VFOPT
VFOPT, Opt, Filename,
Ext, Dir,
Filetype, Fileformat, WRIO
Specifies options for the view factor file and calculates view factors.
-
Opt View factor option:
NEW
—
Calculate view factors, store them in the database, and write them to a file. This is an action option that is executed immediately when the command is issued. For a coupled-field analysis with NLGEOM,ON, issue either the UPGEOM or UPCOORD command before issuing VFOPT,NEW to calculate view factors based on the updated geometry.
OFF
—
Do not recalculate or read view factors if they already exist in the database; otherwise calculate them at the next SOLVE command. Remaining arguments are ignored. This option is the default.
READ
—
If the command is issued in the solution processor (/SOLU), this option reads view factors from the specified binary file when the next SOLVE command is issued.
FileTypemust be set to BINA (binary). For subsequent SOLVE commands, the program switches back to the default option (OFF).If the command is issued in the radiation processor (/AUX12), this option immediately reads view factors from the specified binary file.
FileTypemust be set to BINA (binary). The program switches back to the default option (OFF) after reading the view factors.NONE
—
Do not write view factors to a file when the next SOLVE command is issued. Remaining arguments are ignored.
-
Fname File name for view factor matrix. Default = Jobname.
-
Ext Filename extension for view factor matrix. Default = .vf.
-
Dir Directory path for view factor matrix. If you do not specify a directory path, it will default to your working directory.
-
Filetype View factor file type:
BINA
—
Binary (default).
ASCI
—
ASCII.
-
Fileformat Format for the specified
Filetype:Binary files (
Filetype= BINA):0
—
No compression. (View factor file size may be very large.)
1
—
Zeroes are compressed out. (Useful for large models to reduce the view factor file size.)
ASCII files (
Filetype= ASCI):0
—
10F7.4 (low precision, lower accuracy).
1
—
7F11.8 (high precision, higher accuracy).
-
WRIO Write only the view factors of independent facets for symmetric models. This option is valid when view factor condensation is enabled (VFCO,,,1 or VFCO,,,2) and further increases efficiency by reducing read/write time; for more information, see Considerations for Symmetric Models Using View Factor Condensation below.
ON
—
Writes only the independent view factors when view factor condensation has been enabled, providing additional efficiency gains. After view factors are computed and written to a file,
WRIOis automatically reset to OFF.OFF
—
Turns off option to write only the independent view factors (default).
Notes
The VFOPT command allows you to deactivate
the view factor computation (Opt = OFF)
if the view factors already exist in the database. The default behavior
is OFF upon encountering the second and subsequent SOLVE commands in the solution processor.
The VFOPT command controls view factor calculations and the reading/writing of view factors at the load step level only. It is not supported at the substep level. To update view factors for a coupled-field analysis with NLGEOM,ON at the substep level, you must use the VFUP command.
When Opt = READ, only a previously
calculated view factor binary file is valid. View factors are read only and are not written after
they are read in. Do not issue VFOPT,OFF or VFOPT,NONE
until after the next SOLVE command is executed.
If you want to read in view factors after restarting a radiation analysis, issue VFOPT,READ after ANTYPE,,REST.
Two options are available for calculating view factors when running a distributed-memory parallel solution:
Issue a VFOPT,NEW command -- View factors are calculated and stored in the database. View factor computations are not run in parallel.
Issue a SOLVE command in the /SOLU processor -- View factors are calculated in parallel mode if no view factors were previously calculated. If view factors have already been calculated (by a previous VFOPT,NEW or SOLVE command), they are used in the radiosity calculations, and issuing SOLVE does not re-calculate the view factors.
View factors are not calculated in parallel for 2D analyses.
Considerations for Symmetric Models Using View Factor Condensation
For symmetric models using view factor condensation (VFCO,,,1 or VFCO,,,2), read/write time can be reduced by writing only the independent view factors since they are the only non-zero values in the view factor matrix as described in View Factor Matrix for a Model with Symmetry in the Theory Reference.
When view factor condensation is turned off (VFCO,,,0), the full matrix is written to the view factor file when VFOPT,NEW is issued:
where the view factor matrix is decomposed, and the subscripts, 
and 
, denote independent and dependent. (See View Factor Matrix: General in the Theory Reference for details.)
When view factor condensation is turned on
(VFCO,,,1 or VFCO,,,2), use
WRIO to control what is written to the view factor file:
When VFOPT,NEW,,,,,,OFF is issued, the lumped matrix and zeros are written:
(For the definition of F
L, see Equation 6–21 in the Theory Reference.)When VFOPT,NEW,,,,,,ON is issued, only the lumped matrix is written:
.