I want to apply steel and glass to a physical product for heat transfer to a fluid however if I assemble two different parts using assembly design, Simulia gives error that geometry is not enclosed whereas if I simulate only one whole Physical product the simulation runs but I can apply only one material to one complete part.What is the solution?

I want glass on lower part and mild steel on the chimney.

If I draw one complete assembly and revolve I can run the simulation but only with one material over entire body.