http://depot.umc.edu.dz/handle/123456789/6376 2026-05-31T22:21:17Z http://depot.umc.edu.dz/handle/123456789/14810 Étude du transfert thermique convectif des nanofluides dans des problèmes bidimensionnels et tridimensionnels à géométrie variable. Korei, Zakaria; Benissaad, Smail Nanofluids are considered the working fluids of the future due to their improved thermophysical properties. However, the behavior of nanofluids in terms of improved heat transfer and flow characteristics remains a very interesting topic, whether for their various practical applications in industry or for the fundamental questions it raises. Within the framework of this thesis, many numerical investigations have been carried out on the problem of convection in the presence of nanofluids in various situations and environments in order to acquire a solid understanding of this new type of working fluid. The first part of the thesis deals with the study of the forced convection of (Al2O3/Water) nanofluids flow through a three-dimensional 90° elbow using a two-phase model under turbulent conditions. The effects of Reynolds number, nanoparticle volume fraction and nanoparticle diameter were discussed. The second part offers an in-depth analysis of the problem of mixed convection of (Al2O3- Cu/Water) hybrid nanofluids with the presence of a magnetic field for a wide range of parameters in a cavity having two rounded corners. The third part aims to perform an energetic and exergetic analysis of (Fe3O4/Water) nanofluids flow in three different heat sink scenarios using the finite volume approach. The fourth part presents a highly efficient hybrid approach to improve the thermal performance of the cooling system of an electronic component. The proposed research technique consists of incorporating a magnetic nanofluid, a magnetic field inducer and a porous medium into the system. The two-phase model is used in order to increase the accuracy of the results obtained. The fifth and final part focuses on the impact of a magnetic source placed in the vicinity of the heater under mixed convection conditions in a novel cavity having two arc-shaped plates filled with (Fe3O4/water) magnetic nanofluid. 2023-07-20T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14753 Analyse et comportement de renforcements de structures mécaniques par des patchs composites. Achour, Toufik; Mecibah, Mohamed-Salah; Djebara, Abdelhakim The reinforcement of damaged structures, by bonding composite patches, is a promising and beneficial repair technique, especially in the field of air transport. This method consists in reinforcing preventively damaged structures, in order to delay the initiation of cracks or to stop their propagation. It requires a good understanding of the stress states and the behavior of the structures involved. For the analysis of normal and shear stresses in the patch-glue-structure assembly, Our contribution is composed of two parts. The first part is based on a two-dimensional numerical study using the finite difference method for solving the equilibrium equations and analytical models obtained from the literature. The configuration is a double overlap of an aluminum plate subjected to different types of solicitations. Taking into account the two-dimensional effects and the difference of the Poisson’s ratio allowed us to determine the stress distribution especially in the adhesive layer representing the weakest link. Subsequently, an optimization by the Genetic Algorithm method was considered to determine the optimal fiber orientation for a better design. The second part is represented by two single and double overlap configurations of an Aluminum plate cracked on one side and loaded in tension. Under such conditions, a numerical finite element study in ANSYS 2020 R2 was considered. The stress distribution in the patch, the adhesive, as well as the reduction rate of the stress intensity factor in mode I were determined. The cohesive zone model (CZM) method was introduced using the bilinear delamination interface method (BID) for the study of the decohesion of the patch-glue and structure-glue contact interfaces for different fiber orientations of the composite patch. 2023-06-26T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14747 Elaboration Et modélisation d’un matériau cellulaire auxetique. Fiala, Houssem Eddine; Benmansour, Toufik Currently, cell materials are used in various sectors, such as automobile, transport and aerospace. A cell solid is a solid consisting of a connected network of solid links and/and plates forming the edges and the faces of cells. This type of materials have many beneficial properties such as, density, rigidity and resistance specific to flexion, and an ability to support large static and cyclical flowering loads for long periods. These structural properties are used not only in sandwich panels but also more general in applications where weight constitutes in terms of optimization the objective function for the proper design of mechanical subjects. As an indication, we can cite the automotive, aeronautical and naval design and manufacturing field. A good design of a mechanical object depends on two criteria: increased mechanical performance (robustness) and minimization of mass (economic lightness). The main objective of this study is to propose a methodology which makes it possible to provide preliminary choices of structures which display mechanical performance well suited to needs. Thus, on demand, the manufacture of new cellular structures is offered with adaptable mechanical properties according to the technology and industrial application field. When we have combined two types of cells (cells in honeycomb and retention cells) into a single structure and modified cell relationships, we have obtained three types of structures (traditional bee nest, relationship to emotions and fish ratio Null (ZPR)) and we have also found that it is possible to maintain a constant Young module with the variation of the fish coefficient, and this is what gives us the possibility of controlling its mechanical properties without modifying the properties cell geometrics, only modifying the proportions of cells. The digital models have been generated and compared to the results obtained from structures manufactured experimentally by the 3D printer, where the Young module, the fish factor and the compression deformation are used as a comparison criterion and shows a good concordance between the results of the three investigative approaches respectively analytical, digital, and experimental simulations. 2023-05-11T00:00:00Z http://depot.umc.edu.dz/handle/123456789/14605 Effet des paramètres adimensionnels sur un écoulement en convection mixte (laminaire et turbulente) dans une cavitè. Boulkroune, Sofiane; Kholai, Omar The present study focused on the two-dimensional numerical study of the effect of dimensionless parameters on the transition from mixed convection (laminar and turbulent) within a cavity with an aspect ratio A. The right vertical wall is fixed and maintained a hot temperature TC, the left vertical wall is movable, it is directed upwards with a velocity U0 and kept at a cold temperature. The two horizontal walls are assumed to be adiabatic. The objective set through this is the determination of the modified Richardson number (critical Ri) to determine the limits of passage between the regimes: forced-mixed and mixed-natural. The governing equations were discretized by the finite volume method on an offset mesh and the SIMPLE algorithm was used for the processing of the velocity-pressure coupling. A Fortran computational code was used to solve the partial differential equations describing the flows of mixed laminar and turbulent convection. Indeed, this work is made up of two parts: for the first part, we started with the study of the influence of the variation of the Prandtl number (Pr = 0.015, 0.71, 2, 7.1, 50 and 100) in the case of a square cavity (aspect ratio equal to 1). Then a study of the effect of geometry was carried out for different aspect numbers: A= 0.5, 1 and 1.25. In the second part, a parametric study of turbulent mixed convection was performed in a square cavity with air as a fluid and a constant Pr number. The standard k-ε turbulence model was chosen to model the Reynolds stresses. The critical parameters, λ (modified Richardson) and n necessary for the transition between the different types of convection and which are related to each other by the equation 2025-02-11T00:00:00Z