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Code Coupling


CERFACS has a strong expertise in the development and use of generic code coupling libraries.The couplers developed at CERFACS are daily used to address complex scientific problems such as:

  • chemistry-Atmosphere coupling with OASIS
  • earth system modelisation for climate science
  • multiphysics coupling (heat transfer, fluid/structure interaction …)
  • multi-composant coupling
  • data assimilation
  • multidisciplinary optimization

All these applications rely on the integration of different solvers that interact at different levels between each others following coupling algorithms.

OASIS coupler

The OASIS coupler, currently developed in the framework of the EU FP7 IS-ENES project, is software allowing synchronized exchanges of coupling information between numerical codes representing different components of the climate system. Current OASIS developers are CERFACS (Toulouse, France), DKRZ (Deutsches Klimarechenzentrum, Hamburg, Germany), and Centre National de la Recherche Scientifique (Paris, France).

OASIS3 is the direct evolution of the OASIS coupler developed since about 20 years at CERFACS (Toulouse, France). Low-intrusiveness and portability are OASIS3 key design concepts. At run-time, OASIS3 acts as a separate executable, which main function is to interpolate the coupling fields exchanged between the component models, and as a coupling interface library linked to the component models, the OASIS3 PRISM Model Interface Library (OASIS3 PSMILe). The OASIS3 separate executable can be parallel, each process treating a subset of complete coupling fields; this results in a pseudo-parallelisation of OASIS3 on a field-per-field basis.

The component models remain separate executables with main characteristics, such as internal parallelisation, untouched with respect to their uncoupled mode; the coupling interface library API includes calls to receive and send the coupling fields usually implemented within the model timestep loop. OASIS3 supports 2D coupling fields only. OASIS3 is currently used by approximately 30 climate modelling groups in Europe, USA, Canada, Australia and Asia.


Illustration: convection resolving ICON simulations over the tropical Atlantic.



To efficiently represent complex systems, numerical modelling has to rely on many physical models at a time: an ocean model coupled with an atmospheric model is at the basis of climate modelling; a turbulent reactive fluid model coupled with a radiation and conduction models allows the computation of a combustion chamber temperature. The continuity of the solution is granted only if these models can constantly exchange information. OpenPALM is a software allowing the concurrent execution and the intercommunication of programs based on in-house as well as commercial codes.The OpenPALM team is composed of Cerfacs and Onera people.


Illustration: conjugate heat transfer in a higly loaded low pressure turbine blade.


Published on  September 30th, 2020

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