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-   -   [blockMesh] Axisymmetrical mesh (https://www.cfd-online.com/Forums/openfoam-meshing/61830-axisymmetrical-mesh.html)

Rasmus Gjesing (Gjesing) January 28, 2005 04:21
Axisymmetrical mesh
 
Hi,

I want to make a axi-symmetrical mesh for a cylinder. So I have constructed a 5 degree wedge as explained in the user guide, and defined the front and back as wedge-patches.

Q1.
However, I have a question regarding the points on the radius of the cylinder. Should there coordinates just be calculated as implied by fig. 6.3 in the userguide. So, if the x-axis goes in the radius-direction, the x-coordinate will be lower than the radius.

Q2.
Also, should the wedge be exactly 5 degrees or is this just a recommandation?

Q3.
And what about the curvature of the surface of the cylinder?

Q4.
I have made the outer edge of the cylinder a circle-arc, but it appears as a straight line in paraFoam. Is paraFoam just drawing straight lines between every points? And will openFOAM use/discover the bigger area due to the curvature?

This is perhaps peanuts, but I like to be 100% certain. This is also why I use openFOAM! ;-)

Kind regards,
Rasmus

Hrvoje Jasak (Hjasak) January 28, 2005 04:25
Q1: Yes Q2: Just a recommend
 
Q1: Yes
Q2: Just a recommendation. Should be small enough that the difference between the arc and a straight line at the outer diameter does not matter, but large enough to avoid round-off problems with decimal precision.
Q3: Neglected
Q4: There are no arcs - it is a straight line. Remember, you are really using a 3-D solver to do axi-symmetric.

Enjoy,

Hrv

olivier October 10, 2005 11:06
Hi, I want to test my new sol
 
Hi,
I want to test my new solver, In first time I tested my case with icoFoam in ordre to be sure that there is no probleme with my mesh created with blockMesh.
when I run my case with icoFoam I had "Nan" in the 1st time step!!
I think that I have no devision per zero!
I will be happy If some one tel me what is the probleme with my goemetry or my mesh.
how can I make my case in the forum?
thanks a lot

hjasak October 10, 2005 11:21
You've messed something up - t
 
You've messed something up - try running checkMesh to see if the mesh is correct, check the wedge boundary conditions on the front and back, check the viscosity you've set (non-zero, but not really crucial), check that the differencing schemes are set up correctly and the boundary conditions are not stupid. Check the time step.

In short, check everything :-)

Enjoy,

Hrv

hjasak October 10, 2005 12:15
Yup, the mesh is totally wrong
 
Yup, the mesh is totally wrong:
- it's in 2 pieces
- it is a 90 deg segment and not a wedge
- it's got blocks that are inside out

You will need to sort this out before moving on further. Try putting

setenv FOAM_SIGFPE 1

into your dot-files and you'll get more messages, e.g.:

coyote*138-> blockMesh . wedgeOliverBaily
/*---------------------------------------------------------------------------*\
| ========= | |
| \ / F ield | OpenFOAM: The Open Source CFD Toolbox |
| \ / O peration | Version: 1.2 |
| \ / A nd | Web: http://www.openfoam.org |
| \/ M anipulation | |
\*---------------------------------------------------------------------------*/

Exec : blockMesh . wedgeOliverBaily
Date : Oct 10 2005
Time : 17:15:39
Host : coyote
PID : 6696
Root : /home/coyote/hjasak/OpenFOAM/hjasak-1.2/run/support
Case : wedgeOliverBaily
Nprocs : 1
Create time


Reading block mesh description dictionary

Creating block mesh

Creating blockCorners

Creating curved edges

Creating blocks

Creating patches

Creating block mesh topology
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.35e-07 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.35e-07 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -8.5e-08 for face 2
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.85e-07 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.35e-07 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.35e-07 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 0, probably defined inside-out
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -9.03125e-09 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -9.03125e-09 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -6.02083e-09 for face 2
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.20417e-08 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -9.03125e-09 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -9.03125e-09 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 1, probably defined inside-out
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.70937e-08 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.70938e-08 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.80625e-08 for face 2
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -3.6125e-08 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.70937e-08 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.70937e-08 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 2, probably defined inside-out
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.41563e-06 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.41563e-06 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -4.65583e-07 for face 2
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.36567e-06 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.41562e-06 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.41562e-06 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 3, probably defined inside-out
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -4.24687e-06 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -4.24688e-06 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.39675e-06 for face 2
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -7.097e-06 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -4.24688e-06 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -4.24688e-06 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 4, probably defined inside-out
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -7.66667e-07 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -7.66667e-07 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -7e-07 for face 2
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -8.33333e-07 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -7.66667e-07 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -7.66667e-07 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 5, probably defined inside-out
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.3e-06 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.3e-06 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.1e-06 for face 2
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.5e-06 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.3e-06 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -2.3e-06 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 6, probably defined inside-out
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.0945e-06 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.0945e-06 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.034e-06 for face 2
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.155e-06 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.0945e-06 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.0945e-06 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 7, probably defined inside-out
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -0.000246879 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -0.000246879 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -9.1675e-05 for face 2
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -0.000402083 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -0.000246879 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -0.000246879 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 8, probably defined inside-out
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -9.03125e-09 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -9.03125e-09 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -1.80625e-08 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -9.03125e-09 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -9.03125e-09 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 9, probably defined inside-out
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -3.01042e-09 for face 0
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -3.01042e-09 for face 1
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -6.02083e-09 for face 3
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -3.01042e-09 for face 4
--> FOAM Warning :
From function cellModel::mag(const labelList&, const pointField&)
in file meshes/meshShapes/cellModel/cellModel.C at line 136
zero or negative pyramid volume: -3.01042e-09 for face 5
--> FOAM Warning :
From function blockMesh::createTopology(IOdictionary& meshDescription)
in file createTopology.C at line 372
negative volume block : 10, probably defined inside-out

Default patch type set to empty
Caught arithmetic exception
Abort

Hrv

olivier October 10, 2005 12:36
1.what is wrong with two pices
 
1.what is wrong with two pices?
2.when I use 5deg in a wedge I have a problem with bad elements near to axis.
3. I dont understand what do you mean by:
"it's got blocks that are inside out "
best ragards

hjasak October 10, 2005 12:43
1. Formally nothing, depending
 
1. Formally nothing, depending on exactly what you're trying to do
2. Probably the same reason as here: your block definition is wrong
3. Read the manual (RTFM):

http://www.opencfd.co.uk/openfoam/do...tml#x5-40002.1

Figure 2.3 specifies how a hex block needs to be defined in terms of vertices. If vertices 4, 5, 6, 7 are behind the vertices 0, 1, 2, 3, the block volume according the the figure will be negative. This is what you have done.

olivier October 10, 2005 13:03
thanks for your time and your
 
thanks for your time and your help

ali December 23, 2005 11:16
Could anybody let me know wher
 
Could anybody let me know where (in which dot file) to put 'setenv FOAM_SIGFPE 1'? Is this syntax correct or I have to add something to it.

hjasak December 23, 2005 12:03
Into your ~/.cshrc put sete
 
Into your ~/.cshrc put

setenv FOAM_SIGFPE true

Enjoy,

Hrv

maka April 2, 2007 14:00
round-off errors: January 2
 
round-off errors:

January 28, 2005:
Quote:
small enough that the difference between the arc and a straight line at the outer diameter does not matter, but large enough to avoid round-off problems with decimal precision.
.

How can we check for the later effect? This may come to be critical at high Re turbulent flows. I thought that one way, may be to do the a test computation on the same mesh with single and double precision (new option in V1.3) to check the sensitivity to round-off errors but it seems to be expensive option. Any body knows a better way or recommendation? Thanks.

Best regards,
Maka

Thanks.


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