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periodicity in 2 directions

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Old   October 12, 2011, 06:31
Default periodicity in 2 directions
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Hi everyone,

I want to create a unique mesh with periodicity in 2 directions simultaneously, actually in 2D, . I know that it doesn't have physical meaning but I need this feature to check the capability of a method that I will explain later.

The problem is, I have a rectangular geometry, after meshing I want to populate some properties into the elements. Then I want to test it under 2 different situations (BCs), each one has a periodicity in one direction only. But I don't want to change the mesh configurations (element size, no of elements, ...) which will occur due to periodicity direction because I have to preserve my properties map all the time.

Any suggestion would be appreciated in advance.
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Old   October 13, 2011, 16:45
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Which Mesher/Method are you using...?
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Old   October 14, 2011, 14:00
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ICEM mesher 13.0
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Old   October 14, 2011, 17:00
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By default, ICEM CFD doesn't support Dual Periodicity (or matching as you would see in ANSYS Meshing).

However, you can still fake it by copying edge parameters or curve node spacing from one edge or curve to another...

You said ICEM CFD, but not which method...

For hexa blocking, you can copy the edge parameters from one side to the other to get your periodicity.

For Patch Conforming, you can set the same curve distributions.

For unstructured 3D meshing (such as Octree Tetra), you will start with fixing the edges, but then may also need to copy shell mesh from one periodic side to the other, then merge the nodes with a tolerance and run the volume fill again... I am pretty sure I explained this in detail before... You can look it up here in CFD-Online...
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Old   October 14, 2011, 17:20
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Thanks for your reply. Sorry I am beginner in ICEM CFD mesher.

Sure, I will look for your previous stuffs.

I want to do the periodicity in 2D not 3D and if I remember the method is called "2D planar", is it right?

I tried to resolve the problem by adding 4 extra fake nodes at the original corners of the rectangle, but it doesn't let to define these new points as a new periodic vertices, because in offset parameters we have to set the periodicity direction and if I put (1 0 0) it means there is only one periodicity in x-direction and if I set (1 1 0) it takes opposite diagonal vertices as periodic points.

Ok let me check your previous comments in the forum then I will be back.
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Old   October 14, 2011, 21:13
Default defacto dual periodicity
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Ok, now that I know you are talking about 2D planar blocking...

I would suggest you create points along each side for roughly where you want the verts located. Copy the points to the other periodic side and then associate the vertices to the points to ensure they are periodic. Then for the rest of the edge distributions, you just copy from one side to the other...

You should end up with defacto dual periodicity.
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Old   October 17, 2011, 13:51
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Are you sure this method guarantees periodicity in 2 direction simultaneously?

I already created 4 additional points in my model (as a new "Parts"). If I don't set any offset parameters when I want to pick the vertices I get this error: error 1.jpg

If I set the offset parameters just in one direction, when I want to pick the other points (that I virtually added to the model for the second direction) I get this error: error 2.jpg

I think the main problem is the offset parameters. How can define it when you want to have periodicity in both direction at the same time?

The other problem is when you create additional points it doesn't mean that these points belong to your geometry. Even if they are embedded in your geometry, when you want to mesh the geometry how can mesher distinguish original points and these fake points? where have to be meshed? I mean if you add extra points mesher conflicts to identify which geometry it should take into account. Isn't it?
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Old   October 17, 2011, 16:20
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It is "defacto" periodic...

You won't be able to define those verts as periodic in Hexa because only one direction is supported, but if the vert locations and edge distributions match in the other periodic direction, then the periodic checks will pass when this is sent to the solver...
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Old   October 18, 2011, 04:22
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Ok let say it is possible. What about offset parameters? Should I set (1 1 0)? or anything else?
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Old   October 18, 2011, 06:13
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Now, I got the point . I have the periodicity in both direction.

If I check the periodicity in "check mesh" and it says "no problem found", does it mean everything is ok?
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Old   October 21, 2011, 09:22
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The check is just comparing the nodes in the parts you specify with the periodic setting... So it is really only checking in the one direction.

I guess maybe you could go into the periodic settings switch it to the other way and run your check again, but it may just be easier to send it to the solver and see if that complains...

Simon
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Old   October 21, 2011, 09:34
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ok.

thanks a lot for your patient.

All the best.
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Old   October 21, 2011, 10:02
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I checked it. Unfortunately it is not periodic in the other direction. So, it is still periodic just in one direction.

I am going to do the job from the beginning.
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