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Numerical Simulation of Two-Dimensional Natural Convection in a Confined Environment with the Vorticity-Stream Function Formulation

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Open Journal of Fluid Dynamics 2018年第1期8卷 44-58页

作者： Mame Khady Kane Cheikh Mbow Mamadou Lamine Sow joseph sarr Department of Physics Cheikh Anta Diop University of Dakar Dakar Senegal

A numerical study is presented on the problem of 2D natural convection in a differentially heated cavity. The equations governing this unsteady flow phenomenon were solved using the vorticity-stream function formulation of the Navier-Stokes equations and heat. The results obtained are compared with the results of the literature and make it possible to validate this approach. In this work, we studied the heat transfer in a cavity and we determined the variation of the local Nusselt number which allows obtaining the rate of thermal transfer by convection in an enclosure. We analyzed thermal fields for different Rayleigh numbers by selecting two points to visualize temperature fluctuations over time. Thus, the creation of the ascending and descending movements of the fluid inside the cavity was analyzed. We have also established temperature histograms for the graphical presentation of the temperature distribution. The modeling of the two-dimensional problem was established using a “Fortran 90” calculation code. The results also show the different vorticity contour maps in laminar flow regime. We have presented our results of numerical simulations using a visualization tool. The Rayleigh number varies in the range of 103 to 106 for a Prandtl number equal to 0.72 corresponding to air.

关键词： Numerical Study Differentially Heated Cavity Vorticity Modeling

A Study on Natural Convection of Air in a Square Cavity with Partially Thermally Active Side Walls

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Open Journal of Fluid Dynamics 2017年第4期7卷 623-641页

作者： Mame Khady Kane Cheikh Mbow Mamadou Lamine Sow joseph sarr Department of Physics Cheikh Anta Diop University of Dakar Dakar Senegal

In this present work, we study heat transfer in a confined environment. We have to determine the thermal and dynamics fields of the cavity while observing the effect of the Rayleigh number which depends on the characteristics of the fluid and the temperatures imposed. The behavior of boundary layers in natural convection is analyzed along this square cavity. The central halves of its vertical walls are heated at different temperatures. The left active part is at a higher temperature than the one on the right wall. The remaining inactive parts and the horizontal walls (upper and lower) are adiabatic. The thermal and dynamic modeling of two-dimensional problem was done using a calculation code Fortran 90 and a visualization software ParaView based on the finite volume method. The equations governing this phenomenon of unsteady flow have thus been solved. This allows the modeling of both air flow and heat transfer with a numerical stabilization of the solution. So, we have presented our results of numerical simulations using a visualization tool. The results show the different velocity and temperature curves, velocity vectors and isotherms in laminar flow regime.

关键词： Heat Transfer Natural Convection Square Cavity Laminar Flow Regime

Evolution of Dam Lakes in the Kayanga/Geba Basin: Contribution of Remote Sensing and GIS

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Journal of Geoscience and Environment Protection 2021年第12期9卷 225-243页

作者： Saly Sambou Rene Ndimag Diouf Birane Cisse Ibrahima Diouf joseph sarr Honore Dacosta Department of Geography Faculty of Letters and Human Sciences Cheikh Anta Diop University Dakar Senegal Faculty of Science and Technology of Education and Training Cheikh Anta Diop University Dakar Senegal NOAA Center for Weather and Climate Prediction 5830 University Research Court College Park Maryland USA National Agency for Applied Scientific Research Ministry of Higher Education Research and Innovation Dakar Senega

The Confluent and Niandouba dams were built in 1984 and 1997 respectively to better control water resources, increase agricultural production and promote local development. This article studies their evolution on the Kayanga/Geba River, a transboundary river between Guinea, Senegal and Guinea-Bissau, from its impoundment to the present day. The topographic characteristics analysed through the DTMs (Digital Terrain Models) show a flat shape for the Confluent Dam Lake and long plateaus for the Niandouba Dam Lake. The cross-sections present a variety of morphologies ranging from wide U-shaped valleys with sinuous bottoms to deep V-shaped valleys. The homogenisation and reconstruction of missing values were carried out using the regional vector method. The application of Pettitt’s statistical test on annual rainfall (1932-2019) indicates breaks of stationarity in 1967 or 1969. The post-breakage deficits range from 11.4% to 19.4%. The segmentation method corroborates the results of the Pettitt test. The variations of the surface area of the Confluent and Niandouba water bodies are linked to rainfall, evaporation and withdrawals for different uses. Their monitoring would allow for better management of available water resources but also for good planning of off-season crops.

关键词： Dam Lakes Remote Sensing GIS Watershed Kayanga/Geba

Numerical Simulation of Natural Air Convection in Inclined Eccentric Hemispheres Enclosure

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Open Journal of Applied Sciences 2021年第6期11卷 722-735页

作者： Mariama Néné Koita Mamadou Lamine Sow Oumar Dramé Babacar Mbow Cheikh Mbow joseph sarr Groupe de Recherche sur l’Energie Solaire et les Transferts (GREST) Faculté des Sciences et Techniques Université Cheikh Anta DIOP (UCAD) Dakar Sénégal Laboratoire de Mécanique des Fluides Faculté des Sciences et Techniques Université Cheikh Anta DIOP (UCAD) Dakar Sénégal Laboratoire de Physique des Semi-Conducteurs et D’énergie Solaire Faculté des Sciences et Techniques Université Cheikh Anta DIOP (UCAD) Dakar Sénégal

The subject of natural convection heat transfer is motivated by a wide range of applications in engineering technology. The hemispherical cavity is a part of basic geometries although it is not widely studied. The effect of inclinaison on natural convection fluid motions in the gap between two eccentric hemispheres is numerically studied. The inner hemisphere is subjected to a heat flux of a constant density and the outer one is maintened isothermal. The walls separating the two hemispheres are thermally adiabatic. Equations are formulated with vorticity and stream-functions variables. It is also assumed the fluid incompressible and obeys the approximation of Boussinesq. These equations are written by using bispherical coordinates system and solved by using a finite difference method. The results show the topology of flow is strongly dependent on the inclinaison because the flow can change from a unicellular regime to a multicellular regime by varying the inclination from 0 to π. By increasing the Rayleigh number (103Ra7), the flow intensifies. The results are shown in terms of streamlines and isotherms during their transient evolution.

关键词： Bispherical Coordinates Hemispherical Cavities Rayleigh Number Nusselt Number Eccentricity Streamlines Isotherms

Unsteady Natural Convection between Two Eccentric Hemispheres

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Open Journal of Applied Sciences 2021年第2期11卷 177-189页

作者： Mariama Néné Koita Mamadou Lamine Sow Omar Ngor Thiam Vieux Boukhaly Traoré Cheikh Mbow joseph sarr Groupe de Recherche sur l’Energie Solaire et les Transferts (GREST) Faculté des Sciences et Techniques Université Cheikh Anta DIOP (UCAD) Dakar Sénégal Laboratoire de Mécanique des Fluides Faculté des Sciences et Techniques Université Cheikh Anta DIOP (UCAD) Dakar Sénégal

Natural convection heat transfer in open or closed cavities takes place in different engineering areas. The hemispherical cavity is a part of basic geometries although it is not widely studied. The present paper reports the numerical study of natural convection in a closed hemispherical annulus delimited by two vertically eccentric hemispheres filled with Newtonian fluid (air in this case with Pr = 0.7) is conducted. The inner hemisphere is heated by a heat flux of constant density and the outer one is maintained isothermal. Based on the Boussinesq assumptions, the governing equations are numerically studied using unsteady natural convection formulated with vorticity and stream-function variables. These equations are written by using bispherical coordinates system and solved by using a finite difference method. The effect of the control parameters such as the Rayleigh number (103 ≤ Ra ≤ 106) or the eccentricity (e = ±0.2, ±0.5, 0) in the dynamic and thermal behaviours of the fluid is investigated.

关键词： Natural Convection Hemispherical Cavity Rayleigh Correlations Eccentricity Nusselt Number

Optimization and Modeling of Antireflective Layers for Silicon Solar Cells: In Search of Optimal Materials

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Materials Sciences and Applications 2018年第8期9卷 705-722页

作者： Mamadou Moustapha Diop Alassane Diaw Nacire Mbengue Ousmane Ba Moulaye Diagne Oumar A. Niasse Bassirou Ba joseph sarr Laboratory of Semiconductor and Solar Energy Department of Physics Faculty of Science and Techniques University Cheikh Anta Diop Dakar Senegal

Depositing an antireflection coating on the front surface of solar cells allows a significant reduction in reflection losses. It thus allows an increase in the efficiency of the cells. A modeling of the refractive indices and the thicknesses of an optimal antireflection coating has been proposed. Thus, the average reflective losses can be reduced to less than 8% and less than 2.4% in a large wavelength range respectively for a single-layer and double-layer anti-reflective coating types. However, the difficulty of finding these model materials (materials with the same refractive index) led us to introduce two notions: the refractive index difference and the thickness difference. These two notions allowed us to compare the reflectivity of the antireflection layer in silicon surface. Thus, the lower the refractive index difference is, the more the material resembles to the ideal material (in refractive index), and thus its reflective losses are minimal. SiNx and SiO2/TiO2 antireflection layers, in the wavelength range between 400 and 1100 nm, have reduced the average reflectivity losses to less than 9% and 2.3% respectively.

关键词： Antireflection Layer Reflectivity Refractive Index Thickness

Comparative Analysis of the Hard Hillsides Stability by Empirical Methods and Limit Equilibrium: Case of Ultra Basic and Andesites of Mako and Marbles of Bandafassi (Senegal)

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Geomaterials 2019年第3期9卷 67-79页

作者： Déthié sarr Oustasse Abdoulaye Sall Mapathé Ndiaye Nayini joseph Serge Lompo UFR Sciences de l’Ingénieur University of Thiès Thiès Sénégal

The purpose of this paper is to characterize rock mass stability using basic rock mass method and to compare them. Rock mass quality and strength are determined using rock mass classification and numerical methods. The Factors of safety are calculated with the results of stereographic projection. Results show that quality of ultrabasite and marble are better than quality of andesite. The Slope Mass Ratings (SMR) show that rocks with the best quality are stable and andesite partially stable. The calculation of the factors of Safety by limit equilibrium assigns a stable state for ultrabasite and marble and instable for andesite. Calculation of Safety factor using stereographic parameters in one hand and finite element code in another shows more possibility of planar sliding along discontinuities than rock matrix failure. At last, quality of endogeneous rock mass is correlated with its stability state. The better rock mass is, the more stable the rock it is.

关键词： Geomechanical Classification Mako Bandafassi Slope Stability

Contribution to the Numerical Geological Mapping of the Paleocene in the Western Part of Thiès (Senegal)

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Open Journal of Geology 2014年第10期4卷 495-504页

作者： Mohamadou Moustapha Thiam Mapathé Ndiaye Meissa Fall Raphael sarr joseph O. Medou Laboratoire de Mécanique et Modélisation UFR Sciences de l’Ingénieur Thiès Sénégal Département de Géologie Faculté des Sciences et Techniques Université Cheikh Anta Diop Dakar Sénégal Petrosen-SA Hann-Dakar Sénégal

The locality of Thiès has significant mining and hydrogeological resources that are of major economic interest and necessitates a sustainable management. Most of these resources are contained in the Paleocene. For a better assessment of Paleocene, we elaborated a spatial model using available seismic lines, oil and hydraulic drills. The data were integrated using interpolation, mainly natural neighbor method. The obtained model should make it possible to understand the variation of the lithostratigraphic parameters of the Paleocene. The extraction from the model of the upper and the lower limits showed that the Paleocene is shallow and is outcropping to subout-cropping in the area of Thiès. The model was validated using previously available geological map. Also, a crosscorrelation of the predicted and the observed data showed that the model is accurate.

关键词： Geological Mapping Senegal-Mauritanian Basin Paleocene Seismic Hydraulic Drill

Influence of surface modified mixed metal oxide nanoparticles on the electrochemical and mechanical properties of polyurethane matrix

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Frontiers of Chemical Science and Engineering 2023年第1期17卷 1-14页

作者： joseph Raj Xavier Department of Chemistry Saveetha School of EngineeringSaveetha Institute of Medical and Technical SciencesChennai-602105India

Newly synthesized functional nanoparticles,3-amino-1,2,4-triazole(ATA)/SiO_(2)—TiO_(2)were introduced to the polyurethane(PU)*** techniques were used to investigate the barrier properties of the synthesized PU—ATA/SiO_(2)—TiO_(2)nanocomposite coated steel *** natural seawater,electrochemical impedance spectroscopy experiments indicated outstanding protective behaviour for the PU—ATA/SiO_(2)—TiO_(2)coated *** coating resistance(Rcoat)of PU—ATA/SiO_(2)—TiO_(2)was determined to be 2956.90 kΩ·cm^(−2).The Rcoat of the PU—ATA/SiO_(2)—TiO_(2)nanocomposite coating was found to be over 50%higher than the PU *** current measured along the scratched surface of the PU—ATA/SiO_(2)—TiO_(2)coating was found to be very low(1.65 nA).The enhanced ATA/SiO_(2)—TiO_(2)nanoparticles inhibited the entry of electrolytes into the coating interface,as revealed by scanning electron microscopy/energy dispersive X-ray spectroscopy and X-ray diffraction analysis of the degradation *** contact angle testing validated the hydrophobic nature of the PU—ATA/SiO_(2)—TiO_(2)coating(θ=115.4°).When the concentration of ATA/SiO_(2)—TiO_(2)nanoparticles was 2 wt%,dynamic mechanical analysis revealed better mechanical ***,the newly synthesised PU—ATA/SiO_(2)—TiO_(2)nanocomposite provided excellent barrier and mechanical properties due to the addition of ATA/SiO_(2)—TiO_(2)nanoparticles to the polyurethane,which inhibited material degradation and aided in the prolongation of the coated steel’s life.

关键词： SiO_(2)/TiO_(2)nanoparticle nanocomposite coatings dynamic mechanical analysis electrochemical techniques corrosion colloids and interfaces