Creating a control volume
 

In my recent proyect I´m trying to do a CFD analisys over surface of great extension. I can get the .stl of the surface map (Global Mapper) and import it to HEXPRESS to create a posible .dom. My problem now is that I have to create I control volume and thge surface alone does not count as a close control volume. I´ve been thinking on creating inside Hexpress (CAD manipulation) a box, transform this into a domain and finally import an internal surface (the .stl file from GM mentioned before). I´ve try it several times but I keep getting some error about some .bcs that the programm is not finding while trying to import the internal surface.
Does anybody have any ideas as to how can I create this control volume inside Hexpress or do you think it is better to create this volume in AUTOCAD or any other CAE programm?
Thank you very much for your Help.
Rodrigo

Dear Rodrigo;
I strongly recommend you to use modeling tools like CATIA, Solid Works or UNIGRAPHICS. Inside the Hexpress there is few chance to successfully generate a to z of a model. i think you should check the followings:
- modeling tolerances in your modeling software.
- make sure that your model is defined as a solid in your software. some times your model just includes some sheet bodies rather than a united solid body. this will cause problems in meshing.
- make sure that your model does not contain very small (near zero area) surfaces. this wont let you mesh the volume.

regards