# Macros to compute forces

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 May 3, 2012, 06:49 Macros to compute forces #1 New Member   Join Date: Apr 2012 Posts: 17 Rep Power: 5 Hello, I'm writing a UDF to describe the motion of a particle in a tube fluid flow by computation of forces on particle surface. I found a FACE MACROS that compute the pressure on faces of the dynamic mesh zone, but I also need of the computation of viscous forces on the particle surface . Is there anyone who knows a MACROS to reach this aim? Thank you Last edited by Faby; May 3, 2012 at 06:52. Reason: I change idea

 May 3, 2012, 10:29 #2 Member   Ryne Join Date: Jan 2010 Posts: 32 Rep Power: 7 For viscous forces, I have been using F_STORAGE_R_N3V(f,t1,SV_WALL_SHEAR)[*]; Where the star is the direction vector (0 for x,1 for y). I found this on this site and it was said that this is not found in the UDF manual and that someone found it online. Good Luck

May 3, 2012, 12:45
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 Originally Posted by Rhyno466 For viscous forces, I have been using F_STORAGE_R_N3V(f,t1,SV_WALL_SHEAR)[*]; Where the star is the direction vector (0 for x,1 for y). I found this on this site and it was said that this is not found in the UDF manual and that someone found it online. Good Luck
Wow!!!
But...what is the correct way to use it?
I have to declare

face_t f;
thread *t1;

and SV_WALL_SHEAR ? Is a vector? Do I have to declare it?

Besides, to obtain the resultant shear force, for instance, in x direction, do I have to write something like this:

Fx = F_STORAGE_R_N3V(f,t1,SV_WALL_SHEAR) [0] ?

Or F_STORAGE_R_N3V(f,t1,SV_WALL_SHEAR) computes the value of shear stress? Such as F_P(f,t) provides the value of total pressure and not of pressure force.

I'm sorry for so many questions

 May 3, 2012, 16:15 #4 Member   Ryne Join Date: Jan 2010 Posts: 32 Rep Power: 7 Again, I found this somewhere on this forum and so I'm not completely sure about everything with it, however it is my understanding that this " Fx = F_STORAGE_R_N3V(f,t1,SV_WALL_SHEAR) [0] ? " is correct. I have manually compared the results of this computation to that of the FLUENT output values for viscous forces and they seemed to be relatively in agreement. As for the pressure, I multiply the pressure by the directional cell projected area to get the force.

May 4, 2012, 03:21
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Quote:
 Originally Posted by Rhyno466 Again, I found this somewhere on this forum and so I'm not completely sure about everything with it, however it is my understanding that this " Fx = F_STORAGE_R_N3V(f,t1,SV_WALL_SHEAR) [0] ? " is correct. I have manually compared the results of this computation to that of the FLUENT output values for viscous forces and they seemed to be relatively in agreement. As for the pressure, I multiply the pressure by the directional cell projected area to get the force.
Thank you very much for help! I hope it will work for me!

May 4, 2012, 04:50
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 Originally Posted by Rhyno466 As for the pressure, I multiply the pressure by the directional cell projected area to get the force.
if F_STORAGE_R_N3V(f,t1,SV_WALL_SHEAR) [0] computes the value of the stress shear in direction x, to obtain the corresponding force, you should multiply the stress shear for the projected parallel area to get the force, isn't it?

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