Antoine Monot, Christophe Friess, Jeroen Wackers. Grey Area Mitigation for Detached-Eddy Simulations Using Volume Forcing. International Journal of Computational Fluid Dynamics, 2025, Adaptation for Scale-Resolved Turbulence, 38 (2-3), pp.246-264. ⟨10.1080/10618562.2024.2376851⟩. ⟨hal-04923705⟩ Plus de détails...
Hybrid RANS/LES (HRL) models use LES in complex regions and RANS otherwise. However, HRL models have issues when dealing with the transition between RANS and LES areas. The goal of this paper is to propose a solution to the lack of a mechanism in the DES model for transferring the modelled turbulent kinetic energy (TKE) to the resolved scales. The presented approach uses a volume forcing which amplifies existing velocity fluctuations. It aims at compensating for the modelled TKE dissipated by reinjecting it as resolved kinetic energy, so that the total TKE is unaffected. This solution's effectiveness is evaluated on a turbulent boundary layer over a flat plate, a case where DES is highly sensitive to mesh refinement. Different meshes and time steps are tested to assess the impact of the method on the flow. This approach shows a clear improvement on the turbulent quantities compared to the DES model.
Antoine Monot, Christophe Friess, Jeroen Wackers. Grey Area Mitigation for Detached-Eddy Simulations Using Volume Forcing. International Journal of Computational Fluid Dynamics, 2025, Adaptation for Scale-Resolved Turbulence, 38 (2-3), pp.246-264. ⟨10.1080/10618562.2024.2376851⟩. ⟨hal-04923705⟩
Journal: International Journal of Computational Fluid Dynamics
Raffael Düll, Guido Ciraolo, Hugo Bufferand, Eric Serre, Virginia Quadri, et al.. Implementation of a non-axisymmetric magnetic configuration in SOLEDGE3X to simulate 3D toroidal magnetic ripple effects: Application to WEST. Nuclear Materials and Energy, 2024, 41, pp.101807. ⟨10.1016/j.nme.2024.101807⟩. ⟨hal-04948108⟩ Plus de détails...
The fluid-drift code SOLEDGE3X, developed by CEA/IRFM in collaboration with Aix-Marseille University, is a powerful tool for simulating transport and turbulence in tokamak edge plasmas with axisymmetric magnetic configurations. In tokamaks such as WEST, the pronounced toroidal magnetic ripple significantly affects plasma confinement and power exhaust, modulating both the poloidal and toroidal components of the equilibrium field. Using a discrete Biot-Savart law, the ripple field is calculated as a magnetic perturbation on the SOLEDGE3X mesh. The transport model and parallel gradient solvers have been enhanced to incorporate the new radial magnetic field component. Preliminary simulations of a WEST scenario reveal a heat deposition pattern in the divertor region consistent with observations from infrared camera experiments.
Raffael Düll, Guido Ciraolo, Hugo Bufferand, Eric Serre, Virginia Quadri, et al.. Implementation of a non-axisymmetric magnetic configuration in SOLEDGE3X to simulate 3D toroidal magnetic ripple effects: Application to WEST. Nuclear Materials and Energy, 2024, 41, pp.101807. ⟨10.1016/j.nme.2024.101807⟩. ⟨hal-04948108⟩
N. Fedorczak, C. Arnas, L. Cappelli, L. Colas, Y. Corre, et al.. Survey of tungsten gross erosion from main plasma facing components in WEST during a L-mode high fluence campaign. Nuclear Materials and Energy, 2024, 41 (4), pp.101758. ⟨10.1016/j.nme.2024.101758⟩. ⟨cea-04816563⟩ Plus de détails...
An initial high fluence campaign was performed in WEST, in 2023, on the newly installed actively cooled tungsten divertor composed of ITER-grade monoblocks. The campaign consisted in the repetition of a 60 s long Deuterium L-mode pulse in attached divertor conditions, cumulating over 10000s of plasma exposure. A maximum deuterium fluence of approximately 5 ⋅ 10 26 m -2 was reached in the outer strike point region, representative of a few high performance ITER pulses. Gross tungsten erosion inferred from visible spectroscopy shows that the most eroded plasma facing component is the inner divertor target with rates ten times larger than on the outer divertor target. The outer midplane tungsten bumpers, located a few centimeters from the plasma, show gross erosion rates two times lower than at the outer divertor. We conclude that the outer midplane bumpers have a negligible contribution to the long range tungsten migration and deposition onto the lower divertor. The cumulated gross erosion rate on the inner divertor translates in an effective gross erosion thickness of about 20 μm, while it is about 2 μm for the outer divertor. Strikingly, these orderings coincide with the thickness of deposits found locally on the divertor: the exposed surfaces of high field side monoblocks are covered with several tens of μm tungsten deposits, while on the lower field side, few μm thin tungsten deposits are only found on the magnetically shadowed parts of monoblocks. The strong impact of those deposits on WEST operation, namely perturbation of surface temperature measurement with infra-red thermography, and the emission of flakes causing radiative perturbation of the confined plasma, calls for anticipating similar issues in ITER. In particular, the start of research operation shall consider the definition of a divertor erosion budget in order to anticipate the formation of deleterious deposits.
N. Fedorczak, C. Arnas, L. Cappelli, L. Colas, Y. Corre, et al.. Survey of tungsten gross erosion from main plasma facing components in WEST during a L-mode high fluence campaign. Nuclear Materials and Energy, 2024, 41 (4), pp.101758. ⟨10.1016/j.nme.2024.101758⟩. ⟨cea-04816563⟩
S. Sureshkumar, N. Rivals, P. Tamain, X. Bonnin, R. Pitts, et al.. First SOLEDGE3X-EIRENE simulations of the ITER Neon seeded burning plasma boundary up to the first wall. Nuclear Materials and Energy, 2024, 41, pp.101780. ⟨10.1016/j.nme.2024.101780⟩. ⟨hal-04948159⟩ Plus de détails...
S. Sureshkumar, N. Rivals, P. Tamain, X. Bonnin, R. Pitts, et al.. First SOLEDGE3X-EIRENE simulations of the ITER Neon seeded burning plasma boundary up to the first wall. Nuclear Materials and Energy, 2024, 41, pp.101780. ⟨10.1016/j.nme.2024.101780⟩. ⟨hal-04948159⟩
H. Bufferand, G. Ciraolo, R. Düll, G. Falchetto, N. Fedorczak, et al.. Global 3D full-scale turbulence simulations of TCV-X21 experiments with SOLEDGE3X. Nuclear Materials and Energy, 2024, 41, pp.101824. ⟨10.1016/j.nme.2024.101824⟩. ⟨hal-04948123⟩ Plus de détails...
First principle modelling of edge plasma turbulence including neutrals and plasma recycling on the wall remains a challenge, in particular due to the long time scales necessary to simulate to reach particle balance. In this contribution, we propose a strategy to address these long time scales with the fluid code SOLEDGE, resorting to 2D reduced models for turbulence as well as 3D coarse grid simulations. The approach is applied to simulate TCV-X21 reference plasma scenario for edge turbulence modelling validation.
H. Bufferand, G. Ciraolo, R. Düll, G. Falchetto, N. Fedorczak, et al.. Global 3D full-scale turbulence simulations of TCV-X21 experiments with SOLEDGE3X. Nuclear Materials and Energy, 2024, 41, pp.101824. ⟨10.1016/j.nme.2024.101824⟩. ⟨hal-04948123⟩
J. Garcia Sarmiento, Florian Fichot, Vincent Topin, P. Sagaut. Numerical simulation of corium flow through rod bundle and/or debris bed geometries with a model based on Lattice Boltzmann method. Nuclear Engineering and Design, 2024, 429, pp.113603. ⟨10.1016/j.nucengdes.2024.113603⟩. ⟨hal-04874958⟩ Plus de détails...
A new model is proposed to investigate the relocation and the distribution of hot corium flows in different configurations (rod bundle, porous debris bed) representative of a severe accident in a Light Water Reactor (LWR). Our model relies on the coupling between a modified Lattice Boltzmann Method (LBM), called Free-Surface LBM, that solves hydrodynamics of unsaturated corium and a Finite Volume Method (FVM) that solves heat transfers. Corium solidification and melting are addressed by implementing a correlation between the temperature and the viscosity. Several simulations on representative elementary volumes were performed, varying configurations (debris bed, rod bundle with and without grid). From the results, it is possible to capture important details of the flow at a scale lower than the pore scale and, at the same time, it is possible to take into account the average effects at the scale of several pores. Presented as a proof of concept these preliminary studies show the interest of this kind of CFD approach to identify which parameters at microstructure scale can potentially govern the corium relocation kinetics at macroscopic scale. It will provide useful information that might improve core degradation models in severe accident codes, such as ASTEC.
J. Garcia Sarmiento, Florian Fichot, Vincent Topin, P. Sagaut. Numerical simulation of corium flow through rod bundle and/or debris bed geometries with a model based on Lattice Boltzmann method. Nuclear Engineering and Design, 2024, 429, pp.113603. ⟨10.1016/j.nucengdes.2024.113603⟩. ⟨hal-04874958⟩
Enrique de Dios Zapata Cornejo, David Zarzoso, S.D. Pinches, Andres Bustos, Alvaro Cappa, et al.. A novel unsupervised machine learning algorithm for automatic Alfvénic activity detection in the TJ-II stellarator. Nuclear Fusion, 2024, 64 (12), pp.126057. ⟨10.1088/1741-4326/ad85f4⟩. ⟨hal-04540368⟩ Plus de détails...
A novel sparse encoding algorithm is developed to detect and study plasma instabilities automatically. This algorithm, called Elastic Random Mode Decomposition, is applied to the Mirnov coil signals of a dataset of 1291 discharges of the TJ-II stellarator, enabling the identification of the Alfvénic activity. In the presented approach, each signal is encoded as a collection of basic waveforms called atoms, drawn from a signal’s dictionary. Then the modes are identified using clustering and correlations with other plasma signals. The performance of the proposed algorithm is dramatically increased by using elastic net regularization and taking advantage of GPU architectures, hence the signal size and the number of dictionary elements are no longer limiting factors for encoding complex signals. Once the modes are retrieved from the shots, they can be easily analyzed with standard clustering techniques, thereby describing the physical mode characteristics of this subset of TJ-II shots. The clustering features consider the relationship with the plasma current Ip, the diamagnetic energy W, and inverse squared root electronic density 1/√n, profiling different subtypes of Alfvénic activity. The proposed algorithm can potentially create large databases of labeled modes with unprecedented detail.
Enrique de Dios Zapata Cornejo, David Zarzoso, S.D. Pinches, Andres Bustos, Alvaro Cappa, et al.. A novel unsupervised machine learning algorithm for automatic Alfvénic activity detection in the TJ-II stellarator. Nuclear Fusion, 2024, 64 (12), pp.126057. ⟨10.1088/1741-4326/ad85f4⟩. ⟨hal-04540368⟩
Stefano Di Genova, Alberto Gallo, Luca Cappelli, Nicolas Fedorczak, Hugo Bufferand, et al.. Global analysis of tungsten migration in WEST discharges using numerical modelling. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad82f9⟩. ⟨hal-04739577⟩ Plus de détails...
Plasma discharges in the tungsten (W) Environment Steady-state Tokamak (WEST) are strongly impacted by W contamination. In WEST experiments, due to W contamination, the power radiated in the plasma (PRad) is on average, around 50% of the total power injected into the plasma (PTOT). Furthermore, this radiated power fraction (fRad) is almost insensitive to plasma conditions. The causes behind this experimental trend are not fully understood. In this contribution, a 3D numerical model is used to analyze the W migration in the WEST boundary plasma in different plasma scenarios. The WEST experimental database is sampled to obtain a scan of simulation input parameters. These parameters mimic the WEST plasma conditions over a chosen experimental campaign. The simulation results are compared to WEST diagnostics measurements (reflectometry, Langmuir probes, and visible spectroscopy) to verify that the simulated plasma conditions are representative of the WEST database. The W contamination trend is analysed: the W density (nW) strongly decreases when the radial distance between the separatrix and WEST antennas (Radial Outer Gap, ROG) increases. On the other hand, at a given ROG, nW increases proportionally with the power entering the scrape-off layer (PSOL). PRad is estimated with a simple 0D model. For a fixed ROG, fRad is not sensitive to plasma conditions. These trends are qualitatively and, at times, quantitatively comparable to what is observed in WEST experiments: the simulated trends are related to the poorly screened W influx caused by the erosion of the main chamber Plasma-Facing Components (PFCs). Thus, this numerical analysis suggests a possible interpretation of WEST experimental trends.
Stefano Di Genova, Alberto Gallo, Luca Cappelli, Nicolas Fedorczak, Hugo Bufferand, et al.. Global analysis of tungsten migration in WEST discharges using numerical modelling. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad82f9⟩. ⟨hal-04739577⟩
M. Scotto D’abusco, I. Kudashev, G. Giorgiani, Anna Glasser, F. Schwander, et al.. First integrated core-edge fluid simulation of ITER’s Limiter-Divertor transition with SolEdge-HDG. Nuclear Materials and Energy, 2024, pp.101750. ⟨10.1016/j.nme.2024.101750⟩. ⟨hal-04720290⟩ Plus de détails...
This work explores the Limiter-Divertor transition (L-D) during the current ramp-up of ITER's Q=10 baseline plasma scenario at various central line-integrated density n_(li) values. The analysis, based on transport simulations performed with the latest version of SoleEdge-HDG, focuses on the time evolution of heat and ion particle fluxes, revealing regions of elevated temperature on the inner wall and plasma-facing components (PFCs) despite moderate loads.The investigation also delves into the effects of perpendicular convection flux terms on density build-up, comparing different formulations and their interplay with auxiliary heating sources. Furthermore, the paper shows the impact of taking into account the evolution of the parallel neutral momentum on plasma and neutral density at the targets in the context of an ITER steady-state scenario.
M. Scotto D’abusco, I. Kudashev, G. Giorgiani, Anna Glasser, F. Schwander, et al.. First integrated core-edge fluid simulation of ITER’s Limiter-Divertor transition with SolEdge-HDG. Nuclear Materials and Energy, 2024, pp.101750. ⟨10.1016/j.nme.2024.101750⟩. ⟨hal-04720290⟩
H Betar, David Zarzoso, Jacobo Varela, Diego Del-Castillo-Negrete, Luis Garcia, et al.. Transport and losses of energetic particles in tokamaks in the presence of Alfvén activity using the new full orbit TAPaS code coupled to FAR3d. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad7c66⟩. ⟨hal-04541528v2⟩ Plus de détails...
Recent developments and tools integrated into the TAPaS code are presented, enabling realistic scenario simulations of particle dynamics within experimental tokamak magnetic equilibria. In particular, the enhanced capabilities of TAPaS enable seamless coupling with external simulations, provided the metric and equilibrium magnetic field of the external code are known. Coupling TAPaS with the gyro-fluid code FAR3d, the transport and losses of energetic particles in the presence Alfvén eigenmodes (AEs) in DIII-D plasma discharge #159243 were investigated. Detailed analyses of prompt losses with and without collisions were performed. Then, further analysis was performed in the presence of electromagnetic perturbations resulting from AEs activity. The results indicate that, for the energies and the initial conditions considered here, the presence of AEs enhances the particle losses.
H Betar, David Zarzoso, Jacobo Varela, Diego Del-Castillo-Negrete, Luis Garcia, et al.. Transport and losses of energetic particles in tokamaks in the presence of Alfvén activity using the new full orbit TAPaS code coupled to FAR3d. Nuclear Fusion, 2024, ⟨10.1088/1741-4326/ad7c66⟩. ⟨hal-04541528v2⟩
J. Bucalossi, A. Ekedahl, J. Achard, K. Afonin, O. Agullo, et al.. WEST full tungsten operation with an ITER grade divertor. Nuclear Fusion, 2024, 64 (11), pp.112022. ⟨10.1088/1741-4326/ad64e5⟩. ⟨hal-04948518⟩ Plus de détails...
Abstract The mission of WEST (tungsten-W Environment in Steady-state Tokamak) is to explore long pulse operation in a full tungsten (W) environment for preparing next-step fusion devices (ITER and DEMO) with a focus on testing the ITER actively cooled W divertor in tokamak conditions. Following the successful completion of phase 1 (2016-2021), phase 2 started in December 2022 with the lower divertor made entirely of actively cooled ITER-grade tungsten mono-blocks. A boronization prior the first plasma attempt allowed for a smooth startup with the new divertor. Despite the reduced operating window due to tungsten, rapid progress has been made in long pulse operation, resulting in discharges with a pulse length of 100 s and an injected energy of around 300 MJ per discharge. Plasma startup studies were carried out with equatorial boron nitride limiters to compare them with tungsten limiters, while Ion Cyclotron Resonance Heating assisted startup was attempted. High fluence operation in attached regime, which was the main thrust of the first campaigns, already showed the progressive build up of deposits and appearance of dust, impacting the plasma operation as the plasma fluence increased. In total, the cumulated injected energy during the first campaigns reached 43 GJ and the cumulated plasma time exceeded 5 h. Demonstration of controlled X-Point Radiator regime is also reported, opening a promising route for investigating plasma exhaust and plasma-wall interaction issues in more detached regime. This paper summarises the lessons learned from the manufacturing and the first operation of the ITER-grade divertor, describing the progress achieved in optimising operation in a full W environment with a focus on long pulse operation and plasma wall interaction.
J. Bucalossi, A. Ekedahl, J. Achard, K. Afonin, O. Agullo, et al.. WEST full tungsten operation with an ITER grade divertor. Nuclear Fusion, 2024, 64 (11), pp.112022. ⟨10.1088/1741-4326/ad64e5⟩. ⟨hal-04948518⟩
Q. Mao, Umberto d'Ortona, J. Favier. Hydrodynamic coupling of a cilia–mucus system in Herschel–Bulkley flows. Journal of Fluid Mechanics, 2024, 994, pp.A8. ⟨10.1017/jfm.2024.600⟩. ⟨hal-04735292⟩ Plus de détails...
The yield stress and shear thinning properties of mucus are identified as critical for ciliary coordination and mucus transport in human airways. We use here numerical simulations to explore the hydrodynamic coupling of cilia and mucus with these two properties using the Herschel–Bulkley model, in a lattice Boltzmann solver for the fluid flow. Three mucus flow regimes, i.e. a poorly organized regime, a swirly regime, and a fully unidirectional regime, are observed and analysed by parametric studies. We systematically investigate the effects of ciliary density, interaction length, Bingham number and flow index on the mucus flow regime formation. The underlying mechanism of the regime formation is analysed in detail by examining the variation of two physical quantities (polarization and integral length) and the evolution of the flow velocity, viscosity and shear-rate fields. Mucus viscosity is found to be the dominant parameter influencing the regime formation when enhancing the yield stress and shear thinning properties. The present model is able to reproduce the solid body rotation observed in experiments (Loiseau et al. , Nat. Phys. , vol. 16, 2020, pp. 1158–1164). A more precise prediction can be achieved by incorporating non-Newtonian properties into the modelling of mucus as proposed by Gsell et al. ( Sci. Rep. , vol. 10, 2020, 8405).
Q. Mao, Umberto d'Ortona, J. Favier. Hydrodynamic coupling of a cilia–mucus system in Herschel–Bulkley flows. Journal of Fluid Mechanics, 2024, 994, pp.A8. ⟨10.1017/jfm.2024.600⟩. ⟨hal-04735292⟩
Tom Fringand, Loic Mace, Isabelle Cheylan, Marien Lenoir, Julien Favier. Analysis of Fluid–Structure Interaction Mechanisms for a Native Aortic Valve, Patient-Specific Ozaki Procedure, and a Bioprosthetic Valve. Annals of Biomedical Engineering, 2024, 52 (11), pp.3021-3036. ⟨10.1007/s10439-024-03566-1⟩. ⟨hal-04928780⟩ Plus de détails...
The Ozaki procedure is a surgical technique which avoids to implant foreign aortic valve prostheses in human heart, using the patient’s own pericardium. Although this approach has well-identified benefits, it is still a topic of debate in the cardiac surgical community, which prevents its larger use to treat valve pathologies. This is linked to the actual lack of knowledge regarding the dynamics of tissue deformations and surrounding blood flow for this autograft pericardial valve. So far, there is no numerical study examining the coupling between the blood flow characteristics and the Ozaki leaflets dynamics. To fill this gap, we propose here a comprehensive comparison of various performance criteria between a healthy native valve, its pericardium-based counterpart, and a bioprosthetic solution, this is done using a three-dimensional fluid–structure interaction solver. Our findings reveal similar physiological dynamics between the valves but with the emergence of fluttering for the Ozaki leaflets and higher velocity and wall shear stress for the bioprosthetic heart valve.
Tom Fringand, Loic Mace, Isabelle Cheylan, Marien Lenoir, Julien Favier. Analysis of Fluid–Structure Interaction Mechanisms for a Native Aortic Valve, Patient-Specific Ozaki Procedure, and a Bioprosthetic Valve. Annals of Biomedical Engineering, 2024, 52 (11), pp.3021-3036. ⟨10.1007/s10439-024-03566-1⟩. ⟨hal-04928780⟩
L Cappelli, N Fedorczak, E Serre. Semi-analytical modelling of prompt redeposition in a steady-state plasma. Nuclear Fusion, 2024, 64 (10), pp.106028. ⟨10.1088/1741-4326/ad6c5e⟩. ⟨hal-04685227⟩ Plus de détails...
A steady-state, 1D semi-analytical model for prompt redeposition based on the separation between redeposition caused by the electric field in the sheath and redeposition related to gyromotion is here described. The model allows for the estimation of not only the fraction of promptly redeposited flux but also the energy and angular distribution of the non-promptly redeposited population, along with their average charge state. Thus, the temperature and mean parallel-to-B velocity of the non-promptly redeposited flux are also available. The semi-analytical model was validated against equivalent Monte Carlo simulations across a broad range of input parameters. In this paper the eroded material under exam was tungsten (W) for which the code demonstrated consistent agreement with respect to numerical results, within its defined validity limits. The model can theoretically provide a solution for any material, temperature and electron density profile in the sheath, monotonic potential drop profile, and sputtered particles energy and angular distribution at the wall. As such, this code emerges as a potential tool for addressing the boundary redeposition phenomenon in fluid impurity transport simulations.
L Cappelli, N Fedorczak, E Serre. Semi-analytical modelling of prompt redeposition in a steady-state plasma. Nuclear Fusion, 2024, 64 (10), pp.106028. ⟨10.1088/1741-4326/ad6c5e⟩. ⟨hal-04685227⟩
R Varennes, G Dif-Pradalier, P Ghendrih, V Grandgirard, O Panico, et al.. Turbulent relaxation patterns in SOL plasma. Plasma Physics and Controlled Fusion, 2024, 66 (10), pp.105008. ⟨10.1088/1361-6587/ad705c⟩. ⟨hal-04797031⟩ Plus de détails...
Abstract Relaxations of localized over-density in a plane transverse to the magnetic field are numerically investigated under the effect of drift-wave and interchange drives in SOL conditions. Such a controlled departure from thermodynamic equilibrium allows the investigation of fundamental processes at play in cross-field transport. Interchange instabilities generate ballistic outward radial flux with low amplitude zonal flow patterns, whereas drift-wave instabilities result in symmetric radial flux with large amplitude zonal flow patterns. When both instabilities are considered, the combined effects tend to favor drift-waves, leading to a weaker outward flux with larger zonal flow patterns.
R Varennes, G Dif-Pradalier, P Ghendrih, V Grandgirard, O Panico, et al.. Turbulent relaxation patterns in SOL plasma. Plasma Physics and Controlled Fusion, 2024, 66 (10), pp.105008. ⟨10.1088/1361-6587/ad705c⟩. ⟨hal-04797031⟩
I Kudashev, M Scotto D’abusco, A Glasser, E Serre, F Schwander, et al.. Global particle buildup simulations with gas puff scan: application to WEST discharge. Frontiers in Physics, 2024, 12, ⟨10.3389/fphy.2024.1407534⟩. ⟨hal-04703430⟩ Plus de détails...
This paper deals with the distribution of sources, transport, and exhaust of particles in a tokamak. Knowledge and understanding of all the physical phenomena involved in the global particle buildup are necessary to study and predict density regimes and subsequently to develop optimized scenarios for tokamak operation in order to control heat and particle exhaust. Neutral particles and their interactions with plasma are central in this perspective. This paper discusses the impact of varying the intensity of particle fueling in 2D transport simulations of a WEST discharge. Simulations are performed with an updated version of SOLEDGE-HDG that allows a more realistic transport of neutrals using a self-consistent diffusive model based on charge exchange and ionization processes. New code capabilities allow the entire WEST poloidal cross section to be simulated in a realistic configuration for both geometry and the range of control parameters. A gas puff scan illustrates the main features of the sheathlimited, high-recycling, and detached regimes, such as the buildup of the temperature gradient and the pressure drop in the scrape-off layer (SOL), the target temperature falling to 1 eV, and the ionization source moving away from the targets, as well as the particle flux rollover. A crude estimate of wall erosion is also provided, showing the respective role of each plasma wall component in each of these regimes.
I Kudashev, M Scotto D’abusco, A Glasser, E Serre, F Schwander, et al.. Global particle buildup simulations with gas puff scan: application to WEST discharge. Frontiers in Physics, 2024, 12, ⟨10.3389/fphy.2024.1407534⟩. ⟨hal-04703430⟩
Sajad Mozaffari, Jérôme Jacob, Pierre Sagaut. Assessment of Wall Modeling With Adverse Pressure Gradient for High Reynolds Number Separated Flows. Flow, Turbulence and Combustion, 2024, 113 (4), pp.923-945. ⟨10.1007/s10494-024-00562-2⟩. ⟨hal-04921203⟩ Plus de détails...
This paper applies a recently developed approach for modeling turbulence near wall regions within a lattice Boltzmann solver, in combination with a Hybrid RANS/LES turbulence model, to study turbulent separated flows at high Reynolds numbers. To simulate unsteady detached flows on a non-body-fitted Cartesian grid, wall models are employed to estimate the effects of unresolved near-wall turbulence on the overall flow. The article presents the extension of an equilibrium power law wall model to handle adverse pressure gradients and its application in simulating external aerodynamic flows. Hybrid RANS/LES simulations are conducted for two challenging test cases: a 3D NACA-4412 airfoil near stall and a complex Ahmed body configuration. Comparison with a reference simulation involving resolved boundary layers and experimental data demonstrates the strong performance of the wall model, when considering adverse pressure gradients, in simulating turbulent boundary layers under various conditions, ranging from fully attached to mild to high adverse pressure gradients.
Sajad Mozaffari, Jérôme Jacob, Pierre Sagaut. Assessment of Wall Modeling With Adverse Pressure Gradient for High Reynolds Number Separated Flows. Flow, Turbulence and Combustion, 2024, 113 (4), pp.923-945. ⟨10.1007/s10494-024-00562-2⟩. ⟨hal-04921203⟩
Sajad Mozaffari, Shang-Gui Cai, Jérôme Jacob, Pierre Sagaut. Lattice Boltzmann k-ω SST based hybrid RANS/LES simulations of turbulent flows. Journal of Computational Physics, 2024, pp.113269. ⟨10.1016/j.jcp.2024.113269⟩. ⟨hal-04921212⟩ Plus de détails...
High Reynolds number simulations with lattice Boltzmann method (LBM) have been computationally feasible by means of turbulence models for under-resolved physical scales. Hybrid RANS/LES models are efficient alternatives to accurate but computationally expensive LES techniques. This study investigates extensively the hybrid RANS/LES models in the LBM framework for complex wall-bounded turbulent flow simulations on non-body fitting Cartesian grids. The hybridization processes for these models are applied to a widely used two-equation RANS base model, specifically the k-ω SST turbulence model. The functionality of these hybrid models is validated through the simulation of a three-dimensional fully turbulent flow over an airfoil. In addition, they are assessed by performing LBM simulations of flows surrounding a generic vehicle geometry, the Ahmed body, in order to reproduce the solution of a similar simulation by conventional CFD methods and to compare with wind tunnel experimental data. It is found that the near-wall treatments have significant impacts on the local boundary flow structures and possible remedies are also discussed.
Sajad Mozaffari, Shang-Gui Cai, Jérôme Jacob, Pierre Sagaut. Lattice Boltzmann k-ω SST based hybrid RANS/LES simulations of turbulent flows. Journal of Computational Physics, 2024, pp.113269. ⟨10.1016/j.jcp.2024.113269⟩. ⟨hal-04921212⟩
Elena Alekseenko, A.A. Sukhinov, B. Roux. Modeling of multi-fractional suspended particle pathways in a shallow water basin under influence of strong winds. Regional Studies in Marine Science, 2024, 73, pp.103477. ⟨10.1016/j.rsma.2024.103477⟩. ⟨hal-04515082⟩ Plus de détails...
In this study, we investigate the complex dynamics of multi-fractional suspended particle transport in a shallow water basin subjected to strong wind conditions. Our research focuses on understanding the interplay between wind-induced advection and particle settlement, and its implications for sediment redistribution. Through our analysis, we reveal the distinct behaviors of different sediment fractions. Clay particles, constituting the lowest fraction in sediment cores, remain suspended throughout the simulation due to their low settlement velocity, with relatively stable concentrations. Conversely, the dominant fraction, medium silt, is suspended during intense wind events but quickly settles to the bed due to its higher settling velocity. Wind stress exceeding 0.05 Pa triggers particulate matter erosion, leading to its presence in the water column. Additionally, we explore the 2D distribution of sediment characteristics, including thickness, dry density, and mud fraction, to identify areas prone to erosion and deposition. Our findings demonstrate that coastal areas of the Taganrog Bay experienced significant erosion following strong wind events, exhibiting the thinnest sediment thickness and the highest dry bulk density. Deposition areas, characterized by thicker sediment layers and lower dry density, were often found in proximity to erosion zones, indicating the influence of particle resuspension and settlement processes. Furthermore, we analyze the implications of our findings on the vulnerability of specific regions to erosion and deposition. The central part of the sea contains moderately thicker sediment layers with a moderately high mud fraction, representing a zone of fine sediment accumulation. These fine sediments, including fine silt and clay, remain suspended for longer durations and are redistributed over greater distances by currents. Overall, our study provides valuable understanding into the multi-fractional suspended particle pathways and their interaction with strong winds in shallow water basins. The results contribute to a better understanding of sediment dynamics, which has implications for coastal management, environmental monitoring, and the preservation of benthic ecosystems.
Elena Alekseenko, A.A. Sukhinov, B. Roux. Modeling of multi-fractional suspended particle pathways in a shallow water basin under influence of strong winds. Regional Studies in Marine Science, 2024, 73, pp.103477. ⟨10.1016/j.rsma.2024.103477⟩. ⟨hal-04515082⟩
Alix Limoges, Jacques Piazzola, Christophe Yohia, Quentin Rodier, William Bruch, et al.. Study of the Atmospheric Transport of Sea-Spray Aerosols in a Coastal Zone Using a High-Resolution Model. Atmosphere, 2024, 15 (6), pp.702. ⟨10.3390/atmos15060702⟩. ⟨hal-04779475⟩ Plus de détails...
Fine-scale models for the transport of marine aerosols are of great interest for the study of micro-climates and air quality in areas of complex topography, such as in urbanized coastal areas. To this end, the MIO laboratory implemented the Meso-NH model in its LES version over the northwest Mediterranean coastal zone using a recent sea-spray source function. Simulated meteorological parameters and aerosol concentrations are compared to experimental data acquired in the Mediterranean coastal zone in spring 2008 on board the R/V Atalante. Key findings indicate that the large eddy simulation (LES) mode closely matches with the experimental data, enabling an in-depth analysis of the numerical model ability to predict variations in aerosol concentrations. These variations are influenced by different wind directions, which lead to various fetch distances typical of coastal zones.
Alix Limoges, Jacques Piazzola, Christophe Yohia, Quentin Rodier, William Bruch, et al.. Study of the Atmospheric Transport of Sea-Spray Aerosols in a Coastal Zone Using a High-Resolution Model. Atmosphere, 2024, 15 (6), pp.702. ⟨10.3390/atmos15060702⟩. ⟨hal-04779475⟩
Homam Betar, Daniele Del Sarto, A. Ghizzo, F. Brochard, David Zarzoso. A numerical study of electron-magnetohydrodynamics tearing modes in parameter ranges of experimental interest. Physics of Plasmas, 2024, 1st European Conference on Magnetic Reconnection in Plasmas, 31 (5), pp.052117. ⟨10.1063/5.0205061⟩. ⟨hal-04561813⟩ Plus de détails...
We perform a numerical study of the linear dynamics of tearing modes in slab incompressible electron- magnetohydrodynamics (EMHD) by considering some parameter ranges which can be of interest for laboratory plasmas (e.g., helicon devices) or for astrophysics (e.g., solar-wind turbulence). To this purpose several non-ideal effects are simultaneously retained (finite electron inertia, resistivity and electron viscosity) and we make distinction between the dissipation coefficients in the direction parallel and perpendicular to the guide field. We thus identify some new recon- nection regimes, characterized by a departure from the customary monotonic power-law scalings of the growth rates with respect to the non-ideal parameters. The results here presented can provide a useful indication for future studies of EMHD regimes relevant to experiments and for extensions of the EMHD tearing mode modelling to more complete regimes including kinetic effects (e.g., "electron-only" reconnection in kinetic regimes).
Homam Betar, Daniele Del Sarto, A. Ghizzo, F. Brochard, David Zarzoso. A numerical study of electron-magnetohydrodynamics tearing modes in parameter ranges of experimental interest. Physics of Plasmas, 2024, 1st European Conference on Magnetic Reconnection in Plasmas, 31 (5), pp.052117. ⟨10.1063/5.0205061⟩. ⟨hal-04561813⟩
Louis Lamérand, Didier Auroux, Philippe Ghendrih, Francesca Rapetti, Eric Serre. Inverse problem for determining free parameters of a reduced turbulent transport model for tokamak plasma. Advances in Computational Mathematics, 2024, 50 (3), pp.39. ⟨10.1007/s10444-024-10135-6⟩. ⟨hal-04569449⟩ Plus de détails...
Two-dimensional transport codes for the simulation of tokamak plasma are reduced version of full 3D fluid models where plasma turbulence has been smoothed out by averaging. One of the main issues nowadays in such reduced models is the accurate modelling of transverse transport fluxes resulting from the averaging of stresses due to fluctuations. Transverse fluxes are assumed driven by local gradients, and characterised by ad hoc diffusion coefficients (turbulent eddy viscosity), adjusted by hand in order to match numerical solutions with experimental measurements. However, these coefficients vary substantially depending on the machine used, type of experiment and even the location inside the device, reducing drastically the predictive capabilities of these codes for a new configuration. To mitigate this issue, we recently proposed an innovative path for fusion plasma simulations by adding two supplementary transport equations to the mean-flow system for turbulence characteristic variables (here the turbulent kinetic energy k and its dissipation rate ) to estimate the turbulent eddy viscosity. The remaining free parameters are more driven by the underlying transport physics and hence vary much less between machines and between locations in the plasma. In this paper, as a proof of concept, we explore, on the basis of digital twin experiments, the efficiency of the assimilation of data to fix these free parameters involved in the transverse turbulent transport models in the set of averaged equations in 2D.
Louis Lamérand, Didier Auroux, Philippe Ghendrih, Francesca Rapetti, Eric Serre. Inverse problem for determining free parameters of a reduced turbulent transport model for tokamak plasma. Advances in Computational Mathematics, 2024, 50 (3), pp.39. ⟨10.1007/s10444-024-10135-6⟩. ⟨hal-04569449⟩
Franck Corset, Mitra Fouladirad, Christian Paroissin. Imperfect and worse than old maintenances for a gamma degradation process. Applied Stochastic Models in Business and Industry, 2024, ENBIS 2022, 40 (3), pp.620-639. ⟨10.1002/asmb.2849⟩. ⟨hal-04462980⟩ Plus de détails...
This article considers a condition‐based maintenance for a system subject to deterioration. The deterioration is modeled by a non‐homogeneous gamma process, more precisely the gamma process and the preventive maintenance are imperfect or worse than old. The corrective maintenance actions are as good as new. The maintenance efficiency or non‐efficiency parameters as well as the deterioration parameters are considered to be unknown. The monitoring data under consideration give indirect information on the maintenance parameters. Therefore, an expected maximum algorithm is applied for parameter estimation.
Franck Corset, Mitra Fouladirad, Christian Paroissin. Imperfect and worse than old maintenances for a gamma degradation process. Applied Stochastic Models in Business and Industry, 2024, ENBIS 2022, 40 (3), pp.620-639. ⟨10.1002/asmb.2849⟩. ⟨hal-04462980⟩
Journal: Applied Stochastic Models in Business and Industry
Mathieu Creyssels, Denis Martinand. Stability Analysis of Sheared Thermal Boundary Layers and its Implication for Modelling Turbulent Rayleigh-Bénard Convection. European Journal of Mechanics - B/Fluids, 2024, 105, pp.97-103. ⟨10.1016/j.euromechflu.2023.12.008⟩. ⟨hal-03877608v2⟩ Plus de détails...
Predicting the heat flux through a horizontal layer of fluid confined between a hot bottom plate and a cold top one has always spurred theoretical, numerical and experimental work on Rayleigh–Bénard convection. Customarily, the Nusselt number (the heat flux in non-dimensional form) has been modelled in the form of one or several power-laws of three parameters, the Rayleigh, Prandtl and Reynolds numbers. Quantifying the large-scale flow that spontaneously develops in a turbulent Rayleigh–Bénard cell, the Reynolds number, unlike the Rayleigh and Prandtl numbers, is not a control parameter strictly speaking and, depending on the model, is sought as another power-law or introduced as an external input. Whereas balancing the different transport mechanisms can predict the exponents in these power laws, experimental and numerical results are required to adjust the various prefactors. The early and simple model of Malkus [1] and Howard [2] assumed that the value of the Nusselt number could be directly deduced from the marginal stability of the two sheared thermal boundary layers along the upper and lower plates, interacting via the large-scale flow. Maintaining this simplicity, this work shows that in the classical regime of turbulent convection, considering the linear critical conditions of absolute (as opposed to convective) thermo-convective instabilities alleviates the flaws of the original model. Revisiting available Direct Numerical Simulations from which a Reynolds number can be unambiguously extracted, the present approach then yields the Nusselt number as a function of the Rayleigh and Prandtl numbers agreeing well with the numerical results.
Mathieu Creyssels, Denis Martinand. Stability Analysis of Sheared Thermal Boundary Layers and its Implication for Modelling Turbulent Rayleigh-Bénard Convection. European Journal of Mechanics - B/Fluids, 2024, 105, pp.97-103. ⟨10.1016/j.euromechflu.2023.12.008⟩. ⟨hal-03877608v2⟩
Uwe Ehrenstein. Generalization to differential–algebraic equations of Lyapunov–Schmidt type reduction at Hopf bifurcations. Communications in Nonlinear Science and Numerical Simulation, 2024, 131, pp.107833. ⟨10.1016/j.cnsns.2024.107833⟩. ⟨hal-04408097⟩ Plus de détails...
The Lyapunov-Schmidt procedure, a well-known and powerful tool for the local reduction of nonlinear systems at bifurcation points or for ordinary differential equations (ODEs) at Hopf bifurcations, is extended to the context of strangeness-free differential-algebraic equations (DAEs), by generalizing the comprehensive presentation of the method for ODEs provided in the classical textbook by Golubitsky and Schaeffer [Applied mathematical sciences, {\bf 51}, Springer (1985)]. The appropriate setting in the context of DAEs at Hopf bifurcations is first detailed, introducing suitable operators and addressing the question of appropriate numerical algorithms for their construction as well. The different steps of the reduction procedure are carefully reinterpreted in the light of the DAE context and detailed formulas are provided for systematic and rational construction of the bifurcating local periodic solution, whose stability is shown, likely to the ODE context, to be predicted by the reduced equations. As an illustrative example, a classical DAE model for an electric power system is considered, exhibiting both supercritical and subcritical Hopf bifurcations, demonstrating the prediction capability of the reduced system with regard to the global dynamics.
Uwe Ehrenstein. Generalization to differential–algebraic equations of Lyapunov–Schmidt type reduction at Hopf bifurcations. Communications in Nonlinear Science and Numerical Simulation, 2024, 131, pp.107833. ⟨10.1016/j.cnsns.2024.107833⟩. ⟨hal-04408097⟩
Journal: Communications in Nonlinear Science and Numerical Simulation
Jingtao Ma, Lincheng Xu, Jérôme Jacob, Eric Serre, Pierre Sagaut. An averaged mass correction scheme for the simulation of high subsonic turbulent internal flows using a lattice Boltzmann method. Physics of Fluids, 2024, 36 (3), ⟨10.1063/5.0192360⟩. ⟨hal-04514161⟩ Plus de détails...
This paper addresses the simulation of internal high-speed turbulent compressible flows using lattice Boltzmann method (LBM) when it is coupled with the immersed boundary method for non-body-fitted meshes. The focus is made here on the mass leakage issue. The recent LBM pressure-based algorithm [Farag et al. Phys. Fluids 32, 066106 (2020)] has shown its superiority on classical density-based algorithm to simulate high-speed compressible flows. Following our previous theoretical work on incompressible flows [Xu et al. Phys. Fluids 34, 065113 (2022)], we propose an averaged mass correction technique to mitigate mass leakage when simulating high-Mach-number compressible flows. It is adapted to deal here with a density, which is decoupled from the zero-moment definition. The simulations focus on two generic but canonical configurations of more complex industrial devices, the straight channel at different angles of inclination at Mach numbers (Ma) ranging from 0.2 to 0.8, and the National Aeronautics and Space Administration Glenn S-duct at Ma = 0.6. The present results show that mass leakage can be a critical issue for the accuracy of the solution and that the proposed correction technique effectively mitigates it and leads to significant improvements in the prediction of the solution.
Jingtao Ma, Lincheng Xu, Jérôme Jacob, Eric Serre, Pierre Sagaut. An averaged mass correction scheme for the simulation of high subsonic turbulent internal flows using a lattice Boltzmann method. Physics of Fluids, 2024, 36 (3), ⟨10.1063/5.0192360⟩. ⟨hal-04514161⟩
Raffael Düll, Hugo Bufferand, Eric Serre, Guido Ciraolo, Virginia Quadri, et al.. Introducing electromagnetic effects in Soledge3X. Contributions to Plasma Physics, 2024, pp.e202300147. ⟨10.1002/ctpp.202300147⟩. ⟨hal-04474339⟩ Plus de détails...
In the pedestal region, electromagnetic effects affect the evolution of micro‐instabilities and plasma turbulence. The transport code Soledge3X developed by the CEA offers an efficient framework for turbulent 3D simulation on an electrostatic model with a fixed magnetic field. The physical accuracy of the model is improved with electromagnetic induction, driven by the local value of the parallel component of the electromagnetic vector potential , known from Ampère's law. It is solved implicitly in a coupled system with the vorticity equation on the electric potential . The consequence is a basic electromagnetic behavior in the form of shear Alfvén waves. A finite electron mass prevents unphysical speeds but requires solving for the time evolution of the parallel current density in the generalized Ohm's law. This term can be analytically included with little computational overhead in the system on and and improves its numerical condition, facilitating the iterative solving procedure. Simulations on a periodic slab case let us observe the predicted bifurcation of the wave propagation speed between the Alfvén wave and the electron thermal wave speeds for varying perpendicular wavenumbers. The first results on a circular geometry with a limiter attest to the feasibility of turbulent electromagnetic scenarios.
Raffael Düll, Hugo Bufferand, Eric Serre, Guido Ciraolo, Virginia Quadri, et al.. Introducing electromagnetic effects in Soledge3X. Contributions to Plasma Physics, 2024, pp.e202300147. ⟨10.1002/ctpp.202300147⟩. ⟨hal-04474339⟩
Frédéric Schwander, Eric Serre, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih. Global fluid simulations of edge plasma turbulence in tokamaks: a review. Computers and Fluids, 2024, 270, pp.106141. ⟨10.1016/j.compfluid.2023.106141⟩. ⟨hal-04352255⟩ Plus de détails...
With ITER, the largest tokamak ever built, and the growing number of fusion energy startups in the world, the need for numerical simulations has never been more crucial to progress towards the successful operation of fusion reactors. From fundamental plasma physics to engineering, a hierarchy of models exists from high-fidelity (gyro-)kinetic models in (5D) 6D to 0D fluid transport models. In this paper, we review the state-of-the-art of 3D turbulence fluid simulations in edge tokamak configurations. The widely used drift-reduced Braginskii equations are introduced together with the dedicated boundary conditions modelling plasma wall interactions. If until recently most of the models were focused on electrostatic turbulence driven by interchange-like instabilities, in recent years models have incorporated electromagnetic effects allowing fluctuations of the magnetic field. Specific features of the edge plasma configurations, which make these equations specially challenging to resolve and stressful for the numerical methods, are detailed. In particular, the strong anisotropy of the flow as well as the complex geometric characteristics lead to the development of dedicated discretization schemes and meshing, which are implemented in state-of-the-art codes reviewed here. It appears that the latter can be differentiated by their mesh construction as well by the manner in which they handle parallel gradients (aligned or not along the magnetic field). The review shows that no consensus on the optimal combination between meshing and discretization schemes, if it exists, has been found. Finally, examples of recent achievements show that 3D turbulence simulations of medium-sized tokamaks are currently achievable, but that ITERsize tokamaks and thermonuclear plasmas still require significant progress.
Frédéric Schwander, Eric Serre, Hugo Bufferand, Guido Ciraolo, Philippe Ghendrih. Global fluid simulations of edge plasma turbulence in tokamaks: a review. Computers and Fluids, 2024, 270, pp.106141. ⟨10.1016/j.compfluid.2023.106141⟩. ⟨hal-04352255⟩
Ivan Kudashev, Anna Medvedeva Glasser, Manuel Scotto D’abusco, Eric Serre. Impact of Variable Perpendicular Transport Coefficients in WEST Simulations Using SolEdge-HDG. IEEE Transactions on Plasma Science, 2024, pp.1-6. ⟨10.1109/tps.2024.3384031⟩. ⟨hal-04552343⟩ Plus de détails...
Plasma–wall interaction is one of the key research topics on the way to controlled fusion. To study the best operational designs with reduced heat and particle fluxes onto tokamak plasma facing components (PFCs) comprehensive plasma simulations are required. A recent implementation of a hybridized discontinuous Galerkin scheme into a new version of SolEdge code has the advantage of using magnetic equilibrium-free mesh. This allows us to conduct pioneering 2-D transport simulations of a full discharge in the WEST tokamak. In this work, we implemented plasma transport coefficients as functions of coordinate in the poloidal plane and neutral diffusion as a function of neutral mean free path. Moreover, the perpendicular convection flux terms were added to the code. Using the new features, a few test cases were investigated. The influence of nonconstant transport coefficients on the simulated particle and heat fluxes onto the WEST tokamak PFCs are demonstrated.
Ivan Kudashev, Anna Medvedeva Glasser, Manuel Scotto D’abusco, Eric Serre. Impact of Variable Perpendicular Transport Coefficients in WEST Simulations Using SolEdge-HDG. IEEE Transactions on Plasma Science, 2024, pp.1-6. ⟨10.1109/tps.2024.3384031⟩. ⟨hal-04552343⟩
Jeronimo Garcia, Yevgen Kazakov, Rui Coelho, Mykola Dreval, Elena de la Luna, et al.. Stable Deuterium-Tritium plasmas with improved confinement in the presence of energetic-ion instabilities. Nature Communications, 2024, 15 (1), pp.7846. ⟨10.1038/s41467-024-52182-z⟩. ⟨hal-04948995⟩ Plus de détails...
Providing stable and clean energy sources is a necessity for the increasing demands of humanity. Energy produced by Deuterium (D) and Tritium (T) fusion reactions, in particular in tokamaks, is a promising path towards that goal. However, there is little experience with plasmas formed by D-T mixtures, since most of the experiments are currently performed in pure D. After more than 20 years, the Joint European Torus (JET) has carried out new D-T experiments with the aim of exploring some of the unique characteristics expected in future fusion reactors, such as the presence of highly energetic ions in low plasma rotation conditions. A new stable, high confinement and impurity-free D-T regime, with reduction of energy losses with respect to D, has been found. Multiscale physics mechanisms critically determine the thermal confinement. These crucial achievements importantly contribute to the establishment of fusion energy generation as an alternative to fossil fuels.
Jeronimo Garcia, Yevgen Kazakov, Rui Coelho, Mykola Dreval, Elena de la Luna, et al.. Stable Deuterium-Tritium plasmas with improved confinement in the presence of energetic-ion instabilities. Nature Communications, 2024, 15 (1), pp.7846. ⟨10.1038/s41467-024-52182-z⟩. ⟨hal-04948995⟩
Hassan Hachem, Hai Canh Vu, Mitra Fouladirad. Different methods for RUL prediction considering sensor degradation. Reliability Engineering and System Safety, 2023, 243, pp.109897. ⟨10.1016/j.ress.2023.109897⟩. ⟨hal-04543787⟩ Plus de détails...
Predicting the Remaining Useful Lifetime (RUL) of a system has become one of the primary goals of engineering and reliability researchers. RUL prediction is based on the measurement data collected from sensors (e.g. vibration data, temperature data). The collected data is may be inaccurate owing to sensor problems. These problems are often ignored or modeled by a Gaussian noise in most previous work. However, due to various operation circumstances and the aging impact, the sensor itself will ultimately deteriorate and its performance will deteriorate. The Gaussian noise with a constant mean is then not appropriate to fully capture the sensor degradation. In this context, this study focuses on predicting the RUL considering the sensor degradation. For this purpose, a joint model of sensor degradation and system degradation is firstly developed. In this model, the sensor degradation is modeled by Wiener and Gamma processes instead of Gaussian noise. Then, different estimation methods based on the particle filter, a popular model-based technique, were proposed to predict the RUL based on the joint degradation model. To study the performances of our methods, numerical analyzes were carried out. The obtained results confirm the performance and advantages of the proposed methods.
Hassan Hachem, Hai Canh Vu, Mitra Fouladirad. Different methods for RUL prediction considering sensor degradation. Reliability Engineering and System Safety, 2023, 243, pp.109897. ⟨10.1016/j.ress.2023.109897⟩. ⟨hal-04543787⟩
Journal: Reliability Engineering and System Safety
L. Cappelli, J. Guterl, N. Fedorczak, D.L. Rudakov, G. Sinclair, et al.. Model validation of tungsten erosion and redeposition properties using biased tungsten samples on DiMES. Nuclear Materials and Energy, 2023, 37, pp.101551. ⟨10.1016/j.nme.2023.101551⟩. ⟨hal-04546765⟩ Plus de détails...
An experiment was performed in the DIII-D lower divertor to validate numerical SOL tungsten (W) impurity erosion and redeposition simulations against experimental data. The net and gross erosion of W were calculated as a function of the voltage (or bias) applied to the exposed material. Five samples were inserted into the DIII-D lower divertor using the Divertor Material Evaluation System (DiMES) manipulator and exposed to constant L-mode attached plasma conditions. Each sample was partially coated with W. During plasma shots, samples were biased with respect to the machine vessel ground, ranging from −60 V to 25 V. The ERO2.0 code was used to numerically simulate the experiment aiming to compare the numerical results with experimental measures. A good agreement is found between estimated and measured tungsten erosion at least for negative biases.
L. Cappelli, J. Guterl, N. Fedorczak, D.L. Rudakov, G. Sinclair, et al.. Model validation of tungsten erosion and redeposition properties using biased tungsten samples on DiMES. Nuclear Materials and Energy, 2023, 37, pp.101551. ⟨10.1016/j.nme.2023.101551⟩. ⟨hal-04546765⟩
M Raghunathan, Y Marandet, H Bufferand, G Ciraolo, Ph Ghendrih, et al.. Corrigendum: Multi-temperature generalized Zhdanov closure for scrape-off layer/edge applications (2022 Plasma Phys. Control. Fusion 64 045005). Plasma Physics and Controlled Fusion, 2023, 66 (1), pp.019501. ⟨10.1088/1361-6587/ad05d5⟩. ⟨hal-04948130⟩ Plus de détails...
Jingqi Zhang, Mitra Fouladirad, Nikolaos Limnios. A Semi-Markov Model with Geometric Renewal Processes. Methodology and Computing in Applied Probability, 2023, 25 (4), pp.85. ⟨10.1007/s11009-023-10060-z⟩. ⟨hal-04543367⟩ Plus de détails...
We consider a repairable system modeled by a semi-Markov process (SMP), where we include a geometric renewal process for system degradation upon repair, and replacement strategies for non-repairable failure or upon N repairs. First Pérez-Ocón and Torres-Castro studied this system (Pérez-Ocón and Torres-Castro in Appl Stoch Model Bus Ind 18(2):157–170, 2002) and proposed availability calculation using the Laplace Transform. In our work, we consider an extended state space for up and down times separately. This allows us to leverage the standard theory for SMP to obtain all reliability related measurements such as reliability, availability (point and steady-state), mean times and rate of occurrence of failures of the system with general initial law. We proceed with a convolution algebra, which allows us to obtain final closed form formulas for the above measurements. Finally, numerical examples are given to illustrate the methodology.
Jingqi Zhang, Mitra Fouladirad, Nikolaos Limnios. A Semi-Markov Model with Geometric Renewal Processes. Methodology and Computing in Applied Probability, 2023, 25 (4), pp.85. ⟨10.1007/s11009-023-10060-z⟩. ⟨hal-04543367⟩
Journal: Methodology and Computing in Applied Probability
Alex Karagrigoriou, Ioannis Mavrogiannis, Georgia Papasotiriou, Ilia Vonta. An Exponentiality Test of Fit Based on a Tail Characterization against Heavy and Light-Tailed Alternatives. Risks, 2023, 11 (10), pp.169. ⟨10.3390/risks11100169⟩. ⟨hal-04543899⟩ Plus de détails...
Log-concavity and log-convexity play a key role in various scientific fields, especially in those where the distinction between exponential and non-exponential distributions is necessary for inferential purposes. In the present study, we introduce a testing procedure for the tail part of a distribution which can be used for the distinction between exponential and non-exponential distributions. The conspiracy and catastrophe principles are initially used to establish a characterization of (the tail part of) the exponential distribution, which is one of the main contributions of the present work, leading the way for the construction of the new test of fit. The proposed test and its implementation are thoroughly discussed, and an extended simulation study has been undertaken to clarify issues related to its implementation and explore the extent of its capabilities. A real data case is also investigated.
Alex Karagrigoriou, Ioannis Mavrogiannis, Georgia Papasotiriou, Ilia Vonta. An Exponentiality Test of Fit Based on a Tail Characterization against Heavy and Light-Tailed Alternatives. Risks, 2023, 11 (10), pp.169. ⟨10.3390/risks11100169⟩. ⟨hal-04543899⟩
Mathis Pasquier, Stéphane Jay, Jérôme Jacob, Pierre Sagaut. A Lattice-Boltzmann-Based Modelling Chain for Traffic-Related Atmospheric Pollutant Dispersion at the Local Urban Scale. Building and Environment, 2023, 242, pp.110562. ⟨10.1016/j.buildenv.2023.110562⟩. ⟨hal-04190005⟩ Plus de détails...
Urban traffic-related air pollution is a major source of environmental and health damage and is difficult to quantify due to its inherent physical complexity. We construct a CFD-based simulation framework coupling an efficient numerical method for turbulent fluid flows with a microscopic traffic model and an emissions model to simulate road transport pollutant dispersion at the urban microscale. We improve the open-source Lattice-Boltzmann based CFD software OpenLB to overcome its original stability deficiencies for high Reynolds number flows. A stable recursive regularization procedure with a double distribution function approach is proposed to solve an advection diffusion equation for passive scalar transport at high Reynolds number. The code is successfully validated on three reference cases of increasing complexity and the traffic model SUMO along with a physical engine emissions model are coupled with OpenLB to simulate traffic-induced pollution from a road network in a realistic complex geometry. Transient flow features are analysed and the time-averaged concentration levels in different neighbourhoods of the considered geometry are evaluated: high concentration levels are observed close to the streets but also inside specific building infrastructures due to complex wind dynamics. Analyses of altitudinal concentration variations show that flow recirculations located close to traffic lights can drive pollutant over the buildings and increase concentration levels inside inner courtyards. Time-averaged concentration maps are constructed using both spatially uniform and non-uniform line sources and it is shown that using uniform sources leads to up to 20% local concentration overestimations inside the urban canopy.
Mathis Pasquier, Stéphane Jay, Jérôme Jacob, Pierre Sagaut. A Lattice-Boltzmann-Based Modelling Chain for Traffic-Related Atmospheric Pollutant Dispersion at the Local Urban Scale. Building and Environment, 2023, 242, pp.110562. ⟨10.1016/j.buildenv.2023.110562⟩. ⟨hal-04190005⟩
Isabelle Cheylan, Tom Fringand, Jérôme Jacob, Julien Favier. Analysis of the immersed boundary method for turbulent fluid-structure interaction with Lattice Boltzmann method. Journal of Computational Physics, 2023, 492, pp.112418. ⟨10.1016/j.jcp.2023.112418⟩. ⟨hal-04543923⟩ Plus de détails...
L. Cappelli, N. Fedorczak, J. P. Gunn, S. Di Genova, J. Guterl, et al.. Study of the erosion and redeposition of W considering the kinetic energy distribution of incident ions through a semi-analytical model. Plasma Physics and Controlled Fusion, 2023, 65 (9), pp.095001. ⟨10.1088/1361-6587/ace282⟩. ⟨hal-04190861⟩ Plus de détails...
In today’s nuclear fusion devices, erosion of high-Z metallic plasma-facing materials (PFMs) is mainly caused by physical sputtering. That is, by the exchange of energy between plasma ions and the atoms in the walls. In most of the numerical codes currently in use impinging plasma is approximated as a fluid. By averaging the incident particles’ energy distribution the high-energy population of the eroded material is underestimated. For heavy materials such as W, high-energy eroded particles tend to ionize far from the wall and they are less affected by the sheath electric field hence, not being attracted back to the wall, they have a higher chance to contaminate the core plasma. This could in turn result in an underestimation of the net erosion sources. In this work, a semi-analytical model was developed to include the energy distribution of the incident particles. Then, by Monte Carlo method, the net erosion of tungsten from a smooth PFM was calculated. The results show that the kinetic description in energy is important only for incident particles ionized once. For instance, it is particularly important for plasma ions such as Deuterium. It is seen that Deuterium contribution to the W net sources is not always negligible if compared to light impurities or to tungsten self-sputtering in the range of plasma parameters tested. Finally, results show that the difference between the fluid and kinetic models becomes more pronounced for high-screening plasma conditions.
L. Cappelli, N. Fedorczak, J. P. Gunn, S. Di Genova, J. Guterl, et al.. Study of the erosion and redeposition of W considering the kinetic energy distribution of incident ions through a semi-analytical model. Plasma Physics and Controlled Fusion, 2023, 65 (9), pp.095001. ⟨10.1088/1361-6587/ace282⟩. ⟨hal-04190861⟩
Chenglei Wang, Simon Gsell, Umberto d'Ortona, Julien Favier. Generalized-Newtonian fluid transport by an instability-driven filament. Journal of Fluid Mechanics, 2023, 965, pp.A6. ⟨10.1017/jfm.2023.381⟩. ⟨hal-04544010⟩ Plus de détails...
Cilia are micro-scale hair-like organelles. They can exhibit self-sustained oscillations which play crucial roles in flow transport or locomotion. Recent studies have shown that these oscillations can spontaneously emerge from dynamic instability triggered by internal stresses via a Hopf bifurcation. However, the flow transport induced by an instability-driven cilium still remains unclear, especially when the fluid is non-Newtonian. This study aims at bridging these gaps. Specifically, the cilium is modelled as an elastic filament, and its internal actuation is represented by a constant follower force imposed at its tip. Three generalized Newtonian behaviours are considered, i.e. the shear-thinning, Newtonian and shear-thickening behaviours. Effects of four key factors, including the filament zero-stress shape, Reynolds number ( $Re$ ), follower-force magnitude and fluid rheology, on the filament dynamics, fluid dynamics and flow transport are explored through direct numerical simulation at $Re$ of 0.04 to 5 and through a scaling analysis at $Re \approx 0$ . The results reveal that even though it is expected that inertia vanishes at $Re \ll 1$ , inertial forces do alter the filament dynamics and deteriorate the flow transport at $Re\ge 0.04$ . Regardless of $Re$ , the flow transport can be improved when the flow is shear thinning or when the follower force increases. Furthermore, a linear stability analysis is performed, and the variation of the filament beating frequency, which is closely correlated with the filament dynamics and flow transport, can be predicted.
Chenglei Wang, Simon Gsell, Umberto d'Ortona, Julien Favier. Generalized-Newtonian fluid transport by an instability-driven filament. Journal of Fluid Mechanics, 2023, 965, pp.A6. ⟨10.1017/jfm.2023.381⟩. ⟨hal-04544010⟩
E.V. Kuidjo Kuidjo, M.G. Rodio, R. Abgrall, P. Sagaut. Comparison of bubbles interaction mechanisms of two-group Interfacial Area Transport Equation model. International Journal of Multiphase Flow, 2023, 163, pp.104399. ⟨10.1016/j.ijmultiphaseflow.2023.104399⟩. ⟨cea-04483130⟩ Plus de détails...
This work deals with 3D simulations of complex bubbly, cap-bubbly and churn regimes exhibiting bubbles of different shapes and with broad bubble size distribution. The first contribution of this work is to investigate and compare several bubble interaction mechanisms of coalescence and fragmentation for the 2-Group Interfacial Area Transport Equation (IATE) model. For two of these models, this is the first time their performances are assessed within a CFD code. The second contribution is to propose and assess a novel model of fragmentation and coalescence. Finally, a validation versus experimental data on three different configurations and three different regimes is performed. In particular, the interaction mechanisms are analysed for one specific regime. The implementation of the two-group IATE model has been systematically performed in the 3D NEPTUNE CFD code.
E.V. Kuidjo Kuidjo, M.G. Rodio, R. Abgrall, P. Sagaut. Comparison of bubbles interaction mechanisms of two-group Interfacial Area Transport Equation model. International Journal of Multiphase Flow, 2023, 163, pp.104399. ⟨10.1016/j.ijmultiphaseflow.2023.104399⟩. ⟨cea-04483130⟩
Shang-Gui Cai, Jérôme Jacob, Pierre Sagaut. Immersed boundary based near-wall modeling for large eddy simulation of turbulent wall-bounded flow. Computers and Fluids, 2023, 259, pp.105893. ⟨10.1016/j.compfluid.2023.105893⟩. ⟨hal-04543910⟩ Plus de détails...
Shang-Gui Cai, Jérôme Jacob, Pierre Sagaut. Immersed boundary based near-wall modeling for large eddy simulation of turbulent wall-bounded flow. Computers and Fluids, 2023, 259, pp.105893. ⟨10.1016/j.compfluid.2023.105893⟩. ⟨hal-04543910⟩
E.V. Kuidjo Kuidjo, M.G. Rodio, R. Abgrall, P. Sagaut. Comparison of bubbles interaction mechanisms of two-group Interfacial Area Transport Equation model. International Journal of Multiphase Flow, 2023, 163, pp.104399. ⟨10.1016/j.ijmultiphaseflow.2023.104399⟩. ⟨hal-04543708⟩ Plus de détails...
This work deals with 3D simulations of complex bubbly, cap-bubbly and churn regimes exhibiting bubbles of different shapes and with broad bubble size distribution. The first contribution of this work is to investigate and compare several bubble interaction mechanisms of coalescence and fragmentation for the 2-Group Interfacial Area Transport Equation (IATE) model. For two of these models, this is the first time their performances are assessed within a CFD code. The second contribution is to propose and assess a novel model of fragmentation and coalescence. Finally, a validation versus experimental data on three different configurations and three different regimes is performed. In particular, the interaction mechanisms are analysed for one specific regime. The implementation of the two-group IATE model has been systematically performed in the 3D NEPTUNE CFD code.
E.V. Kuidjo Kuidjo, M.G. Rodio, R. Abgrall, P. Sagaut. Comparison of bubbles interaction mechanisms of two-group Interfacial Area Transport Equation model. International Journal of Multiphase Flow, 2023, 163, pp.104399. ⟨10.1016/j.ijmultiphaseflow.2023.104399⟩. ⟨hal-04543708⟩
Minh Nguyen, Jean-François Boussuge, Pierre Sagaut, Juan-Carlos Larroya-Huguet. Large eddy simulation of a row of impinging jets with upstream crossflow using the lattice Boltzmann method. International Journal of Heat and Mass Transfer, 2023, 212, pp.124256. ⟨10.1016/j.ijheatmasstransfer.2023.124256⟩. ⟨hal-04546755⟩ Plus de détails...
Large eddy simulations of a row of seven jets emerging from a perforated pipe and impinging on a flat heated plate were carried out using a compressible hybrid thermal lattice Boltzmann solver. The average Reynolds number of the emerging jets was , with an exit-to-plate distance of 3 jet diameters. Two levels of upstream crossflow were simulated: one with weak cross flow, with a velocity ratio of , and one with strong cross flow, with a velocity ratio of . The flow field and heat transfer statistics were validated against experimental PIV and infrared thermography data from a recent study, showing good agreement. The effect of varying the Mach number on the wall heat transfer was subsequently tested. It was found that an increased Mach number lead to an increased value of the Nusselt number near the stagnation points.
Minh Nguyen, Jean-François Boussuge, Pierre Sagaut, Juan-Carlos Larroya-Huguet. Large eddy simulation of a row of impinging jets with upstream crossflow using the lattice Boltzmann method. International Journal of Heat and Mass Transfer, 2023, 212, pp.124256. ⟨10.1016/j.ijheatmasstransfer.2023.124256⟩. ⟨hal-04546755⟩
Journal: International Journal of Heat and Mass Transfer
G. Farag, P. Boivin, P. Sagaut. Linear interaction approximation for shock/disturbance interaction in a Noble–Abel stiffened gas. Shock Waves, 2023, ⟨10.1007/s00193-023-01131-8⟩. ⟨hal-04097657⟩ Plus de détails...
When departure from the ideal gas equation of state is considered, the Noble-Abel stiffened gas model is an appealing and versatile candidate due to its simple form. The Linear Interaction Approximation formalism is extended to consider non-ideal gas effects introduced by this equation of state. Kovásznay decomposition and adequate definition of the energy of disturbances are provided in the context of this equation of state. Changes with respect to ideal gas are investigated on transfer functions, critical angle and compression factor. Those differences yield concrete effects on the damping and transfer of fluctuations across shock waves. Those changes are further illustrated by considering the interaction of an entropy spot with a Mach 3 stationary shock wave.
G. Farag, P. Boivin, P. Sagaut. Linear interaction approximation for shock/disturbance interaction in a Noble–Abel stiffened gas. Shock Waves, 2023, ⟨10.1007/s00193-023-01131-8⟩. ⟨hal-04097657⟩
Jérémie Labasse, Uwe Ehrenstein, Guillaume Fasse, Frédéric Hauville. Thrust scaling for a large-amplitude heaving and pitching foil with application to cycloidal propulsion. Ocean Engineering, 2023, 275, pp.114169. ⟨10.1016/j.oceaneng.2023.114169⟩. ⟨hal-04032117⟩ Plus de détails...
A numerical solution procedure using the mesh-superposition approach, known as the Chimera method, together with the OpenFOAM toolbox environment is used to compute the forces generated by large amplitude heaving and pitching foil. The possibility of fitting thrust prediction laws, based on classical potential flow theories, with the numerically computed forces is explored, for a Reynolds number of 5 10 4. It is shown, first for a pure heaving motion and subsequently by adding a harmonic pitching motion, that theoretical scaling may be fitted to numerical time-averaged thrust data, even in the case of large amplitude motions. The thrust-prediction law is shown to still apply to pitching-rotating motions, such as those of blades in cycloidal propulsion devices, the mean pressure correction due to the additional surging motion being small. The synchronized rotation-pitching of three foils typical of a cross-flow propeller configuration is addressed as well. The numerical global thrust results are shown to be in general agreement with the theoretical prediction, but also with blade-embedded load cell measurements for an experimental device developed by the French Naval Academy Research Institute.
Jérémie Labasse, Uwe Ehrenstein, Guillaume Fasse, Frédéric Hauville. Thrust scaling for a large-amplitude heaving and pitching foil with application to cycloidal propulsion. Ocean Engineering, 2023, 275, pp.114169. ⟨10.1016/j.oceaneng.2023.114169⟩. ⟨hal-04032117⟩
Hasan Misaii, Mitra Fouladirad, Firoozeh Haghighi. Optimal task-driven time-dependent covariate-based maintenance policy. Journal of Computational and Applied Mathematics, 2023, pp.115315. ⟨10.1016/j.cam.2023.115315⟩. ⟨hal-04162527⟩ Plus de détails...
Heesik Yoo, Gauthier Wissocq, J. Jacob, J. Favier, Pierre Sagaut. Compressible lattice Boltzmann method with rotating overset grids. Physical Review E , 2023, 107 (4), pp.045306. ⟨10.1103/PhysRevE.107.045306⟩. ⟨hal-04921190⟩ Plus de détails...
Alexandre Di-Marco, Jerome Jacob, Pierre Sagaut. Unsteady characteristics of pressure and swirl distortion in helicopter intake: A lattice Boltzmann method approach. Aerospace Science and Technology, 2023, 138, pp.108333. ⟨10.1016/j.ast.2023.108333⟩. ⟨hal-04543807⟩ Plus de détails...
The present paper focuses on the analysis of the unsteady characteristics of pressure and swirl distortion and their relationship inside a complex air intake, including a plenum chamber, using Large-Eddy Simulation based on the lattice Boltzmann method (LBM). The steady-state analysis of the pressure field and swirl angle in the Aerodynamic Interface Plane (AIP) shows a complex pressure and swirl distortion pattern, as well as a high level of unsteadiness. Additionally, two vortical structures with equal intensity located on the top and bottom sides of the AIP plane were identified. The unsteady pressure distortion analysis highlighted fluctuations between two positions of the maximum circumferential pressure distortion in the AIP plane. One of these positions presents mean and peak distortion values lower than the other position. Furthermore, an alternating vortex pattern between two swirl patterns in the AIP plane is also identified. Finally, the relationship between pressure and swirl unsteadiness was investigated, and a link between the swirl distortion pattern and pressure distortion was identified. The identification of this relationship will allow geometrical changes in the air intake, leading to a reduction of the average circumferential distortion level, as well as a reduction of the maximum peak level achievable during a flight phase.
Alexandre Di-Marco, Jerome Jacob, Pierre Sagaut. Unsteady characteristics of pressure and swirl distortion in helicopter intake: A lattice Boltzmann method approach. Aerospace Science and Technology, 2023, 138, pp.108333. ⟨10.1016/j.ast.2023.108333⟩. ⟨hal-04543807⟩
Imran Afgan, Yacine Kahil, Sofiane Benhamadouche, Mohamed Ali, Ahmed Alkaabi, et al.. Cross flow over two heated cylinders in tandem arrangements at subcritical Reynolds number using large eddy simulations. International Journal of Heat and Fluid Flow, 2023, 100, pp.109115. ⟨10.1016/j.ijheatfluidflow.2023.109115⟩. ⟨hal-04546846⟩ Plus de détails...
This study analyses the heat transfer and flow characteristics of cross-flow over two heated infinite cylinders in a tandem (in-line) configuration. Non-isothermal Large Eddy Simulations (LES) using the dynamic Smagorinsky model were conducted at a fixed Reynolds number of 3, 000 (based on the free stream velocity and the cylinder diameter). A range of cylinder gap ratios (1.0 ≤ L/D ≤ 5.0) was investigated (in increments of 0.25) with two different Prandtl numbers Pr = 0.1 and 1.0. Results show that the flow structures vary according to the order of the patterns: (i) Extended body regime: without attachment for low L/D (1.0 1.25) where cylinders behave as a single bluff body with top–bottom vortex shedding, (ii) Shear layer reattachment regime: with reattachment for moderate L/D (1.5 3.75) where the detached shear layer from the upstream cylinder reattaches to the down- stream cylinder, and (iii) Co-shedding regime: for high gap ratios (3.75 ≤ L/D ≤ 5.0) a phenomenon called “jumping”, where the two cylinders behave as isolated bluff bodies. Furthermore, it was observed that the average Nusselt number of both cylinders experience a drastic variation at a critical spacing ratio (between 3.75 ≤ L/D ≤ 4.0). For L/D ≤ 3.0, the average Nusselt number of the upstream cylinder was found to be higher than that of the downstream one. However, for spacing ratios L/D > 3.0, the average Nusselt number was similar for both cylinders. For the downstream cylinder, the maximum Nusselt number was located at the separation angle and was found to be independent of the spacing ratio
Imran Afgan, Yacine Kahil, Sofiane Benhamadouche, Mohamed Ali, Ahmed Alkaabi, et al.. Cross flow over two heated cylinders in tandem arrangements at subcritical Reynolds number using large eddy simulations. International Journal of Heat and Fluid Flow, 2023, 100, pp.109115. ⟨10.1016/j.ijheatfluidflow.2023.109115⟩. ⟨hal-04546846⟩
Journal: International Journal of Heat and Fluid Flow
Thomas Gianoli, Jean‐françois Boussuge, Pierre Sagaut, Jérôme de Laborderie. Development and validation of Navier–Stokes characteristic boundary conditions applied to turbomachinery simulations using the lattice Boltzmann method. International Journal for Numerical Methods in Fluids, 2023, 95 (4), pp.528-556. ⟨10.1002/fld.5160⟩. ⟨hal-04063964⟩ Plus de détails...
This article reports a procedure to implement as well as to validate non-reflecting boundary conditions applied for turbomachinery simulations, using Navier-Stokes characteristic boundary conditions in a compressible lattice Boltzmann solver. The implementation of both an inlet condition imposing total pressure, total temperature, and flow angles, as well as an outlet condition imposing a static pressure profile that allows the simulation to reach a simplified radial equilibrium, is described within the context of a lattice Boltzmann approach. The treatment at the boundaries relies on the characteristic methodology to derive conditions which are non-reflecting in terms of acoustics and is also compatible with turbulence injection at the inlet. These properties are evaluated on test cases of increasing complexity, ranging from a simple 2D periodic domain to an S-duct stage with turbulence injection.
Thomas Gianoli, Jean‐françois Boussuge, Pierre Sagaut, Jérôme de Laborderie. Development and validation of Navier–Stokes characteristic boundary conditions applied to turbomachinery simulations using the lattice Boltzmann method. International Journal for Numerical Methods in Fluids, 2023, 95 (4), pp.528-556. ⟨10.1002/fld.5160⟩. ⟨hal-04063964⟩
Journal: International Journal for Numerical Methods in Fluids
Richard M Lueptow, Rainer Hollerbach, Eric Serre. Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper: part 1. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2243), ⟨10.1098/rsta.2022.0140⟩. ⟨hal-03989060⟩ Plus de détails...
In 1923, the Philosophical Transactions published G. I. Taylor’s seminal paper on the stability of what we now call Taylor–Couette flow. In the century since the paper was published, Taylor’s ground-breaking linear stability analysis of fluid flow between two rotating cylinders has had an enormous impact on the field of fluid mechanics. The paper’s influence has extended to general rotating flows, geophysical flows and astrophysical flows, not to mention its significance in firmly establishing several foundational concepts in fluid mechanics that are now broadly accepted. This two-part issue includes review articles and research articles spanning a broad range of contemporary research areas, all rooted in Taylor’s landmark paper. This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper (part 1)’.
Richard M Lueptow, Rainer Hollerbach, Eric Serre. Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper: part 1. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2243), ⟨10.1098/rsta.2022.0140⟩. ⟨hal-03989060⟩
Journal: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Rainer Hollerbach, Richard M Lueptow, Eric Serre. Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper: part 2. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2246), ⟨10.1098/rsta.2022.0359⟩. ⟨hal-04057399⟩ Plus de détails...
In 1923, the Philosophical Transactions published G. I. Taylor’s seminal paper on the stability of what we now call Taylor–Couette flow. In the century since the paper was published, Taylor’s ground-breaking linear stability analysis of fluid flow between two rotating cylinders has had an enormous impact on the field of fluid mechanics. The paper’s influence has extended to general rotating flows, geophysical flows and astrophysical flows, not to mention its significance in firmly establishing several foundational concepts in fluid mechanics that are now broadly accepted. This two-part issue includes review articles and research articles spanning a broad range of contemporary research areas, all rooted in Taylor’s landmark paper. This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper (part 2)’.
Rainer Hollerbach, Richard M Lueptow, Eric Serre. Taylor–Couette and related flows on the centennial of Taylor’s seminal Philosophical Transactions paper: part 2. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2246), ⟨10.1098/rsta.2022.0359⟩. ⟨hal-04057399⟩
Journal: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
S. Di Genova, G. Ciraolo, A. Gallo, J. Romazanov, N. Fedorczak, et al.. First 3D modeling of tungsten erosion and migration in WEST discharges adopting a toroidally non-symmetric wall geometry. Nuclear Materials and Energy, 2023, 34, pp.101340. ⟨10.1016/j.nme.2022.101340⟩. ⟨hal-03988791⟩ Plus de détails...
Numerical analyses are a key tool to investigate tungsten (W) sources and contamination in W Environment steady-state tokamak (WEST) plasma discharges. Modelling activity was performed in order to study W erosion and migration at WEST plasma-facing components (PFCs), using for the first time a toroidally asymmetric wall geometry provided by toroidally localized objects representing WEST outer limiter or antennae. 3D non-axisymmetric SOLEDGE transport simulations were performed with simplifying assumptions (pure Deuterium plasma, fluid model for neutrals) to reproduce WEST boundary plasma, and used as background for ERO2.0 simulations modelling W erosion, re-deposition, and migration. On the sides of the toroidally localized limiters/antennae, two thin W stripes were considered in order to model WEST W antennae protections. Simulations suggest antennae protections contribution to dominate W contamination in the considered simulations settings, highlighting the need of further analyses with different configurations using this kind of tools.
S. Di Genova, G. Ciraolo, A. Gallo, J. Romazanov, N. Fedorczak, et al.. First 3D modeling of tungsten erosion and migration in WEST discharges adopting a toroidally non-symmetric wall geometry. Nuclear Materials and Energy, 2023, 34, pp.101340. ⟨10.1016/j.nme.2022.101340⟩. ⟨hal-03988791⟩
Ivan Kudashev, Anna Medvedeva, Nicolas Fedorszak, David Zarzoso, Manuel Scotto d’ Abusco, et al.. Development of a set of synthetic diagnostics for the WEST tokamak to confront 2D transport simulations and experimental data. Journal of Instrumentation, 2023, 18 (02), pp.C02058. ⟨10.1088/1748-0221/18/02/C02058⟩. ⟨hal-04010344⟩ Plus de détails...
Significant scientific effort has been focused on optimizing the scenarios and plasma parameters for tokamak operations. The lack of comprehensive understanding of underlying physical processes leads to simplifications used both in plasma simulation codes and for diagnostics, which is also complicated by the harsh plasma environment. One of the main tools to couple, check and verify these assumptions are the synthetic diagnostics. In this work we demonstrate current results of the development of the set of synthetic diagnostics for the WEST tokamak to couple experimental data with the SolEdge3X-HDG 2D transport code.
Ivan Kudashev, Anna Medvedeva, Nicolas Fedorszak, David Zarzoso, Manuel Scotto d’ Abusco, et al.. Development of a set of synthetic diagnostics for the WEST tokamak to confront 2D transport simulations and experimental data. Journal of Instrumentation, 2023, 18 (02), pp.C02058. ⟨10.1088/1748-0221/18/02/C02058⟩. ⟨hal-04010344⟩
Thomas Cartier-Michaud, Philippe Ghendrih, Virginie Grandgirard, Eric Serre. Verification and accuracy check of simulations with PoPe and iPoPe. Journal of Computational Physics, 2023, 474, pp.111759. ⟨10.1016/j.jcp.2022.111759⟩. ⟨hal-03871954⟩ Plus de détails...
The theoretical background of the PoPe and iPoPe verification scheme is presented. Verification is performed using the simulation output of production runs. The computing overhead is estimated to be at most 10%. PoPe or iPoPe calculations can be done offline provided the necessary data is stored, for example additional time slices, or online where iPoPe is more effective. The computing overhead is mostly that of storing the necessary data. The numerical error is determined and split into a part proportional to the operators, which are combined to form the equations to be solved, thus modifying their control parameters, completed by a residual error orthogonal to these operators. The accuracy of the numerical solution is determined by this modification of the control parameters. The PoPe and iPoPe methods are illustrated in this paper with simulations of a simple mechanical system with chaotic trajectories evolving into a strange attractor with sensitivity to initial conditions. We show that the accuracy depends on the particular simulation both because the properties of the numerical solution depend on the values of the control parameter, and because the target accuracy will depend on the problem that is addressed. One shows that for a case close to bifurcations between different states, the accuracy is determined by the level of detail of the bifurcation phenomena one aims at describing. A unique verification index, the PoPe index, is proposed to characterise the accuracy, and consequently the verification, of each production run. The PoPe output allows one to step beyond verification and analyse for example the numerical scheme efficiency. For the chosen example at fixed PoPe index, therefore at fixed numerical error, one finds that the higher order integration scheme, comparing order 4 to order 2 Runge-Kutta time stepping, reduces the computation cost by a factor 4.
Thomas Cartier-Michaud, Philippe Ghendrih, Virginie Grandgirard, Eric Serre. Verification and accuracy check of simulations with PoPe and iPoPe. Journal of Computational Physics, 2023, 474, pp.111759. ⟨10.1016/j.jcp.2022.111759⟩. ⟨hal-03871954⟩
J Varela, D Spong, L Garcia, Y Ghai, David Zarzoso, et al.. Effect of the neutral beam injector operational regime on the Alfven eigenmode saturation phase in DIII-D plasma. Plasma Physics and Controlled Fusion, 2023, 65 (12), pp.125004. ⟨10.1088/1361-6587/ad05d4⟩. ⟨hal-04541045⟩ Plus de détails...
The aim of this study is to analyze the effect of the neutral beam injector (NBI) operation regime on the saturation phase of the Alfven Eigenmodes (AEs) in DIII-D plasma. The analysis is done using the linear and nonlinear versions of the gyro-fluid code FAR3d. A set of parametric analyses are performed modifying the nonlinear simulation EP β (NBI injection power), EP energy (NBI voltage) and the radial location of the EP density profile gradient (NBI radial deposition). The analysis indicates a transition from the soft (local plasma relaxation) to the hard MHD (global plasma relaxation) limit if the simulation EP β ⩾ 0.02 , leading to bursting MHD activity caused by radial AEs overlapping. MHD bursts cause an enhancement of the EP transport showing ballistic-like features as avalanche-like events. Simulations in the soft MHD limit show an increment of the EP density gradient as the EP β increases. On the other hand, there is a gradient upper limit in the hard MHD limit, consistent with the critical-gradient behavior. AEs induce shear flows and zonal current leading to the deformation of the flux surfaces and the safety factor profile, respectively, particularly strong for the simulation in the hard MHD limit. Simulations in the hard MHD regime show a decrease of the AE frequency in the saturation phase; this is caused by the destabilization of a transitional mode between a 9 / 3 − 10 / 3 TAE and a 9 / 3 RSAE that may explain the AE frequency down-sweeping observed in some DIII-D discharges. Reducing the EP energy in the nonlinear simulations leads to a weakening of the plasma perturbation. On the other hand, increasing the EP energy causes the opposite effect. Nonlinear simulations of off-axis NBI profiles indicate a lower plasma perturbation as the EP density gradient is located further away from the magnetic axis.
J Varela, D Spong, L Garcia, Y Ghai, David Zarzoso, et al.. Effect of the neutral beam injector operational regime on the Alfven eigenmode saturation phase in DIII-D plasma. Plasma Physics and Controlled Fusion, 2023, 65 (12), pp.125004. ⟨10.1088/1361-6587/ad05d4⟩. ⟨hal-04541045⟩
Pierre Sagaut, V.K. Suman, P. Sundaram, M.K. Rajpoot, Y.G. Bhumkar, et al.. Global spectral analysis: Review of numerical methods. Computers and Fluids, 2023, 261, pp.105915. ⟨10.1016/j.compfluid.2023.105915⟩. ⟨hal-04546492⟩ Plus de détails...
The design and analysis of numerical methods are usually guided by the following: (a) von Neumann analysis using Fourier series expansion of unknowns, (b) the modified differential equation approach, and (c) a more generalized approach that analyzes numerical methods globally, using Fourier–Laplace transform to treat the total or disturbance quantities in terms of waves. This is termed as the global spectral analysis (GSA). GSA can easily handle non-periodic problems, by invoking wave properties of the field through the correct numerical dispersion relation, which is central to the design and analysis. This has transcended dimensionality of the problem, while incorporating various physical processes e.g. by studying convection, diffusion and reaction as the prototypical elements involved in defining the physics of the problem. Although this is used for fluid dynamical problems, it can also explain many multi-physics and multi-scale problems. This review describes this powerful tool of scientific computing, with new results originating from GSA: (i) providing a common framework to analyze both hyperbolic and dispersive wave problems; (ii) analyze numerical methods by comparing physical and numerical dispersion relation, which leads to the new class of dispersion relation preserving (DRP) schemes; (iii) developing error dynamics as a distinct tool, identifying sources of numerical errors involving both the truncation and round-off error. Such studies of error dynamics provide the epistemic tool of analysis rather than an aleatoric tool, which depends on uncertainty quantification for high performance computing (HPC). One of the central themes of GSA covers the recent advances in understanding numerical phenomenon like focusing, which defied analysis so far. An application of GSA shown here for the objective evaluation of the so-called DNS by pseudo-spectral method for spatial discretization along with time integration by two-stage Runge–Kutta method is performed. GSA clearly shows that this should not qualify as DNS for multiple reasons. A new design of HPC methods for peta- and exa-flop computing tools necessary for parallel computing by compact schemes are also described.
Pierre Sagaut, V.K. Suman, P. Sundaram, M.K. Rajpoot, Y.G. Bhumkar, et al.. Global spectral analysis: Review of numerical methods. Computers and Fluids, 2023, 261, pp.105915. ⟨10.1016/j.compfluid.2023.105915⟩. ⟨hal-04546492⟩
Gauthier Wissocq, Said Taileb, Song Zhao, Pierre Boivin. A hybrid lattice Boltzmann method for gaseous detonations. Journal of Computational Physics, 2023, 494, pp.112525. ⟨10.1016/j.jcp.2023.112525⟩. ⟨hal-04244340⟩ Plus de détails...
This article is dedicated to the construction of a robust and accurate numerical scheme based on the lattice Boltzmann method (LBM) for simulations of gaseous detonations. This objective is achieved through careful construction of a fully conservative hybrid lattice Boltzmann scheme tailored for multi-species reactive flows. The core concept is to retain LBM low dissipation properties for acoustic and vortical modes by using the collide and stream algorithm for the particle distribution function, while transporting entropic and species modes via a specifically designed finite-volume scheme. The proposed method is first evaluated on common academic cases, demonstrating its ability to accurately simulate multi-species compressible and reactive flows with discontinuities: the convection of inert species, a Sod shock tube with two ideal gases and a steady one-dimensional inviscid detonation wave. Subsequently, the potential of this novel approach is demonstrated in one- and two-dimensional inviscid unsteady gaseous detonations, highlighting its ability to accurately recover detonation structures and associated instabilities for high activation energies. To the authors' knowledge, this study is the first successful simulation of detonation cellular structures capitalizing on the LBM collide and stream algorithm.
Gauthier Wissocq, Said Taileb, Song Zhao, Pierre Boivin. A hybrid lattice Boltzmann method for gaseous detonations. Journal of Computational Physics, 2023, 494, pp.112525. ⟨10.1016/j.jcp.2023.112525⟩. ⟨hal-04244340⟩
Jacob Johnston, Sarah Dischinger, Mostafa Nassr, Ji Yeon Lee, Pedram Bigdelou, et al.. A reduced-order model of concentration polarization in reverse osmosis systems with feed spacers. Journal of Membrane Science, 2023, 675, pp.121508. ⟨10.1016/j.memsci.2023.121508⟩. ⟨hal-04546833⟩ Plus de détails...
Feed spacers in reverse osmosis systems generate complex fluid flows that limit computational fluid dynamics (CFD) simulations to small length and time scales. That limits our ability to simulate mineral scaling and other membrane fouling phenomena, which occur over longer length and time scales. Thus motivated, we develop a reduced model that replaces the CFD simulation of the velocity field with an analytical model that mimics spacers. This focuses the remaining numerical effort on simulating the advection–diffusion equation governing solute transport. We motivate and validate the model with CFD simulations and bench-scale experiments of spacer filaments in three different arrangements, including cases of unsteady vortex shedding. We show that the model produces a roughly 10,000-fold speedup compared to CFD, and accurately reproduces CFD predictions of not only the average and maximum concentrations, but also the local concentration distribution along the membrane. We also demonstrate the model for simulating a feed channel with a length-to-height ratio of 200. The model provides a simple testbed for exploratory studies of multispecies transport, precipitation, and membrane fouling phenomena for which simulating spacers is often prohibitive.
Jacob Johnston, Sarah Dischinger, Mostafa Nassr, Ji Yeon Lee, Pedram Bigdelou, et al.. A reduced-order model of concentration polarization in reverse osmosis systems with feed spacers. Journal of Membrane Science, 2023, 675, pp.121508. ⟨10.1016/j.memsci.2023.121508⟩. ⟨hal-04546833⟩
Franck Corset, Mitra Fouladirad, Christian Paroissin. Imperfect condition-based maintenance for a gamma degradation process in presence of unknown parameters. Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability, 2023, 237 (3), pp.546-561. ⟨10.1177/1748006X221134132⟩. ⟨hal-03842177⟩ Plus de détails...
A system subject to degradation is considered. The degradation is modelled by a gamma process. A condition-based maintenance policy with perfect corrective and an imperfect preventive actions is proposed. The maintenance cost is derived considering a Markov-renewal process. The statistical inference of the degradation and maintenance parameters by the maximum likelihood method is investigated. A sensibility analysis to different parameters is carried out and the perspectives are detailed.
Franck Corset, Mitra Fouladirad, Christian Paroissin. Imperfect condition-based maintenance for a gamma degradation process in presence of unknown parameters. Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability, 2023, 237 (3), pp.546-561. ⟨10.1177/1748006X221134132⟩. ⟨hal-03842177⟩
Journal: Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability
Jingtao Ma, Qiuxiang Huang, Yi Zhu, Yuan-Qing Xu, Fang-Bao Tian. Effects of fluid rheology on dynamics of a capsule through a microchannel constriction. Physics of Fluids, 2023, 35 (9), pp.091901. ⟨10.1063/5.0165614⟩. ⟨hal-04546805⟩ Plus de détails...
This paper numerically investigates the impact of fluid rheology on the behaviors of a spherical capsule through a microchannel constriction. Different flow scenarios are considered: a Newtonian capsule in a viscoelastic matrix, a Newtonian capsule in a Newtonian matrix, and a viscoelastic capsule in a Newtonian matrix. The results demonstrate that the capsule's lengths undergo oscillations during the passage through the constriction, with three stages of evolution. When approaching the constriction, the capsule respectively experiences increase and decrease in its length and height. While within or exiting the constriction, the length of the capsule continuously decreases, and the height generally increases. As the capsule moves away from the constriction, the capsule relaxes to different profiles in different flows. Detailed analysis on the effects of the fluid viscoelasticity on the capsule's lengths in different stages is provided. In addition, the behaviors of a red blood cell passing through a microchannel constriction are also examined. This study sheds light on the complex behaviors of a spherical capsule and red blood cell in microchannel constriction, emphasizing the significant influence of fluid rheology on their deformation and shape changes.
Jingtao Ma, Qiuxiang Huang, Yi Zhu, Yuan-Qing Xu, Fang-Bao Tian. Effects of fluid rheology on dynamics of a capsule through a microchannel constriction. Physics of Fluids, 2023, 35 (9), pp.091901. ⟨10.1063/5.0165614⟩. ⟨hal-04546805⟩
D. Martinand, E. Serre, B. Viaud. Instabilities and routes to turbulence in rotating disc boundary layers and cavities. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2243), pp.20220135. ⟨10.1098/rsta.2022.0135⟩. ⟨hal-03989074⟩ Plus de détails...
Studied for more than a century, first in the field of geophysics, flows over rotating discs present a great diversity of complex instability behaviours that are not yet fully understood. While the primary instabilities are now well characterized experimentally, theoretically and numerically, their role in the transition mechanisms to turbulence remains an open question that still challenges the scientific community. This article brings together the main results of the literature related to the instabilities over rotating discs, but also in the connected problem of rotating cavities, and reviews the main scenarios currently assumed to describe the flow breakdown to turbulence. A particular focus is on more recent studies of generic flows in rotating cavities bounded by two coaxial rotating discs, that occur in many industrial systems, the performances of which and their improvement are linked to a better understanding of these mechanisms. This article is part of the theme issue ‘Taylor–Couette and related flows on the centennial of Taylor's seminal Philosophical Transactions paper (part 1)’.
D. Martinand, E. Serre, B. Viaud. Instabilities and routes to turbulence in rotating disc boundary layers and cavities. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2023, 381 (2243), pp.20220135. ⟨10.1098/rsta.2022.0135⟩. ⟨hal-03989074⟩
Journal: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Hasan Misaii, Firoozeh Haghighi, Mitra Fouladirad. Opportunistic perfect preventive maintenance policy in presence of masked data. Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability, 2022, 236 (6), pp.1024-1036. ⟨10.1177/1748006X211058936⟩. ⟨hal-04064544⟩ Plus de détails...
In this paper, the maintenance optimization problem of multi-component system is considered. It is assumed that the exact cause of system failure might be masked. That is, the exact cause of failure is unknown, and we only know that it belongs to a set called mask set. Both opportunistic perfect preventive maintenance (OPPM) and perfect corrective maintenance are considered. Threshold of OPPM and inter-inspection interval are considered as decision parameters which are optimized using long-run cost rate criteria. The applicability of the proposed maintenance policy is investigated using an illustrative example.
Hasan Misaii, Firoozeh Haghighi, Mitra Fouladirad. Opportunistic perfect preventive maintenance policy in presence of masked data. Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability, 2022, 236 (6), pp.1024-1036. ⟨10.1177/1748006X211058936⟩. ⟨hal-04064544⟩
Journal: Proceedings of the Institution of Mechanical Engineers, Part O: Journal of Risk and Reliability
Philippe Ghendrih, Guilhem Dif-Pradalier, Olivier Panico, Yanick Sarazin, Hugo Bufferand, et al.. Role of avalanche transport in competing drift wave and interchange turbulence. Journal of Physics: Conference Series, 2022, 2397, pp.012018. ⟨10.1088/1742-6596/2397/1/012018⟩. ⟨hal-04498387⟩ Plus de détails...
We complete the 2D 2-fields turbulence model previously used with an interchange-like instability by slightly modifying the parallel loss terms to drive drift wave instabilities. We show that the instability driven by temperature fluctuations of the sheath losses is identical to that of the drift wave turbulence. The linear analysis is performed and used to select control parameters that yield identical maximum growth rates for the interchange alone and drift wave alone instability. Combining the two instabilities doubles the maximum growth rate. The non-linear simulations are used to analyse the SOL width. The simulations allow one to identify a low field side SOL region where interchange and drift wave are unstable and a high field side SOL region where only the drift wave is unstable. The SOL profiles appear exponential in the region close to the source but depart from a simple exponential fall-off in the far SOL. The low field side SOL width is found to be larger in the interchange alone case, slightly smaller when both instabilities are present and finally narrower when only the drift waves. For the high field side SOL, without interchange, the drift wave SOL width is observed to be identical to that on the low field side and larger than that when both instabilities at play. The Sherwood dimensionless parameter, ratio of convective particle flux divided by the diffusive particle flux, is used to compare the efficiency of turbulent transport. The profiles of the Sherwood parameter for time and flux surface averaged transport indicate that turbulent transport is dominant close to the separatrix but is less effective towards the far SOL. The Sherwood parameter evolution, determined with the flux-surface averaged transport, indicates that outward avalanche transport with corrugations governs the case with interchange only. When combining the two instabilities, outward avalanche transport is less pronounced and inward avalanche transport is observed, reducing the overall turbulent transport efficiency. The avalanche transport with drift waves only compared to interchange only is found to be inhibited.
Philippe Ghendrih, Guilhem Dif-Pradalier, Olivier Panico, Yanick Sarazin, Hugo Bufferand, et al.. Role of avalanche transport in competing drift wave and interchange turbulence. Journal of Physics: Conference Series, 2022, 2397, pp.012018. ⟨10.1088/1742-6596/2397/1/012018⟩. ⟨hal-04498387⟩
Samuele Mazzi, David Zarzoso. Parametric Validation of the Reservoir Computing–Based Machine Learning Algorithm Applied to Lorenz System Reconstructed Dynamics. Complex Systems , 2022, 31 (3), pp.311-339. ⟨10.25088/ComplexSystems.31.3.311⟩. ⟨hal-03838327⟩ Plus de détails...
A detailed parametric analysis is presented, where the recent method based on the reservoir computing paradigm, including its statistical robustness, is studied. It is observed that the prediction capabilities of the reservoir computing approach strongly depend on the random initialization of both the input and the reservoir layers. Special emphasis is put on finding the region in the hyperparameter space where the ensemble-averaged training and generalization errors together with their variance are minimized. The statistical analysis presented here is based on the projection on proper elements method.
Samuele Mazzi, David Zarzoso. Parametric Validation of the Reservoir Computing–Based Machine Learning Algorithm Applied to Lorenz System Reconstructed Dynamics. Complex Systems , 2022, 31 (3), pp.311-339. ⟨10.25088/ComplexSystems.31.3.311⟩. ⟨hal-03838327⟩
Ivan Kudashev, Anna Medvedeva, Manuel Scotto D’abusco, Nicolas Fedorszak, Stefano Di Genova, et al.. Development of a set of synthetic diagnostics for the confrontation between 2D transport simulations and WEST tokamak experimental data. Applied Sciences, 2022, 12 (19), pp.9807. ⟨10.3390/app12199807⟩. ⟨hal-03982630⟩ Plus de détails...
Transport codes are frequently used for describing fusion plasmas with the aim to prepare tokamak operations. Considering novel codes, such as SolEdge3X-HDG, synthetic diagnostics are a common technique used to validate new models and confront them with experimental data. The purpose of this study is to develop a set of synthetic diagnostics, starting from bolometer and visible cameras for the WEST tokamak, in order to compare the code results with the experimental data. This research is done in the framework of Raysect and Cherab Python libraries. This allows us to process various synthetic diagnostics in the same fashion in terms of 3D ray tracing with volume emitters developed specifically for fusion plasmas. We were able to implement the WEST tokamak model and the design of bolometer and visible cameras. Synthetic signals, based on full-discharge WEST plasma simulation, were used for to compare the SolEdge3X-HDG output plasma with experimental data. The study also considers the optical properties of the plasma-facing components (PFCs) and their influence on the performance of diagnostics. The paper shows a unified approach to synthetic diagnostic design, which will be further extended to cover the remaining diagnostics on the WEST tokamak.
Ivan Kudashev, Anna Medvedeva, Manuel Scotto D’abusco, Nicolas Fedorszak, Stefano Di Genova, et al.. Development of a set of synthetic diagnostics for the confrontation between 2D transport simulations and WEST tokamak experimental data. Applied Sciences, 2022, 12 (19), pp.9807. ⟨10.3390/app12199807⟩. ⟨hal-03982630⟩
Georis Billo, Michel Belliard, Pierre Sagaut. Comparison of several interpolation methods to reconstruct field data in the vicinity of a finite element immersed boundary. Computers & Mathematics with Applications, 2022, 123, pp.123-135. ⟨10.1016/j.camwa.2022.08.002⟩. ⟨hal-04064030⟩ Plus de détails...
Thermal-hydraulics safety requirements for the second and third generation of nuclear reactors led to the development of innovative passive safety systems. In particular, new devices must be developed involving numerical simulations for turbulent two-phase flows around complex geometries. To reduce the time-consuming mesh generation phase when testing various geometries, we use a fictitious domain approach. More specifically, we choose the Penalized Direct Forcing Method to take into account inflow obstacles. Following a recent work, involving the resolution of the one-phase incompressible Navier-Stokes equations using a projection scheme and the Finite Element Method, this paper focuses on different techniques to recover data from the discrete immersed boundary and different ways to achieve order 2 in space via linear interpolation. Indeed, we investigate two data reconstruction approaches (one based on various weighted averaging, the other based on optimization) and compare their results for cylindrical and NACA0012 airfoil shapes: they provide similar accuracy but the weighting is much faster in terms of execution time. We also investigate three different interpolation types: unidirectional, multi-directional and a new hybrid between the two. The Taylor-Couette flow and the flow around a circular cylinder are used to carry out mesh convergence studies. Globally, order 2 in space is numerically assessed in both 2 and ∞ norms for all the interpolation types, which is consistent with theoretical expectations-even if the space convergence order is a bit higher for the multi-directional approach. For the flow around a circular cylinder, the values of aerodynamic coefficients and Strouhal number are in good agreement with the literature, especially when using directional interpolation. Finally, an industrial case, representative of passive safety systems, is presented to assess the robustness and capability of the method. The simulations tend to show that, here again, the directional interpolation offers the best behavior when dealing with complex geometries and relatively coarse meshes.
Georis Billo, Michel Belliard, Pierre Sagaut. Comparison of several interpolation methods to reconstruct field data in the vicinity of a finite element immersed boundary. Computers & Mathematics with Applications, 2022, 123, pp.123-135. ⟨10.1016/j.camwa.2022.08.002⟩. ⟨hal-04064030⟩
Journal: Computers & Mathematics with Applications
S Mazzi, J Garcia, David Zarzoso, Ye Kazakov, J Ongena, et al.. Gyrokinetic study of transport suppression in JET plasmas with MeV-ions and toroidal Alfvén eigenmodes. Plasma Physics and Controlled Fusion, 2022, 64 (11), pp.114001. ⟨10.1088/1361-6587/ac91f3⟩. ⟨hal-03838290⟩ Plus de détails...
The impact of fast ions, generated in the MeV-range through the efficient application of the three-ion scheme in JET plasmas, on the turbulence properties is presented through complex numerical simulations. The suppression of the ion-scale turbulent transport is studied by means of in-depth gyrokinetic numerical analyses. Such a suppression is demonstrated to be achieved in the presence of toroidal Alfvén eigenmodes (TAEs) destabilized by the highly energetic ions. Details on the TAE excitation are also provided with a multi-code analysis. The inherently nonlinear and multi-scale mechanism triggered by the fast ions, also involving the high-frequency modes and the large-scale zonal flows, is deeply analyzed. Such mechanism is thus demonstrated, with experimental validating studies, to be the main cause of turbulence suppression and improvement of ion thermal confinement. Additional simulations address the implications of reversed shear magnetic equilibrium on the turbulent transport.
S Mazzi, J Garcia, David Zarzoso, Ye Kazakov, J Ongena, et al.. Gyrokinetic study of transport suppression in JET plasmas with MeV-ions and toroidal Alfvén eigenmodes. Plasma Physics and Controlled Fusion, 2022, 64 (11), pp.114001. ⟨10.1088/1361-6587/ac91f3⟩. ⟨hal-03838290⟩
Shang-Gui Cai, Sajad Mozaffari, Jérôme Jacob, Pierre Sagaut. Application of immersed boundary based turbulence wall modeling to the Ahmed body aerodynamics. Physics of Fluids, 2022, 34 (9), pp.095106. ⟨10.1063/5.0098232⟩. ⟨hal-04065468⟩ Plus de détails...
This paper applies a recently developed immersed boundary-turbulence wall modeling approach to turbulent flows over a generic car geometry, known as the Ahmed body, under massive flow separation within a lattice Boltzmann solver. Although the immersed boundary method combined with hierarchical Cartesian grid offers high flexibility in automatic grid generation around complex geometries, the near-wall solution is significantly deteriorated compared to the body-fitted simulation, especially when coupled to wall models for turbulent flows at high Reynolds number. Enhanced wall treatments have been proposed in the literature and validated for attached flow configurations. In this work, the Ahmed body with a slant surface of angle 35 is considered where the flow separates massively over the slant surface and the vertical base. The large eddy simulation is performed with a Reynolds stress constraint near-wall. The eddy viscosity is computed dynamically by taking into account the actually resolved Reynolds stresses. It approaches the mixing length eddy viscosity in attached boundary layers and returns to the subgrid eddy viscosity in detached boundary layers. An explicit equilibrium wall model has also been proposed to accelerate the calculation. Comparison with the no-slip boundary condition on the separated surfaces shows that the near-wall treatments with the equilibrium wall model operate reasonably well on both attached and detached boundary layers.
Shang-Gui Cai, Sajad Mozaffari, Jérôme Jacob, Pierre Sagaut. Application of immersed boundary based turbulence wall modeling to the Ahmed body aerodynamics. Physics of Fluids, 2022, 34 (9), pp.095106. ⟨10.1063/5.0098232⟩. ⟨hal-04065468⟩
Fatemeh Safaei, Jafar Ahmadi, Mitra Fouladirad. Optimal N-policy for the maintenance of k-out-of-n systems with dynamic minor repairs considering second-hand component income. International Journal of Production Research, 2022, pp.1-18. ⟨10.1080/00207543.2022.2120107⟩. ⟨hal-04064518⟩ Plus de détails...
This paper proposes a maintenance policy for a k-out-of-n: F system operating to fulfil several jobs without interruptions. The system is replaced when the Nth job completes or at the kth failure, whichever occurs first. So, there are some non-failed components when a replacement is done. These components can be sold as secondhand products to continue working in other systems for a while. The price of them is also considered in the proposed maintenance policy. An optimal maintenance policy is studied to minimise long-run average cost under the constraint of relative mean operating time. Comprehensive numerical studies are done to assess the effect of the model parameters on the optimal solutions. Also, to demonstrate the applicability of the proposed plan, a data set related to wind turbine generator failures is considered as a case study.
Fatemeh Safaei, Jafar Ahmadi, Mitra Fouladirad. Optimal N-policy for the maintenance of k-out-of-n systems with dynamic minor repairs considering second-hand component income. International Journal of Production Research, 2022, pp.1-18. ⟨10.1080/00207543.2022.2120107⟩. ⟨hal-04064518⟩
Journal: International Journal of Production Research
D Auroux, P Ghendrih, L Lamerand, F Rapetti, E Serre. Asymptotic behaviour, non-local dynamics and data assimilation tailoring of the reduced κ − ε model to address turbulent transport of fusion plasmas. Physics of Plasmas, 2022. ⟨hal-03811621⟩ Plus de détails...
The high-dimensional and multiscale nature of fusion plasma flows require the development of reduced models to be implemented in numerical codes capable of capturing the main features of turbulent transport in a sufficiently short time to be useful during tokamak operation. This paper goes further in the analysis of the dynamics of the κ − ε model based on the turbulent kinetic energy κ and its dissipation rate ε [Baschetti et al., Nuc. Fus 61, 106020 (2021)] to improve the predictability of the transverse turbulent transport in simulation codes. Present 1D results show further capabilities with respect to current models (based on constant effective perpendicular diffusion) and on the standard quasi-linear approach. The nonlinear dependence of D in κ and ε estimated from two additional transport equations allow to introduce some non-locality in the transport model. This is illustrated by the existence of parameter ranges with turbulence spreading. The paper also addresses another issue related to the uncertainties on the inherent free parameters of such reduced model. The study proposes a new approach in the fusion community based on a variational data assimilation involving the minimisation of a cost function defined as the distance between the reference data and the calculated values. The results are good, and show the ability of the data assimilation to reduce uncertainties on the free parameters, which remains a critical point to ensure the total reliability of such an approach.
D Auroux, P Ghendrih, L Lamerand, F Rapetti, E Serre. Asymptotic behaviour, non-local dynamics and data assimilation tailoring of the reduced κ − ε model to address turbulent transport of fusion plasmas. Physics of Plasmas, 2022. ⟨hal-03811621⟩
Samuele Mazzi, Yann Camenen, Jeronimo Garcia, David Zarzoso, D. Frigione, et al.. Effects of the parallel flow shear on the ITG-driven turbulent transport in tokamak plasmas. Nuclear Fusion, 2022, 62 (9), pp.096024. ⟨10.1088/1741-4326/ac7ac2⟩. ⟨hal-03838283⟩ Plus de détails...
Abstract The impact of the parallel flow shear on the tokamak plasma stability and turbulent transport driven by the ion temperature gradient (ITG) modes is analyzed by means of local gyrokinetic numerical analyses. It is shown that the parallel flow shear increases the ITG growth rate in the linear regime, and induces a broadening and shift of the radial spectrum. Then, the different effects of the finite parallel shear on the ITG turbulence characteristics are deeply analyzed in the nonlinear regime. These studies highlight that a reduction of the thermal-ion turbulent heat flux is induced by a complex mechanism involving the nonlinear generation of an enhanced zonal flow activity. Indeed, the turbulent sources of the zonal flows are increased by the introduction of the finite parallel flow shear in the system, beneficially acting on the saturation level of the ITG turbulence. The study has been carried out for the Waltz standard case below the critical threshold of the destabilization of the parallel velocity gradient instability, and then generalized to a selected pulse of a recent JET scenario with substantial toroidal rotation in the edge plasma region. It is, thus, suggested that the investigated complex mechanism triggered by the finite parallel flow shear reducing the ITG turbulent heat fluxes could be complementary to the well-established perpendicular flow shear in a region with sufficiently large plasma toroidal rotation.
Samuele Mazzi, Yann Camenen, Jeronimo Garcia, David Zarzoso, D. Frigione, et al.. Effects of the parallel flow shear on the ITG-driven turbulent transport in tokamak plasmas. Nuclear Fusion, 2022, 62 (9), pp.096024. ⟨10.1088/1741-4326/ac7ac2⟩. ⟨hal-03838283⟩
Tuan Dung Nguyen, Christophe Besse, François Rogier. High-order Scharfetter-Gummel-based schemes and applications to gas discharge modeling. Journal of Computational Physics, 2022, 461, pp.111196. ⟨10.1016/j.jcp.2022.111196⟩. ⟨hal-03352814⟩ Plus de détails...