Doctorat LMD en Génie Mécanique

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Study and analysis of the vibrational behavior of a graphene-based nanocomposite-reinforced beam in a thermal environment.
(University of Tlemcen, 2026-07-16) Mazari,Mohammed Yassine
Advanced composite systems find extensive applications across many engineering fields and of ten operate in harsh thermal environments that can significantly reduce stiffness and pose risks to structural integrity. Therefore, a precise assessment of the environmental impacts is required to de termine their influence on the dynamics of these composite structures. The current thesis explores the dynamic characteristics of advanced composite beams embedded with graphene nanoplatelets under the conditions of thermo-mechanical and electro-thermal interactions. The primary objec tive of this research is to evaluate the contribution of graphene nanoplatelets to enhancing the dynamic response of composite structures while accounting for potential environmental effects. In the first part of the thesis, the problem of dynamic vibration analysis of an advanced composite beam embedded with graphene nanoplatelets operating in a thermal environment is investigated. A refined higher-order beam theory is proposed to accurately model the displacement function of the structure. The governing differential equations are developed using Hamilton’s principle and solved using the Galerkin technique. Moreover, a machine learning method is considered to estimate the natural frequency of the system rapidly and effectively. The second part of this study deals with the vibration analysis of the piezoelectric beam embedded with graphene nanoplatelets under the influence of coupling between thermo-electro-mechanical fields. A quasi-three-dimensional model accounting for the thickness stretching effect is used for the derivation of the equations of mo tion in order to increase the accuracy of the solution. Equations are solved using the DQFEM method, known to produce highly accurate results efficiently. Several comparative analyses have been carried out within this study to confirm the validity and efficiency of the developed theories. As expected, it has been found that the use of graphene nanoplatelets significantly increases the performance of the piezoelectric beam. It can be concluded that the developed theories provide an effective approach to the analysis of nanocomposites.
Thermo-economic study of sorption-based solar thermal refrigeration systems in urban cooling
(University of Tlemcen, 2026-09-20) Abdesselam, Bilal
This work investigates the thermal, exergetic, and economic performance of a solar assisted single-effect LiBr–H₂O absorption refrigeration system under the climatic conditions of Tlemcen, Algeria. Two solar collector technologies, flat-plate collectors (FPC) and evacuated tube collectors (ETC), are compared using hourly summer transient simulations and energetic, exergetic, and economic analyses. The results show that the ETC configuration provides higher useful thermal energy compared to the FPC system. The ETC provides 25–50% higher cooling capacity during the early morning hours and 35–55% higher output during peak solar periods. Moreover, the generator heat input increases by approximately 27–67% throughout the day when using ETCs. However, the higher operating temperatures associated with ETC systems result in a slight decrease in exergetic efficiency of approximately 10–25%. The exergy analysis reveals that the solar collector is the dominant source of irreversibility, accounting for nearly 79% of the total exergy destruction, followed by the generator at approximately 12% and the absorber at approximately 6%. From an economic perspective, the thermo-economic assessment based on key indicators such as NPV, IRR, and payback period demonstrates that both systems are economically feasible under Algerian climatic and energy conditions. Nevertheless, the ETC-based system exhibits superior economic performance, with a higher NPV and a shorter payback period of approximately 12.2 years compared to 15.4 years for the FPC configuration. Although the ETC system requires a higher initial investment, its enhanced thermal performance leads to greater annual energy savings and improved long-term economic performance. Overall, the study confirms that the integration of solar-powered absorption refrigeration systems offers significant potential for mitigating dependence on conventional electricity sources while promoting higher energy performance in solar rich regions such as Algeria, with the ETC configuration emerging as the most suitable option for future solar air-conditioning applications.
Analysis of a New Hybrid Solar Dryer Coupled with a Heat Storage System for Agro-Food Sector Professionals in the El Oued Region
(University of Tlemcen, 2026) Zine,Ali
In light of the challenges associated with preserving agricultural product quality and reducing post-harvest losses, this study focuses on developing solar drying systems adapted to arid regions, particularly the Oued Souf area. An innovative greenhousetype solar dryer was designed for local farmers, aiming to protect products from direct solar radiation while preserving their sensory and chemical properties and reducing spoilage. The study was conducted at the Research and Develop ment Unit for Renewable Energy in Arid Zones at the University of El Oued. The system was first evaluated through mint drying and compared with a conventional direct solar dryer. Results showed improved thermal performance, reduced drying time, and better product quality, especially in terms of color preservation. To address the intermittency of solar energy, the system was later upgraded to a hybrid configuration by integrating a gas energy source. This hybrid dryer was tested on onion drying to analyze drying kinetics, along with economic and environmental assessments, confirm ing its effectiveness in improving performance and reducing drying duration. Further experiments were conducted on tomato drying, including energy, exergy, economic, and environmental analy ses, with continuous comparison to the direct solar dryer. The results indicated enhanced energy and exergy efficiencies, improved economic feasibility, and reduced environmental impact. Finally, a heat recovery system was incorporated, both without and with thermal storage materials. The findings demonstrated that heat recovery significantly reduces thermal losses and extends drying operation even under low solar radiation conditions, thereby improving system autonomy. Overall, the proposed dryer represents a practical and sustainable solution for farmers in the Oued Souf region, contributing to improved product quality, reduced losses, and enhanced energy efficiency.
Contribution to the improvement of the energy efficiency of solar sorption refrigeration systems: application to absorption systems
(University of Tlemcen, 2026-06-18) Chikh, Mohammed El Amine
Solar-driven absorption refrigeration using the ammonia–water (NH₃–H₂O) pair offers a sustainable cooling solution for regions with high solar potential. This thesis develops a steady state thermodynamic model of a single-effect NH₃–H₂O solar absorption refrigeration system, based on mass, energy, and equilibrium balances, and solved using Engineering Equation Solver (EES). A parametric study examined the effects of generator temperature, evaporator temperature, absorber/condenser pressures, and ammonia concentration on the coefficient of performance (COP). Results show COP increases with generator temperature up to an optimum, beyond which irreversibility limits further gains, while higher ammonia concentration improves COP by reducing the circulation ratio. Conversely, increasing evaporator temperature reduces COP due to shifts in solution equilibrium. The maximum COP obtained was 1.28, at Ph = 7 bar, Pb = 1 bar, x = 25%, and a generator temperature of 110–115°C. The model was validated against published data, showing good agreement. These findings identify optimal operating regions and offer design guidelines for improving solar absorption cooling performance in high-irradiation regions such as Algeria.
Dynamic and static study of plates made of porous advanced materials reinforced with carbon nanotubes
(University of Tlemcen, 2026-06-18) Bousmaha,Karima
Functionally graded material (FGM) sandwich plates are widely used as structural components in various branches of engineering such as mechanical, aerospace, civil, and naval engineering. To ensure proper design and performance of these structures, it is essential to analyze and understand their behavior. In this thesis, both the static and dynamic behavior of FGM sandwich plate incorporate the effect of porosity distribution and Carbone nanotube (CNT) reinforcement are analyzed using the p-version of the Finite Element Method (p-FEM) based on the First- order Deformation Theory (FSDT). The sandwich plate consists of three layers, where the core layer is made of functionally graded carbon nanotube-reinforced material (FG-CNTR), including three distribution types: Uniform, FG-X, and FG-O. The top and bottom face sheets are composed of a porous functionally graded material (FGM), modeled using five different porosity distributions: Perfect, Imperfect I, …, V. The numerical results demonstrate convergence and are validated through comparison with previously published data, confirming the accuracy of the proposed formulation. The dynamic behavior is analyzed by comparing the results obtained from the p-version of the (FEM) with the mode superposition approach those derived from a newly developed analytical solution formulated within the framework of the Classical Plate Theory (CPT). The effects of several parameters such as the carbon nanotube distribution pattern, porosity model, CNT volume fraction, geometric characteristics, mechanical loading, volume fraction exponent, damping coefficient, and boundary conditions are thoroughly illustrated and analyzed for static and dynamic responses.
Dynamic behavior of a Micro/Nano-beam made of smart piezoelectric material with property gradient
(University of Tlemcen, 2026-06-04) Khouani,Besma
This thesis investigates the static bending and free vibration of functionally graded magneto-electro-elastic (FG-MEE) microbeams in sandwich, coated, and bi-coated forms. Refined higher-order and quasi-3D beam theories are combined with the Differential Quadrature Finite Element Method (DQ-FEM) to capture electromechanical coupling. Material gradation is modeled by a power-law distribution, ensuring smooth property transitions between MEE and non-MEE layers. The Modified Couple Stress Theory (MCST) is incorporated to account for size-dependent effects, and governing equations are derived via Lagrange’s theorem and Gauss–Lobatto discretization. Validation with published results confirms the model’s accuracy and efficiency. Results show that material composition, gradation index, and geometry strongly affect static and dynamic responses. Increasing BaTiO3 enhances piezoelectric deflection, while CoFe2O4 strengthens magnetostrictive effects. Higher gradation indices and slenderness ratios increase stiffness but reduce electromechanical potentials. Natural frequencies are highly sensitive to boundary conditions. The framework offers an efficient tool for optimizing FG-MEE microbeams in smart microsystems.
Experimental analysis of a new thermal energy storage system for air conditioning
(University of Tlemcen, 2026-06-16) Embarek, Noureddine
Maintaining a stable air temperature over prolonged periods in space heating and drying ap plications using solar air heaters remains a significant challenge, particularly under variable solar irradiance conditions. This thesis presents a comprehensive experimental investigation of a hybrid double-pass solar air heater integrated with a latent heat thermal storage unit, with the aim of developing a reliable and efficient system capable of all-weather operation for space heating and drying applications. To ensure a holistic evaluation of the proposed system, a multi criteria assessment methodology that included energy, exergy, economic, and envi ronmental analyses was used. The experimental study was systematically conducted in three consecutive phases. In the first phase, parametric and dimensional analyses were performed on a baseline double-pass solar air heater to investigate the influence of air gap variation on thermal and exergetic performance, showing that increasing the upper air channel height con siderably improved system performance, with a maximum thermal efficiency of 66.4% achieved at a 12 cm air gap configuration, while smaller gaps led in higher irreversibility and increased exergy destruction. The second phase focused on the integration of an auxiliary electric heater and a latent heat thermal storage unit using paraffin wax to improve thermal stability and extend operating hours. This configuration enabled a stable outlet temperature of 54±1.25 °C, prolonged system operation after sunset, and reduced electrical energy consump tion. At an air mass flow rate of 0.024 kg/s, the system achieved average thermal and exerget ic efficiencies of 72.3% and 3.5%, respectively. The third phase addressed further perfor mance optimization through the integration of wavy fins and the evaluation of auxiliary heater positioning. A fin inclination angle of 45° enhanced thermal efficiency by 13.8% compared to a flat absorber, while positioning the auxiliary heater at the outlet section improved tempera ture regulation, minimized fluctuations, and reduced electrical energy consumption by 4.23%. Overall, the findings demonstrate that using both latent heat thermal storage and heat transfer enhancement techniques significantly improves energy efficiency, thermal stability, sustaina bility, and practical applicability of hybrid solar air heaters, making the proposed system a promising and sustainable solution for agricultural drying and space heating applications.
Combustion Study of Biofuel Derived from Waste Fish Oils in Internal Combustion Engines
(University of Tlemcen, 2026-05-12) Medjahed, Lamia
The rising global energy demand, the depletion of fossil fuel reserves, and the environmental challenges associated with waste cooking oil disposal highlight the need for cleaner and more sustainable fuel alternatives. This thesis investigates the production, characterization, and en gine application of biodiesel derived from waste cooking oil, aiming to establish an efficient and environmentally responsible pathway for its utilization in existing diesel engines. Waste cooking oil was collected, stored, and pretreated following proper handling practices to ensure feedstock quality. Biodiesel was produced through an optimized transesterification pro cess in which the effects of alcohol-to-oil ratio, catalyst concentration, reaction time, and reac tion temperature were evaluated. The produced biodiesel was purified and assessed according to ASTM D6751 and EN 14214 standards to verify its physicochemical suitability as a diesel substitute. Fuel blends of B5, B10, B20, and B30 were then formulated and evaluated to en hance fuel stability and better understand the influence of biodiesel concentration on engine behaviour. Engine tests were conducted on a Deutz Z-MWM D302-1 single-cylinder, naturally aspirated, direct-injection diesel engine. Performance characteristics, fuel consumption, and pollutant emissions were examined across the different biodiesel blends. The validated experimental data were further used to develop a combustion model in CONVERGE CFD, providing numerical access to key spray and combustion characteristics such as in-cylinder pressure, temperature, heat release rate, and ignition delay. The optimized production process yielded high-quality biodiesel fully compliant with ASTM D6751 and EN 14214 specifications. Engine results showed stable operation for all blends, with a modest increase in CO emissions and a clear reduction in NOx, attributed to the intrinsic oxygenated nature of biodiesel and its lower combustion temperature. The modelling results supported and deepened the experimental findings, overcoming limitations in available meas urement techniques. Overall, this work demonstrates the viability of waste cooking oil biodiesel as a sustainable fuel and provides both experimental and computational contributions to the understanding of its combustion behaviour in diesel engines, confirming that WCO biodiesel and its blends represent an efficient, low-cost, and environmentally responsible fuel pathway with strong potential for real-world implementation
Modélisation et optimisation des trajectoires de l’outil de coupe pour les MOCN 5 axes
(University of Tlemcen, 2026-04-18) Ziani,Belkheir
L’usinage CN 5 axes constitue une technologie de pointe permettant la réalisation de formes complexes avec une précision élevée grâce à la liberté de mouvement simultané sur cinq axes. Dans ce cadre, cette recherche propose une approche d’optimisation intelligente des trajectoires d’outil, visant à améliorer la qualité d’usinage, la continuité des trajectoires et la réduction des temps de cycle. Une méthode hybride d’interpolation a été développée, combinant les techniques spline cubique, Lagrange et PCHIP afin d’assurer une meilleure fluidité et précision des trajectoires. Parallèlement, un algorithme d’optimisation adaptatif a été conçu pour ajuster automatiquement les paramètres d’interpolation et minimiser l’erreur quadratique moyenne. Les simulations réalisées sous MATLAB, ainsi que les tests sur des trajectoires réelles générées en G-code, démontrent une amélioration significative des performances d’usinage, notamment lorsqu’il est couplé à un algorithme génétique. Enfin, le système intègre des agents d’intelligence artificielle (basés sur GPT-4, Mistral, et Gemini) pour l’analyse, la validation et la génération automatisée de trajectoires, inscrivant ce travail dans la dynamique de l’Industrie 4.0.
Etude du comportement en fatigue des joints soudés sur les aciers pour pipeline API 5L
(University of Tlemcen, 2026-04-23) Benhamel, Abdelhamid
Cette thèse s’intéresse au comportement mécanique et à la tenue en fatigue des soudures réalisées sur les pipelines en acier API 5L X42. L’objectif principal est d’évaluer la capacité de ces soudures à supporter les sollicitations rencontrées en service et d’identifier les paramètres qui influencent l’initiation puis la propagation des fissures. Trois volets ont été étudiés : les essais de traction, les essais de fatigue et la modélisation numérique sous Abaqus. Dans un premier temps, des essais de traction ont été menés sur des éprouvettes prélevées dans deux tronçons de pipe l’un soudé et l’autre non soudé découpés perpendiculairement au joint. Les zones étudiées incluaient le métal de base, le métal d’apport et la zone affectée thermiquement. Ces essais ont permis de caractériser les propriétés mécaniques locales, de mettre en évidence l’influence du cycle thermique de soudage sur le comportement du matériau et de repérer les zones les plus vulnérables à une perte de performance. Le second volet a porté sur des essais de fatigue effectués sous différentes amplitudes de chargement afin de reproduire, de manière réaliste, les conditions de fonctionnement des pipelines. Enfin, une simulation numérique a été réalisée à l’aide d’Abaqus pour reproduire la réponse en traction des joints soudés. Ce modèle numérique a contribué à identifier les zones sensibles, à estimer la durée de vie des soudures et à conforter les observations issues de l’expérimentation. Les résultats obtenus démontrent que la combinaison d’essais mécaniques et de modélisation numérique constitue une approche pertinente pour évaluer la fiabilité des soudures dans les pipelines en acier API 5L et pour proposer des pistes d’amélioration des procédés de soudage.
Development and thermodynamic characterization of new materials for thermal storage by latent heat
(University of Tlemcen, 2026-04-23) Mahmoudi, Djahida
The need for efficient thermal energy storage materials has escalated with the adoption of sustainable energy systems. Paraffin wax is one of the most widely used phase change materials because of its high latent heat storage capacity, stability, and cost-effectiveness. However, its low thermal conductivity of approximately 0.2 W/m•K and possibility of phase separation hinder its thermal efficiency, despite improvements by nanofilers and carbon additives. A new approach for enhancement, which can be sustained in an efficient manner using Algerian slack wax, an underutilized petroleum derivative with immense potential, shall be proposed in this research work. PCMs with a combination of 6, 10, 15, and 20 wt% slack wax were studied by using a T-history test. The performance analysis reveals a collective advancement in different properties of PCMs, which is not a common phenomenon in PCM enhancement studies, where trade-off is considered. The combination with 20% slack wax proved to be most effective with a maximum increase of 35.65% in latent heat capacity from 106.93 kJ/kg to 145.06 kJ/kg, 30.48% in specific heat capacity from 3.51 kJ/kg•K to 4.58 kJ/kg•K, and a 33% boost in solid-phase thermal conductivity from 0.18 W/m•K to 0.24 W/m•K. Moreover, solidification time reduced by 25% from 165 s to 120 s and melting time reduced by 20% from 125 s to 100 s, respectively. The observed modifications in PCMs can be attributed to intermolecular interaction among paraffin and slack wax, which leads to an improper crystallization pattern with good transport properties. Use of an industrious waste in this manner can prove beneficial for cost-effective production of a higher-performance PC McA in an economical manner with sound eco-green concepts in the energy department in Algeria.
Caractérisation thermo-hydraulique d’un échangeur de chaleur muni de rubans torsadés perforés.
(University of Tlemcen, 2026-02-15) Bouregueba, Amel
L'amélioration du transfert thermique est essentielle pour accroître l'efficacité énergétique et réduire les coûts d'exploitation des systèmes thermiques. Cette étude est motivée par la nécessité de développer des échangeurs de chaleur compacts et rentables grâce à l'utilisation de techniques d'amélioration passive. Les inserts en ruban torsadé ont notamment suscité un intérêt considérable en raison de leur capacité à intensifier le mélange des fluides et à perturber les couches limites thermiques. L'objectif de cette étude est d'étudier numériquement les performances thermiques et hydrauliques d'un tuyau circulaire équipé de trois types d'inserts : ruban torsadé simple (RT), ruban torsadé perforé circulaire (RTPC) et ruban torsadé perforé hexagonal (RTPH). À l'aide d'ANSYS Fluent et de la méthode des volumes finis, des simulations ont été réalisées sous un flux thermique constant pour des nombres de Reynolds compris entre 5 000 et 20 000. Les résultats montrent que toutes les configurations de ruban torsadé améliorent considérablement le transfert de chaleur par rapport à un tube lisse, avec des augmentations du nombre de Nusselt pouvant atteindre 62,37 % pour le RT, 65,85 % pour le RTPC et 76,27 % pour le RTPH. Ces améliorations s'accompagnent d'une augmentation des coefficients de frottement de 150,68 %, 154,31 % et 176,05 %, respectivement. Le critère d'évaluation des performances (PEC) le plus élevé, soit 1,25, a été atteint par le RTPC, ce qui indique son équilibre thermohydraulique optimal. Les résultats de cette étude sont pertinents pour la conception et l'optimisation des échangeurs de chaleur dans diverses applications industrielles, notamment les systèmes solaires thermiques, le traitement chimique et les systèmes CVC.
Optimal Design of Disaster-proof Critical Infrastructure in the Electricity System; A case study of Accra, Ghana
(University of Tlemcen, 2026-02) Paul, Nduhuura
Worldwide there are ongoing concerted efforts to expand access to electricity especially in developing countries, with electricity being touted as an important enabler for socioeconomic transformation. Most of the electrification initiatives are geared towards increasing the number of communities or households connected to the grid. However, in many developing countries including in Africa, those who already have an electricity connection often experience electricity outages with consequences for sustainable development. The frequent outages imply weaknesses in the design and operation of the electricity system – a critical infrastructure. This research investigates the extent to which failures in the electricity system cause power outage occurrences in Accra Ghana, the resultant impacts of power outages on households and the predominant coping measures used by households when faced with outages. Moreover, existing literature shows that the distribution of power outages in communities may be influenced by socioeconomic and political factors. Often, it is those who are already socioeconomically disadvantaged who will face more outages and suffer greater impacts due to lack of sufficient coping capacities. This study uses various datasets (2015 outage statistics, census data and survey data), spatial and non-spatial statistical methods and tools to measure the degree of exposure to outages in different Accra communities, identify common outage impacts and response options in households and their drivers. The results show that, in 2015, Accra communities experienced widespread outages which varied significantly across the communities. The distribution of outages was found to be more influenced by demographic factors (household density and presence of large proportions of minorities) and less predicted by economic factors (wealth). Common outage impacts identified include safety/security issues, economic impacts and disrupted access to social services. Being of a low socioeconomic status, characterized by low education level, low income, and informal employment was associated with less likelihood to report being impacted by outages. Having a high exposure to outages, both in terms of frequency and duration, was generally associated with a high likelihood to report household-level impacts of outages. Other household characteristics, such as living in a large family, seem to diminish the possibility of reporting one kind of outage impact while increasing the likelihood of reporting another kind of outage impact. The study also found that selection of outage coping options in households are generally influenced by the household’s electricity needs/uses. It also supports the general assumption that household economic characteristics impact greatly on selection of coping choices. Availability of some v natural resources also provides potential coping options that households can utilize during outages. The research results provide vital information which can be used to influence decisions and policies towards all-inclusive and sustainable electrification in Ghana and beyond.
Numerical and experimental analysis of the thermo-energetic performance of ventilation in a solar drying chamber
(Universityof Tlemcen, 2025-01-07) Kherrafi, Mohammed Abdelbassit
The rising demand for energy, coupled with environmental concerns and the depletion of fossil fuels, has heightened the need for renewable energy solutions. Solar energy, characterized by its abundance and sustainability, plays a critical role in addressing these challenges. Among its many applications, solar drying has emerged as an efficient and eco-friendly method for preserving agricultural and food products. By leveraging solar energy, drying technologies reduce dependency on conventional energy sources while improving product quality and reducing waste. This thesis investigates the optimization of solar drying systems, focusing on the drying chamber's ventilation and the enhancement of solar collectors. A combination of experimental and numerical analyses was conducted to evaluate the impact of design modifications and material choices on drying performance. Experimental setups at the Applied Research Unit for Renewable Energies in Ghardaia explored various configurations, including the integration of obstacles, ribs, and inserts in both direct and indirect solar dryers. Numerical simulations using ANSYS Fluent provided insights into airflow patterns and heat transfer dynamics, validating experimental findings and guiding design improvements. The results demonstrate that integrating obstacles and other structural enhancements significantly improves heat transfer, airflow distribution, and drying efficiency, reducing drying time and energy consumption. Additionally, the study emphasizes the importance of sustainable materials and advanced monitoring systems to optimize operational parameters and minimize environmental impact. This work contributes to bridging gaps in solar drying research by focusing on internal chamber enhancements and integrating advanced design features. The findings support the development of cost-effective and environmentally friendly solar drying systems, offering practical solutions for food preservation and energy efficiency in agricultural and industrial applications.
Vibration behavior of a smart rotating nanoshaft
(University of Tlemcen, 2025-01-20) Merwan, Behar
This thesis introduces a novel mathematical formulation to investigate the vibration behavior of rotating smart nanoshafts. The model integrates Euler-Bernoulli beam theory with the nonlocal strain gradient theory and Maxwell's electrostatic equations. The smart nanoshaft structure is composed of a single-walled boron nitride nanotube (SWBNNT), chosen for its exceptional piezoelectric and magnetic properties, which make it highly suitable for rotating components in nanoelectromechanical systems (NEMS). The electro-mechanical equations of motion are derived using Hamilton's principle and solved semi-analytically through Galerkin-based closed-form solutions. Forthermore, the effects of rotating speed, mode number, external voltage, temperature change, geometrical parameters, material length scale, and nonlocal parameters on natural frequencies and critical speed are investigated. This work represents the first comprehensive analysis of these factors under various boundary conditions for rotating smart nanoshafts, offering valuable insights into their vibrational dynamics. The results are contextualized within the existing literature, demonstrating the accuracy and efficiency of the proposed model. This establishes the formulation as a robust numerical tool for analyzing the behavior of rotating nanoscale structures.
Etude et analyse des ruptures des soudures par points des peels joints
(University of Tlemcen, 2025-04-29) Benchadli, Ismail
Cette recherche vise à analyser l'influence des paramètres de soudage par résistance par points (RSW) sur les propriétés mécaniques et structurelles des assemblages d'acier inoxydable austénitique AISI 316L d'épaisseur 1,5 mm. L'étude évalue spécifiquement la corrélation entre les variables du procédé - courant électrique, pression des électrodes et durée des cycles - et la résistance au cisaillement en traction des joints. Une attention particulière est portée à la caractérisation de la géométrie du noyau de soudure, notamment le diamètre d'indentation et la profondeur de pénétration, dans des configurations de joints à recouvrement et de type Peel. Cette analyse approfondie permettra d'établir les paramètres optimaux de soudage par points pour ce matériau et de déterminer le facteur d'intensité de contraintes critique (FICC), données essentielles pour garantir l'intégrité structurelle des assemblages dans des applications industrielles exigeantes.
Dynamic of non-uniform rotors made of axially functionally graded materials
(University of Tlemcen, 2025-10-09) Saim,Ahmed
Cette étude présente une analyse numérique du comportement de tourbillonnement d’un arbre creux non uniforme en rotation, constitué de matériaux à gradient fonctionnel axial (FGM). The material properties vary continuously along the axial direction according to a power-law distribution. Using Timoshenko beam theory, the shaft is modeled with the pversion of the finite element method (FEM), while Lagrange’s formalism is applied to derive the differential equations governing the motion of the rotating system. The proposed model is used to analyze the system’s whirl frequencies, critical spinning speeds, and the influence of key parameters on the behavior and stability of dimensionless natural frequencies. These parameters include the slenderness ratio, material composition, radius variation, variable rotating speed, and power-law index, evaluated under various boundary conditions (B.C.). The effects of these factors performance of spinning hollow non-uniform shaft are understood. The validity of the proposed model is confirmed through comprehensive comparisons of numerical and analytical results with existing data in the literature. This work paves the way for innovative industrial applications in advanced rotating structures.
IMPACT DE LA PRESENCE DES NANO FLUIDES DANS UN ECHANGEUR DE CHALEUR A FAISCEAU ET CALANDRE -ETUDE NUMERIQUE
(University of Tlemcen, 2025-11-02) Guendouz,Bouhelal
Cette étude explore la performance thermique d'un échangeur de chaleur à faisceau tubulaire et calandre en optimisant son efficacité grâce à l'utilisation d'un nanofluide Cu-eau circulant côté calandre. Une approche expérimentale et numérique a été adoptée pour analyser et comparer l'influence de différentes concentrations volumiques de nanofluide (2% - 6%) et de divers débits côté froid (0,047 - 4 l/min). L'analyse expérimentale s'est d'abord concentrée sur le transfert de chaleur entre deux fluides de même nature afin d'établir une référence de comparaison. Des simulations numériques ont ensuite été réalisées pour étudier l'impact du nanofluide sur la performance de l'échangeur. Les résultats ont montré qu'à une concentration de 6 %, le transfert de chaleur est significativement amélioré, avec une augmentation de l'écart de température atteignant 6,86 °C sur la calandre et 3,9 °C dans les tubes, un gain d'efficacité thermique de 11,33 % et un coefficient global de transfert de chaleur pouvant atteindre 8 516,87 W pour un débit de 4 l/min, comparativement à des essais réalisés uniquement avec de l'eau. Les simulations numériques indiquent que les nanofluides MWCNT/eau et TiO₂/eau améliorent l'efficacité thermique par rapport au Cu/eau, les gains les plus élevés étant obtenus avec le MWCNT. Pour une concentration de 6%, l'efficacité augmente de 3,3% à 5,0% pour le MWCNT, contre seulement 0,9% à 2,0% pour le TiO₂
Design and Optimization Study of Shell Structures Made of Advanced Materials Under Different Types of Loadings
(University of Tlemcen, 2025-01-23) Zeddoune,Lakhdar
The ongoing advancement in technology leads to increasingly intricate projects, which are more computationally expensive. Shell geometries present additional complexities, including varying curvature and thickness, which can render the formulation and implementation of shell elements more challenging than simpler beam and plate elements. Moreover, they often demand higher computational resources and more sophisticated numerical techniques to accurately capture their behavior, resulting in increased computational cost and complexity. Additionally, the development and validation of shell elements entail extensive experimental and numerical testing, potentially limiting the availability of accurate and reliable formulations compared to beam and plate elements. Lastly, the application of shell elements is typically more specialized and specific to certain industries or engineering disciplines, leading to a narrower research focus compared to the broader applicability of beam and plate elements across various fields. In recent years, the p-version of the finite element method has gained prominence due to its higher accuracy and faster convergence rates compared to traditional methods, requiring fewer degrees of freedom for accurate results. It provides better representation of complex geometries, increased flexibility in mesh adaptation, and reduced spurious oscillations in solutions, making it a valuable tool for engineering simulations. By leveraging the thick shell theory, the p-version of the finite element method is combined with the third-order shear deformation theory (TSDT) to develop a new type of p-version shell element. A computer code based on this element type has been developed, tested, and successfully validated. The code’s performance and robustness were assessed through the analysis of a wide range of shell structures exhibiting free vibration, bending, and thermal buckling behavior, isotropic and bidirectional functionally graded materials, and arbitrary geometrical shapes. The mathematical formulation, code structure, as well as results, are presented in the following sections.
Étude sur la Corrosion et la détection CND des défaillances par ultrasons dans les aciers API 5L X60 - Cas des ouvrages de pipelines d’hydrocarbures – ligne GZ1 40
(University of Tlemcen, 2024-11-30) Benkhedda, Fatima
Les aciers des pipelines sont sujets à des défaillances dues à la corrosion, ce qui pose des problèmes pour la fiabilité du transport par pipeline et pour l'environnement. Dans un premier temps, la thèse se focalise sur le comportement en corrosion des aciers API 5L X60 par les sols du gazoduc GZ1 en employant des méthodes électrochimiques et une solution de sol artificiel. Les échantillons ont été obtenus par coupons découpés dans des tubes corrodés obtenus lors des opérations de maintenance. La deuxième étape est la détection des défauts de surface à l'aide des techniques ultrasons TOFD et C-Scan. Il a été montré par les résultats potentiodynamiques que l'acier est susceptible de se corroder par le sol lorsque la protection est défaillante accentuée par les sols à faible résistivité et le pH, la composition chimique, la teneur en eau, les contraintes mécaniques, etc. Les caractéristiques mécaniques diminuent en fonction de la durée d'immersion. Cette réduction est principalement due à l'effet de corrosion et à la durée d'immersion qui est à l'origine d'une dégradation directe des caractéristiques mécaniques de l'acier. La détection de surface des défauts par méthode ultrasonique sans contact TOFD et par immersion ultrasonore C-Scan a montré que l'onde ultrasonore diffractée se produisant aux bords des défauts n'apparaît pas en l'absence de défauts. Le signal reste stable à tout moment de 0 à 138,2μs à une amplitude maximale de 50 dB. L'image ultrasonique C-scan présente une réflexion unique qui ne change pas même lorsque les curseurs d'amplitude varient. En cas de défauts sous forme de piqûres de corrosion et de défauts de soudure, l'onde ultrasonore diffractée se produit sur les bords de l'acier défectueux. Les défauts de soudure sont confinés au centre de la plaque. L'image ultrasonique montre une distribution résultant de différentes variations d'amplitude et de différentes impédances acoustiques. La vitesse de propagation transversale des ondes ultrasonores est modifiée, montrant une augmentation due à la présence de ces défauts. L'application de la détection par ultrasons des défauts de surface, leur nature, leur localisation et leur taille est étendue à l'expertise en ligne en utilisant l’outil ultrasonique intelligent afin de définir une stratégie de maintenance.

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