Добірка наукової літератури з теми "Micro-Instabilités"
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Дисертації з теми "Micro-Instabilités":
Abaidi, Mohamed. "Instabilités morphologiques de micro-capsules en suspension libre dans un écoulement complexe." Amiens, 2013. http://www.theses.fr/2013AMIE0120.
Wautier, Antoine. "Analyse micro-inertielle des instabilités mécaniques dans les milieux granulaires, application à l'érosion interne." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0289/document.
Dikes are most of the time built of compacted granular materials that are permeable and continuously subjected to internal fluid flows. In some cases, microstructure modifications resulting from internal erosion generate mechanical instability that will lead to unexpected failures in case of serious flooding. This thesis focuses on multi-scale analysis of mechanical instability in granular materials subjected to internal erosion. In this work, the mechanical behavior of such materials is simulated in three dimensions at the scale of representative elementary volumes subjected to different stress states and hydraulic gradients. Thanks to the use of the second order work criterion and micromechanical tools, the mechanical stability of these materials is tested before and after internal erosion. It is established that the micro-inertial origin of the observed instabilities is linked to force chain deconfinement and bending as well as to the development of large plastic strains resulting from force chain collapse. By preventing the development of such plastic strains, it is shown that rattlers contribute to ensure the mechanical stability of granular materials. This key finding is of a particular significance in relation with internal erosion as rattlers can be easily transported under the action of an internal fluid flow. Depending on whether they get clogged or eroded, an internal fluid flow has thus either a stabilizing or a destabilizing effect on the mechanical behavior of granular materials subjected to internal erosion
Kitenbergs, Guntars. "Instabilités hydrodynamiques de fluides magnétiques en écoulements microfluidiques." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066311/document.
Magnetic field induced instabilities of magnetic fluids in microfluidic environment are investigated experimentally. Electrically stabilized water-based magnetic nanocolloids are used and throughout characterized.Magnetic micro-convection, observed at a miscible magnetic fluid-water interface in a Hele-Shaw cell in homogeneous field, is studied quantitatively and compared with theoretical predictions and numerical simulations, micro-convective flows being characterized by particle image velocimetry. Besides the critical field determination, it is shown that an increase of the magnetic field H speeds up the finger growth, which scales as H2, while the size of the fingering pattern is not changed. An application towards mixing enhancement in microfluidics is considered.The micro-convection study reveals a much larger effective diffusion coefficient of the nanoparticles than expected from Stokes - Einstein relation and standard determinations. Investigations with the same setup and with continuous microfluidics show that the effective diffusion mostly arises from a flow induced by the density difference between the miscible fluids. Additionally, the diffusion coefficient seems to be influenced by the particle stabilizing agents.Drops of a concentrated magnetic phase in co-existence with a dilute one are formed by phase separation after salt addition to the magnetic fluid and/or the application of a magnetic field. Their under-field shape deformations allow investigating the time evolution of the concentrated phase. Experiments show that in a precessing field at magic angle, the drops behave as in a rotating field except the initial shape deformation before quick elongation
Prioul, Mathieu. "Etude expérimentale des propulseurs de type Hall : processus collisionnels, comportement dynamique, micro-instabilités et phénomènes de transport." Orléans, 2002. http://www.theses.fr/2002ORLE2058.
Pravda-Starov, Karel. "Etude du pseudo-spectre d'opérateurs non auto-adjoints." Phd thesis, Université Rennes 1, 2006. http://tel.archives-ouvertes.fr/tel-00109895.
Manceau, Jean-Philippe. "Etude du phénomène de relaxation diélectrique dans les capacités Métal-Isolant-Métal." Phd thesis, Université Joseph Fourier (Grenoble), 2008. http://tel.archives-ouvertes.fr/tel-00281081.
Camara, Abdoulaye. "Instabilités transverses et auto-organisation dans un nuage d'atomes froids. Gap labelling dans les quasi-cristaux bidimensionnels." Thesis, Nice, 2015. http://www.theses.fr/2015NICE4080/document.
First, I present our feedback experiment leading to the spontaneous formation of patterns in the cross section of a laser beam passing through a cloud of cold 87Rb atoms and retroreflected by a mirror. In these experiments we were able to identify three mechanisms of nonlinearity: the spin nonlinearity associated with the Zeeman degrees of freedom, the electronic nonlinearity due to the saturation of a two-level atom and the optomechanical nonlinearity due to the spatial bunching of atoms by the dipole force. The instabilities corresponding to each nonlinear mechanism occurs in different range of the experimental parameters and can be selected and studied independently. The experimental observations are compared with various theoretical models. In the second part of the thesis, I present our study of the integrated density of states (IDOS) and the local density of states (LDOS) of the bands of a two-dimensional quasicrystal. In an experiment conducted at Laboratoire de Physique de la Matière Condensée (LPMC), we realized quasicrystals by disposing dielectric resonators operating in the microwave regime on 2D Penrose tiling. A numerical model including experimental parameters is used to compare to the experimental findings
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.
When 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
Gaied, Lamia. "Influence de la rugosité de surfaces de parois sur les instabilités hydrodynamiques d'un écoulement de Couette-Taylor et de Couette-Taylor-Poiseuille." Thesis, Valenciennes, Université Polytechnique Hauts-de-France, 2020. http://www.theses.fr/2020UPHF0018.
This work deals with a numerical and experimental study of the Couette-Taylor flow where the geometry contains rough surfaces, in order to detect the effect of these irregularities on the hydrodynamic instabilities. Firstly, we carried out a 3D mumerical simulation study (CFD) in the case of a Couette-Taylor flow without axial flow, but using several types of surface roughness: isotropic roughness (micro-roughness), anisotropic roughness (macro-roughness) and variation of the amplitude as well as the type of macro-roughness. The obtained results clearly show the effect of this roughness on the reorganization of the flow and the development of the hydrodynamic instabilities. Secondly, we were interested to carry out an experimental study of Couette-Taylor-Poiseuille flows, with and without axial flow by using two protocols (direct and reverse). Indeed, the superposition of an axial flow (Poiseuille) with a Couette-Taylor flow can have a significant effect on the reorganization of the basic and already known hydrodynamic instabilities, constituted by Taylor cells. Therefore, the presence of an axial flow can generate the development of vortices or their breakup or disappearance, and can move the Taylor vortices in the same direction or the opposite direction of the imposed axial flow. Experimentally, we started with a qualitative study by visualizing the hydrodynamic instabilities thanks to kalliroscope particles. Thereafter, a quantitative study using PIV and polarography was carried out in order to characterize the flow regimes of the first instabilities (TVF, WVF, MWVF and TN) with or without axial flow. The polarographic method, using simple circular probes, was then used to quantify the local and instantaneous wall shear stress. The PIV allowed to study the WVF, MWVF and turbulent regimes. Different vortices’ detection criteria (vorticity ω and Q criterion) were then developed and used to correctly identify the turbulent structures
Cannizzo, Andrea. "Mécanique statistique et thermodynamique de l'adhésion, des transformations de phase et de la rupture dans les micro et nanosystèmes." Electronic Thesis or Diss., Centrale Lille Institut, 2023. http://www.theses.fr/2023CLIL0027.
Micro-instability and multi-stability phenomena play a key role in various mechanical and physical systems, both artificial and biological. As such, their understanding is addressed in a wide field of studies, with many practical and theoretical applications. The modeling of the temperature effect on micro-instabilities, appearing in different artificial and biological phenomena, allows the validation of the statistical mechanics for small systems, through the comparison with experimental data obtained using force spectroscopy and micromechanical testing, thus providing useful insights on the responses induced by applied forces or elongations. These analyses are particularly important in the study of all the systems that present two (or more) metastable states such as the adhesion/deadhesion processes, the phase transformations (e.g. the folding/unfolding and pseudo-elastic phenomena), and the cracks and fractures propagation in nano- and micro-scale systems. For example, the temperature strongly influences the phase transformation features of pseudo-elastic nanowires used as actuators and sensors in nanotechnology or modifies the adhesion properties of metastatic cells in cancer invasion processes. The force-extension or stress-strain response is one of the main useful features to understand the effects of micro-instabilities and, in order to be analytically obtained, one needs to evaluate the system partition function, which is the essential tool of statistical mechanics. Hence, the complex potential energy landscape of the problem under investigation is approximated using the spin variables technique, introducing a discrete quantity able to identify the different potential energy wells. The first part of this thesis addresses the state of the art, the open problems, the motivations, and the description of the adopted methodologies. The following part shows how commonly different physical phenomena can be studied by the same modeling approach