# [blockMesh] Axisymmetrical mesh

 Register Blogs Members List Search Today's Posts Mark Forums Read

 January 28, 2005, 05:21 Axisymmetrical mesh #1 Rasmus Gjesing (Gjesing) Guest   Posts: n/a 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

 January 28, 2005, 05:25 Q1: Yes Q2: Just a recommend #2 Hrvoje Jasak (Hjasak) Guest   Posts: n/a 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

 October 10, 2005, 12:06 Hi, I want to test my new sol #3 Member   olivier Petit Join Date: Mar 2009 Location: Göteborg, Sweden Posts: 67 Rep Power: 12 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

 October 10, 2005, 12:21 You've messed something up - t #4 Senior Member   Hrvoje Jasak Join Date: Mar 2009 Location: London, England Posts: 1,849 Rep Power: 28 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 __________________ Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk

 October 10, 2005, 13:15 Yup, the mesh is totally wrong #5 Senior Member   Hrvoje Jasak Join Date: Mar 2009 Location: London, England Posts: 1,849 Rep Power: 28 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 __________________ Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk

 October 10, 2005, 13:36 1.what is wrong with two pices #6 Member   olivier Petit Join Date: Mar 2009 Location: Göteborg, Sweden Posts: 67 Rep Power: 12 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

 October 10, 2005, 13:43 1. Formally nothing, depending #7 Senior Member   Hrvoje Jasak Join Date: Mar 2009 Location: London, England Posts: 1,849 Rep Power: 28 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. __________________ Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk

 October 10, 2005, 14:03 thanks for your time and your #8 Member   olivier Petit Join Date: Mar 2009 Location: Göteborg, Sweden Posts: 67 Rep Power: 12 thanks for your time and your help

 December 23, 2005, 12:16 Could anybody let me know wher #9 Member   Ali Heidari Join Date: Mar 2009 Location: Surrey, London, United Kingdom Posts: 39 Rep Power: 12 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.

 December 23, 2005, 13:03 Into your ~/.cshrc put sete #10 Senior Member   Hrvoje Jasak Join Date: Mar 2009 Location: London, England Posts: 1,849 Rep Power: 28 Into your ~/.cshrc put setenv FOAM_SIGFPE true Enjoy, Hrv __________________ Hrvoje Jasak Providing commercial FOAM/OpenFOAM and CFD Consulting: http://wikki.co.uk

April 2, 2007, 15:00
round-off errors: January 2
#11
Senior Member

Maka Mohu
Join Date: Mar 2009
Posts: 305
Rep Power: 13
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.