How to create mesh on duplicated surface?

Hi,

I was trying to apply a topology optimization on GE bracket geometry, to obtain finer mesh, i think i should create 2D mesh elements and check them in accordance to quality parameters and remesh them as 3D in a new component. In first step, i have imported the geometry and splited the non-design spaces.

In second step, i hided the non-design space and formed a 2D tria mesh on design space, and i applied it again in reverse way.

All 2D meshing process done, i created 2 new components to create 3D mesh.

With tetra mesh, i tried to create 3D mesh elements from 2D elements which created in design space.

"The mesh is not enclosed" error showed up, i hided the non-design space again i saw the common surfaces (design, non-design) can be meshed just once therefore, the mesh design space is not enclosed.

those surfcases have no mesh. therefore, i could not create 3D mesh. 

I would be very glad if you help me out with that.