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[snappyHexMesh] Please help me, I am new to CFD and snappyHexMesh |
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October 19, 2012, 08:00 |
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#21 | |||
Senior Member
Eloïse
Join Date: Jul 2012
Location: Trondheim, Norway
Posts: 113
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Quote:
Quote:
Quote:
geometry { cara.stl { type triSurfaceMesh; name cara; }}; The system/controlDict file in the motorbike tutorial has the line which should also appear in your controlDict functions {#include "forceCoeffs"} It refers to the file forceCoeffs (that you must copy in your system directory) and you must change the patches name from patches ( "motorBike.*" ); to patches ( "cara.*" ); |
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October 19, 2012, 09:04 |
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#22 |
Member
Ben
Join Date: Sep 2012
Posts: 40
Rep Power: 13 |
Thank you for the help.
I have changed the name in the forceCoefs file and when I tried to run the simulation in paraFoam I did not get any results, not just that but I cant even get the options for u or p, so I went into the 0 folder and realised it was still under the name motorbike so I changed all the contents (in files such as p, u, k, omega) files from "motorBike_.*" to "cara.*" I had also tried "cara_.*" but still get the same problem, I cant change to velocity or pressure in para view and cant get any results, does anyone know what else I need to change? |
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October 19, 2012, 12:18 |
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#23 | |
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Anonymous
Join Date: Dec 2011
Location: USA
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Quote:
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October 19, 2012, 14:45 |
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#24 |
Member
Ben
Join Date: Sep 2012
Posts: 40
Rep Power: 13 |
Thank you for the help plucas.
I did as you said and changed the name to motorBike and also edited the snappyHexMesh but the same problem occurs, I will take you through what I did: In the terminal I typed: cp -r 0.org 0 > /dev/null 2>&1 blockMesh snappyHexMesh potentialFoam simpleFoam paraFoam I then hit apply and changed to the number 2 on the top right corner so that I could view my STL geometry, but still no u or p options, I also checked numbers 1 and 0 and still couldn't find anything. |
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October 19, 2012, 15:15 |
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#25 |
Senior Member
Eloïse
Join Date: Jul 2012
Location: Trondheim, Norway
Posts: 113
Rep Power: 13 |
try this:
Code:
cp -r 0.org 0 > /dev/null 2>&1 blockMesh snappyHexMesh cp 3/polymesh/* constant/polymesh/ rm -r 1/ 2/ 3/ potentialFoam simpleFoam paraFoam |
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October 19, 2012, 15:19 |
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#26 |
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,975
Blog Entries: 45
Rep Power: 128 |
Suggestion - replace these three lines:
Code:
snappyHexMesh cp 3/polymesh/* constant/polymesh/ rm -r 1/ 2/ 3/ Code:
snappyHexMesh -overwrite
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October 19, 2012, 16:49 |
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#27 |
Member
Ben
Join Date: Sep 2012
Posts: 40
Rep Power: 13 |
Thank you
I have now got the p and u values but can not view my drag coefficient, on the motorbike tutorial it made a log.simpleFoam file automatically and listed all my drag coefficients but on this example there is no log so I made one separately and still no results, does anyone know how to view these results? |
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October 20, 2012, 16:40 |
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#28 |
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
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Blog Entries: 45
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Hi Ben,
If you are still using the same settings that are present in "system/controlDict" that the "motorBike" case is using, along with the included files it refers to, then you should have the following file present in your case: Code:
forces/0/forceCoeffs.dat
Bruno
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October 21, 2012, 08:22 |
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#29 |
Member
Ben
Join Date: Sep 2012
Posts: 40
Rep Power: 13 |
Thank you for the reply wyldckat I did as you said and found the file called forceCoefs.dat, I opened it and there was a HUGE list of coefficients for the drag but, they were all VERY high, ranging from 2800-1300 for the drag coefficient when I know it should only be around 0.2, why is this happening? Last edited by ben1793; October 21, 2012 at 11:49. |
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October 22, 2012, 16:40 |
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#30 |
Member
Ben
Join Date: Sep 2012
Posts: 40
Rep Power: 13 |
Could anybody please tell me why I am getting such high drag coefficients even though I have not modified anything apart from the snappyHexMeshDict and the STL file in the motorbike tutorial?
Also, if possible could somebody please upload a STL file that the drag coefficient has already been tested on so that I could use it as a guide? Thank you. |
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October 23, 2012, 03:22 |
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#31 |
Senior Member
Eloïse
Join Date: Jul 2012
Location: Trondheim, Norway
Posts: 113
Rep Power: 13 |
Hi Ben,
Think about the definition of a drag coefficient and go to read the file forceCoeffs. There might be some stuff you need to modify in there... Regards, Eloïse |
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October 23, 2012, 05:24 |
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#32 |
Member
Ben
Join Date: Sep 2012
Posts: 40
Rep Power: 13 |
I have tried playing around with the forceCoefs and have also been reading up on the drag coefficient but can not fix the problem, still getting very high drag, I will make a separate thread for this question so that I can post all my code.
Thank you. |
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December 21, 2012, 04:51 |
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#33 |
Member
Malik
Join Date: Dec 2012
Location: Austin, USA
Posts: 53
Rep Power: 13 |
If you did not get any answer on that question :
you have to specify in controlDict a surface and a velocity to define the drag value. I think it is Aref and Umag. there are other variables such as the direction of the velocity. What you found in the motor bike tutorial may not actually be applicable for your case. Hope that helps. |
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