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Ioannis Mavrogiannis, D. Zarzoso, Mitra Fouladirad. Global sensitivity analysis and uncertainty quantification comparison via surrogate models for auxiliary heating of nuclear fusion plasmas. Reliability Engineering and System Safety, 2027, 278 (part 2), pp.113535. ⟨10.1016/j.ress.2026.113535⟩. ⟨hal-05790337⟩ Plus de détails...
Surrogate models are often used to approximate the statistical behavior of complex, non-linear numerical codes, under the influence of input uncertainty. Knowledge of the code’s performance under uncertainty increases the confidence of the code results in realistic situations where parameters do not have a fixed value. Surrogates furthermore facilitate the accurate estimation of global, variance-based sensitivity indices, with a smaller number of samples that would otherwise be required. In this work, we investigate the uncertainty of surrogate model performance, for surrogates trained under different sampling methods and sample sizes. For each surrogate, an uncertainty range is obtained for its accuracy, estimated statistical moments and Sobol’ indices. Computationally fast physical models are employed, making this comparison possible. The physical system chosen concerns the heating of a nuclear fusion plasma, with neutral beam injection (NBI). Such auxiliary heating systems are necessary for reaching the extreme plasma temperatures at which fusion reactions occur. Uncertainties in the thermal plasma equilibrium and ionization cross-sections are propagated through the TAPaS code (Toroidal Accelerated PArticle Simulator), obtaining quantities of interest that describe the beam attenuation in the plasma, the heating power density transferred to the plasma ions and electrons, and the NBI shine-through losses. Such a GSA-UQ analysis setting therefore increases the safety during the plasma pulse. It allows reliable prediction of the shine-through losses, which can damage the machine walls, and can help avoid potential instabilities. It can help maximize the plasma pulse duration, achieving steady-state production of energy.
Ioannis Mavrogiannis, D. Zarzoso, Mitra Fouladirad. Global sensitivity analysis and uncertainty quantification comparison via surrogate models for auxiliary heating of nuclear fusion plasmas. Reliability Engineering and System Safety, 2027, 278 (part 2), pp.113535. ⟨10.1016/j.ress.2026.113535⟩. ⟨hal-05790337⟩
Journal: Reliability Engineering and System Safety
Anna Medvedeva. Synthetic diagnostics and integrated modeling: Bridging the gap between measurement and interpretation in magnetic confinement fusion. Plasma Physics and Controlled Fusion, 2026, ⟨10.1088/1361-6587/aeb280⟩. ⟨hal-05797020⟩ Plus de détails...
In magnetic confinement fusion, we rarely measure physical quantities directly; instead, we measure their indirect signatures -photons, currents, and phase shifts. Bridging the gap between these raw signals and the physical parameters of interest (such as density or temperature) has traditionally relied on the inverse problem, a mathematical reconstruction process often plagued by ambiguity and ill-posedness. This tutorial advocates for a paradigm shift toward forward modeling via Synthetic Diagnostics. By processing simulation data through the same transfer functions as experimental instruments, we can translate theoretical predictions into synthetic signals, enabling a rigorous comparison with experiment. We formalize this approach within the TWINTOK framework, a Digital Twin architecture designed for systematic validation. Through detailed case studies -ranging from the spectroscopic evaluation of divertor detachment to the full-wave modeling of turbulence staircases -we demonstrate how synthetic diagnostics reveal physics that standard inversions often miss, such as the significant contribution of wall reflections to bolometric signals. As the community moves toward ITER and fusion power plants, where diagnostic access will be limited and interpretation challenging, this forward modeling approach provides the essential link to validate our predictive capabilities.
Anna Medvedeva. Synthetic diagnostics and integrated modeling: Bridging the gap between measurement and interpretation in magnetic confinement fusion. Plasma Physics and Controlled Fusion, 2026, ⟨10.1088/1361-6587/aeb280⟩. ⟨hal-05797020⟩
Zohra Laggoune, Yasmine Masmoudi, Valentine Pepe, Elisabeth Badens. Implantable Polymer-Based Medical Devices Go Supercritical: From Cleaning to Sterilization. Annals of Biomedical Engineering, 2026, ⟨10.1007/s10439-026-04392-3⟩. ⟨hal-05782949⟩ Plus de détails...
The biomedical industry has made significant progress in recent years with the emergence of medical devices made from biocompatible polymers, improving implant performance, longevity, and patient safety. However, a major challenge for manufacturers remains the incompatibility of certain polymers with conventional processing techniques involving organic solvents or harsh operating conditions. Supercritical CO2 offers a sustainable and environmentally friendly alternative that can be applied throughout the manufacturing cycle of medical devices, including cleaning, impregnation, foaming, and sterilization. It enables the recovery of a dry, residue-free final product while preserving the integrity and functionality of the material. This article provides a comprehensive and up-to-date review of the latest developments in the use of supercritical CO2 for the different stages of manufacturing and treatment of implantable medical devices. It evaluates scCO2- based process efficiency across various applications and emphasizes processing aspects such as operating modes, key parameters, and process conditions. The review discusses the potential for scale-up and industrial implementation, providing insights into the practical challenges, advantages, limitations, and prospects of scCO2 technology in processing implantable polymer-based medical devices, with a particular focus on chemical engineering aspects.
Zohra Laggoune, Yasmine Masmoudi, Valentine Pepe, Elisabeth Badens. Implantable Polymer-Based Medical Devices Go Supercritical: From Cleaning to Sterilization. Annals of Biomedical Engineering, 2026, ⟨10.1007/s10439-026-04392-3⟩. ⟨hal-05782949⟩
Marcel Désor, Amit Kumar Haldar, Nikolai Kosuch, Wolfgang Polifke, Grégoire Varillon. Large Eddy Simulation of Premixed Hydrogen Flame Flashback Including Conjugate Heat Transfer and Soret Effect. Journal of Engineering for Gas Turbines and Power, 2026, 148 (10), ⟨10.1115/1.4072458⟩. ⟨hal-05733661⟩ Plus de détails...
Boundary-layer flashback is a major risk for lean-premixed combustion of H2-based fuels or fuel blends in low-emission gas turbines. This study demonstrates and critically assesses a methodology based on large eddy simulation (LES) coupled with conjugate heat-transfer (CHT) to predict boundary-layer flashback in turbulent H2 flames without ad hoc parameters. By coupling LES with CHT, we determine flashback limits as observed experimentally on a backward-facing step while avoiding the use of ad hoc thermal boundary conditions. The sensitivity of predictions to modeling and numerical parameters is assessed. It is demonstrated that the model presented is insensitive to external thermal boundary conditions applied on the outer surfaces of the solid parts. Accurate representation of the wall heat-flux in the immediate vicinity of the flame, proper flame resolution, as well as Soret diffusion are identified as key parameters for modeling. In particular, Soret diffusion locally enriches the boundary layer whenever the fuel/air mixture is preheated by heat exchange with solid components. Consequently, neglecting Soret diffusion leads to a nonconservative misprediction of the flashback limit. Flame thickening results in excessive heat loss in the flame zone and consequently leads to a systematic misprediction of the flashback limit. The proposed LES+CHT framework gives insight into the relationship of heat transfer, mixture preheating, and flame motion. The methodology is well-suited to predict thermal runaway limits, where the flame seems stable, but flashes back after sufficiently long operation. The differences between short-term flashback and thermal runaway, and the consequential difficulty of consistent validation with experiment are discussed.
Marcel Désor, Amit Kumar Haldar, Nikolai Kosuch, Wolfgang Polifke, Grégoire Varillon. Large Eddy Simulation of Premixed Hydrogen Flame Flashback Including Conjugate Heat Transfer and Soret Effect. Journal of Engineering for Gas Turbines and Power, 2026, 148 (10), ⟨10.1115/1.4072458⟩. ⟨hal-05733661⟩
Journal: Journal of Engineering for Gas Turbines and Power
François Joseph Chatelon, Miguel Cruz, Jacques Henri Balbi, Thierry Marcelli, Sofiane Meradji, et al.. The Balbi operational model, a simplified physical model for surface fires spread. Part II – model parameterisation and evaluation. International Journal of Wildland Fire, 2026, 35 (9), ⟨10.1071/WF25204⟩. ⟨hal-05739946⟩ Plus de détails...
Background The ‘Balbi model’ is a simplified physical model for surface fires which provides the main physical characteristics of a fire front and its rate of spread (ROS) as a function of general environmental conditions. In the first part of this work, we describe a simplification of this model, which we call Balbi operational model, that leads to a set of explicit algebraic equations. Aims After calibrating the model, we aim to assess its performance by comparing the predicted ROS with laboratory- and field-measured ROS. Methods A small set (n = 40) of laboratory fires was used to find the required model parameters. We evaluated the model against (1) a set of laboratory experimental fires (n = 549), representing a range of fuel bed types and arrangements, and (2) a set of shrubland and grassland field fires (n = 357) from different world regions. We assessed the predictive capacity of the model and compared it with other empirical and semi-empirical models. An analysis on the importance of each heat transfer mechanism is performed. Key results The proposed model performs as well as its previous iteration on shrubland fires and is found to increase accuracy when tested against grassland fires. Conclusions The operational ‘Balbi model’ shares many properties with empirical models, while grounded on physical heat transfer principles. The model is suitable for application to several types of fuels and configurations of slope and wind. Implications Its intrinsic characteristics and verified fit make it a candidate to be used in wildfire propagation simulators.
François Joseph Chatelon, Miguel Cruz, Jacques Henri Balbi, Thierry Marcelli, Sofiane Meradji, et al.. The Balbi operational model, a simplified physical model for surface fires spread. Part II – model parameterisation and evaluation. International Journal of Wildland Fire, 2026, 35 (9), ⟨10.1071/WF25204⟩. ⟨hal-05739946⟩
Jacques Henri Balbi, François-Joseph Chatelon, Miguel Cruz, Thierry Marcelli, Sofiane Meradji, et al.. The Balbi operational model, a simplified physical model for surface fires. Part I – modelling. International Journal of Wildland Fire, 2026, 35 (9), ⟨10.1071/WF25203⟩. ⟨hal-05739945⟩ Plus de détails...
Background Previously published versions of the ‘Balbi model’ describing surface fire propagation consist of a set of equations based on simplified conservation laws. Their main equation calculating the fire rate of spread (ROS) relied on an iterative process to account for the effect of environmental drivers. Aims We formulated a new version of this model that considers a 3D flame front composed of peaks and troughs, integrates distinct radiation and convection heat transfer mechanisms, and outputs the physical characteristics of a flame front as they are influenced by weather, fuel and topographical conditions. A simpler operational version, composed of only one equation, is also exhibited. Methods While maintaining its characteristics (physics-oriented, fully predictive and faster than real time) from older versions, the global structure of the proposed model is changed to obtain a set of algebraic equations easy to solve and to code. Key results We described the model and provided an analysis of model response to key environmental variables. Model evaluation against independent data is provided in a companion paper. Conclusions A simplified physical propagation model for surface fires has been exhibited. Implications The algebraic nature of the model’s equations makes it suitable to incorporate into fire management decision-making tools to support suppression activities.
Jacques Henri Balbi, François-Joseph Chatelon, Miguel Cruz, Thierry Marcelli, Sofiane Meradji, et al.. The Balbi operational model, a simplified physical model for surface fires. Part I – modelling. International Journal of Wildland Fire, 2026, 35 (9), ⟨10.1071/WF25203⟩. ⟨hal-05739945⟩
This paper proposes a quasi-asymptotic-preserving hybrid discontinuous Galerkin (HDG-QAP) scheme for the resolution of highly anisotropic diffusion problems. The HDG-QAP scheme introduces an auxiliary unknown which serves to capture the information on the dominant diffusion scale. We show that it is well posed for any $\varepsilon>0$, with $\varepsilon$ being a small constant and publications-scientifiques-360//\varepsilon$ characterizing the anisotropy strength, and that its solution is bounded uniformly in $\varepsilon$. At this point, the standard HDG procedure, namely the static condensation on the numerical trace, turns out to violate these uniform bounds. Instead, we show that the static condensation on the auxiliary unknown does lead to similar bounds uniform in $\varepsilon$, but its resolution is costly in terms of computational efforts. Therefore, we propose a relaxation method, called the HDG-QAP Uzawa iteration, to overcome this challenge in which each iteration is fast to compute. We show that the HDG-QAP Uzawa iteration converges for any $\varepsilon>0$, but also for $\varepsilon=0$. Finally, we provide some numerical examples to confirm the findings, and in particular to show that the proposed HDG-QAP Uzawa iteration works well even with a severe anisotropy $\varepsilon=10^{-15}$ where the quality of the numerical solutions is unaffected by the anisotropy strength.
Michel Mehrenberger, Tuan Dung Nguyen, Frédéric Schwander, Eric Serre. An iterated quasi-asymptotic-preserving hybrid discontinuous Galerkin method for highly anisotropic diffusion problems. ESAIM: Mathematical Modelling and Numerical Analysis, 2026, 60 (5), pp.2171 - 2203. ⟨10.1051/m2an/2026057⟩. ⟨hal-05234738v2⟩
Journal: ESAIM: Mathematical Modelling and Numerical Analysis
Umberto d'Ortona, Richard Lueptow, Nathalie Thomas. Mechanisms leading to axial segregation of bidisperse particles in rotating tumblers. Physical Review E , 2026, 114 (3), pp.035402. ⟨10.1103/d6jy-d5h7⟩. ⟨hal-05775505⟩ Plus de détails...
The origin of segregated axial bands for size-bidisperse particles in long rotating tumblers is a long-standing question in granular flows and a problem of both fundamental and practical interest. Using DEM simulations, we consider the streamwise and time-dependent development of the underlying instability as well as performing a broad parametric study over a wide range of particle size ratios, tumbler lengths and diameters, species fractions, and fill levels to determine the conditions under which axially segregated bands appear. We show that initial radial segregation of the small and large particles in the surface flowing layer results in a layer of mixed particles with a higher bulk density due to more efficient packing over a layer of nearly monodisperse small particles with a lower bulk density. This leads to a granular Rayleigh-Taylor-like instability that produces recirculation cells driving axial band formation. The appearance of a layer of high-density mixed particles over a layer of lower-density monodisperse particles can be directly connected to the operating conditions, explaining why axially segregated bands appear only under certain conditions. Typically, increasing the particle size ratio improves packing and increases the density of the mixed layer, enhancing the Rayleigh-Taylor instability and accelerating axial segregation.
Umberto d'Ortona, Richard Lueptow, Nathalie Thomas. Mechanisms leading to axial segregation of bidisperse particles in rotating tumblers. Physical Review E , 2026, 114 (3), pp.035402. ⟨10.1103/d6jy-d5h7⟩. ⟨hal-05775505⟩
Iason Tsetoglou, Denis Ricot, Song Zhao, Wilfred Bessem, Eduardo Cardenas, et al.. A new conservative formulation of solid boundary conditions for hybrid Lattice–Boltzmann modeling of compressible flows. International Journal of Heat and Fluid Flow, 2026, Special Issue of the 11th International Symposium on Turbulence, Heat and Mass Transfer, 121, pp.110619. ⟨10.1016/j.ijheatfluidflow.2026.110619⟩. ⟨hal-05728653⟩ Plus de détails...
This work presents a conservative treatment of solid boundaries that enforces strict mass conservation and mass-energy flux consistency at solid boundaries while maintaining the efficiency of the hybrid Lattice-Boltzmann/Finite-Volume (LB/FV) method for simulating compressible fluid flows. In this method, the mass and momentum equations are solved using the hybrid recursive regularized LB (HRR) algorithm, while the total energy equation is solved using a FV scheme. The strategy proposed by Zhao et al. ( 2020) is used to strongly couple LB mass and FV energy fluxes by evaluating the latter directly from the distribution functions of the LBM kinetic part. Furthermore, a modified regularized boundary condition is introduced to reconstruct the pre-collision populations at the boundaries. At boundary nodes, the density is updated from a lattice-consistent continuity balance, in which the mass variation of the boundary control volume is computed from the post-collision population exchange along the available fluid links, while zero mass exchange is imposed across blocked solid links. A series of validation cases involving conservation tests, thermal wall conditions, wall-force evaluation, and compressible-flow benchmarks demonstrates the effectiveness of the proposed boundary treatment in restoring the targeted discrete conservation properties without degrading the prediction of relevant wall and aerodynamic quantities.
Iason Tsetoglou, Denis Ricot, Song Zhao, Wilfred Bessem, Eduardo Cardenas, et al.. A new conservative formulation of solid boundary conditions for hybrid Lattice–Boltzmann modeling of compressible flows. International Journal of Heat and Fluid Flow, 2026, Special Issue of the 11th International Symposium on Turbulence, Heat and Mass Transfer, 121, pp.110619. ⟨10.1016/j.ijheatfluidflow.2026.110619⟩. ⟨hal-05728653⟩
Journal: International Journal of Heat and Fluid Flow
