre of those stars can lead to the birth of a neutron star and the onset of one of those spectacular explosions, thus called core-collapse supernovæ. The mechanisms at work in the innermost part of the star during the first few hundred milliseconds after the initial collapse play a key role in the success or the failure of the explosion. In particular, multi-dimensional instabilities like the standing accretion shock instability (SASI) or the neutrino-driven convection are likely to increase efficiently the matter heating by neutrinos emitted from the proto-neutron star and yield highly asymmetric explosions.In this thesis, those phenomena are studied with the help of numerical simulations of a simplified two dimensional model. This allows for a vast exploration of the parameter space that would be unreachable for more realistic models.The boundary between explosion and collapse into a black hole is established in a three parameter space, namely the stellar rotation, the neutrino heating and the accretion rate —which relates to the progenitor mass. The critical surface so defined allows us to characterise the impact of multi-dimensional instabilities on the explosion threshold. The effects of rotation are important for models with a low accretion rate. These results allow us to reinterpret the seemingly contradictory results of more realistic models. The stochasticity of the results near the explosion threshold is highlighted. This effect is more pronounced for low rotation and accretion rates. The different paths to explosion observed in our simulations are described and illustrated with the analysis of a representative sample of models. The respective roles of the different instabilities and their signatures are discussed.The set of ∼600 simulations constitutes a database offering numerous perspectives for future analysis
Kokkonen, Toni. "CFD analysis of stepped planing vessels." Thesis, KTH, Mekanik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-250023.
Full textGandikota, Vs Gurunath. "Instabilités d'interfaces fluides en apesanteur spatiale lors d'un changement brutal ou périodique d'accélération." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY036/document.
Full textThe behavior of a near-critical fluid subjected to vibration or a rapid variation of acceleration is an extremely interesting topic of research. The resulting physical phenomena are of great interest in view of the fundamental physics involved and have great relevance to the space industry. The thesis addresses mainly three problems: (i) study of the interaction of harmonic vibration with a thermal boundary layer of a supercritical fluid under the absence of gravity, (ii) study of the inter- action of vibration with the liquid−vapor interface of a near−critical fluid under various gravity levels (Faraday and frozen wave instabili- ties, dynamic equilibrium of the interface) (iii) study of the geysering phenomenon inside a reservoir partially filled with a liquid when it is subjected to a rapid variation of gravity. Experiments are conducted onboard the zero−g installations HYLDE and OLGA developed by CEA Grenoble using H2 and O2 as the work- ing fluids. Numerical simulations are carried out using finite volume codes based on SIMPLER (for the problem involving the supercriti- cal fluid) and VOF−PLIC (for the interface dynamics problem under rapid variation of gravity). New and interesting results have been obtained. Various phenom- ena like the Faraday instability and the frozen wave instability in the sub−critical region and the parametric instability and the Rayleigh−vibrational instability in the supercritical region have been quantified. The experiments have successfully explained the reason behind the transition of the Faraday instability into vertical band pattern very close to the critical point. Experiments and numerical simulation of the geysering phenomenon have helped to evolve empir- ical correlations for the bubble rise and geyser edge velocities taking into account the effect of walls on these velocities
McGlinchey, Kristopher. "Radiation-hydrodynamic simulations of the impact of instabilities and asymmetries on inertial confinement fusion." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/57027.
Full textTun, Yarzar. "Nonmodal Analysis of Temporal Transverse Shear Instabilities in Shallow Flows." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36886.
Full textSurville, Clément. "Morphologie et évolution des tourbillons de Rossby bidimensionnels dans les disques protoplanétaires." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4784/document.
Full textThe role of anticyclonic vortices in the protoplanetary disk evolution and in how do planetesimals form are among the most important chalenges of the modern astrophysics. That is why an exhaustive study of the structure and the evolution of these vortices is necessary.Thanks to a numerical code specificly designed for the study of these disks, we have revisited the Rossby Wave Instability in the nonlinear regime, and have discovered that a cascade of the perturbation modes can explain the formation of the vortices created by this instability.We have described the structure of these Rossby vortices with a new gaussian vortex model, which accurately fits the numerical results. A sample of 300 different vortices led us to define the bondaries of the radial and azimuthal extent as well as the vorticity of the vortices. We have distinguished two main families : (i) the incompressible family, which is stable and quasi stationnary ; (ii) the compressible family, moving and exciting density waves. We found them surviving more than 1000 orbits, a clear confirmation of their observability.Finaly, we have caracterized the inward migration of the vortices as a fonction of their shape, their vorticity, but also of the pressure gradient and the scale height of the disk. For the first time, we exhibit a equation relating the migration rate to these parameters. The time scale of the migration ranges from 10^6 to just 100 rotations of the disk. Extremely steep pressure gradients are needed to reverse the migration to an outward regime. Following the alpha viscosity approch, the loss of kinetic momentum due to this migration would be sufficient to sustain the accretion in the dead zone
Lorenzani, Silvia. "Fluid instabilities in precessing ellipsoidal shells." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=964398702.
Full textKeiser, Ludovic. "Formation et déplacement de gouttes confinées : Instabilités et dynamiques." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC080/document.
Full textBiphasic flows in porous media generally lead to the emulsification of one phase into the other. This may be due to several phenomena, such as viscous fingering or pure capillary instabilities. In this experimental thesis, we study a particular emulsifying phenomenon of oil in a model porous medium, as well as the transport of the produced droplets in confined regions. In the first part of the manuscript, the Rayleigh-Taylor instability is revisited in a wedge formed between two centimetric glass plates. The gradient of confinement leads to a capillary force not present in the canonical Rayleigh-Taylor instability. This new force can stabilize liquid layer above air submitted to gravity. The threshold of the instability, the characteristic wavelength and the growth rate are captured by a linear stability analysis of the interface. This characterization of the confinement-induced capillary force drove us to the study of a pure capillary instability occurring when a wetting liquid migrates toward the most confined regions of a wedge, initially filled with a less wetting liquid. The gradient of confinement generates a destabilizing force, leading to the complete inversion of the position of both phases. The less wetting liquid is fully emulsified and the produced droplets are convected towards the less confined regions. A linear stability analysis of the interface here again predicts the characteristic size of the droplets. However, the measured growth rates are not in agreement with the model, based on the Darcy law. This suggests a localization of viscous dissipation in the contact lines displaced during the development of the instability. Another source of viscous dissipation can be in the deposited lubrication films. Those "non-Darcian" dynamics motivated the second part of this thesis, which focuses on the motion of very viscous and non-wetting droplets confined in water. In this configuration, the lubrication film of water between the drop and the substrate ensures the localization of viscous dissipation in those films of low viscosity. This favors the extremely high mobility of the droplets. We also show that wall roughness may induce a thinning of these lubrication films. We shed light on the intricate coupling between viscous friction at the front of the drop and in its bulk. In a last part of this work, we study the capillary instability occurring when a binary droplet of water and alcohol is deposited at the surface of a vegetable oil bath. The dominant evaporation of alcohol at the surface of the drop induces local variations of surface tension. Interfacial Marangoni flows are thus observed, leading to the spectacular destabilization of the spreading droplet
Lamberts-Marcade, Astrid. "Simulations numériques de collisions de vents dans les systèmes binaires." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENY038/document.
Full textThe aim of this thesis is to understand the structure of colliding wind binaries composed of a massive star and a young pulsar, called gamma-ray binaries. They are expected to display a similar structure to colliding wind binaries composed of massive stars, with some particularities due to the relativistic nature of the pulsar wind. The interaction of the supersonic winds from massive stars creates a shocked structure with observational signatures from the radio domain to the X-rays. The structure is affected by various instabilities and by the orbital motion of the stars. To understand their impact, I carried out high resolution simulations of colliding wind binaries with the hydrodynamical code RAMSES. They are computationally demanding, especially when one of the winds strongly dominates the other one. Small scale simulations highlight the importance of the Non-linear Thin Shell Instability in isothermal collisions while the Kelvin-Helmholtz instability may strongly impact the dynamics of adiabatic collisions. I found that, at larger scales, this instability can destroy the expected large scale spiral structure when there is an important velocity gradient between the winds. WR 104 is a system that displays a spiral structure with important dust emission. The simulation of this system shows a good agreement with the observed structure and indicates cooling processes are necessary to enable dust formation. To model the pulsar wind in gamma-ray binaries, an extension of RAMSES has been developed, that incorporates relativistic hydrodynamics. I used this new relativistic code to perform preliminary simulations of gamma-ray binaries. They display a similar structure to colliding wind binaries with small relativistic corrections. We expect to use this code to perform large scale simulations of gamma-ray binaries. It will be part of the next public release of RAMSES and is suited for the study of many astrophysical problems such as relativistic jets, pulsar wind nebulae or gamma-ray bursts
Negretti, Maria Eletta [Verfasser]. "Hydrodynamic instabilities and entrainment in two-layer stratified flows down a slope / von Maria Eletta Negretti." Karlsruhe : Univ.-Verl. Karlsruhe, 2007. http://d-nb.info/985610263/34.
Full textNegretti, Maria Eletta. "Hydrodynamic instabilities and entrainment processes in two-layer density-stratified exchange flows over a submerged sill." [S.l. : s.n.], 2007. http://digbib.ubka.uni-karlsruhe.de/volltexte/1000006966.
Full textPaquier, Anna. "Génération et croissance des vagues à la surface d’un liquide visqueux sous l’effet du vent." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS183/document.
Full textDespite numerous studies on the subject, the development of waves under the action of wind still retains a certain number of open questions. In my PhD, I approach this problem through a fairly uncommon angle: the experimental study of the deformation by wind of the surface of a highly viscous liquid. Indeed, contrary to the major part of the literature on the matter, the liquid I used is not water but a significantly more viscous liquid. Regardless of the fundamental underlying questions, this has the practical advantage of simplifying the problem. Indeed, due to the high viscosity of the liquid, the flow in the liquid stays laminar and the unamplified perturbations of the interface can only propagate over a limited distance. To observe these deformations at the liquid-air interface, I have developed a new experimental set-up upon which the Free Surface Synthetic Schlieren method of visualization was implemented. This non-intrusive technique allowed to measure with a micrometric accuracy the amplitude of the surface deformation and to access the first deformations at low wind velocity. First, experiments were conducted over a liquid thirty times more viscous than water. The experimental data obtained by FS-SS show two regimes of deformation of the liquid-air interface. At low wind velocity, the interface is populated with ``wrinkles'', small-amplitude streamwise spatially disorganized perturbations. These wrinkles can be interpreted as the effect on the interface of the pressure fluctuations in the turbulent wind. At higher windspeed, above a critical velocity, transverse waves appear with quasi-parallel crests perpendicular to the wind direction. The distinctions between the two regimes have been detailed and the nonlinearities emerging above the threshold have also been studied. Then, the viscosity of the liquid has been changed over a large range. It results from the experiments that the two regimes of surface deformation by wind can be identified for all the viscosities explored. Following these results, a model was developed to account for the evolution of the wrinkles' amplitude both with wind velocity and with viscosity
Junk, Veronika [Verfasser], and Andreas [Akademischer Betreuer] Burkert. "Hydrodynamical instabilities and the trace of dark energy within the CMB / Veronika Junk. Betreuer: Andreas Burkert." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2010. http://d-nb.info/1015131158/34.
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