CFD Online Discussion Forums - How do patchGroups work?

Hello all,

I'm working with a geometry that has a lot of different patches, but a lot of them are the same. This means my 0 files are very large but very repetitive. In the motorBike tutorial there's patch groups, but I'm unclear how they're really constructed. Here's my though process:

They appear to be defined in the boundary file. However snappyHexMesh makes this file, so it must be the originator of the boundaries. It looks like the input .obj is assigned to the group through this text:

Code:

geometry

{

    motorBike.obj

    {

        type triSurfaceMesh;

        name motorBike;

    }

So does this mean that any patch defined in the .obj (or an STL in my case) is put into this patch?

If that's true, there's another problem I have with this - I've read that patches can belong to multiple groups. Considering what I said above, I don't see how that's possible unless you modify the boundary file after meshing?

Any helpful hints?
Thanks!