Next projects B review : February 15 2022 Proposal must be submitted before January 31 2022.
Publications and communications which have benefited of mésocentre resources should contain : « Centre de Calcul Intensif d’Aix-Marseille is acknowledged for granting access to its high performance computing resources. »
Recent publications :
2021 |
Paul Eymeoud; Liangzhao Huang; Philippe Maugis Impact of Ni alloying on Fe-C martensite ageing: an atomistic investigation Journal Article In: Scripta materialia, 205 , 2021, ISSN: 1359-6462. @article{WOS:000692550000006, title = {Impact of Ni alloying on Fe-C martensite ageing: an atomistic investigation}, author = {Paul Eymeoud and Liangzhao Huang and Philippe Maugis}, doi = {10.1016/j.scriptamat.2021.114182}, issn = {1359-6462}, year = {2021}, date = {2021-12-01}, journal = {Scripta materialia}, volume = {205}, abstract = {We propose a computational investigation of Ni-alloying impact on Fe-C martensite ageing, at the atomic scale. Using the Climbing Image Nudged Elastic Band technique, we showed the repulsive nature of NiC pairwise interactions in alpha-iron, and demonstrated that Ni alloying lowers the migration energies and force dipole tensor components associated to an interstitial carbon in alpha-iron. Computed values of pair wise interactions, migration energies and dipole components were used to implement a Kinetic Monte Carlo approach. We found that Ni alloying: (i) has negligible impact on martensite thermodynamical stability, (ii) accelerates ageing kinetics, by increasing carbon diffusivity. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We propose a computational investigation of Ni-alloying impact on Fe-C martensite ageing, at the atomic scale. Using the Climbing Image Nudged Elastic Band technique, we showed the repulsive nature of NiC pairwise interactions in alpha-iron, and demonstrated that Ni alloying lowers the migration energies and force dipole tensor components associated to an interstitial carbon in alpha-iron. Computed values of pair wise interactions, migration energies and dipole components were used to implement a Kinetic Monte Carlo approach. We found that Ni alloying: (i) has negligible impact on martensite thermodynamical stability, (ii) accelerates ageing kinetics, by increasing carbon diffusivity. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. |
J V Gomes; M C de Sousa; R L Viana; I L Caldas; Y Elskens Low-dimensional chaos in the single wave model for self-consistent wave particle Hamiltonian Journal Article In: Chaos: An Interdisciplinary Journal of Nonlinear Science, 31 (8), pp. 083104, 2021, ISSN: 1089-7682. @article{Gomes_2021, title = {Low-dimensional chaos in the single wave model for self-consistent wave particle Hamiltonian}, author = {J V Gomes and M C de Sousa and R L Viana and I L Caldas and Y Elskens}, url = {http://dx.doi.org/10.1063/5.0040939}, doi = {10.1063/5.0040939}, issn = {1089-7682}, year = {2021}, date = {2021-08-01}, journal = {Chaos: An Interdisciplinary Journal of Nonlinear Science}, volume = {31}, number = {8}, pages = {083104}, publisher = {AIP Publishing}, abstract = {We analyze nonlinear aspects of the self-consistent wave-particle interaction using Hamiltonian dynamics in the single wave model, where the wave is modified due to the particle dynamics. This interaction plays an important role in the emergence of plasma instabilities and turbulence. The simplest case, where one particle (N = 1) is coupled with one wave (M = 1), is completely integrable, and the nonlinear effects reduce to the wave potential pulsating while the particle either remains trapped or circulates forever. On increasing the number of particles (N = 2, M = 1), integrability is lost and chaos develops. Our analyses identify the two standard ways for chaos to appear and grow (the homoclinic tangle born from a separatrix, and the resonance overlap near an elliptic fixed point). Moreover, a strong form of chaos occurs when the energy is high enough for the wave amplitude to vanish occasionally. }, keywords = {}, pubstate = {published}, tppubtype = {article} } We analyze nonlinear aspects of the self-consistent wave-particle interaction using Hamiltonian dynamics in the single wave model, where the wave is modified due to the particle dynamics. This interaction plays an important role in the emergence of plasma instabilities and turbulence. The simplest case, where one particle (N = 1) is coupled with one wave (M = 1), is completely integrable, and the nonlinear effects reduce to the wave potential pulsating while the particle either remains trapped or circulates forever. On increasing the number of particles (N = 2, M = 1), integrability is lost and chaos develops. Our analyses identify the two standard ways for chaos to appear and grow (the homoclinic tangle born from a separatrix, and the resonance overlap near an elliptic fixed point). Moreover, a strong form of chaos occurs when the energy is high enough for the wave amplitude to vanish occasionally. |
Sudip Das; Marc Jaeger; Marc Leonetti; Rochish M Thaokar; Paul G Chen Effect of pulse width on the dynamics of a deflated vesicle in unipolar and bipolar pulsed electric fields Journal Article In: Physics of Fluids, 33 (8), pp. 081905, 2021, ISSN: 1089-7666. @article{Das_2021, title = {Effect of pulse width on the dynamics of a deflated vesicle in unipolar and bipolar pulsed electric fields}, author = {Sudip Das and Marc Jaeger and Marc Leonetti and Rochish M Thaokar and Paul G Chen}, url = {http://dx.doi.org/10.1063/5.0057168}, doi = {10.1063/5.0057168}, issn = {1089-7666}, year = {2021}, date = {2021-08-01}, journal = {Physics of Fluids}, volume = {33}, number = {8}, pages = {081905}, publisher = {AIP Publishing}, abstract = {Giant unilamellar vesicles subjected to pulsed direct-current (pulsed-DC) fields are promising biomimetic systems to investigate the electroporation of cells. In strong electric fields, vesicles undergo significant deformation, which strongly alters the transmembrane potential, consequently the electroporation. Previous theoretical studies investigated the electrodeformation of vesicles in DC fields (which are not pulsed). In this work, we computationally investigate the deformation of a deflated vesicle under unipolar, bipolar, and two-step unipolar pulses and show sensitive dependence of intermediate shapes on type of pulse and the pulse width. Starting with the stress-free initial shape of a deflated vesicle, which is similar to a prolate spheroid, the analysis is presented for the cases with higher and lower conductivities of the inner fluid medium relative to the outer fluid medium. For the ratio of inner to outer fluid conductivity, σr = 10, the shape always remains prolate, including when the field is turned off. For σr=0.1, several complex dynamics are observed, such as the prolate-to-oblate (PO), prolate-to-oblate-to-prolate (POP) shape transitions in time depending upon the strength of the field and the pulse properties. In this case, on turning off the field, a metastable oblate equilibrium shape is seen, that seems to be a characteristics of a deflated vesicle leading to POPO transitions. When a two-step unipolar pulse (a combination of a strong and a weak subpulse) is applied, a vesicle can reach an oblate or a prolate final shape depending upon the relative durations of the two subpulses. }, keywords = {}, pubstate = {published}, tppubtype = {article} } Giant unilamellar vesicles subjected to pulsed direct-current (pulsed-DC) fields are promising biomimetic systems to investigate the electroporation of cells. In strong electric fields, vesicles undergo significant deformation, which strongly alters the transmembrane potential, consequently the electroporation. Previous theoretical studies investigated the electrodeformation of vesicles in DC fields (which are not pulsed). In this work, we computationally investigate the deformation of a deflated vesicle under unipolar, bipolar, and two-step unipolar pulses and show sensitive dependence of intermediate shapes on type of pulse and the pulse width. Starting with the stress-free initial shape of a deflated vesicle, which is similar to a prolate spheroid, the analysis is presented for the cases with higher and lower conductivities of the inner fluid medium relative to the outer fluid medium. For the ratio of inner to outer fluid conductivity, σr = 10, the shape always remains prolate, including when the field is turned off. For σr=0.1, several complex dynamics are observed, such as the prolate-to-oblate (PO), prolate-to-oblate-to-prolate (POP) shape transitions in time depending upon the strength of the field and the pulse properties. In this case, on turning off the field, a metastable oblate equilibrium shape is seen, that seems to be a characteristics of a deflated vesicle leading to POPO transitions. When a two-step unipolar pulse (a combination of a strong and a weak subpulse) is applied, a vesicle can reach an oblate or a prolate final shape depending upon the relative durations of the two subpulses. |
Elisa Buffa; Jerome Jacob; Pierre Sagaut Lattice-Boltzmann-based large-eddy simulation of high-rise building aerodynamics with inlet turbulence reconstruction Journal Article In: Journal of wind engineering and industrial aerodynamics, 212 , 2021, ISSN: 0167-6105. @article{WOS:000692557000001, title = {Lattice-Boltzmann-based large-eddy simulation of high-rise building aerodynamics with inlet turbulence reconstruction}, author = {Elisa Buffa and Jerome Jacob and Pierre Sagaut}, doi = {10.1016/j.jweia.2021.104560}, issn = {0167-6105}, year = {2021}, date = {2021-05-01}, journal = {Journal of wind engineering and industrial aerodynamics}, volume = {212}, abstract = {A Lattice-Boltzmann-based Large-Eddy Simulation approach for wind load prediction on high-rise building is proposed and validated. An extension of the original incompressible Synthetic Eddy Method to reconstruct inlet turbulence is proposed within the Lattice-Boltzmann framework, including a low-noise frozen density variant. Extensive successful comparisons with experimental data are carried out, for both quantities defined on the building surface and in its wake. A detailed sensitivity analysis of the results with respect to inlet turbulence reconstruction, boundary conditions at the building surface and grid resolution is also provided. An almost unique set of comparisons with experimental data is presented, including mean and rms values, spectra, but also peak values of pressure at the building surface.}, keywords = {}, pubstate = {published}, tppubtype = {article} } A Lattice-Boltzmann-based Large-Eddy Simulation approach for wind load prediction on high-rise building is proposed and validated. An extension of the original incompressible Synthetic Eddy Method to reconstruct inlet turbulence is proposed within the Lattice-Boltzmann framework, including a low-noise frozen density variant. Extensive successful comparisons with experimental data are carried out, for both quantities defined on the building surface and in its wake. A detailed sensitivity analysis of the results with respect to inlet turbulence reconstruction, boundary conditions at the building surface and grid resolution is also provided. An almost unique set of comparisons with experimental data is presented, including mean and rms values, spectra, but also peak values of pressure at the building surface. |
Katherine M Xiang; David M Nataf; E Athanassoula; Nadia L Zakamska; Kate Rowlands; Karen Masters; Amelia Fraser-McKelvie; Niv Drory; Katarina Kraljic Buckling Bars in Nearly Face-on Galaxies Observed with MaNGA Journal Article In: The Astrophysical Journal, 909 (2), pp. 125, 2021, ISSN: 1538-4357. @article{Xiang_2021, title = {Buckling Bars in Nearly Face-on Galaxies Observed with MaNGA}, author = {Katherine M Xiang and David M Nataf and E Athanassoula and Nadia L Zakamska and Kate Rowlands and Karen Masters and Amelia Fraser-McKelvie and Niv Drory and Katarina Kraljic}, url = {http://dx.doi.org/10.3847/1538-4357/abdab5}, doi = {10.3847/1538-4357/abdab5}, issn = {1538-4357}, year = {2021}, date = {2021-03-01}, journal = {The Astrophysical Journal}, volume = {909}, number = {2}, pages = {125}, publisher = {American Astronomical Society}, abstract = {Over half of disk galaxies are barred, yet the mechanisms for bar formation and the life-time of bar buckling remain poorly understood. In simulations, a thin bar undergoes a rapid (<1 Gyr) event called "buckling," during which the inner part of the bar is asymmetrically bent out of the galaxy plane and eventually thickens, developing a peanut/X-shaped profile when viewed side-on. Through analyzing stellar kinematics of N-body model snapshots of a galaxy before, during, and after the buckling phase, we confirm a distinct quadrupolar pattern of out-of-plane stellar velocities in nearly face-on galaxies. This kinematic signature of buckling allows us to identify five candidates of currently buckling bars among 434 barred galaxies in the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) Survey, an integral field unit (IFU) spectroscopic survey that measures the composition and kinematic structure of nearby galaxies. The frequency of buckling events detected is consistent with the 0.5-1 Gyr timescale predicted by simulations. The five candidates we present more than double the total number of candidate buckling bars, and are the only ones found using the kinematic signature.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Over half of disk galaxies are barred, yet the mechanisms for bar formation and the life-time of bar buckling remain poorly understood. In simulations, a thin bar undergoes a rapid (<1 Gyr) event called "buckling," during which the inner part of the bar is asymmetrically bent out of the galaxy plane and eventually thickens, developing a peanut/X-shaped profile when viewed side-on. Through analyzing stellar kinematics of N-body model snapshots of a galaxy before, during, and after the buckling phase, we confirm a distinct quadrupolar pattern of out-of-plane stellar velocities in nearly face-on galaxies. This kinematic signature of buckling allows us to identify five candidates of currently buckling bars among 434 barred galaxies in the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) Survey, an integral field unit (IFU) spectroscopic survey that measures the composition and kinematic structure of nearby galaxies. The frequency of buckling events detected is consistent with the 0.5-1 Gyr timescale predicted by simulations. The five candidates we present more than double the total number of candidate buckling bars, and are the only ones found using the kinematic signature. |
Christophe Brouzet; Raphaël Guiné; Marie-Julie Dalbe; Benjamin Favier; Nicolas Vandenberghe; Emmanuel Villermaux; Gautier Verhille Laboratory model for plastic fragmentation in the turbulent ocean Journal Article In: Phys. Rev. Fluids, 6 , pp. 024601, 2021. @article{PhysRevFluids.6.024601, title = {Laboratory model for plastic fragmentation in the turbulent ocean}, author = {Christophe Brouzet and Raphaël Guiné and Marie-Julie Dalbe and Benjamin Favier and Nicolas Vandenberghe and Emmanuel Villermaux and Gautier Verhille}, url = {https://link.aps.org/doi/10.1103/PhysRevFluids.6.024601}, doi = {10.1103/PhysRevFluids.6.024601}, year = {2021}, date = {2021-02-01}, journal = {Phys. Rev. Fluids}, volume = {6}, pages = {024601}, publisher = {American Physical Society}, abstract = {The fragmentation of solid objects in turbulence is of paramount importance in a large number of situations, especially for marine plastic pollution where small plastic debris are formed by the fragmentation of plastic litter under hydrodynamic forces. Up to now, investigations have focused on the fragmentation of particle aggregates in turbulent flows. Here we study the fragmentation of a single deformable object that behaves elastically up to breakage, in the inertial range of turbulence. Using laboratory experiments with glass fibers as a model system, complemented by numerical simulations and theoretical analyses, we exhibit a comprehensive fragmentation scenario, further modeled by an evolution equation. Our results demonstrate that the fragmentation process is limited at small scales by a physical cutoff length originating from the fluid-structure interactions between the objects and the turbulence, and therefore independent of the brittleness of the fibers. This scenario leads to the accumulation of fragments with a typical length slightly longer than the cutoff scale, as smaller fragments are too short to be deformed and broken by the turbulence.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The fragmentation of solid objects in turbulence is of paramount importance in a large number of situations, especially for marine plastic pollution where small plastic debris are formed by the fragmentation of plastic litter under hydrodynamic forces. Up to now, investigations have focused on the fragmentation of particle aggregates in turbulent flows. Here we study the fragmentation of a single deformable object that behaves elastically up to breakage, in the inertial range of turbulence. Using laboratory experiments with glass fibers as a model system, complemented by numerical simulations and theoretical analyses, we exhibit a comprehensive fragmentation scenario, further modeled by an evolution equation. Our results demonstrate that the fragmentation process is limited at small scales by a physical cutoff length originating from the fluid-structure interactions between the objects and the turbulence, and therefore independent of the brittleness of the fibers. This scenario leads to the accumulation of fragments with a typical length slightly longer than the cutoff scale, as smaller fragments are too short to be deformed and broken by the turbulence. |
Jeroen P J Bruekers; Matthijs A Hellinghuizen; Nicolas Vanthuyne; Paul Tinnemans; Pieter J Gilissen; Wybren Jan Buma; Jean-Valère Naubron; Jeanne Crassous; Johannes A A W Elemans; Roeland J M Nolte Front Cover: Allosteric Guest Binding in Chiral Zirconium(IV) Double Decker Porphyrin Cages (Eur. J. Org. Chem. 4/2021) Journal Article In: European Journal of Organic Chemistry, 2021 (4), pp. 512-512, 2021. @article{https://doi.org/10.1002/ejoc.202001599, title = {Front Cover: Allosteric Guest Binding in Chiral Zirconium(IV) Double Decker Porphyrin Cages (Eur. J. Org. Chem. 4/2021)}, author = {Jeroen P J Bruekers and Matthijs A Hellinghuizen and Nicolas Vanthuyne and Paul Tinnemans and Pieter J Gilissen and Wybren Jan Buma and Jean-Valère Naubron and Jeanne Crassous and Johannes A A W Elemans and Roeland J M Nolte}, url = {https://chemistry-europe.onlinelibrary.wiley.com/doi/abs/10.1002/ejoc.202001599}, doi = {https://doi.org/10.1002/ejoc.202001599}, year = {2021}, date = {2021-01-01}, journal = {European Journal of Organic Chemistry}, volume = {2021}, number = {4}, pages = {512-512}, abstract = {The Front Cover shows a chiral double decker porphyrin cage, which has been resolved into enantiomers (red and blue structures). The compound was characterized by various physical techniques, including X-ray and circular dichroism (spectra in the center). The porphyrin cage compound forms well-defined self-assembled monolayers on HOPG surfaces, which are visible by scanning tunneling microscopy (background). The binding of a guest (viologen) in one of the cages of the compound leads to a contraction of the other cage (indicated by the white wiggles), resulting in a greatly reduced guest binding in the latter cage (negative allosteric effect). More information can be found in the Full Paper by Roeland J.M. Nolte et al.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The Front Cover shows a chiral double decker porphyrin cage, which has been resolved into enantiomers (red and blue structures). The compound was characterized by various physical techniques, including X-ray and circular dichroism (spectra in the center). The porphyrin cage compound forms well-defined self-assembled monolayers on HOPG surfaces, which are visible by scanning tunneling microscopy (background). The binding of a guest (viologen) in one of the cages of the compound leads to a contraction of the other cage (indicated by the white wiggles), resulting in a greatly reduced guest binding in the latter cage (negative allosteric effect). More information can be found in the Full Paper by Roeland J.M. Nolte et al. |
Shang-Gui Cai; Johan Degrigny; Jean-François Boussuge; Pierre Sagaut Coupling of turbulence wall models and immersed boundaries on Cartesian grids Journal Article In: Journal of Computational Physics, 429 , pp. 109995, 2021, ISSN: 0021-9991. @article{CAI2021109995, title = {Coupling of turbulence wall models and immersed boundaries on Cartesian grids}, author = {Shang-Gui Cai and Johan Degrigny and Jean-François Boussuge and Pierre Sagaut}, url = {https://www.sciencedirect.com/science/article/pii/S0021999120307695}, doi = {https://doi.org/10.1016/j.jcp.2020.109995}, issn = {0021-9991}, year = {2021}, date = {2021-01-01}, journal = {Journal of Computational Physics}, volume = {429}, pages = {109995}, abstract = {An improved coupling of immersed boundary method and turbulence wall models on Cartesian grids is proposed, for producing smooth wall surface pressure and skin friction at high Reynolds numbers. Spurious oscillations are frequently observed on these quantities with most immersed boundary wall modeling methods, especially for the skin friction which is found to be very sensitive to the solid surface's position and orientation against the Cartesian grids. The problem originates from the irregularity of the wall distance on the stair-step grid boundaries where the immersed boundary conditions are applied. To reduce this directional error, several modifications are presented to enhance the near wall solution. First, the commonly used interpolation for the flow velocity is replaced by one for the friction velocity, which has much less variation near wall. The concept of using a fictitious point to retrieve flow fields in the wall normal direction is abandoned and the interpolation is performed in the wall parallel plane with existing fluid points. Secondly, the velocity gradients at the approximated boundary are computed with advanced schemes and the normal gradient of the tangential velocity is reconstructed from the wall laws. To further protect the near wall solution, the normal velocity gradient and the working viscosity from the Spalart-Allmaras turbulence model are enforced by their theoretical solutions in the interior fluid close to the wall. Additionally, various post-processing algorithms for reconstructing wall surface quantities and force integrations are investigated. Other related factors are also discussed for their effects on the results. The validity of present method has been demonstrated through numerical benchmark tests on a flat plate at zero pressure gradient, both aligned and inclined with respect to the grid, as well as aerodynamic cases of NACA 23012 airfoil and NASA trap wing.}, keywords = {}, pubstate = {published}, tppubtype = {article} } An improved coupling of immersed boundary method and turbulence wall models on Cartesian grids is proposed, for producing smooth wall surface pressure and skin friction at high Reynolds numbers. Spurious oscillations are frequently observed on these quantities with most immersed boundary wall modeling methods, especially for the skin friction which is found to be very sensitive to the solid surface's position and orientation against the Cartesian grids. The problem originates from the irregularity of the wall distance on the stair-step grid boundaries where the immersed boundary conditions are applied. To reduce this directional error, several modifications are presented to enhance the near wall solution. First, the commonly used interpolation for the flow velocity is replaced by one for the friction velocity, which has much less variation near wall. The concept of using a fictitious point to retrieve flow fields in the wall normal direction is abandoned and the interpolation is performed in the wall parallel plane with existing fluid points. Secondly, the velocity gradients at the approximated boundary are computed with advanced schemes and the normal gradient of the tangential velocity is reconstructed from the wall laws. To further protect the near wall solution, the normal velocity gradient and the working viscosity from the Spalart-Allmaras turbulence model are enforced by their theoretical solutions in the interior fluid close to the wall. Additionally, various post-processing algorithms for reconstructing wall surface quantities and force integrations are investigated. Other related factors are also discussed for their effects on the results. The validity of present method has been demonstrated through numerical benchmark tests on a flat plate at zero pressure gradient, both aligned and inclined with respect to the grid, as well as aerodynamic cases of NACA 23012 airfoil and NASA trap wing. |
Philippe Maugis; Damien Connétable; Paul Eyméoud Stability of Zener order in martensite: an atomistic evidence Journal Article In: Scripta Materialia, 194 , pp. 113632, 2021, ISSN: 1359-6462. @article{MAUGIS2021113632, title = {Stability of Zener order in martensite: an atomistic evidence}, author = {Philippe Maugis and Damien Connétable and Paul Eyméoud}, url = {https://www.sciencedirect.com/science/article/pii/S1359646220307442}, doi = {https://doi.org/10.1016/j.scriptamat.2020.113632}, issn = {1359-6462}, year = {2021}, date = {2021-01-01}, journal = {Scripta Materialia}, volume = {194}, pages = {113632}, abstract = {Martensite is a supersaturated solid solution of carbon in body-centered iron wherein interstitial carbon atoms preferentially occupy a single octahedral sublattice. Despite a century of research, the mechanism of this long-range ordering is still a subject of debate. Recently, Zener’s theory of ordering was challenged both experimentally and theoretically. In an attempt to settle the controversy, we investigated by density functional theory the ground states of Fe-C configurations having various degrees of order. We conclude that the fully Zener-ordered configurations are always the most stable energetically, thus confirming Zener’s theory. Comparison with mean-field elasticity and Ising-type modelling supports the elastic origin of Zener ordering.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Martensite is a supersaturated solid solution of carbon in body-centered iron wherein interstitial carbon atoms preferentially occupy a single octahedral sublattice. Despite a century of research, the mechanism of this long-range ordering is still a subject of debate. Recently, Zener’s theory of ordering was challenged both experimentally and theoretically. In an attempt to settle the controversy, we investigated by density functional theory the ground states of Fe-C configurations having various degrees of order. We conclude that the fully Zener-ordered configurations are always the most stable energetically, thus confirming Zener’s theory. Comparison with mean-field elasticity and Ising-type modelling supports the elastic origin of Zener ordering. |
M Tayyab; S Zhao; Pierre Boivin Lattice-Boltzmann modeling of a turbulent bluff-body stabilized flame Journal Article In: Physics of Fluids, 33 (3), pp. 031701, 2021. @article{tayyab:hal-03160901, title = {Lattice-Boltzmann modeling of a turbulent bluff-body stabilized flame}, author = {M Tayyab and S Zhao and Pierre Boivin}, url = {https://hal.archives-ouvertes.fr/hal-03160901}, doi = {10.1063/5.0038089}, year = {2021}, date = {2021-01-01}, journal = {Physics of Fluids}, volume = {33}, number = {3}, pages = {031701}, publisher = {American Institute of Physics}, abstract = {This letter reports the first large eddy simulation of a turbulent flame using a Lattice-Boltzmann model. To that end, simulation of a bluff-body stabilized propane-air flame is carried out, showing an agreement similar to those available in the literature. Computational costs are also reported, indicating that Lattice-Boltzmann modelling of reactive flows is competitive, with around 1000cpuh required to simulate one residence time in the 1,5m burner. }, keywords = {}, pubstate = {published}, tppubtype = {article} } This letter reports the first large eddy simulation of a turbulent flame using a Lattice-Boltzmann model. To that end, simulation of a bluff-body stabilized propane-air flame is carried out, showing an agreement similar to those available in the literature. Computational costs are also reported, indicating that Lattice-Boltzmann modelling of reactive flows is competitive, with around 1000cpuh required to simulate one residence time in the 1,5m burner. |
D Mandal; Y Elskens; X Leoncini; N Lemoine; F Doveil Sticky islands in stochastic webs and anomalous chaotic cross-field particle transport by E×B electron drift instability Journal Article In: Chaos, Solitons & Fractals, 145 , pp. 110810, 2021, ISSN: 0960-0779. @article{MANDAL2021110810, title = {Sticky islands in stochastic webs and anomalous chaotic cross-field particle transport by E×B electron drift instability}, author = {D Mandal and Y Elskens and X Leoncini and N Lemoine and F Doveil}, url = {https://www.sciencedirect.com/science/article/pii/S0960077921001624}, doi = {https://doi.org/10.1016/j.chaos.2021.110810}, issn = {0960-0779}, year = {2021}, date = {2021-01-01}, journal = {Chaos, Solitons & Fractals}, volume = {145}, pages = {110810}, abstract = {The E×B electron drift instability, present in many plasma devices, is an important agent in cross-field particle transport. In presence of a resulting low frequency electrostatic wave, the motion of a charged particle becomes chaotic and generates a stochastic web in phase space. We define a scaling exponent to characterise transport in phase space and we show that the transport is anomalous, of super-diffusive type. Given the values of the model parameters, the trajectories stick to different kinds of islands in phase space, and their different sticking time power-law statistics generate successive regimes of the super-diffusive transport.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The E×B electron drift instability, present in many plasma devices, is an important agent in cross-field particle transport. In presence of a resulting low frequency electrostatic wave, the motion of a charged particle becomes chaotic and generates a stochastic web in phase space. We define a scaling exponent to characterise transport in phase space and we show that the transport is anomalous, of super-diffusive type. Given the values of the model parameters, the trajectories stick to different kinds of islands in phase space, and their different sticking time power-law statistics generate successive regimes of the super-diffusive transport. |
Nicolas Frangieh; Gilbert Accary; Jean-Louis Rossi; Dominique Morvan; Sofiane Meradji; Thierry Marcelli; François-Joseph Chatelon Fuelbreak effectiveness against wind-driven and plume-dominated fires: A 3D numerical study Journal Article In: Fire Safety Journal, 124 , pp. 103383, 2021, ISSN: 0379-7112. @article{FRANGIEH2021103383, title = {Fuelbreak effectiveness against wind-driven and plume-dominated fires: A 3D numerical study}, author = {Nicolas Frangieh and Gilbert Accary and Jean-Louis Rossi and Dominique Morvan and Sofiane Meradji and Thierry Marcelli and François-Joseph Chatelon}, url = {https://www.sciencedirect.com/science/article/pii/S0379711221001247}, doi = {https://doi.org/10.1016/j.firesaf.2021.103383}, issn = {0379-7112}, year = {2021}, date = {2021-01-01}, journal = {Fire Safety Journal}, volume = {124}, pages = {103383}, abstract = {The effectiveness of a fuelbreak, created in a homogeneous grassland on a flat terrain, was studied numerically. The analysis relies on 3D numerical simulations that were performed using a detailed physical-fire-model (FIRESTAR3D) based on a multiphase formulation. To avoid border effects, calculations were carried out by imposing periodic boundary conditions along the two lateral sides of the computational domain, reproducing that way a quasi-infinitely long fire front. A total of 72 simulations were carried out for various wind speeds, fuel heights, and fuelbreak widths, which allowed to cover a large spectrum of fire behaviour, ranging from plume-dominated fires to wind-driven fires. The results were classified in three main categories: 1- “Propagation” if fire crossed the fuelbreak with a continuous fire front, 2- “Overshooting” and “Marginal” if fire marginally crosses the fuelbreak with the formation of burning pockets, and 3- “No propagation” if fire does not cross at all the fuelbreak. The ratio of fuelbreak width to fuel height, marking the “Propagation”/“No propagation” transition, was found to be scaled with Byram's convection number Nc as 75.07 × Nc−0.46. The numerical results were also compared to an operational wildfire engineering tool (DIMZAL) dedicated to fuelbreaks dimensioning.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The effectiveness of a fuelbreak, created in a homogeneous grassland on a flat terrain, was studied numerically. The analysis relies on 3D numerical simulations that were performed using a detailed physical-fire-model (FIRESTAR3D) based on a multiphase formulation. To avoid border effects, calculations were carried out by imposing periodic boundary conditions along the two lateral sides of the computational domain, reproducing that way a quasi-infinitely long fire front. A total of 72 simulations were carried out for various wind speeds, fuel heights, and fuelbreak widths, which allowed to cover a large spectrum of fire behaviour, ranging from plume-dominated fires to wind-driven fires. The results were classified in three main categories: 1- “Propagation” if fire crossed the fuelbreak with a continuous fire front, 2- “Overshooting” and “Marginal” if fire marginally crosses the fuelbreak with the formation of burning pockets, and 3- “No propagation” if fire does not cross at all the fuelbreak. The ratio of fuelbreak width to fuel height, marking the “Propagation”/“No propagation” transition, was found to be scaled with Byram's convection number Nc as 75.07 × Nc−0.46. The numerical results were also compared to an operational wildfire engineering tool (DIMZAL) dedicated to fuelbreaks dimensioning. |
Romain Pinguet; S Kanner; M Benoit; B Molin Modeling the Dynamics of Freely-Floating Offshore Wind Turbine Subjected to Waves With an Open-Source Overset Mesh Method Technical Manual 2021. @manual{Pinguet2021ModelingTD, title = {Modeling the Dynamics of Freely-Floating Offshore Wind Turbine Subjected to Waves With an Open-Source Overset Mesh Method}, author = {Romain Pinguet and S Kanner and M Benoit and B Molin}, url = {https://www.researchgate.net/publication/349379786_Modeling_the_Dynamics_of_Freely-Floating_Offshore_Wind_Turbine_Subjected_to_Waves_With_an_Open-Source_Overset_Mesh_Method}, year = {2021}, date = {2021-01-01}, abstract = {The aim of this study is to develop a viscous numerical wave tank using a coupled solver between the wave generation and absorption toolbox waves2Foam, developed by Jacobsen et al. [1] and the overset method built in the open source CFD software OpenFOAM©. This wave tank can be used to analyze the behavior of Floating Offshore Wind Turbine (FOWT) in nonlinear waves. A mesh convergence analysis is presented on a simple 2D case in order to validate the CFD model. The results are compared to experimental data from the literature and show good agreement. The response of a floater developed for a FOWT is analyzed. The free surface elevation, heave and pitch motions are compared to experimental results from the literature. Comparisons between experimental data and numerical results are discussed.}, keywords = {}, pubstate = {published}, tppubtype = {manual} } The aim of this study is to develop a viscous numerical wave tank using a coupled solver between the wave generation and absorption toolbox waves2Foam, developed by Jacobsen et al. [1] and the overset method built in the open source CFD software OpenFOAM©. This wave tank can be used to analyze the behavior of Floating Offshore Wind Turbine (FOWT) in nonlinear waves. A mesh convergence analysis is presented on a simple 2D case in order to validate the CFD model. The results are compared to experimental data from the literature and show good agreement. The response of a floater developed for a FOWT is analyzed. The free surface elevation, heave and pitch motions are compared to experimental results from the literature. Comparisons between experimental data and numerical results are discussed. |
Pierre Boivin; M Tayyab; S Zhao Benchmarking a lattice-Boltzmann solver for reactive flows: Is the method worth the effort for combustion? Journal Article In: Physics of Fluids, 33 (7), pp. 071703, 2021. @article{boivin:hal-03276189, title = {Benchmarking a lattice-Boltzmann solver for reactive flows: Is the method worth the effort for combustion?}, author = {Pierre Boivin and M Tayyab and S Zhao}, url = {https://hal.archives-ouvertes.fr/hal-03276189}, doi = {10.1063/5.0057352}, year = {2021}, date = {2021-01-01}, journal = {Physics of Fluids}, volume = {33}, number = {7}, pages = {071703}, publisher = {American Institute of Physics}, abstract = {This Letter reports a validation of a lattice-Boltzmann approach following the Taylor-Green Vortex benchmark presented at the 19th International Congress on Numerical Combustion and recently reported by Abdelsamie et al. ["The Taylor-Green vortex as a benchmark for high-fidelity combustion simulations using low-Mach solvers," Comput. Fluids 223, 104935 (2021)]. The lattice-Boltzmann approach, despite having a time step bound by an acoustic Courant-Friedrichs-Lewy condition, provides results faster than the low-Mach solvers which performed to the benchmark. Such a feat is made possible by the fully explicit nature of the method and indicates very high potential for practical applications.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This Letter reports a validation of a lattice-Boltzmann approach following the Taylor-Green Vortex benchmark presented at the 19th International Congress on Numerical Combustion and recently reported by Abdelsamie et al. ["The Taylor-Green vortex as a benchmark for high-fidelity combustion simulations using low-Mach solvers," Comput. Fluids 223, 104935 (2021)]. The lattice-Boltzmann approach, despite having a time step bound by an acoustic Courant-Friedrichs-Lewy condition, provides results faster than the low-Mach solvers which performed to the benchmark. Such a feat is made possible by the fully explicit nature of the method and indicates very high potential for practical applications. |
Paul Eyméoud; Fabienne Ribeiro; Rémy Besson; Guy Tréglia How to take into account local concentration in Ising-based Monte-Carlo: illustration with zirconium hydrides Journal Article In: Computational Materials Science, 197 , pp. 110547, 2021, ISSN: 0927-0256. @article{EYMEOUD2021110547, title = {How to take into account local concentration in Ising-based Monte-Carlo: illustration with zirconium hydrides}, author = {Paul Eyméoud and Fabienne Ribeiro and Rémy Besson and Guy Tréglia}, url = {https://www.sciencedirect.com/science/article/pii/S0927025621002743}, doi = {https://doi.org/10.1016/j.commatsci.2021.110547}, issn = {0927-0256}, year = {2021}, date = {2021-01-01}, journal = {Computational Materials Science}, volume = {197}, pages = {110547}, abstract = {We present a detailed methodology for treating local concentration dependency of pairwise interactions in Ising-based Monte-Carlo. The procedure is described through the example of interstitial ordering processes in zirconium hydrides, studied by canonical Monte-Carlo based on a concentration-dependent Tight-Binding Ising Model. The path leads to build a phase diagram of hydrogen-vacancy ordering on interstitial tetrahedral sublattice of face-centered cubic Zr-H.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present a detailed methodology for treating local concentration dependency of pairwise interactions in Ising-based Monte-Carlo. The procedure is described through the example of interstitial ordering processes in zirconium hydrides, studied by canonical Monte-Carlo based on a concentration-dependent Tight-Binding Ising Model. The path leads to build a phase diagram of hydrogen-vacancy ordering on interstitial tetrahedral sublattice of face-centered cubic Zr-H. |
Mihael Petač; Julien Lavalle; Arturo Núñez-Castiñeyra; Emmanuel Nezri Testing the predictions of axisymmetric distribution functions of galactic dark matter with hydrodynamical simulations Journal Article In: JCAP, 08 , pp. 031, 2021. @article{petac:hal-03262627, title = {Testing the predictions of axisymmetric distribution functions of galactic dark matter with hydrodynamical simulations}, author = {Mihael Petač and Julien Lavalle and Arturo Núñez-Castiñeyra and Emmanuel Nezri}, url = {https://hal.archives-ouvertes.fr/hal-03262627}, doi = {10.1088/1475-7516/2021/08/031}, year = {2021}, date = {2021-01-01}, journal = {JCAP}, volume = {08}, pages = {031}, abstract = {Signal predictions for galactic dark matter (DM) searches often rely on assumptions regarding the DM phase-space distribution function (DF) in halos. This applies to both particle (e.g. p-wave suppressed or Sommerfeld-enhanced annihilation, scattering off atoms, etc.) and macroscopic DM candidates (e.g. microlensing of primordial black holes). As experiments and observations improve in precision, better assessing theoretical uncertainties becomes pressing in the prospect of deriving reliable constraints on DM candidates or trustworthy hints for detection. Most reliable predictions of DFs in halos are based on solving the steady-state collisionless Boltzmann equation (e.g. Eddington-like inversions, action-angle methods, etc.) consistently with observational constraints. One can do so starting from maximal symmetries and a minimal set of degrees of freedom, and then increasing complexity. Key issues are then whether adding complexity, which is computationally costy, improves predictions, and if so where to stop. Clues can be obtained by making predictions for zoomed-in hydrodynamical cosmological simulations in which one can access the true (coarse-grained) phase-space information. Here, we test an axisymmetric extension of the Eddington inversion to predict the full DM DF from its density profile and the total gravitational potential of the system. This permits to go beyond spherical symmetry, and is a priori well suited for spiral galaxies. We show that axisymmetry does not necessarily improve over spherical symmetry because the (observationally unconstrained) angular momentum of the DM halo is not generically aligned with the baryonic one. Theoretical errors are similar to those of the Eddington inversion though, at the 10–20% level for velocity-dependent predictions related to particle DM searches in spiral galaxies. We extensively describe the approach and comment on the results.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Signal predictions for galactic dark matter (DM) searches often rely on assumptions regarding the DM phase-space distribution function (DF) in halos. This applies to both particle (e.g. p-wave suppressed or Sommerfeld-enhanced annihilation, scattering off atoms, etc.) and macroscopic DM candidates (e.g. microlensing of primordial black holes). As experiments and observations improve in precision, better assessing theoretical uncertainties becomes pressing in the prospect of deriving reliable constraints on DM candidates or trustworthy hints for detection. Most reliable predictions of DFs in halos are based on solving the steady-state collisionless Boltzmann equation (e.g. Eddington-like inversions, action-angle methods, etc.) consistently with observational constraints. One can do so starting from maximal symmetries and a minimal set of degrees of freedom, and then increasing complexity. Key issues are then whether adding complexity, which is computationally costy, improves predictions, and if so where to stop. Clues can be obtained by making predictions for zoomed-in hydrodynamical cosmological simulations in which one can access the true (coarse-grained) phase-space information. Here, we test an axisymmetric extension of the Eddington inversion to predict the full DM DF from its density profile and the total gravitational potential of the system. This permits to go beyond spherical symmetry, and is a priori well suited for spiral galaxies. We show that axisymmetry does not necessarily improve over spherical symmetry because the (observationally unconstrained) angular momentum of the DM halo is not generically aligned with the baryonic one. Theoretical errors are similar to those of the Eddington inversion though, at the 10–20% level for velocity-dependent predictions related to particle DM searches in spiral galaxies. We extensively describe the approach and comment on the results. |
M Bouffard; B Favier; D Lecoanet; M Le Bars Internal gravity waves in a stratified layer atop a convecting liquid core in a non-rotating spherical shell Journal Article In: Geophysical Journal International, 228 (1), pp. 337-354, 2021, ISSN: 0956-540X. @article{10.1093/gji/ggab343, title = {Internal gravity waves in a stratified layer atop a convecting liquid core in a non-rotating spherical shell}, author = {M Bouffard and B Favier and D Lecoanet and M Le Bars}, url = {https://doi.org/10.1093/gji/ggab343}, doi = {10.1093/gji/ggab343}, issn = {0956-540X}, year = {2021}, date = {2021-01-01}, journal = {Geophysical Journal International}, volume = {228}, number = {1}, pages = {337-354}, abstract = {Seismic and magnetic observations have suggested the presence of a stably stratified layer atop Earth’s core. Such a layer could affect the morphology of the geomagnetic field and the evolution of the core, but the precise impact of this layer depends largely on its internal dynamics. Among other physical phenomena, stratified layers host internal gravity waves (IGW), which can be excited by adjacent convective motions. Internal waves are known to play an important role on the large-scale dynamics of the Earth’s climate and on the long-term evolution of stars. Yet, they have received relatively little attention in the Earth’s outer core so far and deserve detailed investigations in this context. Here, we make a first step in that direction by running numerical simulations of IGW in a non-rotating spherical shell in which a stratified layer lies on top of a convective region. We use a nonlinear equation of state to produce self-consistently such a two-layer system. Both propagating waves and global modes coexist in the stratified layer. We characterize the spectral properties of these waves and find that energy is distributed across a wide range of frequencies and length scales, that depends on the Prandtl number. For the control parameters considered and in the absence of rotational and magnetic effects, the mean kinetic energy in the layer is about 0.1 per cent that of the convective region. IGW produce perturbations in the gravity field that may fall within the sensitivity limit of present-day instruments and could potentially be detected in available data. We finally provide a road map for future, more geophysically realistic, studies towards a more thorough understanding of the dynamics and impact of internal waves in a stratified layer atop Earth’s core.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Seismic and magnetic observations have suggested the presence of a stably stratified layer atop Earth’s core. Such a layer could affect the morphology of the geomagnetic field and the evolution of the core, but the precise impact of this layer depends largely on its internal dynamics. Among other physical phenomena, stratified layers host internal gravity waves (IGW), which can be excited by adjacent convective motions. Internal waves are known to play an important role on the large-scale dynamics of the Earth’s climate and on the long-term evolution of stars. Yet, they have received relatively little attention in the Earth’s outer core so far and deserve detailed investigations in this context. Here, we make a first step in that direction by running numerical simulations of IGW in a non-rotating spherical shell in which a stratified layer lies on top of a convective region. We use a nonlinear equation of state to produce self-consistently such a two-layer system. Both propagating waves and global modes coexist in the stratified layer. We characterize the spectral properties of these waves and find that energy is distributed across a wide range of frequencies and length scales, that depends on the Prandtl number. For the control parameters considered and in the absence of rotational and magnetic effects, the mean kinetic energy in the layer is about 0.1 per cent that of the convective region. IGW produce perturbations in the gravity field that may fall within the sensitivity limit of present-day instruments and could potentially be detected in available data. We finally provide a road map for future, more geophysically realistic, studies towards a more thorough understanding of the dynamics and impact of internal waves in a stratified layer atop Earth’s core. |
Guochao Gao; Paul Cristini; Nathalie Favretto-Cristini; Carole Deumié On the reflection of time-domain acoustic spherical waves by a sinusoidal diffraction grating Journal Article In: Acta Acust., 5 , pp. 6, 2021. @article{refId0d, title = {On the reflection of time-domain acoustic spherical waves by a sinusoidal diffraction grating}, author = {Guochao} {Gao and Paul} {Cristini and Nathalie} {Favretto-Cristini and Carole} {Deumié}, url = {https://doi.org/10.1051/aacus/2020033}, doi = {10.1051/aacus/2020033}, year = {2021}, date = {2021-01-01}, journal = {Acta Acust.}, volume = {5}, pages = {6}, abstract = {This work reports on some results obtained from numerical simulations of time-domain acoustic wave propagation in the presence of a periodically rough interface. Emphasis is put on the structure of the reflected signals in the presence of a sinusoidal grating. More specifically, we investigate the effect of the frequency bandwidth of the emitted signal and the effect of the incident wavefront sphericity on the signals reflected from the rough interface and associated with the different diffraction orders.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This work reports on some results obtained from numerical simulations of time-domain acoustic wave propagation in the presence of a periodically rough interface. Emphasis is put on the structure of the reflected signals in the presence of a sinusoidal grating. More specifically, we investigate the effect of the frequency bandwidth of the emitted signal and the effect of the incident wavefront sphericity on the signals reflected from the rough interface and associated with the different diffraction orders. |
Oleg Bessonov; Sofiane Meradji Parallel modeling of wildfires using efficient solvers for ill-conditioned linear systems Journal Article In: The Journal of Supercomputing, 2021. @article{articled, title = {Parallel modeling of wildfires using efficient solvers for ill-conditioned linear systems}, author = {Oleg Bessonov and Sofiane Meradji}, doi = {10.1007/s11227-021-03632-8}, year = {2021}, date = {2021-01-01}, journal = {The Journal of Supercomputing}, abstract = {Numerical simulation of multi-physical processes requires a lot of processor time, especially when solving ill-conditional linear systems arising in fluid dynamics problems. This paper is devoted to the development of efficient parallel methods for such systems for FireStar3D wildfire modeling code. Two alternative approaches are discussed and analyzed, based on the MILU-preconditioned conjugate gradient method and on the algebraic multigrid, respectively. The main difficulties of paral- lelizing these methods are considered and solutions are presented: in the first case, nested twisted factorization with a staircase pipelining, and in the second, a multi- color technique for a new smoother for strongly anisotropic grids. A novel quasi- geometric interpolation technique is presented for solving the problem of positive off-diagonal matrix entries in the multigrid. The limits of applicability of the meth- ods are determined depending on their flexibility, robustness and parallelization capabilities. The performance comparison demonstrates the superiority of the new methods over the widely used variants of the traditional conjugate gradient method.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Numerical simulation of multi-physical processes requires a lot of processor time, especially when solving ill-conditional linear systems arising in fluid dynamics problems. This paper is devoted to the development of efficient parallel methods for such systems for FireStar3D wildfire modeling code. Two alternative approaches are discussed and analyzed, based on the MILU-preconditioned conjugate gradient method and on the algebraic multigrid, respectively. The main difficulties of paral- lelizing these methods are considered and solutions are presented: in the first case, nested twisted factorization with a staircase pipelining, and in the second, a multi- color technique for a new smoother for strongly anisotropic grids. A novel quasi- geometric interpolation technique is presented for solving the problem of positive off-diagonal matrix entries in the multigrid. The limits of applicability of the meth- ods are determined depending on their flexibility, robustness and parallelization capabilities. The performance comparison demonstrates the superiority of the new methods over the widely used variants of the traditional conjugate gradient method. |