[songpen1985]

Hello, I have a question and need help. I have momentum sources at different points, so I want to assign the momentum values in the computational domain.

However, when I write this it seems that it is not OK,
for example, if I want to assign a momentum value to the coordinate (0.5,0.5,0.5), then I will wirte
...
if (x[0]==0.5)&&(x[1]==0.5)&&(x[2]==0.5) source=5;
...
Because in the mesh domain, there is not a point that is exactly equal to 0.5, the aforementioned "if..." would never be true then.

How do you assign source values to different points in the mesh domain? (the data points are not on the mesh nodes!)

Thank you for your help!

Regards,
Ola

[ghost82]

Just set up a small area in which you will apply the momentum source:
define xmin, xmax, ymin, ymax, zmin and zmax and play with if blocks:

if ((x[0] >= xmin) && (x[0] <= xmax))
{ 
   if ((x[1] >= ymin) && (x[1] <= ymax))
   {
     if ((x[2] >= zmin) && (x[2] <= zmax))
     {
        [apply here your equation]
     }
   }
}

Make sure to setup properly the xmin, xmax, etc. values depending on your grid resolution.

With C_CENTROID x[0], x[1] and x[2] always refer to cell centered value:you cannot apply the source in a point, at least you will apply the source in a cell.

[songpen1985]

Originally Posted by ghost82

Just set up a small area in which you will apply the momentum source:
define xmin, xmax, ymin, ymax, zmin and zmax and play with if blocks:

if ((x[0] >= xmin) && (x[0] <= xmax))
{ 
   if ((x[1] >= ymin) && (x[1] <= ymax))
   {
     if ((x[2] >= zmin) && (x[2] <= zmax))
     {
        [apply here your equation]
     }
   }
}

Make sure to setup properly the xmin, xmax, etc. values depending on your grid resolution.

With C_CENTROID x[0], x[1] and x[2] always refer to cell centered value:you cannot apply the source in a point, at least you will apply the source in a cell.

Thank you, ghost82. However, I have many momentum source points (like one thousand). I understand that I cannot assign the source at a point now. But I cannot create the code you suggested for one thousand times, right?

I think it should be solved in some ways. Any other suggestions?
Thank you so much!

/Ola

[Lei Gao]

Hi songpeng,
I am also looking for the answer of this question. So I add my question here as a supplement of yours. Hope you don't mind.
It's usual to use a formula to present the data change in UDF. Is that posible to write the a formula to present the parameters of the points (for example forces on nodes) are random?

Namely,how to give the force to the right node from extern file?

X Y Z Fx Fy Fz
0.1 0.2 0.1 0.0094 0.02 -0.0035
........................................
.......................................
.......................................

Any one have an idea are wellcome, thank you very much!