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HPC simulation of environment and safety

The monitoring of environmental systems relies on high-fidelity simulation capabilities in combination with data-driven modeling approaches such as data assimilation, uncertainty/sensitivity analysis and more generally machine learning. Combining physical and data-driven modeling approaches is a very active field of research at CERFACS for a wide range of applications associated with environment and safety issues.

 

Atmospheric chemistry

Data assimilation for global-scale atmospheric composition around the MOCAGE chemistry-transport model is a well-established activity at CERFACS, both in support of Météo-France operational forecasts and for computation of chemical re-analyses.

CERFACS contributes to the continuous design, implementation and validation of new methodologies specific to chemical data assimilation, for instance to account for model error within the data assimilation process and to directly assimilate satellite radiances in the infrared and ultraviolet spectral areas from instruments such as IASI and GOME-2. Such data assimilation capability provides a way to produce global re-analyses of trace gases using satellites for climate applications and to improve operational air quality forecasts.

This research is done in strong collaborations with CNRM/Météo-France and for instance as part of TOSCA/COPERNICUS research projects.

Regional-to-global air quality forecasts using MOCAGE and data assimilation

 

Micro-scale atmospheric flow in dispersion and wildfire events

Mapping pollutant concentration within the first tens or hundreds of meters from an emission point source occurring during major environmental disasters (industrial accidents or wildfires for instance) remains a simulation challenge. At the forefront of computational fluid dynamics, large-eddy simulations (LES) are a promising way to represent time and space variability of turbulent atmospheric flow and to assess public short-term exposure, especially in urban areas, industrial sites and mountainous areas.

CERFACS contributes to the emergence of LES for environmental flows by designing high-fidelity simulation capabilities based on AVBP and MesoNH (in collaboration with CNRM/Météo-France). Submetric spatial resolution can be used at CERFACS to represent the turbulent flow patterns and the dynamics of the plume at the scale of an event within the atmospheric boundary layer. New methodologies (multi-scale method, metamodeling and data assimilation for instance) are developed in combination with LES to design efficient and accurate tools. For instance, a coupled fire/atmosphere simulation capability has been designed and validated to represent the interactions between a wildfire and the atmosphere, and thereby the atmospheric feedbacks on the wildfire behavior. Data assimilation capabilities involving LES metamodeling and joint state-parameter estimation are being developed to produce the best possible representation of an event.

This research is done in collaboration with CNRM/Météo-France, ONERA and CEREA, and as part of national-to-European research projects (STAE, TOSCA, ANR, MSCA). Specific collaborations are pursued with INRIA and LISN on methodological aspects. The massive computations are performed on GENCI platforms and constitute excellent benchmarks to broaden the range of applications for the HPC tools of CERFACS.

Submetric LES of the MUST field campaign using AVBP (tracer dispersion in idealized urban environment)

Coupled atmosphere/fire simulation using MesoNH-BLAZE based on a LES for the atmosphere (MesoNH) and a fire front-tracking model at the land surface (BLAZE)

Hydrodynamics and floods

Estimating and forecasting the flow of rivers is an important issue for institutions involved in water resource management and in charge of civil security. To observe and understand the dynamics of river flows, we rely on a heterogeneous observation network consisting of in situ and satellite measurements. This network is enriched through the deployment of innovative instruments (in-situ stations, airborne measurements, UAVs, high-resolution altimetry, radar and optical space missions, …) on a local and global scale.  In addition to these observations, the water community uses numerical models that solve Navier-Stokes equations under various simplifying assumptions. Their capabilities are limited by several factors of uncertainty related to the description of bathymetry/topography, hydraulic or hydrological parameters or forcing terms such as hydrological inputs and precipitation. In order to overcome the limits of deterministic simulation, an ensemble approach is favoured. In this context, the impact of input uncertainties on the simulated and predicted variables is estimated with methods inherited from the field of uncertainty quantification. In order to improve the quality and lead time of forecasts, the main sources of uncertainty are then reduced with data assimilation methods. The computational cost related to the quantification and reduction of uncertainties must respect the computational limits of operational flood forecasting, thus, the use of a reduced model in place of the direct model is favoured.

As of today, assimilation of in-situ and remote sensing water level data for operational forecast is a key research activity done at CERFACS to reduce modeling and parametric uncertainties and provide insights into flood and inundation events. CERFACS also contributes to adapting data assimilation algorithms to new types of observations coming from remote sensing (SWOT, Sentinel, Pléïades).  This research is done in strong collaboration with CNES, EDF, Météo-France, IRSTEA, SCHAPI, CEREMA, ARTELIA, JPL and INRIA and as part of national-to-international research projects (TOSCA, SCO, H2020).

Water Surface Elevation with Telemac (colored), in-situ observation (green dots), SWOT like nodes (blue palet) and SWOT like reaches (yellow dots). Assimilation of in-situ and remote sensing observation with MASCARET.

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Oceanography

Data assimilation at CERFACS has its historical roots in physical oceanography, when CERFACS played a leading role in the early development of operational oceanography for Mercator-Océan. Ocean data assimilation underpins many research and operational applications in forecasting and climate reanalysis where accurate ocean state estimates are required for ocean and coupled models.

Central to the ocean data assimilation activity at CERFACS is the variational data assimilation system NEMOVAR, which is developed jointly by CERFACS, ECMWF, Met Office and INRIA. CERFACS contributes to NEMOVAR mainly through developments to the minimization algorithms, the balance operators, and the covariance operators used for representing errors in the background state and the assimilated observations. Making optimal use of ensemble forecasts to improve estimates of the background error covariances is another active area of research.

The ocean data assimilation activity benefits from collaborative work with the NEMOVAR partners (ECMWF, Met Office, INRIA), CNRM/Météo-France and IRIT. This work is supported by the Copernicus Climate Change Service (C3S).

Industrial safety: prediction of explosions

For 5 years, CERFACS has been conducting an innovative scientific program for gas explosions. This subject is an important field of study for many applications related to building and industrial safety. Today URANS codes such as FLACS are used to predict the consequences of accidental flame ignition in buildings, but these codes are based primarily on extensive experience and little on the deterministic and precise resolution of the Navier Stokes equations. More accurate methods such as Large Eddy Simulation (LES), coupled with the development of high performance computing, have the potential to predict very precisely the main characteristics of deflagrations in confined or semi-confined environments.

Large eddy simulation of a gaseous explosion in a semi-confined environment

This work is carried out with the AVBP solver, and was initiated in quite simple configurations with relatively small dimensions. The LEFEX (LES For Explosions) project led by CERFACS in collaboration with Air Liquide, GRTgaz and Total aims to overcome this limitatiion to small-size domains by developing the models, numerical methods, algorithms and methodologies necessary to scale up the AVBP code to industrial-scale applications. The final objective of the project is to perform explosion calculations with AVBP under deflagration conditions in realistic geometries and therefore large dimensions. To achieve this goal, several paths are identified in the project, such as adaptative mesh refinement, turbulence-chemistry interaction modeling aided by data-driven approaches.

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Tribute to Françoise Chatelin

Brigitte Yzel |  23 July 2021

  Tribute to Françoise CHATELIN   Virtual & Face to Face event @ Cerfacs 14 October 2021, CERFACS, Toulouse (France) 2 pm - 6.30 pm   Cerfacs is organizing a half scientific day on Thursday October 14, 2021 in tribute to Françoise Chatelin who left us prematurely on May 14, 2020   After graduating from the Ecole Normale Supérieure in Paris (1960-63), and her PhD in Mathematics at Grenoble University (1971) , Françoise Chatelin led with worldwide recognition her research in many areas, from spectral theory for linear operators in Banach spaces and finite precision to Dickson algebras. Professor Chatelin taught at the Universities Grenoble 2 - Pierre Mendès-France and Paris 9 - Dauphine before moving to Toulouse in 1996. She became Emeritus Professor in 2015. She was a visiting researcher at Berkeley and Stanford Universities, IBM San Jose (Ca) and Yorktown Heights (NY). For almost a decade, she was a scientific manager in Industry (in charge of intensive computing) first at the Centre Scientifique IBM France in Paris (1985 -1992) and then in the Central Research Lab of Thales (known as Thomson-CSF at that time) near Paris (1992-95). Françoise Chatelin was Head of the Qualitative Computing group at the Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (Cerfacs) in Toulouse, France. Professor Chatelin has authored four books; the first three are now classic references available from SIAM. Her second book Valeurs Propres de Matrices (Masson, Paris, 1988) has received the IBM - France prize for « Best Scientific and technical publication 1988 ». Beyond her scientific contribution, Françoise Chatelin played a structuring role on research at CERFACS through multiple thesis on innovative topics. This event is devoted to the human and scientific tribute of her life. As a faithful image of the active and passionate woman that...Read more


CERFACS is involved in the NextSim project

CERFACS |  19 July 2021

The primary objective is to increase the capabilities of Computational Fluid Dynamics tools on extreme-scale parallel computing platforms for aeronautical design. The Kick-Off Meeting took place on 12 March 2021. This project has received funding from the European High-Performance Computing Joint Undertaking (JU) under grant agreement N° 956104. The JU receives support from the European Union’s Horizon 2020 research and innovation programme and Spain, France, Germany. For more information, please visit  EuroHPC website : Project webpage :Read more

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