[boffin5]

My case concerns simpleFoam analysis of a semi-truck, as seen in the attached image. It consists of 7 .stl files: tractor, trailer and 5 wheel pairs. It runs okay with the layers turned off, but fails with them on. Obviously this is not acceptable for understanding the boundary layer flow.

So I looked at the motorBike tutorial, which even more than my truck, consists of a multiplicity of parts, and the layers work fine. In the paraView output you can see the parts listed, but they don't appear in the case setup.
Actually, these parts are imbedded in a single .obj file, which is somehow split up into the constituent parts and placed into groups. Here is a snippet of the .obj file:

f 70674 70296 70216
f 71278 70703 71276
f 71276 70703 70674
g rear-brake-lights%46
f 132630 132583 132613
f 132583 132516 132613
f 132636 132630 132613

In the boundary conditions typically you see:

motorBikeGroup
    {
        type            kqRWallFunction;
        value           $internalField;
    }

And in snappyHexMeshDict are the lines:

refinementSurfaces
    {
        motorBike
        {
            // Surface-wise min and max refinement level
            level (5 6);

            // Optional specification of patch type (default is wall). No
            // constraint types (cyclic, symmetry) etc. are allowed.
            patchInfo
            {
                type wall;
                inGroups (motorBikeGroup);
            }
        }
    }

In the tutorial, how are all of these parts directed to the motorBikeGroup, and how does that then populate the inGroups?

Trying to create and mesh a single .stl file of something as complicated as the tractor has been difficult, and I think that by breaking my truck down into a collection of small parts, I would have a better chance of success, but Solidworks won't let me create a single output .obj file, as was done with the tutorial. Even if I could, I need guidance as to how the tutorial collected these parts into a group, and then worked with that group in the case setup.

After all, the formula 1 people deal with simulations of car suspensions composed of large numbers of parts. How do they set up the case?