Jaafar Khalid-naciri - Academia.edu (original) (raw)
Papers by Jaafar Khalid-naciri
Proceedings of the 9th World Congress on Mechanical, Chemical, and Material Engineering
Proceedings of the 9th World Congress on Mechanical, Chemical, and Material Engineering
Heat Transfer
The forced convective heat transfer for Stokes flow, including viscous dissipation in arbitrary c... more The forced convective heat transfer for Stokes flow, including viscous dissipation in arbitrary corrugated channels, is studied using both an asymptotic method and a numerical solution. The aim is to specify the range of shape parameters for which the validity of the asymptotic approach is ensured, particularly regarding the characteristics of heat transfer. The axial velocity, transversal velocity, pressure, and temperature, for small corrugation's slope compared with unity, are sought as an asymptotic expansion in terms of a parameter that represents the corrugation's slope. The numerical solution is obtained by using ANSYS Fluent solver. Additionally, Python scripting is integrated to automate several parts of the simulations, including the creation of the geometry and a parametric study. Three different types of corrugations are investigated including zigzag, sinusoidal, and arbitrary corrugations defined using a function given by a particular case of the Fourier series....
2018 Renewable Energies, Power Systems & Green Inclusive Economy (REPS-GIE), 2018
The purpose of this study is to examine the effect of drag coefficient on efficiency of a wave en... more The purpose of this study is to examine the effect of drag coefficient on efficiency of a wave energy converter (WEC). The considered floating WEC is a Power Buoy device that is a cylinder connected to the seabed by an extensible Power Take Off system. This study focuses on the case of plane movements of the WEC due to the action of waves, which propagate perpendicular to the axis of the cylinder. The Newton laws written for the WEC device results in a nonlinear second-order differential equation which is solved numerically by a fourth order Runge-Kutta method. The recovered energy is calculated for different drag coefficients. The Morison equation is used to add drag and added mass effects. In the first step, the drag (Cd) and added mass (Cm) coefficients are estimated by a comparison of the results obtained by the numerical code NEMOH and a “Morison” based method. By using last square method and evolutionary algorithm, the values for Cd and Cm corresponding to a non viscous fluid case are determined. Subsequently, for a given Cm, the Cdand the damping coefficient (ß) of the power take off device are changed for the sake of analyzing the effect of drag coefficient on recovered energy. The results show the effect of Cd on recovered energy in various situations.
Physics of Fluids, 2021
The stability of pulsed bi-dimensional flow between two co-oscillating cylinders in a linear Maxw... more The stability of pulsed bi-dimensional flow between two co-oscillating cylinders in a linear Maxwell fluid was studied by Riahi et al. [J. Soc. Rheol. 42, 321–327 (2014)]. In the present paper, we revisit this flow configuration with emphasis on the effect of the non-linear terms in the constitutive equation of the model, measured by the Weissenberg number, on the dynamics of the system. Under these assumptions and using the upper convected Maxwell derivative, we examine this model to large amplitude oscillatory shear giving rise to the appearance, in comparison to the linear Maxwell model, of the azimuthal normal stress in the basic state. Using the spectral method and the Floquet theory for the spatiotemporal resolution of the obtained eigenvalue problem, numerical results exhibit numerous classes of Taylor vortex flows depending on the order of magnitude of the fluid elasticity. The resulting stability diagram consists of several branches intersecting at specific frequencies wher...
Mécanique & Industries, 2005
-L'objectif de ce travail est de déterminer une forme de profil de vitesseà l'entrée d'un tube ci... more -L'objectif de ce travail est de déterminer une forme de profil de vitesseà l'entrée d'un tube circulaire, ainsi que la forme géométrique de la paroi de la conduite correspondant, permettant de maximiser le transfert de chaleurà l'intérieur de la conduite. On considère la convection mixte, bidimensionnelle, laminaire pour un fluide newtonien, en géométrie axisymetrique. Le profil de vitesse axialeà l'entrée du tube optimum, est obtenu numériquement, en résolvant le système d'équations aux dérivées partielles en coordonnées cylindriques, par une méthode aux différences finies. Pratiquement ce profil est obtenu en modifiant sur une longueur donnée, la forme de la paroi de la conduite créée par des perturbations particulières du profil amont, ce qui permet de générer le profil choisi.
Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics-Physics-Astronomy, 1998
In this paper, an analytical resolution of a periodic signal propagation equation is presented. A... more In this paper, an analytical resolution of a periodic signal propagation equation is presented. At a given site of the conduit, the proposed solution allows one to isolate the part linked to the signal emitted at the extremity of the conduit and the part that would exist in its absence. The investigation of the evolution of this signal located at the extremity allows us to determine the length of the tube (in the particular case of a solitary wave) using the analysis of reflections at a given site.
Mécanique & Industries, 2005
-Dans ce papier, nousélaborons une technique d'interprétation des ondes réfléchies. Cette techniq... more -Dans ce papier, nousélaborons une technique d'interprétation des ondes réfléchies. Cette technique est basée sur une approche analytique permettant de maîtriser la propagation pure d'une onde incidente et par suite d'interpréter toute information transportée par l'onde réfléchie. L'objectif essentiel de cette démarche est de développer une méthodologie pour la détermination des sites de réflexions telles que la localisation d'une jonction avec ou sans obstruction.
Comptes Rendus Mécanique, 2004
On propose dans cette étude une solution analytique, valable pour des nombres de Reynolds intermé... more On propose dans cette étude une solution analytique, valable pour des nombres de Reynolds intermédiaires, de perturbations faibles de l'écoulement de Poiseuille dans un canal. La méthode considérée est basée sur la résolution d'une forme linéarisée des équations aux perturbations. La solution obtenue permet de déterminer les deux bases de fonctions propres symétriques et antisymétriques de ces perturbations. Par la suite, ces bases sont orthonormalisées et utilisées pour établir la solution complète de l'écoulement lorsqu'un profil de vitesses, introduisant ce genre de perturbations, est imposé à l'entrée du canal. Pour citer cet article : A.
Comptes Rendus Mécanique, 2002
Front. Heat Mass Transf.
This paper presents an exact analytical solution to the extended Graetz problem in microchannels ... more This paper presents an exact analytical solution to the extended Graetz problem in microchannels and microtubes, including axial heat conduction, viscous dissipation, and rarefaction effects for an imposed constant wall temperature. The flow in the microchannel or microtube is assumed to be hydrodynamically fully developed. At the same time, the first-order slip-velocity and temperature jump models represent the wall boundary conditions. The energy equation is solved analytically, and the solution is obtained in terms of Kummer functions with expansion constants directly determined from explicit expressions. The local and fully developed Nusselt numbers are calculated in terms of the Péclet number, Brinkman number, Knudsen number, and thermal properties of the fluid. The constant pressure drop along the streamwise direction per unit length is imposed at a constant value and independent of the flow parameters, unlike the usual practice of fixing the average velocity. This solution can be used as the reference solution for optimization problems to enhance heat transfer using a fixed pressure drop. It is found that for no viscous dissipation and negligible axial heat conduction, the local Nusselt number is larger for imposed pressure drop compared to imposed average velocity. The thermal entrance length increases as the Knudsen number or the degree of temperature jump increases for imposed pressure drop, while it is approximately unchangeable for imposed average velocity. The quantitative differences between the cases of imposed pressure drop and imposed average velocity in the average Nusselt number over the largest thermal entrance length are reduced with the increase of axial heat conduction or viscous dissipation effects. The fully developed Nusselt number is the same for imposed pressure drop and imposed average velocity.
Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics-Physics-Astronomy, 1999
We propose in this study an analytical solution, valid for intermediate Reynolds numbers, for the... more We propose in this study an analytical solution, valid for intermediate Reynolds numbers, for the Newtonian fluid flow in a deformed axisymetric tube. Forms of foreseeable walls are defined by the relationship R(z) = C exp [C1exp( C2 z )]. The method is based on the resolution of a linearized form of equations of perturbation. The validation is performed by
Proceedings of the 8th World Congress on Mechanical, Chemical, and Material Engineering
A numerical investigation of the heat transfer enhancement through fins using the Ansys Mechanica... more A numerical investigation of the heat transfer enhancement through fins using the Ansys Mechanical solver is presented. Results are given for a uniform fin with elliptical cross-sections and uniform heat flux applied on its base while heat is dissipated to its surroundings by convection from both its lateral surface and tip. The peak temperature at the base of the fin is used to evaluate the thermal performance. Ansys Mechanical solver is automated using Python scripting to run 792 simulations for various materials, fin lengths, and ratios between the minor and major axes of the elliptical cross-sectional shape for both cases of natural and forced convection. The use of the original automated numerical procedure significantly decreases the computational time and the user intervention. It was found that the thermal performance is improved by increasing the length of the fin, using a material with higher thermal conductivity, or having a ratio between the minor and major axes of the ellipse that is farther from unity. Forced convection gives better thermal performance compared to natural convection.
Journal of Biomechanics, 1991
Ahatraet-An asymptotic expression of the wall shear stress (WSS) in an elastic tube is deduced fo... more Ahatraet-An asymptotic expression of the wall shear stress (WSS) in an elastic tube is deduced for small values of the Womersley parameter. In the case of a rigid tube this asymptotic expression is shown to compare better with the exact solution than Poiseuille's or Lambossy's approximations. Its integration in a one-dimensional model of the internal carotid artery blood flow predicts more marked systolic and less marked diastolic WSS than those predicted by the commonly used Poiseuille's approximation.
Archives of Physiology and Biochemistry, 1990
IOP Conference Series: Earth and Environmental Science
The aim of this paper is to present the effects of wave amplitude and wave frequency variations o... more The aim of this paper is to present the effects of wave amplitude and wave frequency variations on the energy recovered by a DEXA Wave, which is a wave energy converter (WEC) device. The two-body articulated floating WEC consists of two connected rigid bodies, the energy is recovered by taking advantage of the relative movement between the two parts set in motion differently by the wave. The results show that the value of the wave amplitude and wave period have an impact on the recovered energy by the WEC. The present work shown that for this type of WEC, an increase in the amplitude of the wave does not necessarily improve the energy recovered by the WEC also it is shown that the considered WEC could be typical for low wave amplitude areas.
International Conference on Fluid Flow, Heat and Mass Transfer
This paper presents an original numerical study for the optimization of the steady laminar fluid ... more This paper presents an original numerical study for the optimization of the steady laminar fluid flow and heat transfer in a two-dimensional corrugated channel with a bottom heated wall and an upper periodically corrugated wall. A python code is used to automate Ansys Fluent and to run the simulation for various shapes of the corrugated wall given by a polynomial function. The optimal values for the coefficients of the fifth-order polynomial defining the shape of the upper wall are determined. The average Nusselt number and the Reynolds number are plotted as a function of two geometrical coefficients. A correlation for the average Nusselt number as a function of the Reynolds number for this flow is proposed. It was found that there exist optimal parameters of the corrugated channel for which the average Nusselt number is higher than that of parallel walls due to the development of secondary flows.
Journal of Mechanics Engineering and Automation, 2016
The asymptotic behaviour of laminar forced convection in a circular duct, for a Herschel-Bulkley ... more The asymptotic behaviour of laminar forced convection in a circular duct, for a Herschel-Bulkley fluid with constant properties, is analysed by taking into account the viscous dissipation effects. The axial heat conduction in the fluid is neglected. The asymptotic temperature field and the asymptotic value of the Nusselt number are determined for every boundary condition that allows a fully developed region. Comparisons with other existing solutions for Newtonian and non-Newtonian cases are presented.
International Journal of Renewable Energy Research, 2019
This paper deals with the optimization of a bottom fixed wave energy converter of heaving point a... more This paper deals with the optimization of a bottom fixed wave energy converter of heaving point absorber type (PAWEC). The PAWEC consists of a unique horizontal cylinder of radius R and length L, connected to the seabed through an extensible Power Take Off device. In this work, an original control strategy is used in order to optimize the PAWEC. The proposed method links the damping coefficient of the power take off device to the relative velocity between the buoy and the wave. This study focus on the comparison of the two cases where a passive control is adopted and where the damping coefficient is a constant. The performance of the WEC in different wave conditions for each of the two cases is investigated. The results show that the recovered energy is considerably increased owing to the adaptation of the damping coefficient with the buoy speed
Proceedings of the 9th World Congress on Mechanical, Chemical, and Material Engineering
Proceedings of the 9th World Congress on Mechanical, Chemical, and Material Engineering
Heat Transfer
The forced convective heat transfer for Stokes flow, including viscous dissipation in arbitrary c... more The forced convective heat transfer for Stokes flow, including viscous dissipation in arbitrary corrugated channels, is studied using both an asymptotic method and a numerical solution. The aim is to specify the range of shape parameters for which the validity of the asymptotic approach is ensured, particularly regarding the characteristics of heat transfer. The axial velocity, transversal velocity, pressure, and temperature, for small corrugation's slope compared with unity, are sought as an asymptotic expansion in terms of a parameter that represents the corrugation's slope. The numerical solution is obtained by using ANSYS Fluent solver. Additionally, Python scripting is integrated to automate several parts of the simulations, including the creation of the geometry and a parametric study. Three different types of corrugations are investigated including zigzag, sinusoidal, and arbitrary corrugations defined using a function given by a particular case of the Fourier series....
2018 Renewable Energies, Power Systems & Green Inclusive Economy (REPS-GIE), 2018
The purpose of this study is to examine the effect of drag coefficient on efficiency of a wave en... more The purpose of this study is to examine the effect of drag coefficient on efficiency of a wave energy converter (WEC). The considered floating WEC is a Power Buoy device that is a cylinder connected to the seabed by an extensible Power Take Off system. This study focuses on the case of plane movements of the WEC due to the action of waves, which propagate perpendicular to the axis of the cylinder. The Newton laws written for the WEC device results in a nonlinear second-order differential equation which is solved numerically by a fourth order Runge-Kutta method. The recovered energy is calculated for different drag coefficients. The Morison equation is used to add drag and added mass effects. In the first step, the drag (Cd) and added mass (Cm) coefficients are estimated by a comparison of the results obtained by the numerical code NEMOH and a “Morison” based method. By using last square method and evolutionary algorithm, the values for Cd and Cm corresponding to a non viscous fluid case are determined. Subsequently, for a given Cm, the Cdand the damping coefficient (ß) of the power take off device are changed for the sake of analyzing the effect of drag coefficient on recovered energy. The results show the effect of Cd on recovered energy in various situations.
Physics of Fluids, 2021
The stability of pulsed bi-dimensional flow between two co-oscillating cylinders in a linear Maxw... more The stability of pulsed bi-dimensional flow between two co-oscillating cylinders in a linear Maxwell fluid was studied by Riahi et al. [J. Soc. Rheol. 42, 321–327 (2014)]. In the present paper, we revisit this flow configuration with emphasis on the effect of the non-linear terms in the constitutive equation of the model, measured by the Weissenberg number, on the dynamics of the system. Under these assumptions and using the upper convected Maxwell derivative, we examine this model to large amplitude oscillatory shear giving rise to the appearance, in comparison to the linear Maxwell model, of the azimuthal normal stress in the basic state. Using the spectral method and the Floquet theory for the spatiotemporal resolution of the obtained eigenvalue problem, numerical results exhibit numerous classes of Taylor vortex flows depending on the order of magnitude of the fluid elasticity. The resulting stability diagram consists of several branches intersecting at specific frequencies wher...
Mécanique & Industries, 2005
-L'objectif de ce travail est de déterminer une forme de profil de vitesseà l'entrée d'un tube ci... more -L'objectif de ce travail est de déterminer une forme de profil de vitesseà l'entrée d'un tube circulaire, ainsi que la forme géométrique de la paroi de la conduite correspondant, permettant de maximiser le transfert de chaleurà l'intérieur de la conduite. On considère la convection mixte, bidimensionnelle, laminaire pour un fluide newtonien, en géométrie axisymetrique. Le profil de vitesse axialeà l'entrée du tube optimum, est obtenu numériquement, en résolvant le système d'équations aux dérivées partielles en coordonnées cylindriques, par une méthode aux différences finies. Pratiquement ce profil est obtenu en modifiant sur une longueur donnée, la forme de la paroi de la conduite créée par des perturbations particulières du profil amont, ce qui permet de générer le profil choisi.
Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics-Physics-Astronomy, 1998
In this paper, an analytical resolution of a periodic signal propagation equation is presented. A... more In this paper, an analytical resolution of a periodic signal propagation equation is presented. At a given site of the conduit, the proposed solution allows one to isolate the part linked to the signal emitted at the extremity of the conduit and the part that would exist in its absence. The investigation of the evolution of this signal located at the extremity allows us to determine the length of the tube (in the particular case of a solitary wave) using the analysis of reflections at a given site.
Mécanique & Industries, 2005
-Dans ce papier, nousélaborons une technique d'interprétation des ondes réfléchies. Cette techniq... more -Dans ce papier, nousélaborons une technique d'interprétation des ondes réfléchies. Cette technique est basée sur une approche analytique permettant de maîtriser la propagation pure d'une onde incidente et par suite d'interpréter toute information transportée par l'onde réfléchie. L'objectif essentiel de cette démarche est de développer une méthodologie pour la détermination des sites de réflexions telles que la localisation d'une jonction avec ou sans obstruction.
Comptes Rendus Mécanique, 2004
On propose dans cette étude une solution analytique, valable pour des nombres de Reynolds intermé... more On propose dans cette étude une solution analytique, valable pour des nombres de Reynolds intermédiaires, de perturbations faibles de l'écoulement de Poiseuille dans un canal. La méthode considérée est basée sur la résolution d'une forme linéarisée des équations aux perturbations. La solution obtenue permet de déterminer les deux bases de fonctions propres symétriques et antisymétriques de ces perturbations. Par la suite, ces bases sont orthonormalisées et utilisées pour établir la solution complète de l'écoulement lorsqu'un profil de vitesses, introduisant ce genre de perturbations, est imposé à l'entrée du canal. Pour citer cet article : A.
Comptes Rendus Mécanique, 2002
Front. Heat Mass Transf.
This paper presents an exact analytical solution to the extended Graetz problem in microchannels ... more This paper presents an exact analytical solution to the extended Graetz problem in microchannels and microtubes, including axial heat conduction, viscous dissipation, and rarefaction effects for an imposed constant wall temperature. The flow in the microchannel or microtube is assumed to be hydrodynamically fully developed. At the same time, the first-order slip-velocity and temperature jump models represent the wall boundary conditions. The energy equation is solved analytically, and the solution is obtained in terms of Kummer functions with expansion constants directly determined from explicit expressions. The local and fully developed Nusselt numbers are calculated in terms of the Péclet number, Brinkman number, Knudsen number, and thermal properties of the fluid. The constant pressure drop along the streamwise direction per unit length is imposed at a constant value and independent of the flow parameters, unlike the usual practice of fixing the average velocity. This solution can be used as the reference solution for optimization problems to enhance heat transfer using a fixed pressure drop. It is found that for no viscous dissipation and negligible axial heat conduction, the local Nusselt number is larger for imposed pressure drop compared to imposed average velocity. The thermal entrance length increases as the Knudsen number or the degree of temperature jump increases for imposed pressure drop, while it is approximately unchangeable for imposed average velocity. The quantitative differences between the cases of imposed pressure drop and imposed average velocity in the average Nusselt number over the largest thermal entrance length are reduced with the increase of axial heat conduction or viscous dissipation effects. The fully developed Nusselt number is the same for imposed pressure drop and imposed average velocity.
Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics-Physics-Astronomy, 1999
We propose in this study an analytical solution, valid for intermediate Reynolds numbers, for the... more We propose in this study an analytical solution, valid for intermediate Reynolds numbers, for the Newtonian fluid flow in a deformed axisymetric tube. Forms of foreseeable walls are defined by the relationship R(z) = C exp [C1exp( C2 z )]. The method is based on the resolution of a linearized form of equations of perturbation. The validation is performed by
Proceedings of the 8th World Congress on Mechanical, Chemical, and Material Engineering
A numerical investigation of the heat transfer enhancement through fins using the Ansys Mechanica... more A numerical investigation of the heat transfer enhancement through fins using the Ansys Mechanical solver is presented. Results are given for a uniform fin with elliptical cross-sections and uniform heat flux applied on its base while heat is dissipated to its surroundings by convection from both its lateral surface and tip. The peak temperature at the base of the fin is used to evaluate the thermal performance. Ansys Mechanical solver is automated using Python scripting to run 792 simulations for various materials, fin lengths, and ratios between the minor and major axes of the elliptical cross-sectional shape for both cases of natural and forced convection. The use of the original automated numerical procedure significantly decreases the computational time and the user intervention. It was found that the thermal performance is improved by increasing the length of the fin, using a material with higher thermal conductivity, or having a ratio between the minor and major axes of the ellipse that is farther from unity. Forced convection gives better thermal performance compared to natural convection.
Journal of Biomechanics, 1991
Ahatraet-An asymptotic expression of the wall shear stress (WSS) in an elastic tube is deduced fo... more Ahatraet-An asymptotic expression of the wall shear stress (WSS) in an elastic tube is deduced for small values of the Womersley parameter. In the case of a rigid tube this asymptotic expression is shown to compare better with the exact solution than Poiseuille's or Lambossy's approximations. Its integration in a one-dimensional model of the internal carotid artery blood flow predicts more marked systolic and less marked diastolic WSS than those predicted by the commonly used Poiseuille's approximation.
Archives of Physiology and Biochemistry, 1990
IOP Conference Series: Earth and Environmental Science
The aim of this paper is to present the effects of wave amplitude and wave frequency variations o... more The aim of this paper is to present the effects of wave amplitude and wave frequency variations on the energy recovered by a DEXA Wave, which is a wave energy converter (WEC) device. The two-body articulated floating WEC consists of two connected rigid bodies, the energy is recovered by taking advantage of the relative movement between the two parts set in motion differently by the wave. The results show that the value of the wave amplitude and wave period have an impact on the recovered energy by the WEC. The present work shown that for this type of WEC, an increase in the amplitude of the wave does not necessarily improve the energy recovered by the WEC also it is shown that the considered WEC could be typical for low wave amplitude areas.
International Conference on Fluid Flow, Heat and Mass Transfer
This paper presents an original numerical study for the optimization of the steady laminar fluid ... more This paper presents an original numerical study for the optimization of the steady laminar fluid flow and heat transfer in a two-dimensional corrugated channel with a bottom heated wall and an upper periodically corrugated wall. A python code is used to automate Ansys Fluent and to run the simulation for various shapes of the corrugated wall given by a polynomial function. The optimal values for the coefficients of the fifth-order polynomial defining the shape of the upper wall are determined. The average Nusselt number and the Reynolds number are plotted as a function of two geometrical coefficients. A correlation for the average Nusselt number as a function of the Reynolds number for this flow is proposed. It was found that there exist optimal parameters of the corrugated channel for which the average Nusselt number is higher than that of parallel walls due to the development of secondary flows.
Journal of Mechanics Engineering and Automation, 2016
The asymptotic behaviour of laminar forced convection in a circular duct, for a Herschel-Bulkley ... more The asymptotic behaviour of laminar forced convection in a circular duct, for a Herschel-Bulkley fluid with constant properties, is analysed by taking into account the viscous dissipation effects. The axial heat conduction in the fluid is neglected. The asymptotic temperature field and the asymptotic value of the Nusselt number are determined for every boundary condition that allows a fully developed region. Comparisons with other existing solutions for Newtonian and non-Newtonian cases are presented.
International Journal of Renewable Energy Research, 2019
This paper deals with the optimization of a bottom fixed wave energy converter of heaving point a... more This paper deals with the optimization of a bottom fixed wave energy converter of heaving point absorber type (PAWEC). The PAWEC consists of a unique horizontal cylinder of radius R and length L, connected to the seabed through an extensible Power Take Off device. In this work, an original control strategy is used in order to optimize the PAWEC. The proposed method links the damping coefficient of the power take off device to the relative velocity between the buoy and the wave. This study focus on the comparison of the two cases where a passive control is adopted and where the damping coefficient is a constant. The performance of the WEC in different wave conditions for each of the two cases is investigated. The results show that the recovered energy is considerably increased owing to the adaptation of the damping coefficient with the buoy speed