[xuankushuocai]

I created the stl file from the Solidworks and then put it into OpenFOAM. It really strange that if I use full model, everything is fine. But if I change blockMeshDict and use half model (the model is symmetric, the range in z direction is from -16 to 16 for full model, and 0 to 16 for half model), there is no layer in the center, also layers are not fully added in other places. It's really strange since I only change the blockMeshDict cutting from the symmetry plane. And it works for another model. Is there anyone who can explain it? Is it the problem of stl file or OpenFOAM code? Thanks so much.

I attached the plots I got after finishing snappyHexMesh. The first two pictures are from the full model case (looking from x direction), and later two are from half model case (looking from x and z direction).

[a_slow_old_man]

I had the same problem before, other times it worked just fine. Maybe someone more experienced with snappyHexMesh might help you find the reason for this.

As a temporary fix:

When this problem occured to me I used the full model and ran a second snappyHexMesh job with only a central plane .stl file along the desired axis, no refinement, no layer addition. Just cutting it in half.

[me3840]

Make sure you set the angles in the layer settings wide enough so the prisms truncate on your symmetry plane.

If you only changed the blockMeshDict locations, then your background mesh (the output of blockMesh) is no longer isotropic. You cut the domain in half, you also must halve the number of points in the cut direction.

[xuankushuocai]

Hi Frederik, what do you mean "use full model but central plane stl."?

[xuankushuocai]

Originally Posted by me3840

Make sure you set the angles in the layer settings wide enough so the prisms truncate on your symmetry plane.

If you only changed the blockMeshDict locations, then your background mesh (the output of blockMesh) is no longer isotropic. You cut the domain in half, you also must halve the number of points in the cut direction.

How to have points in the cut direction?

[a_slow_old_man]

Originally Posted by xuankushuocai

Hi Frederik, what do you mean "use full model but central plane stl."?

Hello Xiaojie,

as an example take the following cylinder [Attachment: 1.png]

You use a "normal" snappyHexMesh job to cut out the 3D geometry [Attachment: 2.png]

Add a second .stl file along the axis you want to use a s a symmetry axis [Attachment: 3.png]

Now use a different, second snappyHexMeshDict, which you run after the first SHM job, with these changes:

castellatedMesh true;
snap            true;
addLayers       false;

[...]

    refinementSurfaces
    {

        plane
        {
            // No refinement, just cutting the cells along the plane
            level (0 0);
            patchInfo
            {
                type patch;
            }
        }      
    }

And your result should look like [Attachment: 4.png]

The symmetry plane will have the name of your plane.stl file but you can change that in the 0/polymesh/boundary file


As I said, it is a very dirty kind of way to get to results, if someone with better knowledge of SHM knows a better way you should listen to them.

[xuankushuocai]

Originally Posted by a_slow_old_man

Hello Xiaojie,

as an example take the following cylinder [Attachment: 1.png]

You use a "normal" snappyHexMesh job to cut out the 3D geometry [Attachment: 2.png]

Add a second .stl file along the axis you want to use a s a symmetry axis [Attachment: 3.png]

Now use a different, second snappyHexMeshDict, which you run after the first SHM job, with these changes:

castellatedMesh true;
snap            true;
addLayers       false;

[...]

    refinementSurfaces
    {

        plane
        {
            // No refinement, just cutting the cells along the plane
            level (0 0);
            patchInfo
            {
                type patch;
            }
        }      
    }

And your result should look like [Attachment: 4.png]

The symmetry plane will have the name of your plane.stl file but you can change that in the 0/polymesh/boundary file


As I said, it is a very dirty kind of way to get to results, if someone with better knowledge of SHM knows a better way you should listen to them.

Thanks a lot for your explanation. I will try.

[devil_09]

would you please attach the two snappyhexmeshdict files , especially the second one, i wasn't quite clear how does it the second one works?