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964 results on '"CERFACS"'

101. Numerical simulation of a counter-rotative open rotor using phase-lagged conditions. Initial validation on a single rotor case

Author: Maxime Fiore, Romain Biolchini, CERFACS [Toulouse], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Safran Aircraft Engines, Centre National de la Recherche Scientifique - CNRS (FRANCE), Centre Européen de Recherche et Formation Avancées en Calcul Scientifique - CERFACS (FRANCE), Institut national des sciences de l'Univers - INSU (FRANCE), and SAFRAN (FRANCE)
Subjects: 02 engineering and technology, Wake, Counter-rotating open rotor, 01 natural sciences, 010305 fluids & plasmas, law.invention, 0203 mechanical engineering, Autre, Large-eddy simulation, Loss analysis, law, 0103 physical sciences, Turbomachinery, Fourier series, Phase-lagged, Mathematics, Computer simulation, Rotor (electric), Mechanical Engineering, Propeller, Mechanics, POD data storage, Boundary layer, 020303 mechanical engineering & transports, [SPI.MECA.STRU]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Structural mechanics [physics.class-ph], Large eddy simulation
Abstract: This paper presents the large Eddy simulation (LES) of a propeller representative of the first rotor of a counter rotative open rotor (CROR) configuration based on a multiple frequency phase-lagged approach in conjunction with a proper orthogonal decomposition (POD) data storage. This method enables to perform unsteady simulations on multistage turbomachinery configurations including multiple frequency flows with a reduction of the computational domain composed of one single blade passage for each row. This approach is advantageous when no circumferential periodicity occurs in the blade rows of the configuration and a full 360 deg simulation would be required. The data storage method is based on a POD decomposition replacing the traditional Fourier series decomposition (FSD). The inherent limitation of phase-shifted periodicity assumption remains with POD data storage but this compression method alleviates some issues associated with the Fourier transform, especially spectrum issues. The paper is first dedicated to compare the flow field obtained with the LES with phase-lagged condition against full-matching URANS, LES simulations, and experimental data available around the blade and in the wake of the rotor. The study shows a close agreement of the phase-lagged LES simulation with other simulations performed and a thicker wake compared with the experiments with lower turbulent activity. The analysis of the losses generated in the configuration, based on an entropy formulation and a splitting between boundary layer and secondary flow structures, shows the strong contribution of the blade boundary layer in the losses generated.
Published: 2020

102. A linear stability analysis of compressible hybrid lattice Boltzmann methods

Author: Florian Renard, Jean-François Boussuge, Gauthier Wissocq, Pierre Sagaut, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Laboratoire de Mécanique, Modélisation et Procédés Propres (M2P2), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), CERFACS, and Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU)
Subjects: Physics and Astronomy (miscellaneous), Coupling instability, Lattice (group), Lattice Boltzmann methods, FOS: Physical sciences, 01 natural sciences, 010305 fluids & plasmas, [SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph], 0103 physical sciences, Applied mathematics, Entropy (information theory), Compressible hybrid LBM, Mode transfer, 010306 general physics, Parametric statistics, Mathematics, Numerical Analysis, Applied Mathematics, Finite difference, Fluid Dynamics (physics.flu-dyn), Physics - Fluid Dynamics, Dissipation, Computational Physics (physics.comp-ph), 16. Peace & justice, Lattice Boltzmann, Computer Science Applications, Computational Mathematics, Von Neumann analysis, High Mach instability, Modeling and Simulation, Linear approximation, Physics - Computational Physics, Numerical stability
Abstract: An original spectral study of the compressible hybrid lattice Boltzmann method (HLBM) on standard lattice is proposed. In this framework, the mass and momentum equations are addressed using the lattice Boltzmann method (LBM), while finite difference (FD) schemes solve an energy equation. Both systems are coupled with each other thanks to an ideal gas equation of state. This work aims at answering some questions regarding the numerical stability of such models, which strongly depends on the choice of numerical parameters. To this extent, several one- and two-dimensional HLBM classes based on different energy variables, formulation (primitive or conservative), collision terms and numerical schemes are scrutinized. Once appropriate corrective terms introduced, it is shown that all continuous HLBM classes recover the Navier-Stokes Fourier behavior in the linear approximation. However, striking differences arise between HLBM classes when their discrete counterparts are analysed. Multiple instability mechanisms arising at relatively high Mach number are pointed out and two exhaustive stabilization strategies are introduced: (1) decreasing the time step by changing the reference temperature $T_{ref}$ and (2) introducing a controllable numerical dissipation $\sigma$ via the collision operator. A complete parametric study reveals that only HLBM classes based on the primitive and conservative entropy equations are found usable for compressible applications. Finally, an innovative study of the macroscopic modal composition of the entropy classes is conducted. Through this study, two original phenomena, referred to as shear-to-entropy and entropy-to-shear transfers, are highlighted and confirmed on standard two-dimensional test cases., Comment: 49 pages, 23 figures
Published: 2020
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103. Evolutions du bilan hydrique du bassin de la Seine aux XXème et XXIème siècles

Author: Nicolas Flipo, Nicolas Gallois, Baptiste Labarthe, Fulvia Baratelli, Pascal Viennot, Jonathan Schuite, Agnès Rivière, Rémy Bonnet, Julien Boe, Centre de Géosciences (GEOSCIENCES), MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Sci Univers CERFACS, URA 1875, and Centre National de la Recherche Scientifique (CNRS)
Subjects: [SDE.IE]Environmental Sciences/Environmental Engineering, [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, [INFO.INFO-MO]Computer Science [cs]/Modeling and Simulation, ComputingMilieux_MISCELLANEOUS
Abstract: International audience
Published: 2019

104. 200 ans d’évolution de la ressource en eau du bassin de la Seine

Author: Nicolas Gallois, Nicolas Flipo, Jonathan Schuite, Agnès Rivière, Pascal Viennot, Fulvia Baratelli, Baptiste Labarthe, Rémy Bonnet, Julien Boe, Centre de Géosciences (GEOSCIENCES), MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, and PIREN Seine
Subjects: [SDE.IE]Environmental Sciences/Environmental Engineering, [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, ComputingMilieux_MISCELLANEOUS
Abstract: National audience
Published: 2019

105. A technique of flux reconstruction at the interfaces of nonconforming grids for aeroacoustic simulations

Author: Christophe Bogey, Hugues Deniau, Sophie Le Bras, CERFACS [Toulouse], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Laboratoire de Mecanique des Fluides et d'Acoustique (LMFA), École Centrale de Lyon (ECL), Université de Lyon-Université de Lyon-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Institut National des Sciences Appliquées de Lyon (INSA Lyon), and Université de Lyon-Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Physics, high-order schemes, non-conforming grids, Applied Mathematics, Mechanical Engineering, Computational Mechanics, Flux, structured grids, Mechanics, 01 natural sciences, 010305 fluids & plasmas, Computer Science Applications, 010101 applied mathematics, [SPI]Engineering Sciences [physics], meshless interpolation, Mechanics of Materials, 0103 physical sciences, Aeroacoustics, 0101 mathematics, finite volumes
Abstract: International audience; A flux reconstruction technique is presented to perform aeroacoustic computations using implicit high-order spatial schemes on multiblock structured grids with nonconforming interfaces. The use of such grids, with mesh spacing discontinuities across the block interfaces, eases local mesh refinements, simplifies the mesh generation process, and thus facilitates the computation of turbulent flows. In this work, the spatial discretization consists of sixth-order finite-volume implicit schemes with low-dispersion and low-dissipation properties. The flux reconstruction is based on the combination of noncentered schemes with local interpolations to define ghost cells and compute flux values at the grid interfaces. The flow variables in the ghost cells are calculated from the flow field in the grid cells using a meshless interpolation with radial basis functions. In this study, the flux reconstruction is applied to both plane and curved nonconforming interfaces. The performance of the method is first evaluated by performing two-dimensional simulations of the propagation of an acoustic pulse and of the convection of a vortex on Cartesian and wavy grids. No significant spurious noise is produced at the grid interfaces. The applicability of the flux reconstruction to a three-dimensional computation is then demonstrated by simulating a jet at a Mach number of 0.9 and a diameter-based Reynolds number of 4 × 10 5 on a Cartesian grid. The nonconforming grid interface located downstream of the jet potential core does not appreciably affect the flow development and the jet sound field, while reducing the number of mesh points by a factor of approximately two.
Published: 2019

106. Ocean dynamics shapes the structure and timing of Atlantic eequatorial modes

Author: Alban Lazar, Irene Polo, Belén Rodríguez-Fonseca, Marta Martín-Rey, Teresa Losada, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Departamento Fisica de la Tierra, Astronomía y Astrofísica [Madrid], Universidad Complutense de Madrid = Complutense University of Madrid [Madrid] (UCM), ANR-13-SENV-0002,MORDICUS,Oscillations et rétroactions climatiques aux échelles décennales : mécanismes, sensibilité et incertitudes(2013), European Project: 603521,EC:FP7:ENV,FP7-ENV-2013-two-stage,PREFACE(2013), European Project: 797236,FESTIVAL, European Project: 817578,TRIATLAS(2019), CERFACS, Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)
Subjects: 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], 0207 environmental engineering, 02 engineering and technology, Oceanography, 01 natural sciences, Physics::Geophysics, symbols.namesake, Geochemistry and Petrology, Downwelling, Earth and Planetary Sciences (miscellaneous), 14. Life underwater, 020701 environmental engineering, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, Tropical Atlantic Variability, Física atmosférica, Rossby wave, Westerlies, Ocean dynamics, Geophysics, 13. Climate action, Space and Planetary Science, Climatology, Physics::Space Physics, symbols, Upwelling, Thermocline, Kelvin wave, Geology
Abstract: International audience; A recent study has brought to light the co‐existence of two distinct Atlantic Equatorial Modes during negative phases of the Atlantic Multidecadal Variability: the Atlantic Niño and Horse‐Shoe (HS) mode. Nevertheless, the associated air‐sea interactions for HS mode have not been explored so far and the prevailing dynamic view of the Atlantic Niño has been questioned. Here, using a forced ocean model simulation, we find that for both modes, ocean dynamics is essential to explain the equatorial SST variations, while air‐sea fluxes control the off‐equatorial SST anomalies. Moreover, we demonstrate the key role played by ocean waves in shaping their distinct structure and timing. For the positive phase of both Atlantic Niño and HS, anomalous westerly winds trigger a set of equatorial downwelling Kelvin waves (KW) during spring‐summer. These dKWs deepen the thermocline, favouring the equatorial warming through vertical diffusion and horizontal advection. Remarkably, for the HS, an anomalous north‐equatorial wind stress curl excites an upwelling Rossby wave (RW), which propagates westward and is reflected at the western boundary becoming an equatorial upwelling KW. The uKW propagates to the east, activating the thermocline feedbacks responsible to cool the sea surface during summer months. This RW‐reflected mechanism acts as a negative feedback causing the early termination of the HS mode. Our results provide an improvement in the understanding of the TAV modes and emphasize the importance of ocean wave activity to modulate the equatorial SST variability. These findings could be very useful to improve the prediction of the Equatorial Modes.
Published: 2019

107. Sensitivity Analysis of the Mascaret model on the Odet River

Author: Tiberi-Wadier, Anne-Laure, Goutal, Nicole, Ricci, Sophie, Sergent, Philippe, Monteil, Céline, Centre d'Etudes et d'Expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement - Equipe-projet HA (Cerema Equipe-projet HA), Centre d'Etudes et d'Expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement (Cerema), Laboratoire d'Hydraulique Saint-Venant / Saint-Venant laboratory for Hydraulics (Saint-Venant), École des Ponts ParisTech (ENPC)-Centre d'Etudes et d'Expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement (Cerema)-EDF R&D (EDF R&D), EDF (EDF)-EDF (EDF), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Centre d'Etudes et d'Expertises sur les Risques, l'Environnement, la Mobilité et l'Aménagement - Equipe-projet HA (Cerema Equipe-projet HA), and TELEMAC-MASCARET Core Group
Subjects: [SDE.IE]Environmental Sciences/Environmental Engineering, Hydrodynamik (532.5), [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, [INFO.INFO-MO]Computer Science [cs]/Modeling and Simulation
Abstract: International audience; A Global Sensitivity Analysis (GSA) is carried out on the Mascaret model of the Odet river (France, Brittany) to identify and rank the major sources of uncertainty at observing stations on the network for the simulated water level, considering the upstream and downstream boundary conditions and the area distributed friction coefficients values. Upstream, ensemble hydrologic forcings are forecasted with the rainfall-runoff distributed model MORDOR-TS, using uncertain hydrologic model parameters drawn from uniform distributions. The downstream maritime boundary condition is perturbed taking into account the temporal correlation of the errors in storm surge. The Sobol' indices are computed at Kervir, Moulin-Vert and Justice stations given hypothesis on the statistical distribution of the aleatory variables. The study focuses on the 23 to the 26 December 2013 event. GSA highlights that the simulated water level at the three stations is mainly controlled by the immediate downstream friction coefficient when the boundary conditions are not perturbed. The flood plain friction coefficients only become important around the peak of the event. However, when the boundary conditions are also taken into account, they become predominant for the simulated water level and the value of the friction coefficients has less influence.
Published: 2019

108. Numerical analysis of a high-order unstructured overset grid method for compressible LES of turbomachinery

Author: J. de Laborderie, Stéphane Moreau, Florent Duchaine, Gaofeng Wang, Olivier Vermorel, Laurent Gicquel, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, and University of Nottingham Ningbo [China]
Subjects: Physics and Astronomy (miscellaneous), Interface (Java), Computer science, turbomachinery ⇤ Corresponding author, 01 natural sciences, 010305 fluids & plasmas, Computational science, high-order interpolation, 0103 physical sciences, Turbomachinery, [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph], 0101 mathematics, Coupling, Numerical Analysis, [SPI.FLUID]Engineering Sciences [physics]/Reactive fluid environment, Applied Mathematics, Numerical analysis, Large-Eddy Simulation, Solver, Computer Science Applications, overset grids, 010101 applied mathematics, Computational Mathematics, Third order, Modeling and Simulation, [PHYS.MECA.THER]Physics [physics]/Mechanics [physics]/Thermics [physics.class-ph], Interpolation, Large eddy simulation
Abstract: International audience; Large-Eddy Simulation (LES) is recognized as a promising method for high-fidelity flow predictions in turbomachinery applications. The presented approach consists of the coupling of several instances of the same LES unstructured solver through an overset grid method. A high-order interpolation, implemented within this coupling method, is introduced and evaluated on several test cases. It is shown to be third order accurate, to preserve the accuracy of various second and third order convective schemes and to ensure the continuity of diffusive fluxes and subgrid scale tensors even in detrimental interface configurations. In this analysis, three types of spurious waves generated at the interface are identified. They are significantly reduced by the high-order interpolation at the interface. The latter having the same cost as the original lower order method, the high-order overset grid method appears as a promising alternative to be used in all the applications.
Published: 2018

109. A note on preconditioning weighted linear least-squares with consequences for weakly constrained variational data assimilation

Author: Serge Gratton, Ehouarn Simon, Selime Gürol, Philippe L. Toint, Algorithmes Parallèles et Optimisation (IRIT-APO), Institut de recherche en informatique de Toulouse (IRIT), Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées, Institut National Polytechnique (Toulouse) (Toulouse INP), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Namur Center for Complex Systems [Namur] (NaXys), Université de Namur [Namur] (UNamur), and ANR-11-IDEX-0002,UNITI,Université Fédérale de Toulouse(2011)
Subjects: Atmospheric Science, 010504 meteorology & atmospheric sciences, linear least-squares, G.1.6, G.1.3, Context (language use), 01 natural sciences, Matrix (mathematics), Data assimilation, weakly constrained 4D-Var, preconditioning, earth sciences, FOS: Mathematics, Applied mathematics, Mathematics - Numerical Analysis, Mathematics - Optimization and Control, data assimilation, 0105 earth and related environmental sciences, Mathematics, 010505 oceanography, 86A5, 86A10, 90C06, 90C30, 15A12, Numerical Analysis (math.NA), Weighting, weakly-constrained 4D-Var, Optimization and Control (math.OC), [MATH.MATH-OC]Mathematics [math]/Optimization and Control [math.OC], Inefficiency, Linear least squares, [MATH.MATH-NA]Mathematics [math]/Numerical Analysis [math.NA]
Abstract: The effect of preconditioning linear weighted least-squares using an approximation of the model matrix is analyzed, showing the interplay of the eigenstructures of both the model and weighting matrices. A small example is given illustrating the resulting potential inefficiency of such preconditioners. Consequences of these results in the context of the weakly-constrained 4D-Var data assimilation problem are finally discussed., 10 pages, 2 figures
Published: 2018

110. Large eddy simulation of explosion deflagrating flames using a dynamic wrinkling formulation

Author: Thomas Schmitt, Pierre Quillatre, Denis Veynante, Pedro S. Volpiani, Olivier Vermorel, Laboratoire d'Énergétique Moléculaire et Macroscopique, Combustion (EM2C), CentraleSupélec-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, and Université Paris Saclay (COmUE)-Centre National de la Recherche Scientifique (CNRS)-CentraleSupélec
Subjects: Turbulent combustion, Laminar flame speed, Explosion, General Chemical Engineering, Flow (psychology), Phase (waves), General Physics and Astronomy, Energy Engineering and Power Technology, 02 engineering and technology, 01 natural sciences, 010305 fluids & plasmas, Physics::Fluid Dynamics, Acceleration, 020401 chemical engineering, 0103 physical sciences, Physics::Chemical Physics, 0204 chemical engineering, Thickened flame model, Turbulence, Chemistry, [SPI.FLUID]Engineering Sciences [physics]/Reactive fluid environment, Large eddy simulation, Laminar flow, General Chemistry, Mechanics, Overpressure, Fuel Technology, Dynamic modeling
Abstract: International audience; Reliable predictions of flames propagating in a semi-confined environment are vital for safety reasons, once they are representative of accidental explosion configurations. Large eddy simulations of deflagrating flames are carried out using a dynamic flame wrinkling factor model. This model, validated from a posteriori analysis, is able to capture both laminar and turbulent flame regimes. At early stages of the flame development, a laminar flame propagates in a flow essentially at rest and the model parameter is close to zero, corresponding to a unity-wrinkling factor. Transition to turbulence occurs when the flame interacts with the flow motions generated by thermal expansion and obstacles. The model parameter and wrinkling factor take higher values at these stages. Three configurations investigated experimentally by Masri et al. 2012, corresponding to different scenarios of flame acceleration are simulated. The first case (OOBS) is characterized by a long laminar phase. In the second one (BBBS) the flame is the most turbulent and the highest overpressure is observed in the vessel. For the last case (BOOS), the flame front is relaminarized after crossing the first row of obstacles. In all configurations, large eddy simulations (LES) predict the flow dynamics and maximum overpressure with good accuracy.
Published: 2017

111. 2D radial-azimuthal particle-in-cell benchmark for E × B discharges

Author: Francesco Taccogna, Marilyn Jimenez, François Pechereau, Bénédicte Cuenot, Olivier Vermorel, Anne Bourdon, Andrei Smolyakov, Thomas Charoy, Laurent Garrigues, Denis Eremin, Dmytro Sydorenko, Antoine Tavant, Federico Petronio, Jean-Pierre Boeuf, Kazuhiko Hara, Pascal Chabert, Andrew Christopher Denig, Alejandro Alvarez-Laguna, Willca Villafana, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Laboratoire de Physique des Plasmas (LPP), Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École polytechnique (X)-Sorbonne Université (SU)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)
Subjects: 010302 applied physics, Physics, electron cyclotron drift instability, modified two-stream instability, Condensed Matter Physics, 01 natural sciences, E × B discharges, 010305 fluids & plasmas, Computational physics, Azimuth, benchmark, [PHYS.PHYS.PHYS-PLASM-PH]Physics [physics]/Physics [physics]/Plasma Physics [physics.plasm-ph], 0103 physical sciences, Benchmark (computing), Particle-in-cell, particle-in-cell, ComputingMilieux_MISCELLANEOUS, plasma-wall interactions
Abstract: In this paper we propose a representative simulation test-case of E B discharges accounting for plasma wall interactions with the presence of both the electron cyclotron drift instability and the modified-two-stream-instability. Seven independently developed particle-in-cell (PIC) codes have simulated this benchmark case, with the same specified conditions. The characteristics of the different codes and computing times are given. Results show that both instabilities were captured in a similar fashion and good agreement between the different PIC codes is reported as main plasma parameters were closely related within a 5% interval. The number of macroparticles per cell was also varied and statistical convergence was reached. Detailed outputs are given in the supplementary data, to be used by other similar groups in the perspective of code verification.
Published: 2021

112. Improved compressible hybrid lattice Boltzmann method on standard lattice for subsonic and supersonic flows

Author: Jean-François Boussuge, Florian Renard, Yongliang Feng, Pierre Sagaut, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Laboratoire de Mécanique, Modélisation et Procédés Propres (M2P2), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), CERFACS [Toulouse], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), and Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU)
Subjects: Shock wave, General Computer Science, Discretization, Lattice Boltzmann methods, FOS: Physical sciences, LBM, 01 natural sciences, Aerodynamic noise, [SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph], 010305 fluids & plasmas, Shock waves, Physics::Fluid Dynamics, Momentum, Compressible, High speed flow, 0103 physical sciences, Supersonic speed, 0101 mathematics, Viscous stress tensor, Physics, Finite volume method, Fluid Dynamics (physics.flu-dyn), General Engineering, Physics - Fluid Dynamics, Mechanics, Computational Physics (physics.comp-ph), 010101 applied mathematics, Compressibility, Physics - Computational Physics
Abstract: A D2Q9 Hybrid Lattice Boltzmann Method (HLBM) is proposed for the simulation of both compressible subsonic and supersonic flows. This HLBM is an extension of the model of Feng et al: [12], which has been found, via different test cases, to be unstable for supersonic regimes. The improvements consist of: (1) a new discretization of the lattice closure correction term making possible to properly simulate supersonic flows, (2) a corrected viscous stress tensor that takes into account polyatomic gases, and (3) a novel discretization of the viscous heat production term fitting with the regularized formalism. The result is a hybrid method that resolves the mass and momentum equations with an LBM algorithm, and resolves the entropy-based energy equation with a finite volume method. This approach fully recovers the physics of the Navier-Stokes-Fourier equations with the ideal gas equation of state, and is valid from subsonic to supersonic regimes. It is then successfully assessed with both smooth flows and flows involving shocks. The proposed model is shown to be an efficient, accurate, and robust alternative to classic Navier-Stokes methods for the simulation of compressible flows, 21 pages, 15 figures
Published: 2021

113. Shear waves elastography for assessment of human Achilles tendon's biomechanical properties: an experimental study

Author: Marc Soubeyrand, Anthony Roux, Thomas-Xavier Haen, Sébastien Laporte, Administrateur Ensam, Compte De Service, CHU Trousseau [APHP], Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Sorbonne Université (SU), Service de pédiatrie orthopédique [CHU Trousseau], Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-CHU Trousseau [APHP], Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Sorbonne Université (SU)-Sorbonne Université (SU), Institut de Biomecanique Humaine Georges Charpak, Université Paris 13 (UP13)-Arts et Métiers ParisTech, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, AP-HP Hôpital Bicêtre (Le Kremlin-Bicêtre), Laboratoire de biomécanique (LBM), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Université Sorbonne Paris Cité (USPC)-Université Paris 13 (UP13), Arts et Métiers ParisTech, HESAM Université (HESAM), Université Paris 13 (UP13)-Université Sorbonne Paris Cité (USPC)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS), and HESAM Université - Communauté d'universités et d'établissements Hautes écoles Sorbonne Arts et métiers université (HESAM)
Subjects: Injury Biomechanics, Shear waves, Materials science, Biomedical Engineering, Achilles Tendon, 030218 nuclear medicine & medical imaging, Biomaterials, Shear modulus, 03 medical and health sciences, 0302 clinical medicine, Tendon Injuries, Elastic Modulus, [SPI.MECA.BIOM] Engineering Sciences [physics]/Mechanics [physics.med-ph]/Biomechanics [physics.med-ph], Ultimate tensile strength, Cadaver, medicine, Humans, Muscle, Skeletal, Achilles Cadaveric tendon, Elastic modulus, Mécanique: Biomécanique [Sciences de l'ingénieur], [SDV.IB] Life Sciences [q-bio]/Bioengineering, Achilles tendon, medicine.diagnostic_test, ingénierie bio-médicale [Sciences du vivant], [SPI.MECA.BIOM]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Biomechanics [physics.med-ph], Anatomy, musculoskeletal system, Biomechanical Phenomena, Tendon, medicine.anatomical_structure, Mechanics of Materials, Elasticity Imaging Techniques, [SDV.IB]Life Sciences [q-bio]/Bioengineering, Shear waves elastography, Elastography, Cadaveric spasm, 030217 neurology & neurosurgery, Biomedical engineering
Abstract: Introduction: Achilles tendon is the most frequently ruptured tendon, but its optimal treatment is increasingly controversial. The mechanical properties of the healing tendon should be studied further. Shear waves elastography (SWE) measures the shear modulus, which is proven to be correlated to elastic modulus in animal tendons. The aim of our study was to study whether the shear moduli of human cadaveric Achilles tendon, given by SWE, were correlated with the apparent elastic moduli of those tendons given by tensile tests. Materials and methods: Fourteen cadaveric lower-limbs were studied. An elastographic study of the Achilles tendon (AT) was first done in clinical-like conditions. SWE was performed at three successive levels (0, 3 and 6 cm from tendon insertion) with elastographic probe oriented parallel to tendon fibers, blindly, for three standardized ankle positions (25° plantar flexion, neutral position, and maximal dorsal flexion). The mean shear moduli were collected through blind offline data-analysis. Then, AT with triceps were harvested. They were subjected to tensile tests. A continuous SWE of the Achilles tendon was performed simultaneously. The apparent elastic modulus was obtained from the experimental stress-strain curve, and correlation with shear modulus (given by SWE) was studied. Results: Average shear moduli of harvested AT, given by SWE made an instant before the tensile tests, were significantly correlated with shear moduli of the same AT made at the same level, previously in clinical-like condition (p < 0.05), only in neutral position. There was a statistical correlation (p < 0.005) and a correlation coefficient R² equal to 0.95 ± 0.05, between shear moduli (SWE) and apparent elastic moduli (tensile tests), for 11 tendons (3 tendons were inoperable due to technical error), before a constant disruption in the correlation curves. Discussion: We demonstrated a significant correlation between SWE of Achilles tendon performed in clinicallike conditions (in neutral position) and SWE performed in harvested tendon. We also found a correlation between SWE performed on harvested tendon and apparent elastic moduli obtained with tensile tests (for 11 specimens). As a consequence, we can suppose that SWE of AT in clinical-like conditions is related to tensile tests. To our knowledge, the ability of SWE to reliably assess biomechanical properties of a tendon or muscle was, so far, only demonstrated in animal models. Conclusion: SWE can provide biomechanical information of the human AT non-invasively.
Published: 2017

114. ASIS v1.0: an adaptive solver for the simulation of atmospheric chemistry

Author: Daniel Cariolle, Béatrice Josse, Luc Giraud, H. Teyssèdre, Franck Lefèvre, Philippe Moinat, Météo-France Direction Interrégionale Sud-Est (DIRSE), Météo-France, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), High-End Parallel Algorithms for Challenging Numerical Simulations (HiePACS), Laboratoire Bordelais de Recherche en Informatique (LaBRI), Université de Bordeaux (UB)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)-Centre National de la Recherche Scientifique (CNRS)-Université de Bordeaux (UB)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)-Centre National de la Recherche Scientifique (CNRS)-Inria Bordeaux - Sud-Ouest, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria), Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), European Union, European Project: 633080,H2020,H2020-Adhoc-2014-20,MACC-III(2014), Météo France, CERFACS, Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)-Université de Bordeaux (UB)-Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB)-Inria Bordeaux - Sud-Ouest, Sorbonne Université (SU)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), and Météo France-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Scheme (programming language), [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, Chemical transport model, Computer science, Computation, lcsh:QE1-996.5, Time evolution, 010103 numerical & computational mathematics, Solver, 01 natural sciences, Computational science, lcsh:Geology, Atmospheric chemistry, Ordinary differential equation, 0101 mathematics, computer, [MATH.MATH-NA]Mathematics [math]/Numerical Analysis [math.NA], 0105 earth and related environmental sciences, computer.programming_language
Abstract: This article reports on the development and tests of the adaptive semi-implicit scheme (ASIS) solver for the simulation of atmospheric chemistry. To solve the ordinary differential equation systems associated with the time evolution of the species concentrations, ASIS adopts a one-step linearized implicit scheme with specific treatments of the Jacobian of the chemical fluxes. It conserves mass and has a time-stepping module to control the accuracy of the numerical solution. In idealized box-model simulations, ASIS gives results similar to the higher-order implicit schemes derived from the Rosenbrock's and Gear's methods and requires less computation and run time at the moderate precision required for atmospheric applications. When implemented in the MOCAGE chemical transport model and the Laboratoire de Météorologie Dynamique Mars general circulation model, the ASIS solver performs well and reveals weaknesses and limitations of the original semi-implicit solvers used by these two models. ASIS can be easily adapted to various chemical schemes and further developments are foreseen to increase its computational efficiency, and to include the computation of the concentrations of the species in aqueous-phase in addition to gas-phase chemistry.
Published: 2017

115. Development of a probabilistic ocean modelling system based on NEMO 3.5: application at eddying resolution

Author: Laurent Bessières, Stéphanie Leroux, Jean-Michel Brankart, Jean-Marc Molines, Marie-Pierre Moine, Pierre-Antoine Bouttier, Thierry Penduff, Laurent Terray, Bernard Barnier, Guillaume Sérazin, Institut de Mathématiques de Bordeaux (IMB), Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS), Institut des Géosciences de l’Environnement (IGE), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut de Recherche pour le Développement (IRD)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019]), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, P.P. Shirshov Institute of Oceanology (SIO), Russian Academy of Sciences [Moscow] (RAS), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), and Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])
Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, lcsh:Geology, 010504 meteorology & atmospheric sciences, lcsh:QE1-996.5, 010502 geochemistry & geophysics, 01 natural sciences, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, ComputingMilieux_MISCELLANEOUS, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, Physics::Geophysics
Abstract: This paper presents the technical implementation of a new, probabilistic version of the NEMO ocean–sea-ice modelling system. Ensemble simulations with N members running simultaneously within a single executable, and interacting mutually if needed, are made possible through an enhanced message-passing interface (MPI) strategy including a double parallelization in the spatial and ensemble dimensions. An example application is then given to illustrate the implementation, performances, and potential use of this novel probabilistic modelling tool. A large ensemble of 50 global ocean–sea-ice hindcasts has been performed over the period 1960–2015 at eddy-permitting resolution (1∕4°) for the OCCIPUT (oceanic chaos – impacts, structure, predictability) project. This application aims to simultaneously simulate the intrinsic/chaotic and the atmospherically forced contributions to the ocean variability, from mesoscale turbulence to interannual-to-multidecadal timescales. Such an ensemble indeed provides a unique way to disentangle and study both contributions, as the forced variability may be estimated through the ensemble mean, and the intrinsic chaotic variability may be estimated through the ensemble spread.
Published: 2017

116. Experimental and numerical investigation of flames stabilised behind rotating cylinders: interaction of flames with a moving wall

Author: Pradip Xavier, Laurent Selle, Michaël Bauerheim, Thierry Poinsot, Abdulla Ghani, Maxence Miguel-Brebion, Daniel Mejia, Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Centre National de la Recherche Scientifique - CNRS (FRANCE), Institut National Polytechnique de Toulouse - INPT (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), and Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Subjects: Materials science, Laminar flame speed, Mécanique des fluides, 020209 energy, Combustion, Thermodynamics, 02 engineering and technology, 01 natural sciences, 010305 fluids & plasmas, Physics::Fluid Dynamics, 0103 physical sciences, Laminar reacting flows, 0202 electrical engineering, electronic engineering, information engineering, Cylinder, [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph], Physics::Chemical Physics, Premixed flame, Flames, Mechanical Engineering, Rotating cylinder flame, Diffusion flame, Laminar flow, Mechanics, Condensed Matter Physics, Heat flux, Mechanics of Materials, Heat transfer
Abstract: International audience; Steady methane/air laminar premixed flames stabilised on a cylindrical bluff body subjected to a continuous rotation are analysed using joint direct numerical simulations (DNS) and experiments. DNS are carried out using a 19 species scheme for methane/air combustion and a lumped model to predict the cylinder temperature. Rotation of the cylinder induces a symmetry breaking of the flow, and leads to two distinct flame branches in the wake of the cylinder. DNS are validated against experiments in terms of flame topologies and velocity fields. DNS are then used to analyse flame structures and thermal effects. The location and structure of the two flames are differently modified by rotation and heat transfer: a superadiabatic flame branch stabilises close to the hot cylinder and burns preheated fresh gases while a subadiabatic branch is quenched over a large zone and anchors far downstream of the cylinder. Local flame structures are shown to be controlled to first order by the local enthalpy defect or excess due to heat transfer between the cylinder and the flow. An analysis of the local wall heat flux around the cylinder shows that, for low rotation speeds, the superadiabatic flame branch contributes to wall heat fluxes that considerably exceed typical values found for classical flame/wall interactions. However, for high rotation speeds, fluxes decrease because the cylinder is surrounded by a layer of burned gases that dilute incoming reactants and shield it from the flame.
Published: 2017

117. Study of flame response to transverse acoustic modes from the LES of a 42-injector rocket engine

Author: Sébastien Ducruix, Bénédicte Cuenot, Thomas Schmitt, Quentin Douasbin, Laurent Selle, Annafederica Urbano, Gabriel Staffelbach, Sébastien Candel, Centre National de la Recherche Scientifique - CNRS (FRANCE), Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), CentraleSupélec (FRANCE), Institut national des sciences de l'Univers - INSU (FRANCE), SAFRAN (FRANCE), Institut de Mécanique des Fluides de Toulouse - IMFT (Toulouse, France), Institut National Polytechnique de Toulouse - INPT (FRANCE), SAFRAN Group, Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Laboratoire d'Énergétique Moléculaire et Macroscopique, Combustion (EM2C), and Université Paris Saclay (COmUE)-Centre National de la Recherche Scientifique (CNRS)-CentraleSupélec
Subjects: Materials science, Rocket propulsion, Mécanique des fluides, General Chemical Engineering, Flame transfer function, Mechanical engineering, 02 engineering and technology, 7. Clean energy, 01 natural sciences, [SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph], 010305 fluids & plasmas, law.invention, Physics::Fluid Dynamics, 0203 mechanical engineering, law, Rayleigh index, 0103 physical sciences, Physical and Theoretical Chemistry, 020301 aerospace & aeronautics, business.industry, Mechanical Engineering, Large-Eddy Simulation, Mechanics, Injector, Transverse plane, Transverse combustion instability, Combustor, Rocket engine, Combustion chamber, Liquid oxygen, Coaxial, business, Large eddy simulation
Abstract: International audience; The Large-Eddy Simulation of a reduced-scale rocket engine operated by DLR has been conducted. This configuration features 42 coaxial injectors fed with liquid oxygen and gaseous hydrogen. For a given set of injection conditions the combustor exhibits strong transverse thermo-acoustic oscillations that are retrieved by the numerical simulation. The spatial structure of the two main modes observed in the LES is investigated through 3D Fourier analysis during the limit cycle. They are respectively associated with the first transverse and first radial resonant acoustic modes of the combustion chamber. The contributions of each individual flame to the unsteady heat release rate and the Rayleigh index are reconstructed for each mode. These contributions are in both cases low in the vicinity of velocity anti-nodes and high near pressure anti-nodes. Moreover it is noticed that these pressure fluctuations lead to large velocity oscillations in the hydrogen stream. From these observations, a driving mechanism for the flame response is proposed and values for the gain and phase of the associated flame transfer function are evaluated from the LES.
Published: 2017

118. Temporal Variance-Based Sensitivity Analysis of the River-Routing Component of the Large-Scale Hydrological Model ISBA–TRIP: Application on the Amazon Basin

Author: C. M. Emery, Mélanie C. Rochoux, Bertrand Decharme, Sylvain Biancamaria, Sophie Ricci, Aaron Boone, Pierre-André Garambois, Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Laboratoire des sciences de l'ingénieur, de l'informatique et de l'imagerie (ICube), Institut National des Sciences Appliquées - Strasbourg (INSA Strasbourg), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-École Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES)-Réseau nanophotonique et optique, Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Matériaux et nanosciences d'Alsace (FMNGE), Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), CERFACS [Toulouse], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Boone, Aaron, Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), École Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES)-Université de Strasbourg (UNISTRA)-Institut National des Sciences Appliquées - Strasbourg (INSA Strasbourg), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Institut National de Recherche en Informatique et en Automatique (Inria)-Les Hôpitaux Universitaires de Strasbourg (HUS)-Centre National de la Recherche Scientifique (CNRS)-Matériaux et Nanosciences Grand-Est (MNGE), Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Réseau nanophotonique et optique, Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique - CERFACS (CERFACS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), and Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
Subjects: [SDE] Environmental Sciences, Atmospheric Science, 010504 meteorology & atmospheric sciences, Scale (ratio), Hydrological modelling, 0208 environmental biotechnology, 02 engineering and technology, [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology, Sciences de l'ingénieur [physics]/Autre, 01 natural sciences, Data assimilation, Sensitivity (control systems), [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, Water cycle, 0105 earth and related environmental sciences, [SDU.STU.ME] Sciences of the Universe [physics]/Earth Sciences/Meteorology, 15. Life on land, 6. Clean water, 020801 environmental engineering, Model output statistics, 13. Climate action, Climatology, [SDE]Environmental Sciences, [SDU.STU.HY] Sciences of the Universe [physics]/Earth Sciences/Hydrology, Environmental science, Surface runoff, Variance-based sensitivity analysis
Abstract: The continental part of the water cycle is commonly represented with hydrological models. Yet, there are limits in their capacity to accurately estimate water storage and dynamics because of their coarse spatial resolution, simplified physics, and an incomplete knowledge of atmospheric forcing and input parameters. These errors can be diminished using data assimilation techniques. The model’s most sensitive parameters should be identified beforehand. The objective of the present study is to highlight key parameters impacting the river-routing scheme Total Runoff Integrating Pathways (TRIP) while simulating river water height and discharge as a function of time focusing on the annual cycle. Thus, a sensitivity analysis based on the decomposition of model output variance (using a method called ANOVA) is utilized and applied over the Amazon basin. Tested parameters are perturbed with correcting factors. First, parameter-correcting coefficients are considered uniform over the entire basin. The results are specific to the TRIP model and show that geomorphological parameters explain around 95% of the water height variance with purely additive contributions, all year long, with a dominating impact of the river Manning coefficient (40%), the riverbed slope (35%), and the river width (20%). The results also show that discharge is essentially sensitive to the groundwater time constant that makes up more than 90% of the variance. To a lesser extent, in rising/falling flow period, the discharge is also sensitive to geomorphological parameters. Next, the Amazon basin is divided into nine subregions and the sensitivity analysis is carried out for regionalized parameter-correcting coefficients. The results show that local-region parameters impact water height, while upstream-region parameters affect discharge.
Published: 2016

119. Uncovering Hidden Block Structure for Clustering

Author: Luce Le Gorrec, Daniel Ruiz, Sandrine Mouysset, Philip A. Knight, Iain S. Duff, Algorithmes Parallèles et Optimisation (IRIT-APO), Institut de recherche en informatique de Toulouse (IRIT), Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, STFC Rutherford Appleton Laboratory (RAL), Science and Technology Facilities Council (STFC), Department of Mathematics and Statistics [Univ Strathclyde], University of Strathclyde [Glasgow], Institut National Polytechnique (Toulouse) (Toulouse INP), IRIT, Brefeld, Ulf, Fromont, Elisa, Hotho, Andreas, Knobbe, Arno, Maathuis, Marloes, and Robardet, Céline
Subjects: Clustering and unsupervised learning, Scale (ratio), Community detection, Computer science, Shape detection, Process (computing), 010103 numerical & computational mathematics, Doubly-stochastic scaling, 01 natural sciences, Spectral clustering, Combinatorics, 010104 statistics & probability, Matrix (mathematics), Cluster (physics), Unsupervised learning, [INFO]Computer Science [cs], Adjacency matrix, 0101 mathematics, QA, Cluster analysis
Abstract: ISBN 978-3-030-46149-2; International audience; We present a multistage procedure to cluster directed and undirected weighted graphs by finding the block structure of their adjacency matrices. A central part of the process is to scale the adjacency matrix into a doubly-stochastic form, which permits detection of the whole matrix block structure with minimal spectral information (theoretically a single pair of singular vectors suffices). We present the different stages of our method, namely the impact of the doubly-stochastic scaling on singular vectors, detection of the block structure by means of these vectors, and details such as cluster refinement and a stopping criterion. Then we test the algorithm’s effectiveness by using it on two unsupervised classification tasks: community detection in networks and shape detection in clouds of points in two dimensions. By comparing results of our approach with those of widely used algorithms designed for specific purposes, we observe that our method is competitive (for community detection) if not superior (for shape detection) in comparison with existing methods.
Published: 2019

120. 2D axial-azimuthal particle-in-cell benchmark for low-temperature partially magnetized plasmas

Author: Anne Bourdon, Denis Eremin, Igor Kaganovich, Thomas Charoy, Bénédicte Cuenot, Andrei Smolyakov, Andrew Powis, Laurent Garrigues, Dmytro Sydorenko, Johan Carlsson, Jean-Pierre Boeuf, Willca Villafana, Olivier Vermorel, Antoine Tavant, Kazuhiko Hara, Pascal Chabert, Laboratoire de Physique des Plasmas (LPP), Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École polytechnique (X)-Sorbonne Université (SU)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Groupe de Recherche Energétique, Plasmas et Hors Equilibre (LAPLACE-GREPHE), LAboratoire PLasma et Conversion d'Energie (LAPLACE), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Ruhr University Bochum (RUB), Texas A&M University [College Station], Princeton Plasma Physics Laboratory (PPPL), Princeton University, University of Saskatchewan [Saskatoon] (U of S), University of Alberta, Université Paris-Saclay-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris-Sud - Paris 11 (UP11)-École polytechnique (X)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)
Subjects: Physics, [PHYS]Physics [physics], Correctness, Particle-In-Cell, Plasma, Electron drift instability Submitted to: Plasma Sources Sci Technol, Benchmark, Condensed Matter Physics, 01 natural sciences, 010305 fluids & plasmas, Computational physics, Azimuth, [PHYS.PHYS.PHYS-PLASM-PH]Physics [physics]/Physics [physics]/Plasma Physics [physics.plasm-ph], Electric field, ExB discharges, 0103 physical sciences, Convergence (routing), Benchmark (computing), Electron temperature, Particle-in-cell, 010306 general physics, ComputingMilieux_MISCELLANEOUS
Abstract: International audience; The increasing need to demonstrate the correctness of computer simulations has highlighted the importance of benchmarks. We define in this paper a representative simulation case to study low-temperature partially-magnetized plasmas. Seven independently developed Particle-In-Cell codes have simulated this benchmark case, with the same specified conditions. The characteristics of the codes used, such as implementation details or computing times and resources, are given. First, we compare at steady-state the time-averaged axial profiles of three main discharge parameters (axial electric field, ion density and electron temperature). We show that the results obtained exhibit a very good agreement within 5% between all the codes. As ExB discharges are known to cause instabilities propagating in the direction of electron drift, an analysis of these instabilities is then performed and a similar behaviour is retrieved between all the codes. A particular attention has been paid to the numerical convergence by varying the number of macroparticles per cell and we show that the chosen benchmark case displays a good convergence. Detailed outputs are given in the supplementary data, to be used by other similar codes in the perspective of code verification. 2D axial-azimuthal Particle-In-Cell benchmark for low-temperature partially ..
Published: 2019

121. Improving the scalability of the ABCD Solver with a combination of new load balancing and communication minimization techniques

Author: Duff, Iain, Leleux, Philippe, Ruiz, Daniel, Torun, F, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, STFC Rutherford Appleton Laboratory (RAL), Science and Technology Facilities Council (STFC), Algorithmes Parallèles et Optimisation (IRIT-APO), Institut de recherche en informatique de Toulouse (IRIT), Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées, Institut National Polytechnique (Toulouse) (Toulouse INP), Ankara Yıldırım Beyazıt University (AYBU), and This work was supported by the Energy oriented Centre of Excellence (EoCoE), grant agreement number 676629, funded within the Horizon2020 framework of the European Union. We acknowledge PRACE for awarding us access to MareNostrum4 at the Barcelona Supercomputing Center (BSC), Spain.
Subjects: sparse matrix, Block Cimmino, hybrid solver, iterative solver, [INFO.INFO-DC]Computer Science [cs]/Distributed, Parallel, and Cluster Computing [cs.DC], [INFO.INFO-NA]Computer Science [cs]/Numerical Analysis [cs.NA], distributed memory parallelism
Abstract: International audience; The hybrid scheme block row-projection method implemented in the ABCD Solver is designed for solving large sparse unsymmetric systems of equations on distributed memory parallel computers. The method implements a block Cimmino iterative scheme, accelerated with a stabilized block conjugate gradient algorithm. An augmented pseudo-direct variant has also been developed to overcome convergence issues. Both methods are included in the ABCD solver with a hybrid parallelization scheme.The parallel performance of the ABCD Solver is improved in the first non-beta release, version 1.0, which we present in this paper. Novel algorithms for the distribution of partitions to processes are introduced to minimize communication as well as to balance the workload. Furthermore, the master-workers approach on each subsystem is also improved in order to achieve higher scalability through run-time placement of processes. We illustrate the improved parallel scalability of the ABCD Solver on a distributed memory architecture by solving several problems from the SuiteSparse Matrix Collection.
Published: 2019

122. Compréhension des 3 lois de Newton chez des élèves ingénieurs

Author: Jean-François Parmentier, Julitte Huez, Dominique Poquillon, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Institut de Recherche pour l’Enseignement des Sciences de Toulouse (IRES), Toulouse INP-ENSIACET, Centre interuniversitaire de recherche et d'ingenierie des matériaux (CIRIMAT), Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut National Polytechnique (Toulouse) (Toulouse INP), and Université Fédérale Toulouse Midi-Pyrénées-Institut de Chimie du CNRS (INC)
Subjects: Force Concept Inventory, mécanique, [SHS.EDU]Humanities and Social Sciences/Education, mesure, [PHYS.MECA]Physics [physics]/Mechanics [physics], conception
Abstract: International audience; L’Université Fédérale de Toulouse s’est investie depuis plusieurs années dans la transformation pédagogique de l’enseignement supérieur. Or, assurer une transformation pédagogique effective nécessite la présence d’indicateurs de mesure. Dans ce cadre, deux enseignants-chercheurs contribuant à l’enseignement de la mécanique à l’INP-ENSIACET ont choisi de mesurer systématiquement la compréhension conceptuelle des lois de Newton chez les étudiants suivant leur cours. En effet, depuis une vingtaine d’années, la recherche internationale a montré que ces concepts sont souvent mal compris des étudiants. La mesure s’est effectuée en utilisant une adaptation du Force Concept Inventory, proposée par l’Association Française de Mécanique, et a concerné les étudiants de L3 et M1 sur quatre années consécutives. L’analyse des résultats montre d’une part que les étudiants entrants possèdent des lacunes sur la notion de force, le principe d’inertie et la loi des actions réciproques. D’autre part une progression significative entre le L3 et le M1 est observée, mais avec un résultat final encore faible pour les attendus de niveau master : environ 60% des étudiants maitrisant la notion de force, 44% le principe d’inertie et 65% la loi des actions réciproques.
Published: 2019

123. Couplage implicite-explicite intégration temporelle méthode pour les écoulements compressibles instables

Author: Guillaume Puigt, Laurent Muscat, Pierre Brenner, Marc Montagnac, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, ArianeGroup, ONERA / DMPE, Université de Toulouse [Toulouse], and ONERA-PRES Université de Toulouse
Subjects: Physics and Astronomy (miscellaneous), Computer science, Computation, FOS: Physical sciences, FORMULATION VOLUME FINI, Context (language use), 010103 numerical & computational mathematics, HYBRID TIME INTEGRATION, 01 natural sciences, Stability (probability), [SPI]Engineering Sciences [physics], Applied mathematics, 0101 mathematics, Coupling, [PHYS]Physics [physics], Numerical Analysis, Applied Mathematics, ANALYSE DE STABILITE EN ESPACE/TEMPS, Fluid Dynamics (physics.flu-dyn), COMPRESSIBLE UNSTEADY FLOWS, Ranging, Physics - Fluid Dynamics, Computational Physics (physics.comp-ph), SPACE-TIME STABILITY ANALYSIS, INTEGRATION TEMPORELLE HYBRIDE, Computer Science Applications, ECOULEMENTS COMPRESSIBLES INSTATIONNAIRES, 010101 applied mathematics, Computational Mathematics, Boundary layer, Modeling and Simulation, FINITE VOLUME FORMULATION, Reynolds-averaged Navier–Stokes equations, Physics - Computational Physics, Large eddy simulation
Abstract: International audience; This paper addresses how two time integration schemes, the Heun's scheme for explicit time integration and the second-order Crank-Nicolson scheme for implicit time integration, can be coupled spatially. This coupling is the prerequisite to perform a coupled Large Eddy Simulation / Reynolds Averaged Navier-Stokes computation in an industrial context, using the implicit time procedure for the boundary layer (RANS) and the explicit time integration procedure in the LES region. The coupling procedure is designed in order to switch from explicit to implicit time integra-tions as fast as possible, while maintaining stability. After introducing the different schemes, the paper presents the initial coupling procedure adapted from a published reference and shows that it can amplify some numerical waves. An alternative procedure, studied in a coupled time/space framework, is shown to be stable and with spectral properties in agreement with the requirements of industrial applications. The coupling technique is validated with standard test cases, ranging from one-dimensional to three-dimensional flows.; Ce papier explique comment deux schémas d'intégration temporelle (schéma de Heun en explicite et schéma de Crank-Nicolson en implicite) peuvent être couplés spatialement. Ce couplage est un prérequis pour faire des simulations couplées LES / RANS dans un contexte industriel pour lequel la couche limite (RANS) est calculée en implicite et l'intégrateur explicite est utilisé pour la LES. La méthodologie de couplage est choisie pour passer très vite de l'explicite à l'implicite tout en garantissant la stabilité. Après avoir introduit les deux schémas, le papier présente une méthode de couplage adaptée de la littérature qui amplifie certains nombres d'onde. Une approche alternative, étudiée dans un contexte couplé espace/temps, est stable et présente des propriétés spectrales en accord avec les prérequis des applications industrielles. Le couplage est validé sur des cas tests classiques en 1D et 3.
Published: 2019

124. A coupled implicit-explicit time integration method for compressible unsteady flows

Author: Muscat, Laurent, Puigt, Guillaume, Montagnac, Marc, Brenner, Pierre, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, ArianeGroup, ONERA / DMPE, Université de Toulouse [Toulouse], and ONERA-PRES Université de Toulouse
Subjects: [PHYS]Physics [physics], [SPI]Engineering Sciences [physics], FINITE VOLUME FORMULATION, ANALYSE DE STABILITE EN ESPACE/TEMPS, COMPRESSIBLE UNSTEADY FLOWS, FORMULATION VOLUME FINI, HYBRID TIME INTEGRATION, SPACE-TIME STABILITY ANALYSIS, INTEGRATION TEMPORELLE HYBRIDE, ECOULEMENTS COMPRESSIBLES INSTATIONNAIRES
Abstract: International audience; This paper addresses how two time integration schemes, the Heun's scheme for explicit time integration and the second-order Crank-Nicolson scheme for implicit time integration, can be coupled spatially. This coupling is the prerequisite to perform a coupled Large Eddy Simulation / Reynolds Averaged Navier-Stokes computation in an industrial context, using the implicit time procedure for the boundary layer (RANS) and the explicit time integration procedure in the LES region. The coupling procedure is designed in order to switch from explicit to implicit time integra-tions as fast as possible, while maintaining stability. After introducing the different schemes, the paper presents the initial coupling procedure adapted from a published reference and shows that it can amplify some numerical waves. An alternative procedure, studied in a coupled time/space framework, is shown to be stable and with spectral properties in agreement with the requirements of industrial applications. The coupling technique is validated with standard test cases, ranging from one-dimensional to three-dimensional flows.; Ce papier explique comment deux schémas d'intégration temporelle (schéma de Heun en explicite et schéma de Crank-Nicolson en implicite) peuvent être couplés spatialement. Ce couplage est un prérequis pour faire des simulations couplées LES / RANS dans un contexte industriel pour lequel la couche limite (RANS) est calculée en implicite et l'intégrateur explicite est utilisé pour la LES. La méthodologie de couplage est choisie pour passer très vite de l'explicite à l'implicite tout en garantissant la stabilité. Après avoir introduit les deux schémas, le papier présente une méthode de couplage adaptée de la littérature qui amplifie certains nombres d'onde. Une approche alternative, étudiée dans un contexte couplé espace/temps, est stable et présente des propriétés spectrales en accord avec les prérequis des applications industrielles. Le couplage est validé sur des cas tests classiques en 1D et 3.
Published: 2019

125. Numerical and experimental studies of the flow around a partially submerged vertical cylinder

Author: Valentin Ageorges, Jorge Peixinho, Gaële Perret, Ghislain Lartigue, Vincent Moureau, Laboratoire Ondes et Milieux Complexes (LOMC), Centre National de la Recherche Scientifique (CNRS)-Université Le Havre Normandie (ULH), Normandie Université (NU)-Normandie Université (NU), Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Complexe de recherche interprofessionnel en aérothermochimie (CORIA), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences appliquées Rouen Normandie (INSA Rouen Normandie), Institut National des Sciences Appliquées (INSA)-Normandie Université (NU)-Institut National des Sciences Appliquées (INSA)-Normandie Université (NU)-Université de Rouen Normandie (UNIROUEN), Normandie Université (NU), and Peixinho, Jorge
Subjects: Free-surface, [SPI.FLUID]Engineering Sciences [physics]/Reactive fluid environment, Numerical simulations, [SPI.FLUID] Engineering Sciences [physics]/Reactive fluid environment, Experiments, Air-entrainment
Abstract: International audience; L'écoulement et l'injection d'air autour d'un cylindre vertical partiellement immergé, en translation, est étudié expérimentalement et numériquement. Le régime d'écoulement est turbulent avec 15 000 < Re < 60 000 et 0.4 < F r < 1.7, où Re et F r sont les nombres de Reynolds et de Froude adimensionnés à l'aide du diamètre D du cylindre. Une cavité à l'aval du cylindre est observée. L'objectif de ce travail est d'étudier les efforts de traînée, l'élévation de la surface libre et la vitesse critique à partir de laquelle il y a entraînement d'air. Un bon accord entre les expériences et les simulations a été trouvé, évaluant ainsi la profondeur de la cavité, le coefficient de traînée et la vitesse critique d'injection d'air. Abstract : The flow around a vertical cylinder piercing the free-surface is studied experimentally and numerically. The cylinder has a free-end and the range of velocities are in the regime of turbulent wake with experiments and simulations carried out for 15 000 < Re < 60 000 and 0.4 < F r < 1.7, where Re and F r are the Reynolds and Froude numbers based on the cylinder diameter D. A cavity downstream the cylinder is observed. The focus here is on drag force measurement, free-surface elevation, and critical velocity for air-entrainment. Specifically, a good agreement between experiments and simulations is obtained for the cavity depth, the drag coefficient and the critical velocity.
Published: 2019

126. Inclusion of CO2 flux modelling in an urban canopy layer model and an evaluation over an old European city centre

Author: Robert Schoetter, Marine Goret, Marie-Pierre Moine, Valéry Masson, Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), and CERFACS
Subjects: Atmospheric Science, 010504 meteorology & atmospheric sciences, Microclimate, Energy balance, Biosphere, Climate change, Context (language use), Vegetation, lcsh:QC851-999, 15. Life on land, 010501 environmental sciences, Atmospheric sciences, 01 natural sciences, lcsh:Environmental pollution, 13. Climate action, Urban planning, Greenhouse gas, lcsh:TD172-193.5, 11. Sustainability, [SDE]Environmental Sciences, Environmental science, lcsh:Meteorology. Climatology, 0105 earth and related environmental sciences, General Environmental Science
Abstract: In the context of climate change, the reduction of greenhouse gas emissions is a global concern. Recent publications estimate that 30–40% of total anthropogenic greenhouse gases are directly emitted by urban areas. This paper focuses on CO2, which is the main anthropogenic greenhouse gas, and presents an implementation of CO2 flux modelling in urban areas within the urban canopy model Town Energy Balance (TEB). Highly weather-dependent contributors to CO2 fluxes (buildings and vegetation) are explicitly modelled by TEB using the Building Energy Model (BEM) for buildings and Interactions between Soil, Biosphere and Atmosphere (ISBA) for urban vegetation. This approach allows the impacts of the urban microclimate on CO2 fluxes to be simulated. Non-weather-dependent contributors (traffic and human respiration) are simulated using simpler approaches. A sensitivity study applied to the centre of Toulouse, France, highlights the relevance of detailed input data related to traffic, building use and human behaviour to simulate accurate CO2 fluxes. The results show that traffic (48.5%) and buildings (42%) are the main contributors to the annual mean CO2 flux. A comparison of the model results with independent eddy-covariance flux data shows good agreement with a root mean square error of 15.3 μmol m−2 s−1 and demonstrates that the model is able to reproduce seasonally averaged daily cycles of CO2 fluxes. In future studies, this model can be used to quantify the impacts on CO2 fluxes of different urban development scenarios such as urban expansion, changes in urban form, changes in practices related to the heating of buildings or urban greening strategies. Keywords: CO2fluxes, Eddy covariance, Cities, Urban canopy layer model, Model evaluation
Published: 2019

127. Evaluation of CMIP6 DECK Experiments With CNRM‐CM6‐1

Author: David Saint-Martin, Yann Meurdesoif, Julie Deshayes, Sophie Belamari, D. Salas y Melia, Robin Waldman, Stephane Sénési, Jeanne Colin, Sophie Valcke, Gurvan Madec, Roland Séférian, Olivier Geoffroy, Hervé Douville, Romain Roehrig, Pierre Nabat, Matthieu Chevallier, Laurent Franchistéguy, Jean-François Guérémy, Sarah Berthet, Christophe Cassou, I. Beau, Bertrand Decharme, Julien Cattiaux, Antoinette Alias, M. P. Moine, Rym Msadek, Emilia Sanchez-Gomez, Christian Ethé, C. Lévy, Aurélien Ribes, Aurore Voldoire, Laurent Terray, Martine Michou, Groupe de Météorologie de Grande Échelle et Climat (GMGEC), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Nucleus for European Modeling of the Ocean (NEMO R&D ), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), ANR-13-MONU-0008,CONVERGENCE,Convergence en Science du Climat à l'ère du Big Data et des challenges de l'Exascale.(2013), European Project: 641816,H2020,H2020-SC5-2014-two-stage,CRESCENDO(2015), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), CERFACS, Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)
Subjects: 010504 meteorology & atmospheric sciences, Magnitude (mathematics), climate model, 010502 geochemistry & geophysics, 01 natural sciences, lcsh:Oceanography, CMIP6 DECK, Range (statistics), Sea ice, Environmental Chemistry, lcsh:GC1-1581, 14. Life underwater, Sensitivity (control systems), lcsh:Physical geography, 0105 earth and related environmental sciences, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Global and Planetary Change, Coupled model intercomparison project, geography, geography.geographical_feature_category, CNRM‐CM6‐1, 13. Climate action, Climatology, Spatial ecology, General Earth and Planetary Sciences, Environmental science, Climate sensitivity, Climate model, lcsh:GB3-5030
Abstract: International audience; This paper describes the main characteristics of CNRM-CM6-1, the fully coupled atmosphere-ocean general circulation model of sixth generation jointly developed by Centre National de Recherches Météorologiques (CNRM) and Cerfacs for the sixth phase of the Coupled Model Intercomparison Project 6 (CMIP6). The paper provides a description of each component of CNRM-CM6-1, including the coupling method and the new online output software. We emphasize where model's components have been updated with respect to the former model version, CNRM-CM5.1. In particular, we highlight major improvements in the representation of atmospheric and land processes. A particular attention has also been devoted to mass and energy conservation in the simulated climate system to limit long-term drifts. The climate simulated by CNRM-CM6-1 is then evaluated using CMIP6 historical and Diagnostic, Evaluation and Characterization of Klima (DECK) experiments in comparison with CMIP5 CNRM-CM5.1 equivalent experiments. Overall, the mean surface biases are of similar magnitude but with different spatial patterns. Deep ocean biases are generally reduced, whereas sea ice is too thin in the Arctic. Although the simulated climate variability remains roughly consistent with CNRM-CM5.1, its sensitivity to rising CO 2 has increased: the equilibrium climate sensitivity is 4.9 K, which is now close to the upper bound of the range estimated from CMIP5 models.
Published: 2019

128. The Tropical Atlantic Observing System

Author: G. R. Foltz, P. Brandt, I. Richter, B. Rodríguez-Fonseca, F. Hernandez, M. Dengler, R. R. Rodrigues, J. O. Schmidt, L. Yu, N. Lefevre, L. Cotrim Da Cunha, M. J. McPhaden, M. Araujo, J. Karstensen, J. Hahn, M. Martín-Rey, C. M. Patricola, P. Poli, P. Zuidema, R. Hummels, R. C. Perez, V. Hatje, J. F. Lübbecke, I. Polo, R. Lumpkin, B. Bourlès, F. E. Asuquo, P. Lehodey, A. Conchon, P. Chang, P. Dandin, C. Schmid, A. Sutton, H. Giordani, Y. Xue, S. Illig, T. Losada, S. A. Grodsky, F. Gasparin, T. Lee, E. Mohino, P. Nobre, R. Wanninkhof, N. Keenlyside, V. Garcon, E. Sánchez-Gómez, H. C. Nnamchi, M. Drévillon, A. Storto, E. Remy, A. Lazar, S. Speich, M. Goes, T. Dorrington, W. E. Johns, J. N. Moum, C. Robinson, C. Perruche, R. B. de Souza, A. T. Gaye, J. López-Parages, P.-A. Monerie, P. Castellanos, N. U. Benson, M. N. Hounkonnou, J. Trotte Duhá, R. Laxenaire, N. Reul, Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS), NOAA Atlantic Oceanographic and Meteorological Laboratory (AOML), National Oceanic and Atmospheric Administration (NOAA), Leibniz-Institut für Meereswissenschaften (IFM-GEOMAR), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Instituto de Geociencias, Universidad Complutense de Madrid = Complutense University of Madrid [Madrid] (UCM)-Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), Departamento Fisica de la Tierra, Astronomía y Astrofísica [Madrid], Universidad Complutense de Madrid = Complutense University of Madrid [Madrid] (UCM), Hydrosciences Montpellier (HSM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Helmholtz Centre for Ocean Research [Kiel] (GEOMAR), Instituto Federal de Santa Catarina [Brazil] (IFSC), Helmholtz zentrum für Schwerionenforschung GmbH (GSI), Woods Hole Oceanographic Institution (WHOI), Austral, Boréal et Carbone (ABC), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Laboratório de Oceanografia Física Estuarina e Costeira, Depto. Oceanografia, Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD [France-Ouest]), Collecte Localisation Satellites (CLS), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Centre National d'Études Spatiales [Toulouse] (CNES), Météo-France Direction Interrégionale Sud-Est (DIRSE), Météo-France, Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Departamento de Geofisica y Meteorologia [Madrid], Nansen Environmental and Remote Sensing Center [Bergen] (NERSC), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Centre for Maritime Research and Experimentation - Science and Technology Organisation (CMRE - STO), Mercator Océan, Société Civile CNRS Ifremer IRD Météo-France SHOM, Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Océan et variabilité du climat (VARCLIM), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), University of Amsterdam [Amsterdam] (UvA), School of Environmental Sciences [Norwich], University of East Anglia [Norwich] (UEA), Laboratoire de Physique de l'Atmosphère et de l'Océan Siméon Fongang (LPAO-SF), École Supérieure Polytechnique de Dakar (ESP), Université Cheikh Anta Diop [Dakar, Sénégal] (UCAD)-Université Cheikh Anta Diop [Dakar, Sénégal] (UCAD), Laboratoire d'Océanographie Physique et Spatiale (LOPS), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Institut Pierre-Simon-Laplace (IPSL (FR_636)), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU), Groupe d'étude de l'atmosphère météorologique (CNRM-GAME), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Météo France, Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), CERFACS, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Consejo Superior de Investigaciones Científicas [Spain] (CSIC)-Universidade Complutense Madrid, Universidad Complutense de Madrid [Madrid] (UCM), Institut de Recherche pour le Développement (IRD)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), GEOMAR - Helmholtz Centre for Ocean Research [Kiel] (GEOMAR), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National d'Études Spatiales [Toulouse] (CNES)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS Paris)-École normale supérieure - Paris (ENS Paris), and Université Cheikh Anta Diop [Dakar, Sénégal] (UCAD)
Subjects: 0106 biological sciences, lcsh:QH1-199.5, 010504 meteorology & atmospheric sciences, [SDE.MCG]Environmental Sciences/Global Changes, Ocean Engineering, lcsh:General. Including nature conservation, geographical distribution, Aquatic Science, Tropical Atlantic, Oceanography, 01 natural sciences, biogeochemistry, Ecosystem, 14. Life underwater, lcsh:Science, Life Below Water, climate, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Water Science and Technology, [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph], Global and Planetary Change, Ecology, 010604 marine biology & hydrobiology, Física atmosférica, Biogeochemistry, observing system, Climate Action, tropical Atlantic Ocean, 13. Climate action, weather, Environmental science, lcsh:Q, hurricanes, ecosystems, coupled model bias
Abstract: The tropical Atlantic is home to multiple coupled climate variations covering a wide\ud range of timescales and impacting societally relevant phenomena such as continental\ud rainfall, Atlantic hurricane activity, oceanic biological productivity, and atmospheric\ud circulation in the equatorial Pacific. The tropical Atlantic also connects the southern and northern branches of the Atlantic meridional overturning circulation and receives\ud freshwater input from some of the world’s largest rivers. To address these diverse,\ud unique, and interconnected research challenges, a rich network of ocean observations\ud has developed, building on the backbone of the Prediction and Research Moored Array\ud in the Tropical Atlantic (PIRATA). This network has evolved naturally over time and out of\ud necessity in order to address the most important outstanding scientific questions and\ud to improve predictions of tropical Atlantic severe weather and global climate variability\ud and change. The tropical Atlantic observing system is motivated by goals to understand\ud and better predict phenomena such as tropical Atlantic interannual to decadal variability\ud and climate change; multidecadal variability and its links to the meridional overturning\ud circulation; air-sea fluxes of CO2 and their implications for the fate of anthropogenic CO2;\ud the Amazon River plume and its interactions with biogeochemistry, vertical mixing, and\ud hurricanes; the highly productive eastern boundary and equatorial upwelling systems;\ud and oceanic oxygen minimum zones, their impacts on biogeochemical cycles and\ud marine ecosystems, and their feedbacks to climate. Past success of the tropical\ud Atlantic observing system is the result of an international commitment to sustained\ud observations and scientific cooperation, a willingness to evolve with changing research\ud and monitoring needs, and a desire to share data openly with the scientific community\ud and operational centers. The observing system must continue to evolve in order to\ud meet an expanding set of research priorities and operational challenges. This paper\ud discusses the tropical Atlantic observing system, including emerging scientific questions\ud that demand sustained ocean observations, the potential for further integration of the\ud observing system, and the requirements for sustaining and enhancing the tropical\ud Atlantic observing system.
Published: 2019

129. Training convolutional neural networks to estimate turbulent sub-grid scale reaction rates

Author: Nicolas Cazard, Denis Veynante, Antony Misdariis, Thierry Poinsot, Corentin Lapeyre, CERFACS, Laboratoire d'Énergétique Moléculaire et Macroscopique, Combustion (EM2C), Université Paris Saclay (COmUE)-Centre National de la Recherche Scientifique (CNRS)-CentraleSupélec, Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, Centre National de la Recherche Scientifique - CNRS (FRANCE), Institut National Polytechnique de Toulouse - INPT (FRANCE), Université Paris-Saclay (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), CentraleSupélec (FRANCE), Centre Européen de Recherche et Formation Avancées en Calcul Scientifique - CERFACS (FRANCE), Laboratoire d'Énergétique Moléculaire et Macroscopique, Combustion - EM2C (Châtenay-Malabry, France), and Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Subjects: Turbulent combustion, Scale (ratio), Computer science, Flame surface density, Mécanique des fluides, General Chemical Engineering, Direct numerical simulation, General Physics and Astronomy, Energy Engineering and Power Technology, FOS: Physical sciences, 02 engineering and technology, 01 natural sciences, Convolutional neural network, [SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph], Physics::Fluid Dynamics, 020401 chemical engineering, 0103 physical sciences, 0204 chemical engineering, Physics::Chemical Physics, 010304 chemical physics, business.industry, Turbulence, Deep learning, 80A32, Fluid Dynamics (physics.flu-dyn), General Chemistry, Density estimation, Physics - Fluid Dynamics, Grid, Fuel Technology, Flow (mathematics), Artificial intelligence, business, Algorithm
Abstract: This work presents a new approach for premixed turbulent combustion modeling based on convolutional neural networks (CNN). We first propose a framework to reformulate the problem of subgrid flame surface density estimation as a machine learning task. Data needed to train the CNN is produced by direct numerical simulations (DNS) of a premixed turbulent flame stabilized in a slot-burner configuration. A CNN inspired from a U-Net architecture is designed and trained on the DNS fields to estimate sub-grid scale wrinkling. It is then tested on an unsteady turbulent flame where the mean inlet velocity is increased for a short time and the flame must react to a varying turbulent incoming flow. The CNN is found to efficiently extract the topological nature of the flame and predict subgrid scale wrinkling, outperforming classical algebraic models. This method can be seen as a data-driven extension of dynamic formulations, where topological information was extracted in a hand-designed fashion.
Published: 2019

130. State-parameter estimation approach for data-driven wildland fire spread modeling: Application to the 2012 RxCADRE S5 field-scale experiment

Author: Annabelle Collin, Cong Zhang, Philippe Moireau, Arnaud Trouvé, Mélanie C. Rochoux, Department of Fire Protection Engineering [College Park], University of Maryland [College Park], University of Maryland System-University of Maryland System, Modélisation Mathématique pour l'Oncologie (MONC), Institut de Mathématiques de Bordeaux (IMB), Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS)-Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS)-Institut Bergonié [Bordeaux], UNICANCER-UNICANCER-Inria Bordeaux - Sud-Ouest, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria), Mathematical and Mechanical Modeling with Data Interaction in Simulations for Medicine (M3DISIM), Laboratoire de mécanique des solides (LMS), École polytechnique (X)-MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)-MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Inria Saclay - Ile de France, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1 (UB)-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS)-Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1 (UB)-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS)-Institut Bergonié [Bordeaux], École polytechnique (X)-Mines Paris - PSL (École nationale supérieure des mines de Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)-Mines Paris - PSL (École nationale supérieure des mines de Paris), and ANR-16-CE04-0006,FireCaster,Plateforme de prévision incendie et de réponse d'urgence.(2016)
Subjects: 040101 forestry, Scale (ratio), Estimation theory, Computer science, Mode (statistics), General Physics and Astronomy, 020101 civil engineering, 04 agricultural and veterinary sciences, 02 engineering and technology, General Chemistry, Image segmentation, Kalman filter, Similarity measure, 7. Clean energy, 0201 civil engineering, [SPI]Engineering Sciences [physics], Data assimilation, 0401 agriculture, forestry, and fisheries, General Materials Science, State observer, Safety, Risk, Reliability and Quality, Algorithm
Abstract: Data assimilation is an emerging and powerful tool towards real-time flame front monitoring for wildland fire applications. The key idea is to regularly update the state and/or parameters of a fire spread model using observed firelines in order to improve a forecast on future fire locations. The merits of combining state estimation and parameter estimation through a hybrid state-parameter estimation algorithm are demonstrated through the 2012 RxCADRE S5 field-scale controlled burn experiment. For state estimation, we adopt a cost-effective Luenberger observer formulation to reconstruct a complete view of the burning state at a given time. For parameter estimation, we use an ensemble transform Kalman filter to solve the inverse modeling problem consisting of inferring more realistic wind conditions given observations of the actual burning state. The data-driven model relies on a front shape similarity measure derived from image segmentation theory to quantify position errors. We show that the hybrid approach provides an efficient framework to address all sources of model uncertainties and to select burning scenarios that are most likely to occur. Parameter estimation is a key component of the data-driven model by reducing model bias. Using the fire spread model in forecast mode is then an asset to accurately track the flame front dynamics at future lead times.
Published: 2019

131. Synthesis of Ocean Observations Using Data Assimilation for Operational, Real-Time and Reanalysis Systems: A More Complete Picture of the State of the Ocean

Author: Stefano Ciavatta, Arthur Vidard, Jim Cummings, Matthew Martin, Sergey Frolov, Anna Teruzzi, Peter R. Oke, Andrea Storto, Bruce D. Cornuelle, Anthony T. Weaver, Magdalena Balmaseda, Pierre F. J. Lermusiaux, Santha Akella, Paolo Oddo, Laurent Bertino, Andrew M. Moore, Hernan G. Arango, Computer Laboratory [Cambridge], University of Cambridge [UK] (CAM), United Kingdom Met Office [Exeter], NASA Goddard Space Flight Center (GSFC), Institute of Marine and Coastal Sciences and Department of Geological Sciences, Rutgers, The State University of New Jersey [New Brunswick] (RU), Rutgers University System (Rutgers)-Rutgers University System (Rutgers), European Centre for Medium-Range Weather Forecasts (ECMWF), Nansen Environmental and Remote Sensing Center [Bergen] (NERSC), Plymouth Marine Laboratory (PML), Plymouth Marine Laboratory, Scripps Institution of Oceanography (SIO), University of California [San Diego] (UC San Diego), University of California-University of California, IMSG@National Center for Environmental Predictions, Naval Research Laboratory (NRL), Massachusetts Institute of Technology (MIT), Centre for Maritime Research and Experimentation - Science and Technology Organisation (CMRE - STO), CSIRO Marine and Atmosphere Research [Hobart], Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Istituto Nazionale di Geofisica e di Oceanografia Sperimentale (OGS), Mathematics and computing applied to oceanic and atmospheric flows (AIRSEA), Inria Grenoble - Rhône-Alpes, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Laboratoire Jean Kuntzmann (LJK ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes [2016-2019] (UGA [2016-2019])-Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Scripps Institution of Oceanography (SIO - UC San Diego), and University of California (UC)-University of California (UC)
Subjects: 0106 biological sciences, Ocean observations, lcsh:QH1-199.5, 010504 meteorology & atmospheric sciences, Computer science, ensembles, Ocean Engineering, lcsh:General. Including nature conservation, geographical distribution, Aquatic Science, Oceanography, 01 natural sciences, Data assimilation, 14. Life underwater, lcsh:Science, data assimilation, 0105 earth and related environmental sciences, Water Science and Technology, Global and Planetary Change, 010604 marine biology & hydrobiology, calculus of variations, modeling, 13. Climate action, Systems engineering, lcsh:Q, Kálmán filters, [MATH.MATH-OC]Mathematics [math]/Optimization and Control [math.OC], State (computer science), Kalman filters
Abstract: International audience; Ocean data assimilation is increasingly recognized as crucial for the accuracy of real-time ocean prediction systems and historical re-analyses. The current status of ocean data assimilation in support of the operational demands of analysis, forecasting and reanalysis is reviewed, focusing on methods currently adopted in operational and real-time prediction systems. Significant challenges associated with the most commonly employed approaches are identified and discussed. Overarching issues faced by ocean data assimilation are also addressed, and important future directions in response to scientific advances, evolving and forthcoming ocean observing systems and the needs of stakeholders and downstream applications are discussed.
Published: 2019

132. Effect of colored noise on heteroclinic orbits

Author: Jean-Régis Angilella, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), and CERFACS
Subjects: Hamiltonian mechanics, Physics, [PHYS]Physics [physics], Scale (ratio), Dynamics (mechanics), Classical Physics (physics.class-ph), FOS: Physical sciences, Physics - Classical Physics, 01 natural sciences, 010305 fluids & plasmas, Hamiltonian system, symbols.namesake, Colors of noise, 0103 physical sciences, symbols, Dissipative system, Limit (mathematics), Statistical physics, 010306 general physics, Noise (radio), ComputingMilieux_MISCELLANEOUS
Abstract: The dynamics of a weakly dissipative Hamiltonian system submitted to stochastic perturbations has been investigated by means of asymptotic methods. The probability of noise-induced separatrix crossing, which drastically changes the fate of the system, is derived analytically in the case where noise is an additive Kubo-Anderson process. This theory shows how the geometry of the separatrix, as well as the noise intensity and correlation time, affect the statistics of crossing. Results can be applied to a wide variety of systems, and are valid in the limit where the noise correlation time scale is much smaller than the time scale of the undisturbed Hamiltonian dynamics.
Published: 2019

133. A conceptual model of the flame stabilization mechanisms for a lifted Diesel-type flame based on direct numerical simulation and experiments

Author: Gilles Bruneaux, Louis-Marie Malbec, Thierry Poinsot, Perrine Pepiot, Fabien Tagliante, Lyle M. Pickett, Christian Angelberger, Centre National de la Recherche Scientifique - CNRS (FRANCE), Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE), IFP Energies Nouvelles - IFPEN (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), Centre Européen de Recherche et Formation Avancées en Calcul Scientifique - CERFACS (FRANCE), Sandia (USA), Institut de Mécanique des Fluides de Toulouse - IMFT (Toulouse, France), IFP Energies nouvelles (IFPEN), Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, Sandia National Laboratories [Livermore], Sandia National Laboratories - Corporation, CERFACS [Toulouse], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Sibley School of Mechanical and Aerospace Engineering (MAE), and Cornell University [New York]
Subjects: Work (thermodynamics), Materials science, DNS, 020209 energy, General Chemical Engineering, Mécanique des fluides, Direct numerical simulation, General Physics and Astronomy, Energy Engineering and Power Technology, 02 engineering and technology, law.invention, Physics::Fluid Dynamics, [SPI]Engineering Sciences [physics], Diesel fuel, 020401 chemical engineering, law, 0202 electrical engineering, electronic engineering, information engineering, Triple flame, 0204 chemical engineering, Diffusion (business), Physics::Chemical Physics, Jet (fluid), Lift-Off Length, Auto-ignition, Diesel combustion, General Chemistry, Mechanics, Fuel injection, Lift-off length, [SPI.MECA.GEME]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Mechanical engineering [physics.class-ph], Ignition system, Fuel Technology, 13. Climate action, Flame stabilization, Event (particle physics)
Abstract: International audience; This work presents an analysis of the stabilization of diffusion flames created by the injection of fuel into hot air, as found in Diesel engines. It is based on experimental observations and uses a dedicated Direct Numerical Simulation (DNS) approach to construct a numerical setup, which reproduces the ignition features obtained experimentally. The resulting DNS data are then used to classify and analyze the events that allow the flame to stabilize at a certain Lift-Off Length (LOL) from the fuel injector. Both DNS and experiments reveal that this stabilization is intermittent: flame elements first auto-ignite before being convected downstream until another sudden auto-ignition event occurs closer to the fuel injector. The flame topologies associated to such events are discussed in detail using the DNS results, and a conceptual model summarizing the observation made is proposed. Results show that the main flame stabilization mechanism is auto-ignition. However, multiple reaction zone topologies, such as triple flames, are also observed at the periphery of the fuel jet helping the flame to stabilize by filling high-temperature burnt gases reservoirs localized at the periphery, which trigger auto-ignitions.
Published: 2019

134. An extended spectral analysis of the lattice Boltzmann method: modal interactions and stability issues

Author: Jean-François Boussuge, Gauthier Wissocq, Pierre Sagaut, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Laboratoire de Mécanique, Modélisation et Procédés Propres (M2P2), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), and Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Curve veering, Physics and Astronomy (miscellaneous), Discretization, Spectral radius, Lattice Boltzmann methods, 010103 numerical & computational mathematics, 01 natural sciences, [SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph], von Neumann analysis, 0101 mathematics, Eigenvalues and eigenvectors, Physics, Numerical Analysis, Applied Mathematics, Mathematical analysis, Numerical stability, Observable, Eigenvalues, Dissipation, Boltzmann equation, Lattice Boltzmann, Computer Science Applications, 010101 applied mathematics, Computational Mathematics, Modeling and Simulation, Eigenvectors
Abstract: International audience; An extension of the von Neumann linear analysis is proposed for the study of the discrete-velocity Boltzmann equation (DVBE) and the lattice Boltzmann (LB) scheme. While the standard technique is restricted to the investigation of the spectral radius and the dissipation and dispersion properties, a new focus is put here on the information carried by the modes. The technique consists in the computation of the moments of the eigenvectors and their projection onto the physical waves expected by the continuous linearized Navier-Stokes (NS) equations. The method is illustrated thanks to some simulations with the BGK (Bhatnagar-Gross-Krook) collision operator on the D2Q9 and D2V17 lattices. The present analysis reveals the existence of two kinds of modes: non-observable modes that do not carry any macroscopic information and observable modes. The latter may carry either a physical wave expected by the NS equations, or an unphysical information. Further investigation of modal interactions highlights a phenomenon called curve veering occurring between two observable modes: a swap of eigenvectors and dissipation rate is observed between the eigencurves. Increasing the Mach number of the mean flow yields an eigenvalue collision at the origin of numerical instabilities of the BGK model, arising from the error in the time and space discretization of the DVBE. (C) 2019 Elsevier Inc. All rights reserved.
Published: 2019

135. Influence of kinetics on DDT simulations

Author: Omar Dounia, Thierry Poinsot, Olivier Vermorel, Antony Misdariis, Airbus (FRANCE), Centre National d'Études Spatiales - CNES (FRANCE), Centre National de la Recherche Scientifique - CNRS (FRANCE), EDF (FRANCE), Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE), Office National d'Etudes et Recherches Aérospatiales - ONERA (FRANCE), Total (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), Météo France (FRANCE), SAFRAN (FRANCE), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, and Institut National Polytechnique de Toulouse - INPT (FRANCE)
Subjects: Work (thermodynamics), Hydrogen, DNS, General Chemical Engineering, Mécanique des fluides, Detailed chemistry, Detonation, General Physics and Astronomy, Energy Engineering and Power Technology, chemistry.chemical_element, Hot spot (veterinary medicine), 02 engineering and technology, 01 natural sciences, DDT, 020401 chemical engineering, 0103 physical sciences, [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph], 0204 chemical engineering, Flame acceleration- Detonation onset, Deflagration to detonation transition, 010304 chemical physics, Shock (fluid dynamics), [SPI.FLUID]Engineering Sciences [physics]/Reactive fluid environment, General Chemistry, Mechanics, Temperature gradient, Fuel Technology, chemistry, Deflagration, Detonation deflagration transition
Abstract: International audience; Deflagration to Detonation Transition (DDT) is an intricate problem that has been tackled numerically, until recently, using single-step chemical schemes. These studies (summarized in Oran and Gamezo, 2007) [1] showed that DDT is triggered when a gradient of reactivity forms inside a pocket of unreacted material. However, recent numerical simulations of hydrogen/air explosions using detailed reaction mechanisms (Liberman et al., 2010; Ivanov et al., 2011) [2], [3] showed that detonation waves can emerge from the flame brush, unlike what was usually seen in the single-step simulations. The present work focuses on chemistry modeling and its impact on DDT. Using the idealized Hot Spot (HS) problem with constant temperature gradient, this study shows that, in the case of hydrogen/air mixtures, the multi-step chemical description is far more restrictive than the single-step model when it comes to the necessary conditions for a hot spot to lead to detonation. A gas explosion scenario in a confined and obstructed channel filled with an hydrogen/air mixture is then considered. In accordance with the HS analysis, the Zeldovich’s (1970) mechanism [4] is responsible for the detonation initiation in the single-step case, whereas another process, directly involving the deflagration front, initiated DDT in the complex chemistry case. In the latter, a shock focusing event leads to DDT in the flame brush through Pressure Pulse (PP) amplification
Published: 2019

136. Assimilation of Synthetic SWOT River Depths in a Regional Hydrometeorological Model

Author: Aaron Boone, Sylvain Biancamaria, Eric Martin, Vincent Häfliger, Sophie Ricci, Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Risques, Ecosystèmes, Vulnérabilité, Environnement, Résilience (RECOVER), Aix Marseille Université (AMU)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), CERFACS [Toulouse], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), and Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
Subjects: earth_sciences_other, lcsh:Hydraulic engineering, 010504 meteorology & atmospheric sciences, Hydrological modelling, Geography, Planning and Development, 0207 environmental engineering, Drainage basin, 02 engineering and technology, Aquatic Science, [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology, 01 natural sciences, Biochemistry, Troposphere, lcsh:Water supply for domestic and industrial purposes, Data assimilation, overland flow, lcsh:TC1-978, Hydrometeorology, [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, 020701 environmental engineering, data assimilation, 0105 earth and related environmental sciences, Water Science and Technology, Hydrology, lcsh:TD201-500, geography, geography.geographical_feature_category, satellite altimetry, hydrological modelling, 6. Clean water, Ocean surface topography, Environmental science, Surface runoff, Surface water
Abstract: The SWOT (Surface Water and Ocean Topography) mission, to be launched in 2021, will provide water surface elevations, slopes, and river width measurements for rivers wider than 100 m. In this study, synthetic SWOT data are assimilated in a regional hydrometeorological model in order to improve the dynamics of continental waters over the Garonne catchment, one of the major French catchments. The aim of this paper is to demonstrate that the sequential assimilation of SWOT-like river depths allows the correction of river bed roughness coefficients and thus simulated river depths. An extended Kalman filter is implemented and the data assimilation strategy was applied to four experiments of gradually increasing complexity regarding observation and model error over the 1995&ndash, 2000 period. With respect to a &ldquo, true&rdquo, river state, assimilating river depths allows the proper retrieval of constant and spatially distributed roughness coefficients with a root mean square error of 1 m1/3 s&minus, 1, and the estimation of associated river depths. It was also shown that river depth differences can be assimilated, resulting in a higher root mean square error for roughness coefficients with respect to the true river state. Finally, the last experiment shows how one can take into account more realistic sources of SWOT error measurements, in particular the importance of the estimation of the tropospheric water content in the process.
Published: 2019

137. A joint experimental and numerical study of ignition in a spray burner

Author: Gilles Cabot, Eleonore Riber, Javier Marrero-Santiago, Bruno Renou, Bénédicte Cuenot, Félix Collin-Bastiani, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Complexe de recherche interprofessionnel en aérothermochimie (CORIA), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences appliquées Rouen Normandie (INSA Rouen Normandie), Institut National des Sciences Appliquées (INSA)-Normandie Université (NU)-Institut National des Sciences Appliquées (INSA)-Normandie Université (NU)-Université de Rouen Normandie (UNIROUEN), and Normandie Université (NU)
Subjects: 020209 energy, General Chemical Engineering, Flame structure, Context (language use), 02 engineering and technology, Combustion, 7. Clean energy, 01 natural sciences, Large Eddy Simulation, 010305 fluids & plasmas, law.invention, Physics::Fluid Dynamics, Laser diagnostics, law, 0103 physical sciences, 0202 electrical engineering, electronic engineering, information engineering, Physical and Theoretical Chemistry, Physics::Chemical Physics, Mechanical Engineering, [SPI.FLUID]Engineering Sciences [physics]/Reactive fluid environment, Mechanics, Ignition, Ignition system, Spray flame, Particle image velocimetry, 13. Climate action, Planar laser-induced fluorescence, Combustor, Large eddy simulation
Abstract: International audience; Partly due to stringent restrictions on pollutant emissions, aeronautical engine manufacturers target lean operating conditions which raise new difficulties such as combustion stability as well as ignition and re-ignition at high altitude. The injection of liquid fuel introduces additional complexity due to the spray-flame interaction. It is then crucial to better understand the physics behind these phenomena and to develop the capacity to predict them in an industrial context. In this work, a comprehensive joint experimental and numerical investigation of the academic swirled-confined version of the KIAI-Spray burner is carried out. Experimental diagnostics, such as Phase Doppler Anemometry (PDA), Planar Laser Induced Fluorescence (OH-PLIF), high-speed visualization and high-speed particle image velocimetry (HS-PIV), together with Large Eddy Simulations coupled to Discrete Particle Simulations are used to study spray flame structure and spray ignition. The analysis of the swirled-stabilized spray flame highlights the main effects of the presence of droplets on the turbulent combustion, and the complementarity and validity of the joint experiment and simulation approach. Ignition sequences are then studied. Both experiment and simulation show the same behaviors, and relate the flame kernel evolution and the possible success of ignition to the local non reacting flow properties at the sparking location, in terms of turbulence intensity and presence of droplets.
Published: 2019

138. Modelling spatially correlated observation errors in variational data assimilation using a diffusion operator on an unstructured mesh

Author: Anthony T. Weaver, Xavier Vasseur, Selime Gürol, Serge Gratton, Yann Michel, Oliver Guillet, Centre national de recherches météorologiques (CNRM), Météo France-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Département d'Ingénierie des Systèmes Complexes (DISC), Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Algorithmes Parallèles et Optimisation (IRIT-APO), Institut de recherche en informatique de Toulouse (IRIT), Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées, Institut National Polytechnique (Toulouse) (Toulouse INP), ANR-19-P3IA-0004,ANITI,Artificial and Natural Intelligence Toulouse Institute(2019), Airbus (FRANCE), Centre National d'Études Spatiales - CNES (FRANCE), Centre National de la Recherche Scientifique - CNRS (FRANCE), EDF (FRANCE), Institut Supérieur de l'Aéronautique et de l'Espace - ISAE-SUPAERO (FRANCE), Office National d'Etudes et Recherches Aérospatiales - ONERA (FRANCE), Total (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), Université Toulouse - Jean Jaurès - UT2J (FRANCE), Université Toulouse 1 Capitole - UT1 (FRANCE), Météo France (FRANCE), SAFRAN (FRANCE), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université Toulouse Capitole (UT Capitole), Université de Toulouse (UT)-Université de Toulouse (UT)-Université Toulouse - Jean Jaurès (UT2J), Université de Toulouse (UT)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Toulouse Mind & Brain Institut (TMBI), Université Toulouse - Jean Jaurès (UT2J), Université de Toulouse (UT)-Université de Toulouse (UT)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université Toulouse Capitole (UT Capitole), and Université de Toulouse (UT)
Subjects: Atmospheric Science, Diffusion equation, 010504 meteorology & atmospheric sciences, Discretization, Covariance matrix, Directional derivative, Modélisation et simulation, 01 natural sciences, Backward Euler method, [INFO.INFO-MO]Computer Science [cs]/Modeling and Simulation, Finite element method, 010305 fluids & plasmas, Correlation function (statistical mechanics), Operator (computer programming), 0103 physical sciences, Applied mathematics, Variational data assimilation, 0105 earth and related environmental sciences, Mathematics
Abstract: International audience; We propose a method for representing spatially correlated observation errors in variational data assimilation. The method is based on the numerical solution of a diffusion equation, a technique commonly used for representing spatially correlated background errors. The discretization of the pseudo‐time derivative of the diffusion equation is done implicitly using a backward Euler scheme. The solution of the resulting elliptic equation can be interpreted as a correlation operator whose kernel is a correlation function from the Matérn family.In order to account for the possibly heterogeneous distribution of observations, a spatial discretization technique based on the finite element method (FEM) is chosen where the observation locations are used to define the nodes of an unstructured mesh on which the diffusion equation is solved. By construction, the method leads to a convenient operator for the inverse of the observation‐error correlation matrix, which is an important requirement when applying it with standard minimization algorithms in variational data assimilation. Previous studies have shown that spatially correlated observation errors can also be accounted for by assimilating the observations together with their directional derivatives up to arbitrary order. In the continuous framework, we show that the two approaches are formally equivalent for certain parameter specifications. The FEM provides an appropriate framework for evaluating the derivatives numerically, especially when the observations are heterogeneously distributed.Numerical experiments are performed using a realistic data distribution from the Spinning Enhanced Visible and InfraRed Imager (SEVIRI). Correlations obtained with the FEM‐discretized diffusion operator are compared with those obtained using the analytical Matérn correlation model. The method is shown to produce an accurate representation of the target Matérn function in regions where the data are densely distributed. The presence of large gaps in the data distribution degrades the quality of the mesh and leads to numerical errors in the representation of the Matérn function. Strategies to improve the accuracy of the method in the presence of such gaps are discussed.
Published: 2019

139. Role of wind stress in driving SST biases in the tropical Atlantic

Author: Aurore Voldoire, Emilia Sanchez-Gomez, Noel Keenlyside, Anna-Lena Deppenmeier, Jonathan K. P. Shonk, Chloé Prodhomme, Katarina Goubanova, Eleftheria Exarchou, Teferi Demissie, Claudia Frauen, Wilco Hazeleger, Thomas Toniazzo, Shunya Koseki, Abdoul-Khadre Traoré, Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Barcelona Supercomputing Center - Centro Nacional de Supercomputacion (BSC - CNS), CERFACS [Toulouse], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Bjerknes Centre for Climate Research (BCCR), Department of Biological Sciences [Bergen] (BIO / UiB), University of Bergen (UiB)-University of Bergen (UiB), Wageningen University and Research [Wageningen] (WUR), Royal Netherlands Meteorological Institute (KNMI), Centro de Estudios Avanzados en Zonas Aridas (CEAZA), Geophysical Institute [Bergen] (GFI / BiU), University of Bergen (UiB), NCAS-Climate [Reading], Department of Meteorology [Reading], University of Reading (UOR)-University of Reading (UOR), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL)
Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Meteorologie en Luchtkwaliteit, Atmospheric Science, WIMEK, 010504 meteorology & atmospheric sciences, Meteorology and Air Quality, Advection, Equator, Wind stress, Context (language use), Tropical Atlantic, 010502 geochemistry & geophysics, 01 natural sciences, Sea surface temperature, Plant Breeding, Laboratorium voor Plantenveredeling, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, 13. Climate action, Climatology, Life Science, Environmental science, Climate model, Precipitation, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences
Abstract: International audience; Coupled climate models used for long-term future climate projections and seasonal or decadal predictions share a systematic and persistent warm sea surface temperature (SST) bias in the tropical Atlantic. This study attempts to better understand the physical mechanisms responsible for the development of systematic biases in the tropical Atlantic using the so-called Transpose-CMIP protocol in a multi-model context. Six global climate models have been used to perform seasonal forecasts starting both in May and February over the period 2000-2009. In all models, the growth of SST biases is rapid. Significant biases are seen in the first month of forecast and, by 6 months, the root-mean-square SST bias is 80% of the climatological bias. These control experiments show that the equatorial warm SST bias is not driven by surface heat flux biases in all models , whereas in the southeastern Atlantic the solar heat flux could explain the setup of an initial warm bias in the first few days. A set of sensitivity experiments with prescribed wind stress confirm the leading role of wind stress biases in driving the equatorial SST bias, even if the amplitude of the SST bias is model dependent. A reduced SST bias leads to a reduced precipitation bias locally, but there is no robust remote effect on West African Monsoon rainfall. Over the southeastern part of the basin, local wind biases tend to have an impact on the local SST bias (except in the high resolution model). However, there is also a non-local effect of equatorial wind correction in two models. This can be explained by sub-surface advection of water from the equator, which is colder when the bias in equatorial wind stress is corrected. In terms of variability, it is also shown that improving the mean state in the equatorial Atlantic leads to a beneficial intensification of the Bjerknes feedback loop. In conclusion, we show a robust effect of wind stress biases on tropical mean climate and variability in multiple climate models.
Published: 2019

140. Teleconnection processes linking the intensity of the Atlantic Multidecadal Variability to the climate impacts over Europe in boreal winter

Author: Saïd Qasmi, Julien Boé, Christophe Cassou, CECI, CERFACS / CNRS (CECI), Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), and CERFACS
Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Atmospheric Science, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Advection, Atmospheric circulation, Cloud cover, Diabatic, FOS: Physical sciences, Tropical Atlantic, 010502 geochemistry & geophysics, 01 natural sciences, Physics - Atmospheric and Oceanic Physics, Boreal, 13. Climate action, Ocean gyre, Climatology, Atmospheric and Oceanic Physics (physics.ao-ph), Environmental science, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Teleconnection
Abstract: The teleconnection between European climate and Atlantic Multidecadal Variability (AMV) remains difficult to isolate in observations because of internal variability and anthropogenically-forced signals. Using model sensitivity experiments proposed within the CMIP6/DCPP-C framework, the wintertime AMV/Europe teleconnection is investigated in large ensembles of pacemaker-type simulations in the CNRM-CM5 global circulation model. To evaluate the sensitivity of the model response to the AMV amplitude, experiments with AMV-forcing pattern multiplied by 2 and 3 (hereafter 2xAMV and 3xAMV, respectively) are performed in complement to the reference ensemble (1xAMV). Based on a flow analog method, the AMV-forced atmospheric circulation is found to cool down the European continent, whereas the residual signal, mostly including thermodynamical processes, contributes to warming. In 1xAMV, both terms cancel each other, explaining the overall weak AMV-forced atmospheric signal. In 2xAMV and 3xAMV, the thermodynamical contribution overcomes the dynamical cooling and is responsible for milder and wetter conditions. The thermodynamical term includes the advection of warmer and more humid oceanic air penetrating inland and the modification of surface radiative fluxes linked to (i) altered cloudiness and (ii) snow-cover reduction acting as a positive feedback with the AMV amplitude. The dynamical anomalous circulation combines (i) a remote response to enhanced diabatic heating acting as a Rossby-wave source in the western tropical Atlantic and (ii) a local response associated with warmer SST over the subpolar gyre favorizing an anomalous High. The weight between the tropical-extratropical processes and associated feedbacks is speculated to partly explain the nonlinear sensibility of the response to the AMV-forcing amplitude, challenging thus the use of the so-called pattern-scaling technique., Comment: 34 pages, 8 figures, submitted to Journal of Climate
Published: 2019
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141. Comparison between the assimilation of IASI Level 2 ozone retrievals and Level 1 radiances in a chemical transport model

Author: Emanuele Emili, Brice Barret, Daniel Cariolle, Eric Le Flochmoën, CERFACS, Laboratoire d'aérologie (LAERO), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées, Météo-France [Paris], Météo France, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), and Météo-France
Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Atmospheric Science, 010504 meteorology & atmospheric sciences, Chemical transport model, RTTOV, lcsh:TA715-787, lcsh:Earthwork. Foundations, Assimilation (biology), 010501 environmental sciences, Infrared atmospheric sounding interferometer, Atmospheric sciences, 01 natural sciences, Latitude, lcsh:Environmental engineering, Troposphere, Microwave Limb Sounder, 13. Climate action, [SDE]Environmental Sciences, Radiative transfer, Environmental science, lcsh:TA170-171, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract: The prior information used for Level 2 (L2) retrievals in the thermal infrared can influence the quality of the retrievals themselves and, therefore, their further assimilation in atmospheric composition models. In this study we evaluate the differences between assimilating L2 ozone profiles and Level 1 (L1) radiances from the Infrared Atmospheric Sounding Interferometer (IASI). We minimized potential differences between the two approaches by employing the same radiative transfer code (Radiative Transfer for TOVS, RTTOV) and a very similar setup for both the L2 retrievals (1D-Var) and the L1 assimilation (3D-Var). We computed hourly 3D-Var analyses assimilating L1 and L2 data in the chemical transport model MOCAGE and compared the resulting O3 fields among each other and against ozonesondes. We also evaluated the joint assimilation of limb measurements from the Microwave Limb Sounder (MLS) in combination with IASI to assess the impact of stratospheric O3 on tropospheric analyses. Results indicate that significant differences can arise between L2 and L1 assimilation, especially in regions where the L2 prior information is strongly biased (at low latitudes in this study). In these regions the L1 assimilation provides a better variability of the free-troposphere ozone column. L1 and L2 assimilation instead give very similar results at high latitudes, especially when MLS measurements are used to constrain the stratospheric O3 column. A critical analysis of the potential benefits and drawbacks of L1 assimilation is given in the conclusions. We also list remaining issues that are common to both the L1 and L2 approaches and that deserve further research.
Published: 2019

142. Sparsified discrete wave problem involving radiation condition on a prolate spheroidal surface

Author: Barucq, Hélène, Fares, M'Barek, Kruse, Carola, Tordeux, Sébastien, Advanced 3D Numerical Modeling in Geophysics (Magique 3D), Laboratoire de Mathématiques et de leurs Applications [Pau] (LMAP), Université de Pau et des Pays de l'Adour (UPPA)-Centre National de la Recherche Scientifique (CNRS)-Université de Pau et des Pays de l'Adour (UPPA)-Centre National de la Recherche Scientifique (CNRS)-Inria Bordeaux - Sud-Ouest, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria), Université de Pau et des Pays de l'Adour (UPPA)-Centre National de la Recherche Scientifique (CNRS), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), and CERFACS
Subjects: Dirichlet-to-Neumann operator, Absorbing boundary condition, Prolate spheroidal coordinates, Scattering problems, [MATH.MATH-NA]Mathematics [math]/Numerical Analysis [math.NA]
Abstract: International audience; We develop and analyze a high-order outgoing radiation boundary condition for solving three-dimensional scattering problems by elongated obstacles. This Dirichlet to Neumann (DtN) condition is constructed using the classical method of separation of variables that allows to define the scattered field in a truncated domain. It reads as an infinite series which is truncated for numerical purposes. The radiation condition is implemented in a finite element framework represented by a large dense matrix. Fortunately, the dense matrix can be decomposed into a full block matrix which involves the degrees of freedom on the exterior boundary and a sparse finite element matrix. The inversion of the full block is avoided by using a Sherman-Morrison algorithm which reduces the memory usage drastically. Despite being of high-order, this method has only a low memory cost. Many applications such as sonar, radar or geophysical exploration involve exterior Helmholtz problems which raise the question of handling the unbounded propagation domain. One accurate approach consists in using boundary element methods (BEM), see Bendali & Fares (2008) and their references. The linear partial differential equation is reformulated as an integral equation which is set on the boundary of the scatterer. BEMs have thus the advantage of providing an exact reformulation of the exterior problem in a bounded region without introducing any kind of approximation before discretization. However , boundary element discretizations lead to dense matrices which increase both storage requirements and computational costs of the solution algorithm, especially in three dimensions. A popular alternative is the usage of volume finite element methods (FEM) Harari & Hughes (1992b) once the computational domain has been truncated. The truncation is performed by introducing an artificial boundary surrounding the scatterer which requires transforming the exterior problem into a mixed one corresponding to the initial volume formulation of the problem set in the bounded domain and coupled with a suitable boundary condition set on the external boundary. To get an accurate representation of the wave field into the bounded domain, the external boundary should not generate any reflection. This point is managed with †
Published: 2019

143. Delineating loss sources within a linear cascade with upstream cavity and purge flow

Author: Jean-François Boussuge, Maxime Fiore, Eric Lippinois, Nicolas Gourdain, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Département Aérodynamique Energétique et Propulsion (DAEP), Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO), Safran Aircraft Engines, Institut Supérieur de l'Aéronautique et de l'Espace - ISAE-SUPAERO (FRANCE), Centre Européen de Recherche et Formation Avancées en Calcul Scientifique - CERFACS (FRANCE), SAFRAN (FRANCE), and Département Aérodynamique Energétique et Propulsion - DAEP (Toulouse, France)
Subjects: Materials science, Low-pressure turbine, Mass flow, Mécanique des fluides, 02 engineering and technology, LBM, 01 natural sciences, Purge, Turbine, 010305 fluids & plasmas, Physics::Fluid Dynamics, symbols.namesake, 0203 mechanical engineering, Large-eddy simulation, Cavité flow, 0103 physical sciences, [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph], Mechanical Engineering, Reynolds number, Mechanics, Vortex, Boundary layer, 020303 mechanical engineering & transports, Cascade, symbols, Environnement et Société, Large eddy simulation
Abstract: Purge air is injected in cavities at the hub of axial turbines to prevent hot mainstream gas ingestion into interstage gaps. This process induces additional losses for the turbine due to an interaction between the purge and mainstream flow. This paper investigates the flow in a low-speed linear cascade rig with upstream hub cavity at a Reynolds number commonly observed in modern low-pressure turbine stages by the use of numerical simulation. Numerical predictions are validated by comparing against experimental data available. Three different purge mass flow rates are tested using three different rim seal geometries. Numerical simulations are performed using a large-eddy simulation (LES) solver on structured grids. An investigation of the different mechanisms associated with the turbine flow including cavity and purge air is intended through this simplified configuration. The underlying mechanisms of loss are tracked using an entropy formulation. Once described for a baseline case, the influence of purge flow and rim seal geometry on flow mechanisms and loss generation is described with the emphasis to obtain design parameters for losses reduction. The study quantifies loss generation due to the boundary layer on wetted surfaces and secondary vortices developing in the passage. The analysis shows different paths by which the purge flow and rim seal geometry can change loss generation including a modification of the shear layer between purge and mainstream, interaction with secondary vortices, and a modification of the flow behavior close to hub compared with a smooth configuration. The study shows the influence of purge flow rate and swirl on the strengthening of secondary vortices in the passage and the ability of axial overlapping rim seal to delay the development of secondary vortices compared with simple axial gaps.
Published: 2019

144. Evaluation of CNRM Earth‐System model, CNRM‐ESM 2‐1: role of Earth system processes in present‐day and future climate

Author: Sophie Valcke, Marie-Pierre Moine, Christine Delire, Jeanne Colin, Julie Deshayes, Marc Mallet, Laurent Franchistéguy, David Saint-Martin, Gurvan Madec, Matthieu Chevallier, Olivier Geoffroy, Emilie Joetzjer, Robin Waldman, Pierre Nabat, Matthias Rocher, Christian Ethé, Aurore Voldoire, Aurélien Ribes, Roland Séférian, Stephane Sénési, Martine Michou, Laurent Terray, Jessica Vial, Olivier Aumont, Romain Roehrig, David Salas-y-Mélia, Emilia Sanchez, Rym Msadek, Sarah Berthet, Jean-François Guérémy, Laurent Bopp, Bertrand Decharme, Groupe de Météorologie de Grande Échelle et Climat (GMGEC), Centre national de recherches météorologiques (CNRM), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Laboratoire de Météorologie Dynamique (UMR 8539) (LMD), Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-École des Ponts ParisTech (ENPC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Climat, Environnement, Couplages et Incertitudes [Toulouse] (CECI), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Nucleus for European Modeling of the Ocean (NEMO R&D ), Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)-Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), H2020 CONSTRAIN under the grant agreement 820829, LEFE CYBER/GMMC PISCO project, ANR-13-MONU-0008,CONVERGENCE,Convergence en Science du Climat à l'ère du Big Data et des challenges de l'Exascale.(2013), European Project: 641816,H2020,H2020-SC5-2014-two-stage,CRESCENDO(2015), Groupe d'étude de l'atmosphère météorologique (CNRM-GAME), Institut national des sciences de l'Univers (INSU - CNRS)-Météo France-Centre National de la Recherche Scientifique (CNRS), Météo France-Centre National de la Recherche Scientifique (CNRS), Laboratoire Géomatériaux et Environnement (LGE), Université Paris-Est Marne-la-Vallée (UPEM), CAS-PHABIO, Institut de Physique Nucléaire de Lyon (IPNL), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Météo France, Université Pierre et Marie Curie - Paris 6 (UPMC), Laboratoire d'aérologie (LA), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP)-Université Toulouse III - Paul Sabatier (UPS), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées, Laboratoire de Génie Electrique de Grenoble (G2ELab), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut Polytechnique de Grenoble - Grenoble Institute of Technology-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA), Institut de Radioprotection et de Sûreté Nucléaire (IRSN), Politecnico di Torino [Torino] (Polito), CERFACS, Laboratoire de physique des océans (LPO), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS), Department of Physical Oceanography, Woods Hole Oceanographic Institution (WHOI), Institut Pierre-Simon-Laplace (IPSL), École normale supérieure - Paris (ENS Paris)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National d'Études Spatiales [Toulouse] (CNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), CERFACS-Centre National de la Recherche Scientifique (CNRS), Institut Pierre-Simon-Laplace (IPSL (FR_636)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut Pierre-Simon-Laplace (IPSL (FR_636)), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-École polytechnique (X)-Centre National d'Études Spatiales [Toulouse] (CNES)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut de Recherche pour le Développement (IRD)-Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)
Subjects: 010504 meteorology & atmospheric sciences, Forcing (mathematics), Present day, [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology, 010502 geochemistry & geophysics, Atmospheric sciences, 01 natural sciences, Carbon cycle, lcsh:Oceanography, Environmental Chemistry, Earth system modeling, lcsh:GC1-1581, [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, lcsh:Physical geography, climate modeling, CMIP6, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Global and Planetary Change, Coupled model intercomparison project, Vegetation, biogeochemical cycles, 15. Life on land, Earth system science, 13. Climate action, [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, Atmospheric chemistry, General Earth and Planetary Sciences, Environmental science, Climate model, future projections, lcsh:GB3-5030, aerosols
Abstract: International audience This study introduces CNRM‐ESM2‐1, the Earth system (ES) model of second generation developed by CNRM‐CERFACS for the sixth phase of the Coupled Model Intercomparison Project (CMIP6). CNRM‐ESM2‐1 offers a higher model complexity than the Atmosphere‐Ocean General Circulation Model CNRM‐CM6‐1 by adding interactive ES components such as carbon cycle, aerosols, and atmospheric chemistry. As both models share the same code, physical parameterizations, and grid resolution, they offer a fully traceable framework to investigate how far the represented ES processes impact the model performance over present‐day, response to external forcing and future climate projections. Using a large variety of CMIP6 experiments, we show that represented ES processes impact more prominently the model response to external forcing than the model performance over present‐day. Both models display comparable performance at replicating modern observations although the mean climate of CNRM‐ESM2‐1 is slightly warmer than that of CNRM‐CM6‐1. This difference arises from land cover‐aerosol interactions where the use of different soil vegetation distributions between both models impacts the rate of dust emissions. This interaction results in a smaller aerosol burden in CNRM‐ESM2‐1 than in CNRM‐CM6‐1, leading to a different surface radiative budget and climate. Greater differences are found when comparing the model response to external forcing and future climate projections. Represented ES processes damp future warming by up to 10% in CNRM‐ESM2‐1 with respect to CNRM‐CM6‐1. The representation of land vegetation and the CO2‐water‐stomatal feedback between both models explain about 60% of this difference. The remainder is driven by other ES feedbacks such as the natural aerosol feedback.
Published: 2019

145. Modeling reproductive traits of an invasive bivalve species under contrasting climate scenarios from 1960 to 2100

Author: Yves-Marie Paulet, Gonçalo M. Marques, Sebastien Petton, Yoann Thomas, Christophe Cassou, Mélaine Gourault, Elodie Fleury, Laure Pecquerie, Stephane Pouvreau, Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Institut de Recherche pour le Développement (IRD), Instituto Superior Técnico, Universidade Técnica de Lisboa (IST), CERFACS [Toulouse], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), and Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS)
Subjects: 0106 biological sciences, [SDE.MCG]Environmental Sciences/Global Changes, Dynamic energy budget, Population, Climate change, [SDU.STU.ME]Sciences of the Universe [physics]/Earth Sciences/Meteorology, Aquatic Science, Oceanography, 010603 evolutionary biology, 01 natural sciences, Phytoplankton, Hindcast, 14. Life underwater, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, education, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, Ecology, Evolution, Behavior and Systematics, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, education.field_of_study, IPCC scenarios, biology, Reproductive success, Ecology, ACL, 010604 marine biology & hydrobiology, Bay of Brest, Pacific oyster, biology.organism_classification, Reproductive traits, [SDU]Sciences of the Universe [physics], [SDU.STU.CL]Sciences of the Universe [physics]/Earth Sciences/Climatology, 13. Climate action, Crassostrea gigas, [SDE.BE]Environmental Sciences/Biodiversity and Ecology, Bay, DEB model
Abstract: International audience; Identifying the drivers that control the reproductive success of a population is vital to forecasting the consequences of climate change in terms of distribution shift and population dynamics. In the present study, we aimed to improve our understanding of the environmental conditions that allowed the colonization of the Pacific oyster, Crassostrea gigas, in the Bay of Brest since its introduction in the 1960s. We also aimed to evaluate the potential consequences of future climate change on its reproductive success and further expansion.Three reproductive traits were defined to study the success of the reproduction: the spawning occurrence, synchronicity among individuals and individual fecundity. We simulated these traits by applying an individual-based modeling approach using a Dynamic Energy Budget (DEB) model. First, the model was calibrated for C. gigas in the Bay of Brest using a 6-year monitoring dataset (2009–2014). Second, we reconstructed past temperature conditions since 1960 in order to run the model backwards (hindcasting analysis) and identified the emergence of conditions that favored increasing reproductive success. Third, we explored the regional consequences of two contrasting IPCC climate scenarios (RCP2.6 and RCP8.5) on the reproductive success of this species in the bay for the 2100 horizon (forecasting analysis). In both analyses, since phytoplankton concentration variations were, at that point, unknown in the past and unpredicted in the future, we made an initial assumption that our six years of observed phytoplankton concentrations were informative enough to represent “past and future possibilities” of phytoplankton dynamics in the Bay of Brest. Therefore, temperature is the variable that we modified under each forecasting and hindcasting runs.The hindcasting simulations showed that the spawning events increased after 1995, which agrees with the observations made on C. gigas colonization. The forecasting simulations showed that under the warmer scenario (RCP8.5), reproductive success would be enhanced through two complementary mechanisms: more regular spawning each year and potentially precocious spawning resulting in a larval phase synchronized with the most favorable summer period. Our results evidenced that the spawning dates and synchronicity between individuals mainly relied on phytoplankton seasonal dynamics, and not on temperature as expected. Future research focused on phytoplankton dynamics under different climate change scenarios would greatly improve our ability to anticipate the reproductive success and population dynamics of this species and other similar invertebrates.
Published: 2019

146. Uncertainties for Thermoacoustics: A First Analysis

Author: Aissatou Ndiaye, Franck Nicoud, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Institut Montpelliérain Alexander Grothendieck (IMAG), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Charles Hirsch, Dirk Wunsch, Jacek Szumbarski, Łukasz Łaniewski-Wołłk, and Jordi Pons-Prats
Subjects: 020301 aerospace & aeronautics, Computer science, Monte Carlo method, Mode (statistics), Thermoacoustics, Bilinear interpolation, 02 engineering and technology, Risk factor (finance), 01 natural sciences, [INFO.INFO-MO]Computer Science [cs]/Modeling and Simulation, 010305 fluids & plasmas, symbols.namesake, 0203 mechanical engineering, Surrogate models, Helmholtz free energy, 0103 physical sciences, symbols, Applied mathematics, Uncertainty Quantification, Risk factor, Uncertainty quantification, Reduced cost, Combustion instabilities
Abstract: International audience; An Uncertainty Quantification analysis of a swirled stabilized combustor experiment is performed. Theobjective is to estimate the modal risk factor of the system, i.e. the probability of a thermoacoustic mode tobe unstable, which may facilitate the development and optimization of suitable control methods. Topropagate uncertainties, a Monte Carlo method is initially used based on 4000 Helmholtz-basedthermoacoustic simulations with random perturbations on the flame input parameters. The analysis of theMonte Carlo database suggests that a reduced two-step Uncertainty Quantification strategy may beefficient to deal with thermoacoustic systems. First, three bilinear surrogate models are tuned from amoderate number of Helmholtz solutions (a few tens). Then, these algebraic models are used to perform aMonte Carlo analysis at reduced cost and approximate the risk factor of the mode. Good agreements areobtained when comparing the risk factor from the full Monte Carlo database and the risk factor fromsurrogate models.
Published: 2019

147. Wall-modeling in large-eddy simulations for turbomachinery flows

Author: Catchirayer, M., CATCHIRAYER, Mathieu, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Safran Tech, CIFRE n°2015/0193, Aix-Marseille Université, Pierre Sagaut, and Jean-François Boussuge
Subjects: modèle de paroi, [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Mechanics of the fluids [physics.class-ph], turbomachine, wall-model, couche limite, turbulence, [PHYS.PHYS.PHYS-COMP-PH] Physics [physics]/Physics [physics]/Computational Physics [physics.comp-ph], WMLES, [SPI.MECA.MEFL] Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph], [INFO.INFO-NA]Computer Science [cs]/Numerical Analysis [cs.NA], boundary layer, [INFO.INFO-MO]Computer Science [cs]/Modeling and Simulation, [SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph], [PHYS.PHYS.PHYS-COMP-PH]Physics [physics]/Physics [physics]/Computational Physics [physics.comp-ph], [INFO.INFO-NA] Computer Science [cs]/Numerical Analysis [cs.NA], [PHYS.MECA.MEFL] Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph], [INFO.INFO-MO] Computer Science [cs]/Modeling and Simulation, turbomachinery
Abstract: Due to the energetic challenges faced by aeronautical engine manufacturers, a better understanding of the flows governing their gas turbines is required. Numerical simulations through Large-Eddy Simulation (LES) approach is well suited to this quest for innovation. However, its computational cost is prohibitive in the case of boundary layers at Reynolds numbers encountered in aeronautics. One way to tackle this limitation is to use a WMLES (Wall-Modeled LES) approach: near-wall turbulence is modeled thanks to a wall-model. Nonetheless, this approach is still an open issue for industrials flows. Therefore, a new suited wall-model is developed in this study: the iWMLES (integral WMLES). The velocity and temperature profiles are parameterized, and unknown coefficients are determined by matching boundary conditions obeying the integral boundary layer equations. It allows compressibility, temperature and pressure gradients effects to be taken into account at a low computational cost. The proposed wall-model is then assessed on academic flows. First, adiabatic and isothermal plane channel flows at several friction Reynolds and Mach numbers are simulated. In all cases, mean profiles, wall fluxes, and turbulent fluctuations are in agreement with direct numerical simulation data. Especially, the supersonic flow cases show that the iWMLES has a wider domain of validity than standard wall-models. Second, an experimental boundary layer under adverse pressure gradient is considered. The iWMLES is shown to predict correctly the one-point turbulence statistics. Finally, the iWMLES is applied to an axial compressor stage, proving its robustness, and results are compared with LES data., Les défis énergétiques rencontrés par les motoristes aéronautiques requiert une compréhension plus fine des écoulements régissant leurs turbomachines. La simulation aux grandes échelles (LES) peut combler ce besoin. Cependant, dans le cas de couches limites à des nombres de Reynolds typiques de ceux rencontrés en aéronautique, son coût de calcul devient prohibitif. Une manière d'éviter cet écueil est de recourir à une approche WMLES (Wall-Modeled LES) : la turbulence en proche paroi est modélisée par un modèle de paroi. Toutefois, l'utilisation d'une WMLES sur des géométries industrielles reste une question ouverte. Ainsi, un modèle de paroi adapté aux écoulements de turbomachines est ici développé : l'iWMLES (integral WMLES). Les profils de vitesse et de température sont paramétrisés et les paramètres inconnus sont déterminés pour respecter des conditions aux limites issues des équations de couche limite intégrales. L'iWMLES peut alors prendre en compte les effets de compressibilité, de gradients de température et de pression à un faible coût de calcul. Sa validation est réalisée sur des écoulements académiques : des cas de canal plan isothermes et adiabatiques à différents nombres de Reynolds et de Mach sont considérés, ainsi qu'une couche limite soumise à un gradient de pression adverse. À chaque fois, les moments statistiques jusqu'à l'ordre un sont en accord avec les données de référence. Ces différentes simulations montrent que l'iWMLES a un domaine de validité plus étendu que les modèles de paroi classiques. Enfin, l'iWMLES est appliqué sur un étage de compresseur axial, démontrant sa robustesse, et les résultats sont comparés avec ceux d'une LES résolue en paroi.
Published: 2019

148. Surrogates for combustion instabilities in annularcombustors

Author: Michaël Bauerheim, Aissatou Ndiaye, Franck Nicoud, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology [Zürich] (ETH Zürich), Institut Montpelliérain Alexander Grothendieck (IMAG), Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Charles Hirsch, Dirk Wunsch, Jacek Szumbarski, Łukasz Łaniewski-Wołłk, and Jordi Pons-Prats
Subjects: UQ, adjoint, Computer science, 010103 numerical & computational mathematics, Mechanics, Combustion, 01 natural sciences, Plenum space, Instability, [INFO.INFO-MO]Computer Science [cs]/Modeling and Simulation, 010305 fluids & plasmas, Power (physics), surrogate models, 0103 physical sciences, Combustor, analytical expressions, annular combustors, Sensitivity (control systems), 0101 mathematics, Combustion chamber, Network model
Abstract: International audience; While the computational power is still increasing, thus arousing theinterest for high-fidelity simulations, the need of low-order models is also feltto both predict and understand combustion instabilities at low costs. Historicallyapplied to simple systems like longitudinal Rijke tubes to unveil the driven mechanismsleading to instability, they have recently been adapted to more complexconfigurations such as annular combustors. A network model is presented here topredict thermo-acoustic modes in an annular combustion chamber fed by burnersconnected to an annular plenum, typical of modern combustor designs. Explicitexpressions of the growth rate are derived in several cases showing key parameterscontrolling the stability. In more general situations, no explicit solution canbe obtained. Nevertheless, such an analytical model can be solved numerically atlow-cost compared with 3D acoustic tools and high-fidelity simulations. In thisframework, efficient sensitivity techniques and UQ methods can be developed totackle the UQ problem: “How can we assess the risk of instability in industrialcombustors at the predesign stage?”.
Published: 2019

149. Flame–wall interaction effects on the flame root stabilization mechanisms of a doubly-transcritical LO2/LCH4 cryogenic flame

Author: Dario Maestro, Thierry Poinsot, Laurent Selle, Bénédicte Cuenot, Thomas Schmitt, Gabriel Staffelbach, Florent Duchaine, Christophe Laurent, Lucas Esclapez, Centre National de la Recherche Scientifique - CNRS (FRANCE), Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE), Université Toulouse III - Paul Sabatier - UT3 (FRANCE), CentraleSupélec (FRANCE), Centre Européen de Recherche et Formation Avancées en Calcul Scientifique - CERFACS (FRANCE), Institut de Mécanique des Fluides de Toulouse - IMFT (Toulouse, France), Institut National Polytechnique de Toulouse - INPT (FRANCE), Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), CERFACS, Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, Laboratoire d'Énergétique Moléculaire et Macroscopique, Combustion (EM2C), and CentraleSupélec-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)
Subjects: Splitter plate, General Chemical Engineering, Mécanique des fluides, Cryogenic flame, Conjugate heat transfer, Flame structure, Kinetic scheme, 02 engineering and technology, Combustion, 01 natural sciences, 010305 fluids & plasmas, law.invention, 0203 mechanical engineering, law, Cryogenic flames doubly transcritical, 0103 physical sciences, Real-gas thermodynamics, [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph], Physical and Theoretical Chemistry, Diffusion (business), Adiabatic process, Flame anchoring, Mechanical Engineering, Injector, Mechanics, 020303 mechanical engineering & transports, 13. Climate action, Coaxial, Flame–wall interaction
Abstract: International audience; High-fidelity numerical simulations are used to study flame root stabilization mechanisms of cryogenic flames, where both reactants (O2 and CH4) are injected in transcritical conditions in the geometry of the laboratory scale test rig Mascotte operated by ONERA (France). Simulations provide a detailed insight into flame root stabilization mechanisms for these diffusion flames: they show that the large wall heat losses at the lips of the coaxial injector are of primary importance, and require to solve for the fully coupled conjugate heat transfer problem. In order to account for flame–wall interaction (FWI) at the injector lip, detailed chemistry effects are also prevalent and a detailed kinetic mechanism for CH4 oxycombustion at high pressure is derived and validated. This kinetic scheme is used in a real-gas fluid solver, coupled with a solid thermal solver in the splitter plate to calculate the unsteady temperature field in the lip. A simulation with adiabatic boundary conditions, an hypothesis that is often used in real-gas combustion, is also performed for comparison. It is found that adiabatic walls simulations lead to enhanced cryogenic reactants vaporization and mixing, and to a quasi-steady flame, which anchors within the oxidizer stream. On the other hand, FWI simulations produce self-sustained oscillations of both lip temperature and flame root location at similar frequencies: the flame root moves from the CH4 to the O2 streams at approximately 450 Hz, affecting the whole flame structure.
Published: 2019

150. Front shape similarity measure for data-driven simulations of wildland fire spread based on state estimation: Application to the RxCADRE field-scale experiment

Author: Philippe Moireau, Mélanie C. Rochoux, Annabelle Collin, Cong Zhang, Arnaud Trouvé, Department of Fire Protection Engineering [College Park], University of Maryland [College Park], University of Maryland System-University of Maryland System, Modélisation Mathématique pour l'Oncologie (MONC), Institut de Mathématiques de Bordeaux (IMB), Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1 (UB)-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS)-Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1 (UB)-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS)-Institut Bergonié [Bordeaux], UNICANCER-UNICANCER-Inria Bordeaux - Sud-Ouest, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria), Mathematical and Mechanical Modeling with Data Interaction in Simulations for Medicine (M3DISIM), Laboratoire de mécanique des solides (LMS), École polytechnique (X)-Mines Paris - PSL (École nationale supérieure des mines de Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)-Mines Paris - PSL (École nationale supérieure des mines de Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Inria Saclay - Ile de France, Université Paris-Saclay, Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS), Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS)-Université Bordeaux Segalen - Bordeaux 2-Université Sciences et Technologies - Bordeaux 1-Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux (Bordeaux INP)-Centre National de la Recherche Scientifique (CNRS)-Institut Bergonié [Bordeaux], École polytechnique (X)-MINES ParisTech - École nationale supérieure des mines de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)-MINES ParisTech - École nationale supérieure des mines de Paris, and CERFACS
Subjects: 010504 meteorology & atmospheric sciences, General Chemical Engineering, 020101 civil engineering, Image processing, 02 engineering and technology, Similarity measure, 01 natural sciences, Measure (mathematics), 0201 civil engineering, Data assimilation, Position (vector), Position errors, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], Physical and Theoretical Chemistry, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, Mechanical Engineering, Front (oceanography), [INFO.INFO-MO]Computer Science [cs]/Modeling and Simulation, Euclidean distance, 13. Climate action, Flame spread, [MATH.MATH-OC]Mathematics [math]/Optimization and Control [math.OC], Wildland fire, Algorithm, State estimation
Abstract: International audience; Data-driven wildfire spread modeling is emerging as a cornerstone for forecasting real-time fire behavior using thermal-infrared imaging data. One key challenge in data assimilation lies in the design of an adequate measure to represent the discrepancies between observed and simulated firelines (or "fronts"). A first approach consists in adopting a Lagrangian description of the flame front and in computing a Euclidean distance between simulated and observed fronts by pairing each observed marker with its closest neighbor along the simulated front. However, this front marker registration approach is difficult to generalize to complex front topology that can occur when fire propagation conditions are highly heterogeneous due to topography, biomass fuel and micrometeorology. To overcome this issue, we investigate in this paper an object-oriented approach derived from the Chan-Vese contour fitting functional used in image processing. The burning area is treated as a moving object that can undergo shape deformations and topological changes. We combine this non-Euclidean measure with a state estimation approach (a Luenberger observer) to perform simulations of the time-evolving fire front location driven by discrete observations of the fireline. We apply this object-oriented data assimilation method to the three-hectare RxCADRE S5 field-scale experiment. We demonstrate that this method provides more accurate forecast of fireline propagation than if either the fire spread model or the observations were taken separately. Results show that when the observation frequency becomes lower than 1/60 s −1 , the forecast performance of data assimilation is improved compared to simply extrapolating observation data. This highlights the need of a physics-based forward model to forecast flame front propagation. We also demonstrate that the front shape similarity measure is suitable for both Eulerian and Lagrangian-type front-tracking solvers and thereby can provide a unified framework to track moving structures such as flame front position and topology in combustion problems.
Published: 2019

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