After I run the file,it does not generate anything.I think there maybe something wrong with BEAMPOS.I want to define a point source directly above the fiber, which is perpendicular to the fiber，if it have something wrong?
Can you please share your updated flair file?
As soon as I open the geometry tab, I can see that there is the “Errors found” message, which means that you have errors in your geometry. Fluka cannot work if there are errors in geometry.
Please, have a look at the lectures about geometry and geometry editor and then fix the errors. You should at least try to debug your input before asking for help.