Hexa meshing of bifurcations
 

Dear all,
I have got a problem meshing (Hexa mesh; O-grid) a vessel geometry consisting of several bifurcating vessels. I created the geometry using Inventor by creating the single vessels and merged them afterwards (using HeeksCad). Unfortunately, inside the merged vessel the geometry of the single vessels stays visible (I tried to avoid this by using Gambit for merging, but the single vessels are nonreal/virtual and cannot be converted and cannot be merged via Gambit therefore).
When I am trying to mesh this geometry using ICEM I get problems with the geometry at the bifurcations and the mesh is really poor (see pic 2) since each of the single merged vessels is meshed (I think) and the mesh doesn’t reach to the surface of the geometry at the some parts of the bifurcations as well (see pic 1).
I don’t know whether this is important, but I created some curves at the branch-vessels at each bifurcation and associated the curves to the edges of the blocks there.
Does anybody have an idea how I could solve this problem? I am really thankful for each idea and help!
WBR
Lilly