Symmetry conditon Error in CFX with hex mesh generated by ICEM CFD

Mason liu · October 22, 2014, 21:25

Hi,

I encountered a error when start simulation with CFX. This error's description said that 'the mesh face set to a symmetry condition should be a plane or a axis, but my mesh face is not in a plane.'

This is really confused me, the mesh is generated by ICEM CFD with block method, all hex bricks. But how can the mesh on a certain face is not in a plane?

Can you help me with this? Please give any comments or whatever about this, thanks a lot.

Thomas MADELEINE · October 23, 2014, 03:35

Hi,
when you define a block you usually need a geometry to be glued to it. then you need to move the verticle to the extremity of your geometric plane...
But even with all this some mistakes can occur during the meshing step if your mesh is a little to coarse...

The best thing to do is to specify a larger tolerance inside CFX-Pre by
right-click on solver
insert => expert parameter
Discretization panel (the first one)
activate vector parallel tolerance and set a value of 5 (for instance)
(you can check in CFX Help to have more explanation of this parameter)
re-run your case

it will decrease the tolerance of CFX to consider some surface as a plane

JuPa · October 23, 2014, 05:30

Quote:

Originally Posted by Thomas MADELEINE

Hi,
when you define a block you usually need a geometry to be glued to it. then you need to move the verticle to the extremity of your geometric plane...
But even with all this some mistakes can occur during the meshing step if your mesh is a little to coarse...

The best thing to do is to specify a larger tolerance inside CFX-Pre by
right-click on solver
insert => expert parameter
Discretization panel (the first one)
activate vector parallel tolerance and set a value of 5 (for instance)
(you can check in CFX Help to have more explanation of this parameter)
re-run your case

it will decrease the tolerance of CFX to consider some surface as a plane

I wouldn't do this. Instead I would invest time tidying your mesh.

A good quality mesh, with edges appropriately assigned to curves, faces to surfaces etc can really enhance your mesh, and hence solution.

You should use expert parameters as a last resort. Fixing your mesh is the first resort.

Your mesh issues your having can be signs of other underlying mesh issues.

ghorrocks · October 23, 2014, 07:08

+1 for Mr CFD.

Don't patch over the problem by allowing a larger tolerance - the tolerance is there for a reason. It is bound to cause other errors as well. Fix the root cause as Mr CFD says.

Mason liu · October 24, 2014, 04:53

Thanks a lot, you all, really appreciate your comments all

.

I have assigned all edges to curves from memory, but maybe there are still some other lines, faces or vertexes not been well associated. I'll have a good check in ICEM CFD.

And can I find this mesh problem in ICEM CFD? with some certain mesh check method? Because I want to find this problem early, not to find this until do CFX simulation. I do mesh at home and then do simulation in my office ,so I want find this at home, then to modify.\

Thank you all.

JuPa · October 24, 2014, 05:33

Yes, in ICEM go to:
1) Edit Mesh tab
2) Check Mesh icon (it's the green box with a tick)
3) Check your mesh for all errors and possible problems.

The best thing to do is ask in the ICEM forums. They're more knowledgeable about these things than I am.

Make sure you associate your vertices to points, edges to curves, faces to surfaces etc. If you then snap project vertices and then update sizes in pre-mesh params then I think you should be fine.

Mason liu · October 28, 2014, 02:55

Thanks a lot for your all help.

End up with that I involved 2 face into 1 symmetry condition before, that's the problem, obviously the mesh face not lie in one single plane.
Because I was used to deal with symmetry boundary condition in CFX with mesh from internal mesh module, there is no problem when 2 face in one symmetry condition, BCZ CFX knows that the two faces are symmetry face respectively.

Thank you all.
Mason

pizzaspinate · May 22, 2015, 06:54

Hey Mason,

I am facing the same issue as you did. How did you figure out that you assigned faces wrong?

Thank you

singer1812 · May 29, 2015, 09:53

Simple to fix in ICEM.

From CFX you should know the plane that is giving you trouble. Go back into ICEM and into "Edit Mesh"

Move nodes on your sym plane. You can snap them to a uniform plane location.

I am assuming you dont have gross errors in your mesh build and this is just a result of a small offset of node(s) on the offending plane(s).

October 22, 2014, 21:25	Symmetry conditon Error in CFX with hex mesh generated by ICEM CFD	#1
Mason liu New Member Mason Join Date: Sep 2014 Posts: 22 Rep Power: 11	Hi, I encountered a error when start simulation with CFX. This error's description said that '*the mesh face set to a symmetry condition should be a plane or a axis, but my mesh face is not in a plane*.' This is really confused me, the mesh is generated by ICEM CFD with block method, all hex bricks. But how can the mesh on a certain face is not in a plane? Can you help me with this? Please give any comments or whatever about this, thanks a lot.

October 23, 2014, 03:35		#2
Thomas MADELEINE Senior Member Thomas MADELEINE Join Date: Oct 2014 Posts: 126 Rep Power: 11	Hi, when you define a block you usually need a geometry to be glued to it. then you need to move the verticle to the extremity of your geometric plane... But even with all this some mistakes can occur during the meshing step if your mesh is a little to coarse... The best thing to do is to specify a larger tolerance inside CFX-Pre by right-click on solver insert => expert parameter Discretization panel (the first one) activate vector parallel tolerance and set a value of 5 (for instance) (you can check in CFX Help to have more explanation of this parameter) re-run your case it will decrease the tolerance of CFX to consider some surface as a plane Mason liu likes this.

October 23, 2014, 07:08		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	+1 for Mr CFD. Don't patch over the problem by allowing a larger tolerance - the tolerance is there for a reason. It is bound to cause other errors as well. Fix the root cause as Mr CFD says. Mason liu likes this.

October 24, 2014, 04:53		#5
Mason liu New Member Mason Join Date: Sep 2014 Posts: 22 Rep Power: 11	Thanks a lot, you all, really appreciate your comments all. I have assigned all edges to curves from memory, but maybe there are still some other lines, faces or vertexes not been well associated. I'll have a good check in ICEM CFD. And *can I find this mesh problem in ICEM CFD?* with some certain mesh check method? Because I want to find this problem early, not to find this until do CFX simulation. I do mesh at home and then do simulation in my office ,so I want find this at home, then to modify.\ Thank you all.

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October 24, 2014, 05:33		#6
JuPa Senior Member Mr CFD Join Date: Jun 2012 Location: Britain Posts: 361 Rep Power: 14	Yes, in ICEM go to: 1) Edit Mesh tab 2) Check Mesh icon (it's the green box with a tick) 3) Check your mesh for all errors and possible problems. The best thing to do is ask in the ICEM forums. They're more knowledgeable about these things than I am. Make sure you associate your vertices to points, edges to curves, faces to surfaces etc. If you then snap project vertices and then update sizes in pre-mesh params then I think you should be fine.

October 28, 2014, 02:55		#7
Mason liu New Member Mason Join Date: Sep 2014 Posts: 22 Rep Power: 11	Thanks a lot for your all help. End up with that I involved 2 face into 1 symmetry condition before, that's the problem, obviously the mesh face not lie in one single plane. Because I was used to deal with symmetry boundary condition in CFX with mesh from internal mesh module, there is no problem when 2 face in one symmetry condition, BCZ CFX knows that the two faces are symmetry face respectively. Thank you all. Mason

May 22, 2015, 06:54		#8
pizzaspinate Member Join Date: Dec 2012 Posts: 81 Rep Power: 13	Hey Mason, I am facing the same issue as you did. How did you figure out that you assigned faces wrong? Thank you

May 29, 2015, 09:53		#9
singer1812 Senior Member Edmund Singer P.E. Join Date: Aug 2010 Location: Minneapolis, MN Posts: 511 Rep Power: 20	Simple to fix in ICEM. From CFX you should know the plane that is giving you trouble. Go back into ICEM and into "Edit Mesh" Move nodes on your sym plane. You can snap them to a uniform plane location. I am assuming you dont have gross errors in your mesh build and this is just a result of a small offset of node(s) on the offending plane(s).