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SEVEN KEYSFOR PRACTICAL UNDERSTANDING AND USE OF
CGNSMarc Poinot, SAFRAN
Christopher Rumsey, NASA LaRCAIAA SciTech 2018
Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
Motivation
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
CGNSisalibraryCGNScannotfitmyowndatastructureTherearetoomanywaystodescribethesamefeatureinCGNSCGNScannothandleparallelprocessingCGNSisonlyforarchivaldataCGNSfilesaretoobigTherecommendedimplementationisHDF5butonlyADFisavailableTherearefewusefultoolsforCGNSmanipulationIalreadyhaveHDF5andIdonotneedCGNSCGNSinefficientlystorestimedataandstatistics
CGNS is well known in the CFD community, but:- often mismatched with its mid-level library- only understood as mesh storage on disk
We have seen some initiatives to develop a new standard to:- define an implementation-independent data model- add Computer-Aided Design (CAD) related features- implement in HDF5
è This looks quite close to CGNS
We propose to gather initiatives rather than creating entropy: let us refresh our comprehension…
Common comments:
Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
CGNS entities and their acronyms
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
Acronym Meaning Entity
CGNS CFDGeneralNotationSystem Identifier
CGNS/SC SteeringCommittee Groupofpeople
CGNS/SIDS StandardInterfaceDataStructure Textualdocument
CGNS/CPEX CGNSProposalforEXtension Procedureandtextualdocument
CGNS/FMM FileMappingManual Textualdocument
CGNS/HDF5 HDF5implementation Textualdocument
CGNS/Python Pythonimplementation Textualdocument
CGNS/MLL Mid-LevelLibrary Softwarelibrary
Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
Abstract model> What is the data I want to define?> How do I define it?
Interoperability> How to go from CAD to mesh, to post-processing, visualisation and then back to CAD?> How to exchange data during CFD/CSM, CFD/CAA or any multiphysics workflows?
Functional coverage> Do I have enough functions to describe my data?> What is the remaining volume data I need to define/store?
High performance> Is there a High Performance Computing (HPC) efficient representation for my data model?> Who is going to support it?
Versatile implementation> Can I manipulate my data in a flexible way?> Do I have to re-invent all the functions I need for my data processing?
Extensibility> How can I describe out-of-CFD data, such as chemistry, high order, CSM features, new CFD trends?> Does the standard belong to NASA?
Open System> Can I connect the simulation elements together as black boxes?> Is there a mandatory implementation?
Seven keys
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
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Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
Abstract model
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
Amodeliswhatyouwanttospecifybutnothowyouwanttoimplementit
TypesandIndexingconventions
SIDStypedefinitions
Formaldefinition,supportedusingagrammar
Informaldefinition,textualnon-exhaustivedescription
Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
Interoperability
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
Thehighestlevelofinteroperabilityistheuser'smeaningThelowestistheimplementation
CAD/Topology
CFD/Flows
Motion/Deformation
Families are the means to hold user’s information
• Topology entities, CAD reference• Same entity for different models• Entities with special features• Simulation specialized entities
Simultaneous families allowedHierarchy of families
èInsure traceability through processes
è Allows high level interoperability
CFD/CSM/FSI/Experimental
Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
Functional coverage
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
The CGNS tree changes all along the simulation workflow> It covers our CFD needs and more> It doesn't cover everything, but it could eventually fulfill any needs: CPEX
99%ofthevolumeofthedataalreadyisdefined
CAD CFD POSTPRE
FamilyDimensionalUnitsUserDefinedData
BaseZone/GridPeriodicity/SymmetryGoverningEquationsBC
Solution/ZoneSubRegionGridLocation/DataArray
BaseIteration/ZoneIterationlinks
Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
HPC implementation> HDF5
w HDF Group support for portage/tuningw Very large data but limited number of typesw Fast memory/disk swapw Smart memory mappingw Parallel features
High performance
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
> The HDF5 implementation specification is publicw Write your own applicationw Specific node orientationw Specific memory mapping (interlaced, non-contiguous, partial, out-of-core…)
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Gluing/prototyping the easy way> Python/numpy
w Your C/Fortran array IS your python arrayw Reuse of the very large python librariesw No-class paradigm, easy serialization/deserialization
> Memory to memory exchange (same process, inter-process, inter-nodes, inter-hosts…)> Fast creation/modification of CGNS trees
Versatile implementation
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
Change all BCs to family defined
Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
• A support for user needs> CPEX
w Propose your own extensionw Do not break already used features
> Examplesw NGON HPC redefinitionw Arbitrary High orderw Enhanced Chemical data modelw Arbitrary Reference Frame
> PROSw Arguing often leads to better ideasw Once adopted, everyone uses your data model / implementation
> CONSw Lengthy processw You have to explain your ideas
Extensibility
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
user has a need
check CGNS/SIDS
check CGNS/CPEX
submit informal email on cgnstalk@lists.nasa.gov
create informal working group
submit more formal proposal
motivation/ rationale/ examples
CGNS/SIDS update proposal
CGNS/FMM update proposal
CGNS/MLL update proposal
review
CGNS/SC vote
CGNS/SIDS release
CGNS/MLL release
Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
Specification & connection only through public interfaces> High Level: CGNS/SIDS> Low Level: CGNS/FMM> Implementation: CGNS/HDF5, CGNS/Python
> Any compliant implementation can 'connect' to others> Dedicated implementation is required for HPC
Open system
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
CGNS/SIDSdata model
CGNS/FMMper-node mapping
CGNS/ADF CGNS/HDF5 CGNS/Pythonsingle-node mappings
your own implementations
CGNS/MLL
CHLone
pyCGNS
Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
Answers to remarks
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
CGNSisalibraryCGNScannotfitmyowndatastructureXMListhewaytodescribedataExtensionprocessistoolongformeTherearetoomanywaystodescribethesamefeatureinCGNSCGNScannothandleparallelprocessingHPCcannotwastetimeondatamodelCGNSisonlyforarchivaldataCGNSfilesaretoobigTherecommendedimplementationisHDF5butonlyADFisavailableTherearefewusefultoolsforCGNSmanipulationIalreadyhaveHDF5andIdonotneedCGNSCGNSinefficientlystorestimedataandstatistics
CGNSisonlyforCFD
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Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.
Conclusion
AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
You now have a broader view of CGNS
CGNS is far more than a library è it is a means for CFD workflow interoperability
Join
www.cgns.orgcgnstalk@lists.nasa.gov
Doyou want toadd CADtraceability?Doyou havesuch astandardforCSM,FSI,CAA,orother field?
Doyou want moredatastructure,morededicated implementations?
Ce document et les informations qu’il contient sont la propriété de Safran. Ils ne doivent pas être copiés ni communiqués à un tiers sans l’autorisation préalable et écrite de Safran.AIAA-SciTech 2018 / Seven keys for practical understanding and use of CGNS
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