GiD forum

Hello,
I am trying to create a box that has two different meshes (one Hexa and one Tetra) at the same time. So far, if I want to mesh this complete model with Tetras alone or Hexas alone, it successfully meshes it, on the contrary if I want to combine these two meshes, the error "Incompatibility between Volume number __ element type and its contour surfaces element type." appears:
Is there someone that have had this problem before?
Many Thanks in advance!

Off course the mesh of a geometric entity will be a partition of this geometry. Is not possible to set an entity 'to be meshed twice'

To do what you want you must do dark tricks, like create two volumes on the same location (e.g. copying an entity with displacement zero and without collapse)
If the surfaces are shared by both volumes then its mesh must be compatible with the volume mesh.
Triangles won't be compatible with hexahedra and quadrilaterals won't be compatible with tetrahedra, then in your case can't share surfaces, must duplicate them.

Another approach could be enable the GiD variable that allow to create a mesh without delete previous meshes, and then generate the mesh in two steps of generation, but I recommend the first approach: create two geometric volumes to have two volume meshes.