The information in this section is supplied for the sake of completeness. It is identical with the information found in the Overview.
The purpose of CGNS is to provide a standard for recording and recovering computer data associated with the numerical solution of the equations of fluid dynamics. The format implemented by this standard is (1) general, (2) portable, (3) expandable, and (4) durable.
The CGNS system consists of a collection of conventions, and software implementing those conventions, for the storage and retrieval of CFD (computational fluid dynamics) data. The system consists of two parts: (1) a standard format for recording the data, and (2) software that reads, writes and modifies data in that format. The format is a conceptual entity established by the documentation; the software is a physical product supplied to enable developers to access and produce data recorded in that format. The CGNS standard, applied through the use of the supplied software, is intended to do the following:
The CGNS project originated around 1994-1995 through a series of meetings between Boeing and NASA that addressed improved means for transferring NASA technology to industrial use. It was held that a principal impediment to technology transfer was the disparity in I/O formats employed by various flow codes, grid generators, and so forth. The CGNS system was conceived as a means to promote "plug-and-play" CFD.
Agreement was reached to develop CGNS at Boeing, under NASA Contract NAS1-20267, with active participation by a team of CFD researchers from
The principal target of CGNS is the data normally associated with compressible viscous flow (i.e., the Navier-Stokes equations), but the standard is also applicable to subclasses such as Euler and potential flows.
CGNS Version 1.0, released 5/15/98, was limited to problems described by multiblock structured grids. Version 1.1 addresses grids, flowfields, boundary conditions, and block-to-block connection information. Also included are a number of auxiliary items, including nondimensionalization, reference state, and equation set specifications. The extension to time-dependent flows and unstructured grids is addressed in Version 2. Also included are links between CGNS data and CAD geometry. Any mix of the following types of field data can be recorded:
Much of the standard and the software is applicable to computational field physics in general. Disciplines other than fluid dynamics would need to augment the data definitions and storage conventions, but the fundamental database software, which provides platform independence, is not specific to fluid dynamics.
The term CGNS includes specifications and software libraries. The libraries are provided in order to implement the data structure described in the specification. There are two libraries, MLL stands for the Mid-level library and SLL for the Storage-level library.
This SIDS-to-HDF File Mapping Manual describes both the SLL node interface and the SLL mapping to HDF5.