CFD Online Discussion Forums

CFD Online Discussion Forums (
-   STAR-CCM+ (
-   -   import solids (

Alessio85 October 22, 2011 13:03

import solids
i'm new to use Star CCM and my issue is that i have created a new assembly model in Catia and I want to import it in Star as a solid part but i can't do it...
when i import the .igs file the program imports only surfaces..
How can i do to import solids?

abdul099 October 22, 2011 23:28

You are kidding, aren't you? There is material inside of the surfaces. It's the strange, radioactive, invisible Star-CCM+ material used by the programmers to drive newbies into suicide since they can't understand how to perform a simulation with just a surface. Something related with the dark material from astro physicists who are researching about the structure of the universe. Some say, it was invented by a middle age alchemist, but in fact it's much older, it also has killed the dinosaurs to prove its power and to teach CFD newbies the meaning of fear! Be careful when looking into an imported surface, this invisible material has also done the impossible won a fight against Chuck Norris! Two times!

Okay, back to serious mode. Even in a CAD, the difference between a surface and a solid body is just the information on which side of the surface should be material. And that's easy: On the side enclosed by a closed surface. Like in the real world. There is no material in the real world not enclosed by any surface. Or did you ever see a cube of metal without surface? Maybe a point would satisfy this, as the dimensions and therefore the surface is infinite small, but the volume as well.
So the definition of any body in CAD is just a surface.

Star-CCM+ just says "okay, let's import this surface definition". The same as in CATIA. The only thing is the display, as most CAD calculate a new surface when they should display a section. Star-CCM+ doesn't do this when creating a section of a surface representation. But anyway, the surface stays exactly the same, no matter if it displays any section surface or not.

So let's summarize: No matter which CAD data you import, no matter if importing as part or as region, no matter which format, it will ALWAYS be a surface! That's enough since the material of a body is always enclosed by surfaces. It makes no sense to have material somewhere where it wouldn't be enclosed by a surface. So what more do you want?

The only way to import "a volume" is to import a volume mesh when you've got a pre-defined one. But usually it's your job to create a volume mesh, not to import it. That's one of the most important jobs of a CFD engineer, as it can mess up the whole simulation.

But what is a volume mesh? It is nothing else than a discretized representation of the space enclosed by a surface. One can say, a surface filled with some other surfaces - so called cells. Every cell has some properties during solution like a virtual amount of liquid inside, a velocity of the virtual amount of liquid etc, but it is still a VIRTUAL amount of material - there will be no material created inside your computer. Otherwise you will get the Nobel prize for sure!

We can even go further: What is a surface? Just some points and a definition, this points would enclose a surface...
What is a point? Some numbers and a definition, this numbers would be coordinates...


Luke October 25, 2011 05:07

Hey abdul099,

please ask the cd-adapco support about including your description in the user guide, because it may help all newbies :D
Very good and extraordinary answer. Keep writing such things.
Nice day

rabat November 8, 2011 09:27

Good answer
That's the right way

willimanili November 8, 2011 14:23

Look for surface repair in the user guide if you have problems to get a volumemesh in your volume defined by your imported surfaces. Run a surface diagnostic and look for free or non manifold edges.
And dont forget to create a mesh and physics continuum before meshing.

By the way, if you have imported a valid volume as part or region create a plane section (derived parts) through your body and you will see there is material inside. :eek:
Usually it isnt black material but dark grey material. ;)

abdul099 November 11, 2011 14:16

willimanili, a plane section will not show more than an outline when there's no volume mesh. This is because the material is a strange, radioactive and invisible material. :cool:
No, I'm just kidding. But right after importing a part or what surface definition ever, it's just a surface. So a plane section will show only the section of the plane with this surface, which is a set of lines. It's the same you can see when showing only outlines.

All times are GMT -4. The time now is 05:47.