This file type is valid only for triangular and tetrahedral grids. Select FAST under File Type and select the scalars you want to write in the Functions to Write list.
You have the option of exporting data at specified intervals during the calculation through the Solver/Execute Commands... menu option. See Section 4.12.18 for the complete details.
Click the Write... button to save the file for the specified function(s), using the Select File dialog box. The following files are written:
file/export/fast-grid file name