https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Fri, 12 Jun 2026 12:11:42 GMT 2026-06-12T12:11:42Z http://hdl.handle.net/10985/9961 Critical evaluation of three hemodynamic models for the numerical simulation of intra-stent flows CHABI, Fatiha; CHAMPMARTIN, Stephane; SARRAF, Christophe; NOGUERA, Ricardo We evaluate here three hemodynamic models used for the numerical simulation of bare and stented artery flows. We focus on two flow features responsible for intra-stent restenosis: the wall shear stress and the re-circulation lengths around a stent. The studied models are the Poiseuille profile, the simplified pulsatile profile and the complete pulsatile profile based on the analysis of Womersley. The flow rate of blood in a human left coronary artery is considered to compute the velocity profiles. “Ansys Fluent 14.5” is used to solve the Navier–Stokes and continuity equations. As expected our results show that the Poiseuille profile is questionable to simulate the complex flow dynamics involved in intra-stent restenosis. Both pulsatile models give similar results close to the strut but diverge far from it. However, the computational time for the complete pulsatile model is five times that of the simplified pulsatile model. Considering the additional “cost” for the complete model, we recommend using the simplified pulsatile model for future intra-stent flow simulations. Thu, 01 Jan 2015 00:00:00 GMT http://hdl.handle.net/10985/9961 2015-01-01T00:00:00Z CHABI, Fatiha CHAMPMARTIN, Stephane SARRAF, Christophe NOGUERA, Ricardo We evaluate here three hemodynamic models used for the numerical simulation of bare and stented artery flows. We focus on two flow features responsible for intra-stent restenosis: the wall shear stress and the re-circulation lengths around a stent. The studied models are the Poiseuille profile, the simplified pulsatile profile and the complete pulsatile profile based on the analysis of Womersley. The flow rate of blood in a human left coronary artery is considered to compute the velocity profiles. “Ansys Fluent 14.5” is used to solve the Navier–Stokes and continuity equations. As expected our results show that the Poiseuille profile is questionable to simulate the complex flow dynamics involved in intra-stent restenosis. Both pulsatile models give similar results close to the strut but diverge far from it. However, the computational time for the complete pulsatile model is five times that of the simplified pulsatile model. Considering the additional “cost” for the complete model, we recommend using the simplified pulsatile model for future intra-stent flow simulations. http://hdl.handle.net/10985/9978 On the Determination of Pore size distribution from Injection of yield stress fluids through model porous media RODRIGUEZ DE CASTRO, Antonio; MALVAULT, Guillaume; AHMADI-SENICHAULT, Azita; AMBARI, Abdelhak; BRUNEAU, Denis; CHAMPMARTIN, Stephane; OMARI, Aziz Current methods used to determine pore size distribution of porous media (as mercury porosimetry) present several drawbacks the main of which is their toxicity An innovative method using yield stress fluids has been proposed in the literature. The main idea in these works is that using fluids with a threshold below which the fluid does not flow allows obtaining the pore size distribution by simply measuring the evolution of the flow rate versus pressure gradient. In fact this attractive method should be carefully handled and very precise experimental results are needed to make the method tractable in order to meet the targeted objective. This will be discussed through presentation of our recent experimental results. In these experiments two kinds of fluids where specifically formulated and rheologically characterized. These fluids were injected in both simple and complex artificial porous media and flow rate-pressure gradient relationships where established allowing us to estimate the pore size distribution. Sun, 01 Jan 2012 00:00:00 GMT http://hdl.handle.net/10985/9978 2012-01-01T00:00:00Z RODRIGUEZ DE CASTRO, Antonio MALVAULT, Guillaume AHMADI-SENICHAULT, Azita AMBARI, Abdelhak BRUNEAU, Denis CHAMPMARTIN, Stephane OMARI, Aziz Current methods used to determine pore size distribution of porous media (as mercury porosimetry) present several drawbacks the main of which is their toxicity An innovative method using yield stress fluids has been proposed in the literature. The main idea in these works is that using fluids with a threshold below which the fluid does not flow allows obtaining the pore size distribution by simply measuring the evolution of the flow rate versus pressure gradient. In fact this attractive method should be carefully handled and very precise experimental results are needed to make the method tractable in order to meet the targeted objective. This will be discussed through presentation of our recent experimental results. In these experiments two kinds of fluids where specifically formulated and rheologically characterized. These fluids were injected in both simple and complex artificial porous media and flow rate-pressure gradient relationships where established allowing us to estimate the pore size distribution. http://hdl.handle.net/10985/11146 New procedure to measure simultaneously the surface tension and contact angle CHAMPMARTIN, Stephane; AMBARI, Abdelhak; LE POMMELLEC, Jean Yves This paper proposes a new procedure to simultaneously measure the static contact angle and the surface tension of a liquid using a spherical geometry. Unlike the other existing methods, the knowledge of one of both previous parameters and the displacement of the sphere are not mandatory. The technique is based on the measurement of two simple physical quantities: the height of the meniscus formed on a sphere at the very contact with a liquid bath and the resulting vertical force exerted on this object at equilibrium. The meniscus height, whose exact value requires the numerical resolution of the Laplace equation, is often estimated with an approximate 2D model, valid only for very large spheres compared to the capillary length. We develop instead another simplified solution of the Young-Laplace equation based on the work of Ferguson for the meniscus on a cylinder and adapted for the spherical shape. This alternative model, which is less restrictive in terms of the sphere size, is successfully compared to numerical solutions of the complete Young-Laplace equation. It appears to be accurate for sphere radii larger than only two capillary lengths. Finally the feasibility of the method is experimentally tested and validated for three common liquids and two “small” steel spheres. Fri, 01 Jan 2016 00:00:00 GMT http://hdl.handle.net/10985/11146 2016-01-01T00:00:00Z CHAMPMARTIN, Stephane AMBARI, Abdelhak LE POMMELLEC, Jean Yves This paper proposes a new procedure to simultaneously measure the static contact angle and the surface tension of a liquid using a spherical geometry. Unlike the other existing methods, the knowledge of one of both previous parameters and the displacement of the sphere are not mandatory. The technique is based on the measurement of two simple physical quantities: the height of the meniscus formed on a sphere at the very contact with a liquid bath and the resulting vertical force exerted on this object at equilibrium. The meniscus height, whose exact value requires the numerical resolution of the Laplace equation, is often estimated with an approximate 2D model, valid only for very large spheres compared to the capillary length. We develop instead another simplified solution of the Young-Laplace equation based on the work of Ferguson for the meniscus on a cylinder and adapted for the spherical shape. This alternative model, which is less restrictive in terms of the sphere size, is successfully compared to numerical solutions of the complete Young-Laplace equation. It appears to be accurate for sphere radii larger than only two capillary lengths. Finally the feasibility of the method is experimentally tested and validated for three common liquids and two “small” steel spheres. http://hdl.handle.net/10985/15875 Comparison of various hemodynamic models for applications to cfd in stented arteries CHABI, Fatiha; NOGUERA, Ricardo; MAUREL, Blandine; CHAMPMARTIN, Stephane; SARRAF, Christophe A design study of propeller hydrokinetic turbines is explored in the present paper, where the optimized blade geometry is determined by the classical Glauert theory applicable to the design of axial flow turbines (hydrokinetic and wind turbines). The aim of the present study is to evaluate the optimized geometry for propeller hydrokinetic turbines, observing the effect of the number of blades in the runner design. The performance of runners with different number of blades is evaluated in a specific low-rotational-speed operating conditions, using blade element momentum theory (BEMT) simulations, confirmed by measurements in wind tunnel experiments for small-scale turbine models. The optimum design values of the power coefficient, in the operating tip speed ratio, for two-, three- and four-blade runners are pointed out, defining the best configuration for a propeller 10 kW hydrokinetic machine. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/15875 2014-01-01T00:00:00Z CHABI, Fatiha NOGUERA, Ricardo MAUREL, Blandine CHAMPMARTIN, Stephane SARRAF, Christophe A design study of propeller hydrokinetic turbines is explored in the present paper, where the optimized blade geometry is determined by the classical Glauert theory applicable to the design of axial flow turbines (hydrokinetic and wind turbines). The aim of the present study is to evaluate the optimized geometry for propeller hydrokinetic turbines, observing the effect of the number of blades in the runner design. The performance of runners with different number of blades is evaluated in a specific low-rotational-speed operating conditions, using blade element momentum theory (BEMT) simulations, confirmed by measurements in wind tunnel experiments for small-scale turbine models. The optimum design values of the power coefficient, in the operating tip speed ratio, for two-, three- and four-blade runners are pointed out, defining the best configuration for a propeller 10 kW hydrokinetic machine. http://hdl.handle.net/10985/19436 Kinematics of a Cylindrical Particle at Low Reynolds Numbers in Asymmetrical Conditions CHAMPMARTIN, Stephane; AMBARI, Abdelhak; BEN RICHOU, Abderrahim This paper concerns the hydrodynamic interactions on a cylindrical particle in non-dilute regime at low Reynolds numbers. The particle moves between two parallel walls with its axis parallel to the boundaries. A numerical finite-volume procedure is implemented and a generalized resistance matrix is built by means of the superposition principle. Three problems are solved: the settling of the particle, the transport of a neutrally and of a non-neutrally buoyant particle in a Poiseuille flow. Concerning sedimentation, the settling velocity is maximal off the symmetry plane and decreases when the confinement increases. The particle rotates in the direction opposite to that of contact rolling. The particle induces a high pressure zone in the front and a low pressure zone in the back, the difference of which is maximal in the symmetry plane. For a neutrally-buoyant particle, the hydrodynamic interactions lead to a velocity lag between the particle and the undisturbed flow. The magnitude of the velocity lag increases with confinement and eccentricity. The angular velocity and pressure difference are opposite to the previous case. For a non-neutrally buoyant particle, three situations are found depending on a dimensionless parameter similar to an inverse Shields number. For its extreme low and high values, the particle is respectively either carried by the flow or settles against it whatever its position. For intermediate values, the particle either settles close to the walls or is dragged by the flow close to the symmetry plane. Similar results are obtained for the angular velocity and the pressure difference. All these results question the assumption usually met in particulate transport in which the kinematics of the particle is often supposed to be that of the flow. Tue, 01 Jan 2019 00:00:00 GMT http://hdl.handle.net/10985/19436 2019-01-01T00:00:00Z CHAMPMARTIN, Stephane AMBARI, Abdelhak BEN RICHOU, Abderrahim This paper concerns the hydrodynamic interactions on a cylindrical particle in non-dilute regime at low Reynolds numbers. The particle moves between two parallel walls with its axis parallel to the boundaries. A numerical finite-volume procedure is implemented and a generalized resistance matrix is built by means of the superposition principle. Three problems are solved: the settling of the particle, the transport of a neutrally and of a non-neutrally buoyant particle in a Poiseuille flow. Concerning sedimentation, the settling velocity is maximal off the symmetry plane and decreases when the confinement increases. The particle rotates in the direction opposite to that of contact rolling. The particle induces a high pressure zone in the front and a low pressure zone in the back, the difference of which is maximal in the symmetry plane. For a neutrally-buoyant particle, the hydrodynamic interactions lead to a velocity lag between the particle and the undisturbed flow. The magnitude of the velocity lag increases with confinement and eccentricity. The angular velocity and pressure difference are opposite to the previous case. For a non-neutrally buoyant particle, three situations are found depending on a dimensionless parameter similar to an inverse Shields number. For its extreme low and high values, the particle is respectively either carried by the flow or settles against it whatever its position. For intermediate values, the particle either settles close to the walls or is dragged by the flow close to the symmetry plane. Similar results are obtained for the angular velocity and the pressure difference. All these results question the assumption usually met in particulate transport in which the kinematics of the particle is often supposed to be that of the flow. http://hdl.handle.net/10985/16977 Highly-repeatable generation of very small nanoparticles by Pulsed-Laser Ablation in Liquids of a high-speed rotating target RESANO-GARCIA, Amandine; CHAMPMARTIN, Stephane; BATTIE, Yann; KOCH, Alain; EN NACIRI, Aotmane; AMBARI, Abdelhak; CHAOUI, Nouari By irradiating a cylindrical silver target rotated at a high-speed within the range 300–2400 rpm (lateral speed 0.16–1.25 m/s) in pure water, we prepare ligand-free Ag nanoparticles (NPs) with a size of 4 ± 2 nm which are likely to be primary particles. Usually, the generation of NPs showing such a small size requires either a laser post-treatment and/or chemical additives. As the rotation rate of the target is increased, calculated 3D flow patterns revealed different hydrodynamic regimes which clearly influence the ablation rate and repeatability of the process as well as the colloidal properties. In addition to revealing the importance of fluid dynamics in pulsed-laser ablations in liquids, this study provides a way for producing in one step pure NPs with sizes below 5 nm which are suitable for applications in catalysis. Fri, 01 Jan 2016 00:00:00 GMT http://hdl.handle.net/10985/16977 2016-01-01T00:00:00Z RESANO-GARCIA, Amandine CHAMPMARTIN, Stephane BATTIE, Yann KOCH, Alain EN NACIRI, Aotmane AMBARI, Abdelhak CHAOUI, Nouari By irradiating a cylindrical silver target rotated at a high-speed within the range 300–2400 rpm (lateral speed 0.16–1.25 m/s) in pure water, we prepare ligand-free Ag nanoparticles (NPs) with a size of 4 ± 2 nm which are likely to be primary particles. Usually, the generation of NPs showing such a small size requires either a laser post-treatment and/or chemical additives. As the rotation rate of the target is increased, calculated 3D flow patterns revealed different hydrodynamic regimes which clearly influence the ablation rate and repeatability of the process as well as the colloidal properties. In addition to revealing the importance of fluid dynamics in pulsed-laser ablations in liquids, this study provides a way for producing in one step pure NPs with sizes below 5 nm which are suitable for applications in catalysis. http://hdl.handle.net/10985/20316 Development of a Model Based on Physical Mechanisms for the Explanation of Drug Release: Application to Diclofenac Release from Polyurethane Films ABBASNEZHAD, Navideh; KEBDANI, Mohamed; SHIRINBAYAN, Mohammadali; CHAMPMARTIN, Stephane; TCHARKHTCHI, Abbas; KOUIDRI, SMAINE; BAKIR, Farid In this study, we present a method for prediction of the drug-release profile based on the physical mechanisms that can intervene in drug release from a drug-carrier. The application presented here incorporates the effects of drug concentration and Reynolds number defining the circulating flow in the testing vein. The experimental data used relate to the release of diclofenac from samples of non-degradable polyurethane subjected to static and continuous flow. This case includes simultaneously three mechanisms: burst-release, diffusion and osmotic pressure, identified beforehand here as being able to contribute to the drug liberation. For this purpose, authors coded the Sequential Quadratic Programming Algorithm to solve the problem of non-linear optimization. The experimental data used to develop the mathematical model obtained from release studies carried out in water solution at 37 °C, for three concentrations of diclofenac and two water flow rates. We discuss the contribution of mechanisms and kinetics by considering two aforementioned parameters and, following that, we obtain the specific-model and compare the calculated results with the experimental results for the reserved cases. The results showed that drug percentage mostly affect the burst release, however flow rate has affected the osmotic release. In addition, release kinetics of all the mechanisms have increased by increasing the values of two considered parameters. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/20316 2021-01-01T00:00:00Z ABBASNEZHAD, Navideh KEBDANI, Mohamed SHIRINBAYAN, Mohammadali CHAMPMARTIN, Stephane TCHARKHTCHI, Abbas KOUIDRI, SMAINE BAKIR, Farid In this study, we present a method for prediction of the drug-release profile based on the physical mechanisms that can intervene in drug release from a drug-carrier. The application presented here incorporates the effects of drug concentration and Reynolds number defining the circulating flow in the testing vein. The experimental data used relate to the release of diclofenac from samples of non-degradable polyurethane subjected to static and continuous flow. This case includes simultaneously three mechanisms: burst-release, diffusion and osmotic pressure, identified beforehand here as being able to contribute to the drug liberation. For this purpose, authors coded the Sequential Quadratic Programming Algorithm to solve the problem of non-linear optimization. The experimental data used to develop the mathematical model obtained from release studies carried out in water solution at 37 °C, for three concentrations of diclofenac and two water flow rates. We discuss the contribution of mechanisms and kinetics by considering two aforementioned parameters and, following that, we obtain the specific-model and compare the calculated results with the experimental results for the reserved cases. The results showed that drug percentage mostly affect the burst release, however flow rate has affected the osmotic release. In addition, release kinetics of all the mechanisms have increased by increasing the values of two considered parameters. http://hdl.handle.net/10985/20795 Viscoelastic Behavior of Drug-Loaded Polyurethane ABBASNEZHAD, Navideh; SHIRINBAYAN, Mohammadali; CHABI, Fatiha; CHAMPMARTIN, Stephane; TCHARKHTCHI, Abbas; BAKIR, Farid Drug-eluting stents are desirable platforms for local medicine delivery. However, the incorporation of drugs into polymers can influence the mechanical and physicochemical properties of said matrix, which is a topic that is still poorly understood. In fact, this is more noticeable since the apposition is most often accompanied by mechanical stresses on the polymer coating, which can induce therapeutic failure that can result in death. It is therefore necessary to better understand their behavior by examining their properties in conditions such as those in living beings. We studied polyurethane drug carriers made in-house. Diclofenac epolamine was chosen as a model hydrophilic medicine. We used thermal measurements (DMTA) and tensile tests. The aim was to establish the influence of the loading and release of the drug on the physicochemical properties of this polymer in the presence of a stagnant or circulating fluid medium, phosphate-buffered saline (PBS). For the two PU/drug loadings studied, the effect of the initial drug load was more marked. The free volume fraction and the number of pores in the samples increased with the increasing percent of the drug and with release time. The kinetic profiles were accelerated with the loading ratio and with the presence of flow. Young′s modulus and ultimate stress were not significantly influenced by the release time. A relevant relationship between the tensile properties and the viscoelastic behavior of the samples was developed. Our results have implications for optimizing the performance of drug coatings for stents. Fri, 01 Jan 2021 00:00:00 GMT http://hdl.handle.net/10985/20795 2021-01-01T00:00:00Z ABBASNEZHAD, Navideh SHIRINBAYAN, Mohammadali CHABI, Fatiha CHAMPMARTIN, Stephane TCHARKHTCHI, Abbas BAKIR, Farid Drug-eluting stents are desirable platforms for local medicine delivery. However, the incorporation of drugs into polymers can influence the mechanical and physicochemical properties of said matrix, which is a topic that is still poorly understood. In fact, this is more noticeable since the apposition is most often accompanied by mechanical stresses on the polymer coating, which can induce therapeutic failure that can result in death. It is therefore necessary to better understand their behavior by examining their properties in conditions such as those in living beings. We studied polyurethane drug carriers made in-house. Diclofenac epolamine was chosen as a model hydrophilic medicine. We used thermal measurements (DMTA) and tensile tests. The aim was to establish the influence of the loading and release of the drug on the physicochemical properties of this polymer in the presence of a stagnant or circulating fluid medium, phosphate-buffered saline (PBS). For the two PU/drug loadings studied, the effect of the initial drug load was more marked. The free volume fraction and the number of pores in the samples increased with the increasing percent of the drug and with release time. The kinetic profiles were accelerated with the loading ratio and with the presence of flow. Young′s modulus and ultimate stress were not significantly influenced by the release time. A relevant relationship between the tensile properties and the viscoelastic behavior of the samples was developed. Our results have implications for optimizing the performance of drug coatings for stents. http://hdl.handle.net/10985/19437 Scaling laws explain foraminiferal pore patterns RICHIRT, Julien; CHAMPMARTIN, Stephane; SCHWEIZER, Magali; MOURET, Aurelia; PETERSEN, Jassin; AMBARI, Abdelhak; JORISSEN, Frans Due to climate warming and increased anthropogenic impact, a decrease of ocean water oxygenation is expected in the near future, with major consequences for marine life. In this context, it is essential to develop reliable tools to assess past oxygen concentrations in the ocean, to better forecast these future changes. Recently, foraminiferal pore patterns have been proposed as a bottom water oxygenation proxy, but the parameters controlling foraminiferal pore patterns are still largely unknown. Here we use scaling laws to describe how both gas exchanges (metabolic needs) and mechanical constraints (shell robustness) control foraminiferal pore patterns. The derived mathematical model shows that only specific combinations of pore density and size are physically feasible. Maximum porosity, of about 30%, can only be obtained by simultaneously increasing pore size and decreasing pore density. A large empirical data set of pore data obtained for three pseudocryptic phylotypes of Ammonia, a common intertidal genus from the eastern Atlantic, strongly supports this conclusion. These new findings provide basic mechanistic understanding of the complex controls of foraminiferal pore patterns and give a solid starting point for the development of proxies of past oxygen concentrations based on these morphological features. Pore size and pore density are largely interdependent, and both have to be considered when describing pore patterns. Tue, 01 Jan 2019 00:00:00 GMT http://hdl.handle.net/10985/19437 2019-01-01T00:00:00Z RICHIRT, Julien CHAMPMARTIN, Stephane SCHWEIZER, Magali MOURET, Aurelia PETERSEN, Jassin AMBARI, Abdelhak JORISSEN, Frans Due to climate warming and increased anthropogenic impact, a decrease of ocean water oxygenation is expected in the near future, with major consequences for marine life. In this context, it is essential to develop reliable tools to assess past oxygen concentrations in the ocean, to better forecast these future changes. Recently, foraminiferal pore patterns have been proposed as a bottom water oxygenation proxy, but the parameters controlling foraminiferal pore patterns are still largely unknown. Here we use scaling laws to describe how both gas exchanges (metabolic needs) and mechanical constraints (shell robustness) control foraminiferal pore patterns. The derived mathematical model shows that only specific combinations of pore density and size are physically feasible. Maximum porosity, of about 30%, can only be obtained by simultaneously increasing pore size and decreasing pore density. A large empirical data set of pore data obtained for three pseudocryptic phylotypes of Ammonia, a common intertidal genus from the eastern Atlantic, strongly supports this conclusion. These new findings provide basic mechanistic understanding of the complex controls of foraminiferal pore patterns and give a solid starting point for the development of proxies of past oxygen concentrations based on these morphological features. Pore size and pore density are largely interdependent, and both have to be considered when describing pore patterns. http://hdl.handle.net/10985/8480 Numerical simulation and experimental study of thrust air bearings with multiple orifices CHARKI, Abdérafi; DIOP, Khadim; CHAMPMARTIN, Stephane; AMBARI, Abdelhak The objective of this paper is to provide a numerical simulation and an experimental study in order to assess stiffness and damping characteristics of thrust air bearings with multiple orifices. Finite element modeling is used to solve the non-linear Reynolds equation while taking into account the movement equation for the bearing. The numerical results obtained show that performance characteristics are related to bearing design type. An experimental investigation allows us to analyze the behavior of thrust air bearings with several orifices as well as that of groove or porous material bearings. Frequency response measurements have been realized in order to compare the dynamic properties of the different bearings. The frequency responses obtained demonstrate that air bearings with multiple orifices have a damping higher than the other types in certain conditions. Air bearings with multiple orifices offer many advantages from a dynamic point of view. Their performance may be characterized not only by flow conditions but also by the number or diameter of the orifices in the bearing surface. http://dx.doi.org/10.1016/j.ijmecsci.2013.03.006 Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/8480 2013-01-01T00:00:00Z CHARKI, Abdérafi DIOP, Khadim CHAMPMARTIN, Stephane AMBARI, Abdelhak The objective of this paper is to provide a numerical simulation and an experimental study in order to assess stiffness and damping characteristics of thrust air bearings with multiple orifices. Finite element modeling is used to solve the non-linear Reynolds equation while taking into account the movement equation for the bearing. The numerical results obtained show that performance characteristics are related to bearing design type. An experimental investigation allows us to analyze the behavior of thrust air bearings with several orifices as well as that of groove or porous material bearings. Frequency response measurements have been realized in order to compare the dynamic properties of the different bearings. The frequency responses obtained demonstrate that air bearings with multiple orifices have a damping higher than the other types in certain conditions. Air bearings with multiple orifices offer many advantages from a dynamic point of view. Their performance may be characterized not only by flow conditions but also by the number or diameter of the orifices in the bearing surface.