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 December 16, 2012, 11:50 how can I apply this BC? please help me #1 Senior Member     Mostafa Mahmoudi Join Date: Jan 2012 Posts: 318 Rep Power: 7 Hi everybody, I want to apply this BC to my U: Code: `du/dx=-dv/dy , dv/dx=0` which the u is the x-component and v is the y-component of U. any body knows how can I define this BC? any hint will valuable for me. Thank you.

 December 16, 2012, 15:01 #2 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 18 what shape does your boundary have?is it aligned with x or y axis or any other? Can't you simplify the formula on the boundary?

December 16, 2012, 15:22
#3
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Mostafa Mahmoudi
Join Date: Jan 2012
Posts: 318
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Quote:
 Originally Posted by immortality what shape does your boundary have?is it aligned with x or y axis or any other? Can't you simplify the formula on the boundary?
It's not a matter that my bc is horizontal or vertical, I want to know how can I apply such a bc.

 December 18, 2012, 07:55 #4 Senior Member     ata kamyabi Join Date: Aug 2009 Location: Kerman Posts: 322 Rep Power: 10 Hi Is your problem 2-D? If yes first BC says that div(V)=0 so I think this may be a problematic BC. For the second one I think you can use OF BCs.

December 18, 2012, 08:23
#5
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Mostafa Mahmoudi
Join Date: Jan 2012
Posts: 318
Rep Power: 7
Quote:
 Originally Posted by ata Hi Is your problem 2-D? If yes first BC says that div(V)=0 so I think this may be a problematic BC. For the second one I think you can use OF BCs.
ِDear ata,

These conditions are for only one boundary. I want to apply this two conditions for my boundary simultaneously.
yes, I's 2D.
the complete form of my bc is attached.

thank you.
Attached Images
 mybc.PNG (9.6 KB, 16 views)

 December 18, 2012, 09:40 #6 New Member   Joe Nick Join Date: Dec 2012 Posts: 3 Rep Power: 5 Hello, without knowing the context of your problem, a good answer will be difficult. Which process do you calculate? What are P, theta, in and out in the attached figure? Have you tried to reformulate the BC using the PDE that is being solved?

December 18, 2012, 10:26
#7
Senior Member

Mostafa Mahmoudi
Join Date: Jan 2012
Posts: 318
Rep Power: 7
Quote:
 Originally Posted by joenick Hello, without knowing the context of your problem, a good answer will be difficult. Which process do you calculate? What are P, theta, in and out in the attached figure? Have you tried to reformulate the BC using the PDE that is being solved?
Thanks Joe,

Assume a cavity that its right wall is open and the conditions I refered above are the conditions at this open side. my solver is buoyantBoussinesqSimpleFoam and as I mentioned above the pressure is P=0 and the theta is the temperature.

What is your meaning of 'reformulation of BC using the PDE that is being solved'?

Thank you

 December 18, 2012, 13:12 #8 New Member   Joe Nick Join Date: Dec 2012 Posts: 3 Rep Power: 5 Hello, I'm afraid I cannot help, because I don't know this solver. What I mean by reformulating the BC is to make use of the differential equations for U in your solver to simplify your BC. Just a thought. If you explain why you choose this BC instead of showing only the equation, somebody might be able to help. What are you trying to solve conceptually, not mathematically? dv/dx=0 seems to make assumptions about the normal direction of the boundary and can't be applicable in general unless you have some anisotropic forces.

 December 18, 2012, 13:30 #9 Senior Member     Mostafa Mahmoudi Join Date: Jan 2012 Posts: 318 Rep Power: 7 thank you Joe, As I mentioned in my last post, I want to model an open cavity. this kind of cavities have an open side that have special conditions that I want to model it. I tried to replace it with other boundary conditions and even with a huge space with special BCs that might make my desired BC. but all of them failed. I will try if can I include this bc in my solver or not!!

 December 24, 2012, 09:10 #10 Super Moderator   Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 9,644 Blog Entries: 39 Rep Power: 99 Greetings to all, Since adambarfi sent me an email the other day about this and although I'm not much of help here, here's what I know on the subject: To create a new boundary condition, check this page: http://openfoamwiki.net/index.php/Ho...dary_condition Look into the source code of all of the other boundary conditions for clues on how to do this. For simulating open areas, AFAIK there are a few standard boundary conditions already in OF:Symmetry patch - probably not exactly what you're looking for, but it's possibly the closest you'll find in OF that will respect such a boundary condition. Atmospheric patches: "atmBoundaryLayerInletEpsilon", "atmBoundaryLayerInletVelocity" and "pressureInletOutletVelocity". For more ideas, run: Code: `find \$FOAM_TUTORIALS -name U | xargs grep -isl atm` and check the tutorials listed by that command line. Best regards, Bruno __________________ OpenFOAM: FAQ | Getting started Forum: How to get help, to post code/output and forum guide What am I doing/planning: blog/wiki Read this before sending me PM

 December 26, 2012, 14:57 #11 Senior Member     Mostafa Mahmoudi Join Date: Jan 2012 Posts: 318 Rep Power: 7 thank you Bruno, I simplified my problem so that my problematic boundary has just one condition: Code: `dv/dx=0` which the v is y-component of U. any body knows how can I apply this condition? Thanks

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