Browsing by Author "Mokhtari, Faiza"
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Item 3D anisotropic stress analysis during kyropoulos growth of sapphire single crystal(Wiley, 2019) Zermout, S.; Mokhtari, Faiza; Nehari, A.; Lasloudji, I.; Haddad, F.; Merah, A.By using 3D finite element calculations, numerical simulations are performed to predict the thermal field as well as the thermal stress in a c‐axis sapphire single crystal grown by Kyropoulos technique. The effects of additional resistive heating (placed under the crucible bottom) and crystal rotation are investigated and a comparison is made between the isotropic and anisotropic analysis. The anisotropy of the elastic constants and thermal expansion coefficients as well as their temperature dependence are considered in the anisotropy calculations while Young's modulus and the Poisson ratio are used in the isotropic analysis. Thermal stress is found to be smaller in the anisotropy analysis than that in the isotropic analysis and significant differences are found in their respective distribution patterns. Additional resistive heating acts to decrease both of the crystal–melt interface convexity and the von Mises stress. In addition, crystal rotation combined with additional resistive heating decreases significantly the thermal stress inside the sapphire crystal and along the melt–crystal interface. Therefore, optimizing the heating conditions and using a suitable crystal rotation rate seem to be favorable to control the growth interface shape and to reduce thermal‐stress‐related defects during the growth processItem 3D Numerical study of magnetohydrodynamic instability in liquid metal taylor-couette flow(2015) Merah, Abdelkrim; Mokhtari, Faiza; Bouabdallah, A.; Adnane, M.This purpose is about a 3D study of magnetohydrodynamic (MHD) instability in liquid matal Taylor-Couette flow, this problem is receiving more and more research interest due to its application in the engineering, oceanography and the astrophysical research The Taylor-Couette system consists of two coaxial cylinders in differential rotation, which is considered as a hydrodynamic model system, allowed researchers to progress in understanding the laminar-turbulent transition phenomena. A set of states found in narrow gap of Taylor-Couette systems where the outer cylinder is held fixed and the inner cylinder speed increased. The symmetry breaking parameter is the Taylor number Ta that gives a measure of the ratio of centrifugal forces to viscous forces. When the liquid is replaced by an electrically conducting fluid and an external magnetic field is applied, this leads to MHD Taylor-Couette flow. Additional body force, Lorentz force, acting on the fluid arises. Lorentz force is in the direction perpendicular to both magnetic and electric fields. The behaviour of flow depends on strength and geometry of applied field, magnetic and electric properties of the liquid, cylinders and endplates. In this work, the MHD instability Taylor-Couette flow is considered for liquid sodium with its magnetic Prandtl number Pm <1. The results of pressure and angular momentum in the Taylor-Couette flow under the effect of an external uniform axial magnetic field B=4 Tesla are investigated numerically for the different cases of electrically conducting or insulating walls at the Ekman cell, at the middle of the first Taylor-votex flow (TVF) and between two cells.Item Free surface study in silicon czochralski melt(2014) Mokhtari, Faiza; Merah, Abdelkrim; Bouabdallah, Ahcene; Rouaiguia, LeilaItem Instabilities in silicon Czochralski crystal growth process in different geometries(2010) Merah, Abdelkrim; Bouabdallah, Ahcene; Mokhtari, Faiza; Hanchi, S.; Alemany, A.Item Numerical investigation of magnetic field effect on pressure in cylindrical and hemispherical silicon CZ crystal growth(Wiley, 2012) Mokhtari, Faiza; Bouabdallah, Ahcene; Merah, Abdelkrim; Oualli, HamidItem A numerical investigation of the flow pattern between finite–length conical cylinders(2017) Merah, Abdelkrim; Mokhtari, Faiza; Kelaiaia, Ridha; Hamrani, Abderrachid; Lalaoua, AdelItem Numerical study of the effect of transverse magnetic field on cylindrical and hemispherical CZ crystal growth of silicon(Thomson Scientific, 2010) Mokhtari, Faiza; Bouabdallah, Ahcene; Merah, AbdelkrimItem Résolution d'un problème de convection naturelle en 2D et 3D par la méthode spectrale(AFM, Association Française de Mécanique, 2017) Bouarab, Samia; Mokhtari, Faiza; Kaddeche, Slim; Hamrani, Abderrachid; Merah, Abdelkrim; Haddad, FadilaL'objectif de ce travail consiste à étudier le problème de la convection naturelle à l'intérieur d'une cavité carrée différemment chauffée à l'aide de la méthode spectrale. Les simulations numériques bidimensionnelles et tridimensionnelles sont effectuées pour différents nombres de Prandtl et de Rayleighcaractéristiquesde l'écoulement du fluide à l'intérieur de la cavité connu sous le nom d'écoulement de Hadley. La simulation numérique des écoulements incompressibles par les méthodes classiques tels que les différences finies, volumes finis et éléments finis, nécessite des temps de calcul relativement longs et une capacité de stockage très importante. Un modèle basé sur les méthodes spectrales a été développé et a mis en valeur la précision, la simplicité et la rapidité d'une telle méthode, notamment pour des simulations voulues de plus en plus proches de la réalité des processus multi-physiques complexes. La méthode spectrale sera utilisée dans notre étude afin d'effectuer des modélisations bidimensionnelles et tridimensionnelles des écoulements incompressibles en formulation vorticité-fonction de courant pour le modèle 2D et en utilisant la méthode d'Uzawa pour le modèle 3D. Les résultats de la simulation d'écoulements incompressibles par méthodes spectrales seront comparés à ceux obtenus par différences finies et en termes de temps de calcul et précision des résultatsItem Symmetry breaking in electromagnetic spherical Cz crystal growth with rotating crystal and crucible(American Scientific Publishers, 2013) Mokhtari, Faiza; Bouabdallah, A.; Merah, AbdelkrimItem Three-dimensional effect of high frequency vibration on convection in silicon melt(American Physical Society, 2020) Mokhtari, Faiza; Kaddeche, Slim; Henry, Daniel; Bouarab, Samia; Medelfef, Abdessamed; Botton, ValéryUsing the Chebyshev spectral method, the effect of high frequency (HF) vibrations on a cubic cell heated from the side and containing a liquid metal is investigated. This study extends the numerical and theoretical two-dimensional results presented in the authors’ past work [Phys. Fluids 31, 043605 (2019)] about the influence of HF vibration direction on the flow structure in a rectangular crucible filled with a liquid metal. The vibration direction can now be three dimensional, and not limited to the main flow plane. In practice, the study considers that the vibration vector is contained in one of the three principal planes of the cavity (xz,xy, and yz planes). Two different cases, i.e., under weightlessness and gravity conditions, are considered for each type of vibration to better understand the separate effect of both vibration and buoyancy forces and also their combined effects. Each type of vibration has its own features and affects the flow intensity and patterns differentlyItem Three-dimensional study of the pressure field and advantages of hemispherical crucible in silicon Czochralski crystal growth(Wiley, 2010) Mokhtari, Faiza; Bouabdallah, Ahcene; Merah, Abdelkrim; Zizi, M.; Hanchi, S.; Alemany, A.