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cfsplit may be used to split structured zones in a common grid (.cgd) or common flow (.cfl) file into multiple zones. This may be useful in splitting a large zone into smaller zones for parallel computation on multiple processors.

Input to cfsplit is specified in a keyword input file, with the three-letter extension .inp. Lines in the input file starting with a "/" are comments. The following keywords and parameters may be specified.

    CHECK   Checks the input file for errors without performing any operations.

FILE file_in The input .cgd or .cfl file, containing zones to be split.

OUTPUT file_out The output common file, with the split zones. If the file is a .cgd file, coupling data is also generated and included in the output file. Note, though, that coupling data is not generated if originally self-coupled boundaries are uncoupled by splitting a self-closing zone in the self-closing direction.

NOLAP nplanes The number of planes to overlap the zones when OVERLAPPING split mode is being used. (See the SPLIT keyword below.) Note that this value can be changed between SPLIT commands to change the overlap size for particular zones.

FRGSIZ nplanes The number of planes to create fringe points on when OVERLAPPING split mode is being used. (See the SPLIT keyword below.) Note that this value can be changed between SPLIT commands. The value of FRGSIZ must be between 1 and NOLAP.

HALFCELL Indicates that the split will occur halfway between the specified "split" index and the next higher index. This option overrides and ignores any OVERLAPPING or NOLAP specifications. Using this option allows more accurate coupling, particularly when using the COUPLING MODE ROE HIGH keyword when running Wind-US. For .cfl files, the split zones may be re-combined using the cfcombine utility with its HALFCELL keyword.

SPLIT [OVERLAPPING] ZONE nzone AT [I irange] [J jrange] [K krange]
A series of SPLIT keywords tell cfsplit what zone to split, and where. Any zones not specified will be copied unsplit into the output file.

The irange, jrange, and krange parameters are each of the form n1 n2, where n1 and n2 specify the indices in the relevant direction to be included in the split-off zone. A value of 0 may be used for n2 to specify the maximum value in that direction. Any irange, jrange, or krange parameter not specified defaults to the entire range.

A zone must be split in contiguous sections covering the whole zone. Thus, at least two SPLIT keywords must be used.

If the OVERLAPPING parameter is included, the split zones will be overlapped by the number of planes specified by NOLAP. The number of overlapping planes is added to the n2 values.

Example 1

Suppose we have the simple single-zone two-dimensional grid shown in the following figure.

Single-zone grid for two-dimensional diverging duct

Single-zone mesh, input to cfsplit

A three-zone grid may be created using the following input file for cfsplit, named cfsplit1to3.inp.

   / Input grid file
   FILE testa.cgd
   / Output grid file
   OUTPUT testb.cgd
   / Split into three zones
   SPLIT ZONE 1 AT I 1   9
   SPLIT ZONE 1 AT I 9  17
   SPLIT ZONE 1 AT I 17  0

The terminal session is shown below. Lines in a slanted font are typed by the user.

   % cfsplit
                                ***** cfsplit *****
             Select the desired version from the following list.
   0) END
   1) cfsplit
   Single program automatically selected.
   Omit the .inp extension!
   Enter cfsplit INPUT FILE ............. (<CR>=cfsplit.inp) : cfsplit1to3
    cfsplit - Version 1.15 (last changed 2007/03/01 21:04:55)
    * Warning: This software contains technical data whose export is           *
    * restricted by the Arms Export Control Act (Title 22, U.S.C., Sec 2751,   *
    * et seq.) or Executive Order 12470. Violation of these export-control     *
    * laws is subject to severe criminal penalties. Dissemination of this      *
    * software is controlled under DoD Directive 5230.25 and AFI 61-204.       *

The resulting three-zone grid is shown below.

Three-zone grid

Three-zone mesh, output from cfsplit

Example 2

In three dimensions, the following SPLIT commands would be used to split a 23×15×19 zone into a 10×15×19 zone, a 14×15×5 zone, and a 14×15×15 zone.

   SPLIT ZONE 2 AT I  1 10  K 1 0
   SPLIT ZONE 2 AT I 10  0  K 1 5
   SPLIT ZONE 2 AT I 10  0  K 5 0
Example 3

The following three commands will split zone 3 into two zones; the first containing I planes 1-23 from the original zone, and the second containing planes 21-IMAX.

   NOLAP 2

Last updated 26 Aug 2015