[ICEM] How to avoid single edges at boundaries in 2D models?

Gandin · January 19, 2012, 06:33

Hello everybody. I am new in ICEM CFD meshing. I have done some tutorials about hexa meshing, and I now I am trying to simulate in Fluent the movement of a fluid in a kind of ring by natural convection (like a thermosiphon).

I have made a 2D model and I have meshed it, by blocking strategy, pre-meshing and conversion to unstructured mesh. The quality of the resulting mesh is good, but I have found a big problem: when I check the mesh to find errors and possible problems, single edges reveal in all the elements of the domain boundary.

After this, I have tried meshing simple 2D shapes, as a square. I have created the geometry (4 points, 4 curves and a surface) and I have meshed by using different methods (blocking; surface meshing by Mesh>Compute mesh>Surface mesh only) but the problem of single edges at boundary always returns.

How can I avoid it? Thank you very much in advance!

Far · January 19, 2012, 08:41

attach tin and blocking file

Gandin · January 19, 2012, 09:40

Far, the files are now attached. Thanks.

kiran · January 19, 2012, 10:11

Hi

you don't need to worry about the single edges this isn't a problem.

you can continue with the analysis.

Thanks
Kiran

Gandin · January 19, 2012, 10:14

Thanks, Kiran.

Far · January 19, 2012, 10:41

Today I check one of my mesh on 32 and 64 bit systems. On 64 bit system I dont get this problem whereas on32 bit I am getting this problem. I guess this is due to round off error since meshing spacing is smaller than computer round off error.

Far · January 19, 2012, 11:04

When opened your files, I am not getting any error or warning message. Strange !!!!

Gandin · January 19, 2012, 11:11

Far, I have imported the mesh to Fluent, as Kiran said, and solved a case. Non error or warning message has been shown, and the solution seems valid.

Thank you both.

PSYMN · January 20, 2012, 17:18

For a little more explanation...

Single edges is on the list of "Possible Problems". If you were doing a 3D analysis and didn't have any baffles, then single edges would be a concern.

But you should expect single edges along all your boundaries for 2D analysis. You should also expect single edges along the edges of baffles in 3D, etc.

Far · January 21, 2012, 00:17

What does single edges imply in the mesh? Like we know that skewness shows the distorted cell in the mesh.

PSYMN · January 21, 2012, 13:14

A double edge of a shell element is an edge shared by two shells (normal situation). A triple edge is an edge shared by three shells (like a T-connection), which could be normal if you expected a T-connection or could suggest a problem. Rather than have a special diagnosis for "triple edge", we just have one for "multiple edge", which could be three or more shells meeting at an edge...

By the same logic, a single edge is an edge connected to only a single shell... In practice, it is the perimeter of a 2D or zero thickness shell model. Perfectly acceptable in those circumstances, but potentially a problem if you were trying to form a closed volume so you could fill with delaunay or hexa dominant fills...

When the mesh check tells me I have one of these situations, even if I am expecting it, I just ask for the subset. Then I add one or two layers to the subset so I can get an idea of what is going on. You can also right click on shells to have it highlight these single or multiple edges. Either way, don't decide if it is a problem or what to do until you have seen it in context.

maalan · February 18, 2013, 16:54

Hi, Simon!!

Just a simple question... I am trying to mesh a 2D circular cylinder, so you can imagine which my problem is: single edes! also you told single edges is not always a problem (above all in 2D meshes), if I export my bidimensional mesh to fluent without checking, I found an error from fluent when reading. So, could you tell me how to face this problem?? I am sure it has to do a very easy solution as I was getting excellent results from 3D hexa meshes...

Best,
Antonio

gg33 · October 16, 2014, 07:00

Hello everybody,
i am using icem cfd for 1 year and i am creating my first 3D mesh.
My cfd calculation give me an error with that mesh only on some elements.
Mesh quality is good for icem but there is a problem with some single edges,
these edges and faces are precisely the elements making problems during the
computation.
I dont' know how to deal with that problem, would you know what to do ?
Thanks
Jérôme

January 19, 2012, 06:33	How to avoid single edges at boundaries in 2D models?	#1
Gandin New Member Ivan Fernandez Join Date: Aug 2011 Posts: 7 Rep Power: 15	Hello everybody. I am new in ICEM CFD meshing. I have done some tutorials about hexa meshing, and I now I am trying to simulate in Fluent the movement of a fluid in a kind of ring by natural convection (like a thermosiphon). I have made a 2D model and I have meshed it, by blocking strategy, pre-meshing and conversion to unstructured mesh. The quality of the resulting mesh is good, but I have found a big problem: when I check the mesh to find errors and possible problems, single edges reveal in all the elements of the domain boundary. After this, I have tried meshing simple 2D shapes, as a square. I have created the geometry (4 points, 4 curves and a surface) and I have meshed by using different methods (blocking; surface meshing by Mesh>Compute mesh>Surface mesh only) but the problem of single edges at boundary always returns. How can I avoid it? Thank you very much in advance!

January 19, 2012, 10:41		#6
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	Today I check one of my mesh on 32 and 64 bit systems. On 64 bit system I dont get this problem whereas on32 bit I am getting this problem. I guess this is due to round off error since meshing spacing is smaller than computer round off error. Last edited by Far; January 19, 2012 at 11:42.

January 20, 2012, 17:18		#9
PSYMN Senior Member Simon Pereira Join Date: Mar 2009 Location: Ann Arbor, MI Posts: 2,663 Blog Entries: 1 Rep Power: 47	For a little more explanation... Single edges is on the list of "Possible Problems". If you were doing a 3D analysis and didn't have any baffles, then single edges would be a concern. But you should expect single edges along all your boundaries for 2D analysis. You should also expect single edges along the edges of baffles in 3D, etc. __________________ ----------------------------------------- Please help guide development at ANSYS by filling in these surveys Public ANSYS ICEM CFD Users Survey This second one is more general (Gambit, TGrid and ANSYS Meshing users welcome)... CFD Online Users Survey

January 21, 2012, 13:14	Single - double - multiple...	#11
PSYMN Senior Member Simon Pereira Join Date: Mar 2009 Location: Ann Arbor, MI Posts: 2,663 Blog Entries: 1 Rep Power: 47	A double edge of a shell element is an edge shared by two shells (normal situation). A triple edge is an edge shared by three shells (like a T-connection), which could be normal if you expected a T-connection or could suggest a problem. Rather than have a special diagnosis for "triple edge", we just have one for "multiple edge", which could be three or more shells meeting at an edge... By the same logic, a single edge is an edge connected to only a single shell... In practice, it is the perimeter of a 2D or zero thickness shell model. Perfectly acceptable in those circumstances, but potentially a problem if you were trying to form a closed volume so you could fill with delaunay or hexa dominant fills... When the mesh check tells me I have one of these situations, even if I am expecting it, I just ask for the subset. Then I add one or two layers to the subset so I can get an idea of what is going on. You can also right click on shells to have it highlight these single or multiple edges. Either way, don't decide if it is a problem or what to do until you have seen it in context. vivek05 likes this. __________________ ----------------------------------------- Please help guide development at ANSYS by filling in these surveys Public ANSYS ICEM CFD Users Survey This second one is more general (Gambit, TGrid and ANSYS Meshing users welcome)... CFD Online Users Survey

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January 19, 2012, 08:41		#2
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	attach tin and blocking file

January 19, 2012, 10:11	hi	#4
kiran Member kiran Ambilpur Join Date: Jun 2010 Location: India Posts: 50 Rep Power: 16	Hi you don't need to worry about the single edges this isn't a problem. you can continue with the analysis. Thanks Kiran

January 19, 2012, 10:14		#5
Gandin New Member Ivan Fernandez Join Date: Aug 2011 Posts: 7 Rep Power: 15	Thanks, Kiran.

January 19, 2012, 11:04		#7
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	When opened your files, I am not getting any error or warning message. Strange !!!!

January 19, 2012, 11:11		#8
Gandin New Member Ivan Fernandez Join Date: Aug 2011 Posts: 7 Rep Power: 15	Far, I have imported the mesh to Fluent, as Kiran said, and solved a case. Non error or warning message has been shown, and the solution seems valid. Thank you both.

January 21, 2012, 00:17		#10
Far Senior Member Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,558 Blog Entries: 6 Rep Power: 54	What does single edges imply in the mesh? Like we know that skewness shows the distorted cell in the mesh.

February 18, 2013, 16:54		#12
maalan Member Join Date: Jun 2011 Posts: 80 Rep Power: 15	Hi, Simon!! Just a simple question... I am trying to mesh a 2D circular cylinder, so you can imagine which my problem is: single edes! also you told single edges is not always a problem (above all in 2D meshes), if I export my bidimensional mesh to fluent without checking, I found an error from fluent when reading. So, could you tell me how to face this problem?? I am sure it has to do a very easy solution as I was getting excellent results from 3D hexa meshes... Best, Antonio

October 16, 2014, 07:00		#13
gg33 New Member Join Date: Oct 2014 Posts: 1 Rep Power: 0	Hello everybody, i am using icem cfd for 1 year and i am creating my first 3D mesh. My cfd calculation give me an error with that mesh only on some elements. Mesh quality is good for icem but there is a problem with some single edges, these edges and faces are precisely the elements making problems during the computation. I dont' know how to deal with that problem, would you know what to do ? Thanks Jérôme