Try to adapt the CaseFloating scenario to meet your needs. If you look at the batch / bash script for CaseFloating, you'll see that boundaryvtk is being used to save the floating data in surface form.
As per page 60 of the user guide, the convention is that the mk number referred to in the batch / bash script for boundary particles is mk + 11. Since the floating box in CaseFloating has a mk value of 50 in CaseFloating_Def.xml, boundaryvtk uses an mk value of 61 in the batch / bash script.
As always, try to run each of the demos and consult the documentation. The answers are (almost always) there.
Comments
As per page 60 of the user guide, the convention is that the mk number referred to in the batch / bash script for boundary particles is mk + 11. Since the floating box in CaseFloating has a mk value of 50 in CaseFloating_Def.xml, boundaryvtk uses an mk value of 61 in the batch / bash script.
As always, try to run each of the demos and consult the documentation. The answers are (almost always) there.