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-   -   F_CENTROID (http://www.cfd-online.com/Forums/fluent/32821-f_centroid.html)

co2 January 8, 2004 21:30

F_CENTROID
 
I was looking at the following simple code for a UDF.

F_CENTROID(x,f,thread); y = x[1]; F_PROFILE(f, thread, nv) = 20.*(1.- y*y/(.0745*.0745));

x is the position vector defined as: float x[3]; /* this will hold the position vector*/

Question: wouldn't y=x[1] assignment pick up the x coordinate of the face centroid? the original formula for the velocity is

u(y) = 20 [ 1 - (y/0.0745)^2]

So I was wondering if we need to write y=x[2]

ap January 9, 2004 02:53

Re: F_CENTROID
 
No, in C all arrays starst from the 0 position. So you'll have x[0], x[1] and x[2], which contains, in the order, x, y, and z.

P.S. Better to define x as:

real x[ND_ND];

because FLUENT manages real type as a float or double according to the chosen solver.

ND_ND allows to keep the code more general because ND_ND = 2 for a 2D case and ND_ND = 3 for a 3D case.

Hi :)

ap

niravtm007 September 1, 2011 01:49

x{nd-nd}
 
please can you tell me how will the code for 3d parabolic inlet will be modified.
i have cubical section. with circular inlet of 0.1 radius on one face.
should i use x[ND_ND] & take y=x(2) as variaion will be in both directions y,z. it should be paraboloid.? please give some idea


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