Im having the same problem.
I would like to couple the results from FLOW in the PART tracking module.
However the flow model does not create a 'COM' file and output of
Delft3D flow I could not select the 'online coupling' bottom.
What could i do?
If you couldn't see the 'Export WAQ input' option, or in older FLOW
GUI versions, the 'online coupling' at the bottom of the output
section, that could only be if you have a very old version of the FLOW
GUI (>5 years). Email to firstname.lastname@example.org for a newer
version of the (oss) GUI.
If you also don't see a com-file, things you could check are the
start and stop timers and the interval. When the interval is zero, the
com-file will not be produced. The same goes for the preferred 'Export
WAQ input' option, that will only produce a hyd-file (that is directly
usable by PART) when the timings are correct.