Thank you so much!Â
But actually  I have already solved this in other way. I have generated particles in the box/bath with Ansys Rocky, then exported genereted particles as stl file by using postprocessing script "Export particle Beds and Geometries as Binary stl file" from ROCKY_ADDITIONAL_PACKAGE. Then I imported this stl file into Ansys SpaceClaim and convert it to geometry with Autoskin tool. Then I save the gemetry as STEP file and finnaly was able to import it into my HFSS file. Just for fun below is the picture
 
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You are navigating away from the AIS Discovery experience