The Viewfactor code was designed primarily to support and enhance the thermal analysis capability in P⁄THERMAL. Although Viewfactor is a stand-alone executable, we will be primarily concerned with its use in conjunction with Patran and Patran Thermal. Viewfactor was designed to work closely with the Patran Thermal module, and thus uses many of the same files as Patran Thermal.

The relationship of the Viewfactor code to Patran and Patran Thermal is shown schematically in Figure 2‑1. Patran Thermal’s PATQ takes the geometric and boundary condition data from a Patran neutral file and converts it to data about the thermally radiating surfaces. The data is then output to the VFINDAT file. The TEMPLATEDAT file is the Patran Thermal template file, with the addition of a new template, called VFAC (Viewfactor). The template data is necessary for Viewfactor to make thermal network resistors for Patran Thermal. The Viewfactor run is a noninteractive process whose execution is controlled by data in the VFCTL file.

Viewfactor transforms the data in the VFINDAT file into viewfactor data, which is output to the intermediate file VFRAWDAT. This intermediate file permits you to change the surface properties in the TEMPLATEDAT file and generate new thermal network resistors without having to redo the computationally expensive viewfactor calculations. The intermediate raw viewfactor data file also makes possible the use of Viewfactor to generate just viewfactor information for use other than interfacing directly to Patran Thermal.

Next, the raw viewfactor data in VFRAWDAT and the information in the surface template file, TEMPLATEDAT will be combined by Viewfactor to make thermal network resistors and radiosity nodes for Patran Thermal. The resistors will be output in the binary file VFRESDAT and the radiosity nodes will be put out in the VFNODEDAT file. These two files will be input by Patran Thermal and used in the thermal analysis of the problem. The results of the thermal analysis are output by Patran Thermal in the file QOUTDAT and nodal results files. These files may be displayed along with the geometric model using the postprocessing capabilities of Patran.

There are several other files shown in Figure 2‑1 which we have not yet discussed. These are VFRESTXT, VFDIAG, and VFMSG. These files do not participate in the computer analysis of the problem. They are provided to assist you in determining that the problem is correctly modeled and the analysis has been correctly performed. In the event you have an error, they will be helpful in finding and correcting it.

VFRESTXT is a text version of VFRESDAT. Since VFRESDAT is stored in binary form, it cannot be read by most computer file editors. The capability to translate the binary VFRESDAT file into a text file, VFRESTXT, is provided in Patran Thermal’s PATQ. You may then examine the thermal network resistors generated by Viewfactor using the text editor of your choice. VFRESDAT files tend to be large and are best implemented in binary form, which is more compact than text form. You will find, in most cases, that the VFRESTXT file is too large to be examined in detail.

The files VFDIAG and VFMSG contain information useful in evaluating a Viewfactor execution. VFMSG predominately contains text information concerning the progress of the Viewfactor program execution and reports of any errors which were detected. You are strongly advised to examine the VFMSG file for error messages, since this is the only way to know if errors occurred. The VFDIAG file contains predominately numerical data relating to the sums of viewfactors to each surface. This data can often be compared to expected values for the sums of viewfactors and thus used to judge the correctness of the viewfactor analysis.