Agenda

CGNS meeting, June 24, 2003, Orlando, FL

• Status of CGNS and outstanding issues
• Discussion of recent issues raised on CGNStalk
  • UserDefined extension
  • BCDataSet extension
  • CGNSVersion
  • Possible need for GridLocation=FaceCenter in ZoneGridConnectivity
• Future directions, needs, and other issues

Status of CFD General Notation System (CGNS)

Christopher L. Rumsey
June 24, 2003, Orlando FL

Outline

• Introduction
• Recent accomplishments
• Where we are
• Current issues/needss
• Where we are going

What is CGNS?

• Standard for defining & storing CFD data
  • Self-descriptive
  • Machine-independent
  • Very general and extendable
  • Administered by international steering committee
• AIAA recommended practice (AIAA R-101-2002)
• In process of becoming international ISO standard
• Free and open software
• www.cgns.org

Typical CGNS file

Makeup of CGNS

• Standard Interface Data Structures (SIDS) is the core of CGNS - defines the intellectual content
• Low level implementation is currently Advanced Data Format (ADF)
  • Basic direct I/O operations
  • Software has no knowledge of data structure or contents
  • Tree-based (nodal parent/child) structure
• Mid-level library (MLL) is currently available for C and Fortran
  • This is what most users employ
  • Software has some knowledge of SIDS
  • C++ and Python extensions also available

Recent accomplishments

• CGNS now maintained on and available from SourceForge (sourceforge.net)
• Latest version is 2.2
• Utility "adfviewer" available for viewing & translating CGNS files
• Extensive web-based and pdf documentation available
• CGNStalk@grc.nasa.gov discussion group

Where we are

• SIDS & software reliable and well-tested
• Most current proposals for extension (to SIDS) are relatively minor/specific
• Acceptance as ISO standard is progressing (but stalled in 2003 due to budgeting problem)
• Many people beginning to use CGNS, but mostly as an "option" - it has yet to gain full acceptance as a standard

Current issues/needs

• Replacement of underlying ADF with HDF5
  • Prototype (written by Poinot) is available
  • Needs evaluation and further work
  • Adds parallel capability and would help propel CGNS to wider use/acceptance
• Need to reconcile ISO specs (STEP documents) with latest SIDS
• New proposals for extension need review, then implementation

Where we are going

• Resolve current issues/needs (last slide)
• Replace ADF with HDF5 for commonality and growth
• Continue "advertising": Poinot et al. abstract submitted for Reno 2004, "Impact of CGNS on CFD Workflow"
• Push to get more of the widely-used CFD codes to implement CGNS
• Maintain an active & diverse steering committee

Discussion of recent issues raised on CGNSTalk

UserDefined extension

• Allow the following additional children:
  • PointRange, PointList, GridLocation, FamilyName, Ordinal
• Would need new MLL functions, e.g.:
  • cg_ptset_write, cg_ptset_read, cg_ptset_info
• Purpose: extends usefulness of UserDefined node

BCDataSet extension

• Allow the following additional children:
  • PointRange, PointList, GridLocation
• Would need new MLL functions, e.g.:
  • cg_ptset_write, cg_ptset_read, cg_ptset_info
• Purpose: allows auxiliary BC data info to reside at different grid location from the indices that define the BC patch

CGNSVersion issue

• Problem: if write CGNS file without CGNSLibraryVersion node, then reading the file using MLL can cause problems
• Current fix: make CGNSLibraryVersion node mandatory part of CGNS file (this is a fix to the documentation only)
• Question: is a proposal for a separate CGNSVersion node needed?
  • Maybe not, because MLL and SIDS maintain the same numbering (e.g., "2.2")

GridLocation issue

• Currently, connectivity information is always with respect to the vertices for abutting-type interfaces, and can be either Vertex or CellCenter for overset-type
• Should GridLocation=FaceCenter also be allowed?
  • Particularly desirable for unstructured grids