# Velocity BC

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 May 22, 2013, 12:31 Velocity BC #1 Member     Felice Join Date: Nov 2010 Posts: 44 Rep Power: 8 Hi all, I have this problem: basically I have a rotating mesh that is a cylinder with a hexahedric hole inside. I have to apply a rotation to the whole mesh in order to rotate the hex. Now the boundaries of the cylinder have a velocity due to the rotation of the mesh. What I want to do is to impose an opposite velocity BC on the walls of the cylinder in order to compensate the velocity that was applied by the mesh rotation. Actually in OF there is a fixedValue velocity BC but it is not possible to impose a different direction for each point of the cylinder. The magnitude is also in my case constant v=r*omega but the direction should be tangent the the wall (cylinder external surface) and the normal to that surface changes for each element. Can someone help me writing such BC? I'm quite new in with OF and I'm actually not able to do that. Regards F.

 May 24, 2013, 12:55 #2 Member     Felice Join Date: Nov 2010 Posts: 44 Rep Power: 8 Nobody can help me? F.

 May 27, 2013, 07:56 #3 Member     Felice Join Date: Nov 2010 Posts: 44 Rep Power: 8 Please guys, I really need help! F.

 May 27, 2013, 10:47 #4 Member   Eysteinn Helgason Join Date: Sep 2009 Location: Gothenburg, Sweden Posts: 53 Rep Power: 10 Hi, So. . . I haven't done this myself but this hopefully gets you in the right direction. There is a library called groovyBC that allow you to set arbitrary BC using expressions. This libary is now included in swak4Foam. (So that is what you should install ) Check out these pages. It should be simple to implement the rotating BC that you want, there are some examples on those pages ( even though I'm not sure about how stable this will be. ) /Eysteinn

May 31, 2013, 14:36
#5
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Felice
Join Date: Nov 2010
Posts: 44
Rep Power: 8
Quote:
 Originally Posted by eysteinn Hi, So. . . I haven't done this myself but this hopefully gets you in the right direction. There is a library called groovyBC that allow you to set arbitrary BC using expressions. This libary is now included in swak4Foam. (So that is what you should install ) Check out these pages. It should be simple to implement the rotating BC that you want, there are some examples on those pages ( even though I'm not sure about how stable this will be. ) /Eysteinn
Tanks a lot!

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