[ashish.vinayak]

Hi,

I am trying to create a mesh where I have placed two cylinders of different diameters on to one another (Fig1).
There will be a simple inlet and outlet patch and the lateral surfaces will be in a wall patch. However, I am unable to select the patches (Fig2)

geometry and refinementSurfaces definitions are as follows:

geometry
{
testObject
{
type triSurfaceMesh;
file "testObject.stl";
regions
{
topSurface_lateral
{
name topSurface_lateral;
}
topInlet
{
name topInlet;
}
bottomSurface_lateral
{
name bottomSurface_lateral;
}
}
}
}
************************************************** *******
refinementSurfaces
{
testObject
{
// Surface-wise min and max refinement level
level (1 2); // was (2 2)
regions
{
topSurface_lateral
{
level (1 3);
patchInfo
{
type wall;
}
}
topInlet
{
level (1 3);
patchInfo
{
type wall;
}
}
bottomSurface_lateral
{
level (1 3);
patchInfo
{
type patch;
}
}
}
}
*************************
I have tried quite a bit of things but I am unable to understand why creating patches is such a difficult task. Can someone help me figure this out?

[RobertHB]

If i understand your post correctly, your stl contains both the smaller cylinder as well as the larger on. And the meshing process doesn't correctly represent the out shape of your domain?
What i did in a similar situation was to use two stl. files. One for each cylinder. That worked for me.

[ashish.vinayak]

Originally Posted by RobertHB

If i understand your post correctly, your stl contains both the smaller cylinder as well as the larger on. And the meshing process doesn't correctly represent the out shape of your domain?
What i did in a similar situation was to use two stl. files. One for each cylinder. That worked for me.

You mean to say that instead of using a single closed stl I should use 2 closed stl files (one for each cylinder) ?

[RobertHB]

Exactly. In my case i connected three single, same diameter, cylinders to form a tube because i needed a single patch in the middle of the domain. Still looks and behaves like on big cylinder though.

[ashish.vinayak]

Brilliant ! Your idea works.


The surfaces are behaving in a better way now. However, if I use two separate cylinders, SHM thinks that I want to cut one cylinder with the second one. The end result is only one cylinder and some kind of weird patchy hole. I'm wondering if I'm facing some kind of numerical error at the interface? Any ideas?

PS. I know it is patchy because my blockMesh is coarse at the moment. But I am certain it is not causing this error.

[ashish.vinayak]

Switched on debug mode:

The upper cylinder disappears during the castellation steps. (see images)

[RobertHB]

Strange. Since both cylinders show up in the first step of sHM (right?) your setup should be correct until then.

What is the value of the tolerance <value>; setting? Maybe the points from the lower cylinder do not connect to the upper one?


I'm not at work anymore, but i could send you my sHM dict on Monday if you don't figure out your problem until then.

[ashish.vinayak]

I don't think the points connecting together is a problem. While making the stl I take care to see that the top face of the lower cylinder and bottom face of upper cylinder match.

I was working with a tolerance of 1.0. I now set it to 3.0 and set debug to 1.

I was inspecting the time directories. During the initial stages I see that the patches from the upper cylinder are recognised (nFaces >> 0) However, after time = 0.07 it just sets nFaces = 0 on all the upper cylinder patches. Could you please help me solve this?


Thanks for your help Schönes Wochenende.

[RobertHB]

Hey,
i think i promised to much. My case that i had in mind does not consist of two stl files and my snappyHexMeshDict doesn't work for connecting two stl's - just tested it.

[ashish.vinayak]

Another weird thing I've noticed today. Looking at the Clip in Paraview one sees that SHM recognizes the bottom cylinder as a solid shape but the top cylinder as a hollow shape with no internal mesh. Really weird.


@Robert That sucks for me. :/ But thanks anyway!