View Issue Details
ID | Project | Category | View Status | Date Submitted | Last Update |
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0002008 | OpenFOAM | Bug | public | 2016-02-28 17:12 | 2020-11-21 21:32 |
Reporter | things.are.clear | Assigned To | henry | ||
Priority | high | Severity | major | Reproducibility | always |
Status | closed | Resolution | suspended | ||
Platform | Linux x64 | OS | OpenSuSE | OS Version | 13.2 |
Summary | 0002008: viewFactorsGen produces incorrect view factors in a very thin gap | ||||
Description | Thermal radiation between two concentric spheres are examined. Consider three cases distinguished from one another only by the gap between the spheres: 1 mm, 10 mm, and 100 mm. The units are unimportant here; it’s the order of magnitude that is really relevant to the problem. Mesh cells' characteristic size is 10 mm for all the cases in question. Here are ViewFactorsGen output for 3 cases 1 mm case ViewFactorsGen output: F00: 0 F01: 24.05267 F10: 21.62112 F11: 0.01200849 10 mm case ViewFactorsGen output: F00: 0 F01: 1.01395 F10: 0.8505047 F11: 0.1242975 100 mm case ViewFactorsGen output: F00: 0 F01: 1.001733 F10: 0.2489729 F11: 0.7506583 As you can see, in case 1 (gap 1 mm) view factors are totally wrong. The error is enormous! The results in case 2 are tolerable. The last case (100 mm) looks OK! The question is Why? | ||||
Steps To Reproduce | The simulation case can be downloaded from: https://drive.google.com/file/d/0Bz9jCmNem157a18zNmpISjRNRDA/view?usp=sharing. "mesh" folder contains 3 sub-folders with mesh files. Run in terminal: star4ToFoam -ascii -solids mesh/001mm/star // mesh/001mm/star or mesh/010mm/star or mesh/100mm/star splitMeshRegions -cellZonesOnly -overwrite then: faceAgglomerate -region cellZone_2 -dict constant/viewFactorsDict > log.faceAgglomerate.$i 2>&1 viewFactorsGen -region cellZone_2 > log.viewFactorsGen.$i 2>&1 | ||||
Additional Information | I started a thread on CFD-Online forum to discuss the problem: http://www.cfd-online.com/Forums/openfoam-pre-processing/166634-viewfactorsgen-produces-incorrect-view-factors-very-thin-gap.html#post585056. There you might find some additional information like, e.g., pictures with view factor field on a surface. | ||||
Tags | thermal radiation, view factors, viewFactorsGen | ||||
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Can you provide a patch to fix the problem? |
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No, I can't. Unfortunately, my expertise is not equal to the task of developing a patch. I might try to look into the source code to see where the issue comes from. |
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If you switch on in the viewFactorsDict the debug 1; //- Dump connectivity rays dumpRays true; you can load in the ./allVisibleFaces.vtk and see that you only get a few rays in between the two shells. Since the shells are so close together and the agglomeration centres on inside and outside shell are not synchronised you will not get any perpendicular rays; instead all your rays are very shallow. I assume this causes the error. |
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Pending funding |
Date Modified | Username | Field | Change |
---|---|---|---|
2016-02-28 17:12 | things.are.clear | New Issue | |
2016-02-28 17:15 | things.are.clear | Tag Attached: thermal radiation | |
2016-02-28 17:15 | things.are.clear | Tag Attached: view factors | |
2016-02-28 17:15 | things.are.clear | Tag Attached: viewFactorsGen | |
2016-02-28 17:19 | henry | Note Added: 0005985 | |
2016-03-05 17:44 | things.are.clear | Note Added: 0005994 | |
2016-03-05 17:44 | things.are.clear | Note Edited: 0005994 | |
2016-06-03 16:47 | MattijsJ | Note Added: 0006364 | |
2020-11-21 21:32 | henry | Assigned To | => henry |
2020-11-21 21:32 | henry | Status | new => closed |
2020-11-21 21:32 | henry | Resolution | open => suspended |
2020-11-21 21:32 | henry | Note Added: 0011722 |