Viewfactor > Preparation for Analysis > 4.4 VFCTL, the Viewfactor Program Execution Control File
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4.4 VFCTL, the Viewfactor Program Execution Control File
The Viewfactor program execution control file, VFCTL, contains the information needed by Viewfactor to know which parts of the Viewfactor program should be executed, the names of various files needed by Viewfactor and some data or parameters which will influence the viewfactor calculations.
Note:  
For execution spawned from Patran Thermal, this file is automatically created based on input data in the Patran Thermal Analysis Forms.
Philosophy and Structure of the VFCTL File
The VFCTL file is analogous to a session or command file in that it can be thought of as containing commands which set parameters and filenames in the Viewfactor program. This was done because the Viewfactor program will typically be submitted as a batch job or run as a subroutine call. In both cases, the user is not interacting with the program and the run control commands need to be already stored in the VFCTL file.
You may use any nonconflicting legal file name for the VFCTL file. The default name is in the default directory and named VFCTL. A nondefault name must be entered as a parameter on the command line submitting a Viewfactor job (see Analysis (Ch. 5).
The file may contain comment lines and data lines. Comment lines begin with an asterisk. Data lines begin with a keyword, followed by some data (sometimes optional data). The valid keywords are defined in Keywords in the VFCTL File, 88. Lines may contain leading blanks.
Default values are provided automatically for all run control data. You do not need to enter data lines if the default is the desired value. The default values are given in Keywords in the VFCTL File, 88. The data lines may be placed in any order and only one occurrence of each keyword is allowed. A complete VFCTL file from a VAX/VMS platform is shown below. The filenames have been made generic, but the $PATH is not generic.
Invalid keywords cause a fatal error. This prevents a costly Viewfactor execution with invalid data.
Example VFCTL File
Keywords in the VFCTL File
Presently, there are 19 valid keywords available for use in the VFCTL file. All keywords here begin with "$" and end with ":". The valid keywords are:
$PATH:
$MESSAGE_FILE:
$STATUS_FILE:
$DIAGNOSTIC_FILE:
$TITLE:
$RESTART_FILE:
$IN_DATA:
$TEMPLATE_FILE:
$RAW_DATA:
$OUT_DATA:
$RAD_NODE_FILE:
$RUN_CONTROL:
$RESTART_FLAG:
$CONVERGE:
$ZERO:
$APPROX_CURVE:
$GAUSS_ORDER:
$AXISYM_SURFACE:
$EOF:
Each keyword will be described in detail with the following information given:
1. purpose,
2. required or optional,
3. default value,
4. valid range, and
5. suggested values.
The order of the keywords in the VFCTL file does not matter, with the exception that the $EOF: keyword should be last. Data will not be read after an $EOF: keyword is encountered.
If a keyword is not present, its data will assume the default values.
$PATH: pathname
Purpose of the Keyword
"$PATH:" is to name a path for Viewfactor files. The pathname will be prefixed to all other filenames used in this particular execution of Viewfactor. This feature is provided so that long pathnames do not need to be entered with every filename, provided they are common and the same as that given in pathname. If you adopt a standard convention for filenames and group different models and cases into directories or paths, then these may be accessed by Viewfactor merely by changing the pathname in VFCTL. If the pathname is blank, then nothing will be prefixed to the filenames and your current default directory will be used.
Required or Optional
Optional.
Default Value
Default is a blank string.
Valid Range
Valid pathnames are computer system dependent.
Suggested Values
None.
$MESSAGE_FILE: filename
Purpose of the Keyword
"$MESSAGE_FILE:" is to name the file that will contain text messages from Viewfactor. See VFMSG, 101 and VFMSG, the Viewfactor Message File, 103
Required or Optional
Optional.
Default Value
VFMSG.
Valid Range
Valid filenames are computer system dependent.
Suggested Values
None.
$STATUS_FILE: filename
Purpose of the Keyword
"$STATUS_FILE:" is to name the file to be used for restart status data for Viewfactor. This capability is not presently supported.
Required or Optional
Optional.
Default Value
VFRESTARTSTAT.
Valid Range
Valid filenames are computer system dependent.
Suggested Values
None.
$DIAGNOSTIC_FILE: filename
Purpose of the Keyword
"$DIAGNOSTIC_FILE:" is to name the file that will contain numerical diagnostic data from Viewfactor. See VFDIAG, 101 and VFDIAG, the Viewfactor Diagnostic Data File, 106.
Required or Optional
Optional.
Default Value
VFDIAG.
Valid Range
Valid filenames are computer system dependent.
Suggested Values
None.
$TITLE: title
Purpose of the Keyword
"$TITLE:" is to identify a character string title that will be output to various files in Viewfactor to aid in identifying the analysis case to which a file belongs.
Required or Optional
Optional.
Default Value
Default is a black string.
Valid Range
The character string should have less than 80 characters.
Suggested Values
None.
$RESTART_FILE: filename
Purpose of the Keyword
"$RESTART"_FILE:" is to name the file that will contain data for restarting Viewfactor. This capability is not presently available.
Required or Optional
Optional.
Default Value
VFRESTARTDAT.
Valid Range
Valid filenames are computer system dependent.
Suggested Values
None.
$IN_DATA: filename
Purpose of the Keyword
"$IN_DATA:" is to name the file that must contain the input data for Viewfactor.
Required or Optional
Optional.
Default Value
VFINDAT.
Valid Range
Valid filenames are computer system dependent.
Suggested Values
None.
$TEMPLATE_FILE: filename
Purpose of the Keyword
"$TEMPLATE_FILE:" is to name the file that must contain the VFAC templates for this model.
Required or Optional
Optional.
Default Value
TEMPLATEDAT.
Valid Range
Valid filenames are computer system dependent.
Suggested Values
None.
$RAW_DATA: filename
Purpose of the Keyword
"$RAW_DATA:" is to name the file which will contain the raw viewfactor data. Viewfactor creates and outputs raw viewfactor data as well as reads in the raw viewfactor data when making Patran Thermal radiation resistors. See VFRAWDAT, 102.
Required or Optional
Optional.
Default Value
VFRAWDAT.
Valid Range
Valid filenames are computer system dependent.
Suggested Values
None.
$OUT_DATA: filename
Purpose of the Keyword
"$OUT_DATA:" is to name the file which will contain the Patran Thermal radiation resistor data created by Viewfactor. See VFRESDAT, 102.
Required or Optional
Optional.
Default Value
VFRESDAT.
Valid Range
Valid filenames are computer system dependent.
Suggested Values
None.
$RAD_NODE_FILE: filename
Purpose of the Keyword
"$RAD_NODE_FILE:" is to name the file which will contain the node definition data for Patran Thermal for radiosity nodes created by Viewfactor. See VFNODEDAT, 102.
Required or Optional
Optional.
Default Value
VFNODEDAT.
Valid Range
Valid filenames are computer system dependent.
Suggested Values
None.
$RUN_CONTROL: value
Purpose of the Keyword
"$RUN_CONTROL:" is to set a run control value. The run control value determines the execution sequence for Viewfactor. It is this parameter that allows the user to calculate viewfactors before the VFAC templates are ready (set value to 1), calculate or recalculate the Patran Thermal radiation resistors from existing raw viewfactor data (set value to 2), or calculate viewfactors and make radiation resistors in the same execution (set value to 0). For additional information, see Viewfactor Data and Program Flow, 16 and Changing VFCTL, 122.
 
The valid values of the $RUN_CONTROL: parameter and their effects are:
0 Check data, and if the data checking status = OK, calculate viewfactors and make radiation resistors.
1 Check data, and if the data checking status = OK, calculate viewfactors only.
2 Calculate radiation resistors only, using existing raw viewfactor data. This process involves extensive data checking as the calculations are being done and since no significant CPU time saving is realized, no data checking is done before the calculations.
 
100 Check the data for making viewfactors and radiation resistors and then stop. Do not calculate viewfactors or make resistors.
101 Check the data for making viewfactors and then stop. Do not calculate viewfactors.
102 Check that the appropriate files are present for making radiation resistors from raw viewfactor data. Do not make the radiation resistors.
 
200 Check the data for making viewfactors and radiation resistors. If the data checking status = OK or the data only generated warning messages, proceed with the viewfactor calculations and the creation of the radiation resistors. If the data checking generated an error message, stop.
201 Check the data for making viewfactors only. If the data checking status = OK or the data only generated warning messages, proceed with the viewfactor calculations only. If the data checking generated an error message, stop.
202 This option is functionally the same as 2 above.
 
1000 Skip data checking and proceed directly to calculating the viewfactors and making the radiation resistors.
1001 Skip the data checking and proceed directly to calculating the viewfactors only.
1002 This option is functionally the same as 2 above.
Required or Optional
Optional.
Default Value
0.
Valid Range
Valid values are the integers listed above.
Suggested Values
None.
$RESTART_FLAG: value
Purpose of the Keyword
"$RESTART_FLAG:" is to set the Viewfactor restart flag. The restart flag value controls restarting Viewfactor. Presently this capability is not supported.
Required or Optional
Optional.
Default Value
0.
Valid Range
The only valid value is the integer 0.
Suggested Values
None.
$CONVERGE: value
Purpose of the Keyword
"$CONVERGE:" is to set the parameter that controls convergence checking in Viewfactor. If the value entered is less than or equal to zero, a convergence criteria is calculated by Viewfactor based on the number of surfaces in each enclosure. This number will be recalculated as each enclosure is processed. The formula for convergence criteria used by Viewfactor to calculate the default value is:
converge_value = 0.01/(number of surfaces in enclosure)0.7.
Required or Optional
Optional.
Default Value
-1.0.
Valid Range
Valid values are real numbers and representable on the computer.
Suggested Values
The suggested value is the default value, -1.0. If a faster execution time is desired, at the cost of lost accuracy, a value around 0.1 may be appropriate. Until you gain some experience with Viewfactor, it is best to use the default value. The convergence criteria is not an absolute requirement. You don’t know how fast the numerical scheme converges. The fact that it appears to have converged over a few iterations is no guarantee that it has converged. The default values are based on previous user's experience. As you gain experience you may be able to improve on these default values.
$ZERO: value
Purpose of the Keyword
"$ZERO:" is used to establish a cut off value. Viewfactors below the zero cutoff value will be set to zero. This is a convenient way to eliminate viewfactors and their associated radiation resistors for viewfactors which are close to zero. You must exercise discretion here. For example, in a model with 10,000 surfaces, viewfactors smaller than 0.000001 may be very significant. If the value is less than -0.5, then the zero cutoff value will be set equal to the convergence criteria value. (See $CONVERGE: value, 92.
The program gives the user the ability to not make radiation resistors if the viewfactor between nodal subareas is less than a user specified cutoff value. The zero cutoff value is set using the $ZERO: parameter in the VFCTL file.
Required or Optional
Optional.
Default Value
0.0.
Valid Range
Valid values are real numbers less than or equal to 1.0.
Suggested Values
The default value of 0.0 is highly recommended. The use of numbers greater than the default convergence criteria value is definitely not recommended.
In general, the use of nonzero cutoff values is not recommended. If you want to use them anyway, set the zero cutoff value to zero during the calculation of raw viewfactor data and then set it to the desired cutoff value during the creation of resistors from the raw viewfactor data. This will give you the flexibility of changing the zero cutoff value without having to redo the viewfactor calculations. This procedure requires that you submit Viewfactor twice, once with "$RUN_CONTROL:" set to 1 and $ZERO: set to 0.0 and again with "$RUN_CONTROL:" set to 2 and "$ZERO:" set to the desired cutoff value.
$APPROX_CURVE: value
Purpose of the Keyword
"$APPROX_CURVE:" is to set the parameter that controls the number of subdivisions a curved surface or line will undergo as it is approximated by plane triangles or straight line segments. These linear subdivisions are used for obstruction checking. The smaller the value, the more subdivisions will be required to approximate a curved surface or line. As more subdivisions are created, the accuracy of the calculations will generally increase and the CPU time will increase dramatically.
Required or Optional
Optional.
Default Value
0.1.
Valid Range
Valid values are real numbers less than or equal to 0.5 and greater than or equal to 0.00001 and representable on the computer.
Suggested Values
The default value of 0.1 is the recommended value.
$GAUSS_ORDER: contours double_area weighting
Purpose of the Keyword
"$GAUSS_ORDER:" is to set the value that will determine the maximum integration order that Viewfactor will attempt to use while trying to satisfy its convergence criteria. The three different values are applied to three different types of integration. Contours applies to contour integration around the border of a surface. Double_area, applies to integration over the surface areas of surface pairs for which partially obstructed viewfactors are being calculated. Weighting, applies to calculations to weight the surface to surface viewfactors according to the finite element interpolation functions.
 
The values of the parameters do not correspond exactly to the integration order. The correspondence is shown in Table 4‑1:
Table 4‑1 Correspondence between Parameter Values and Integration Order
 
In general, the larger the parameter value, the more accurate and more CPU costly the Viewfactor analysis will be. The integration orders jump in larger step sizes as they increase because, for example, an increase from 39 to 40 has little effect, whereas an increase from 3 to 4 may have a significant effect.
Required or Optional
Optional.
Default Value
The default values are 8, 8, and 8.
Valid Range
Valid values are integers between and including 3 and 16.
Suggested Values
In general, the suggested values are the default values.
The maximum integration order is only used when the numerical integration scheme has not converged. In most cases, this happens before the maximum integration order is reached. Thus you only pay for the higher integration orders when they are needed for accuracy. If you wish to do a test run at less expense than the actual analysis run, the CPU time may be cut down by reducing the GAUSS_ORDER parameters. In general, you will make the weighting parameter less than or equal to the other parameters, although this is not required.
$AXISYM_SURFACE: minimum maximum
Purpose of the Keyword
"$AXISYM_SURFACE:" is to set the two parameters that control the minimum and maximum number of effective subdivisions the three-dimensional image of an axisymmetric surface is subdivided into for obstruction and viewfactor calculations. Here again, Viewfactor does convergence checking and stops iterating when convergence has occurred. The actual number of subdivisions is not the same as the value of the parameter. They correspond in the same way as the integration orders in Table 4‑1.
Required or Optional
Optional.
Default Value
3 for the minimum, 13 for the maximum.
Valid Range
Valid values are integers , and maximum greater than or equal to minimum.
Suggested Values
These parameters have the greatest effect of any of the parameters on the execution time and accuracy of an axisymmetric model submitted for viewfactor calculation. The execution time will increase approximately as the square of the number of subdivisions. Unfortunately, the accuracy does not improve in a like manner. In general, the recommended values are the default values. However, the user may find with some experience that values of maximum as low as 8 give satisfactory results.
$EOF:
Purpose of the Keyword
"$EOF:" is to signal the end of the VFCTL file.
Required or Optional
Optional.
Default Value,
Valid Range,
Suggested Values
There is no parameter to receive a default value, be checked for validity, or receive a recommended value.
This concludes the description of the VFCTL keywords.
A sample VFCTL file is delivered with the Viewfactor program. This file is reproduced here.
Note:  
The above file corresponds to the defaults set when a Viewfactor job is spawned directly from Patran.