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Old   September 8, 2011, 08:39
Default problem with udf
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Harpreet
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hello,

pls help

i am trying to vary the inlet velocity profile for which i have made a following udf
#include "udf.h"
DEFINE_PROFILE(variable_velocity,t,i)
{
real x[ND_ND];
real y;
face_t f;
begin_f_loop(f,t)
{
F_CENTROID(x,f,t);
y=x[1];
F_PROFILE(f,t,i)=7.36+0.368*y;
}
end_f_loop(f,t)
}
but the problem with it is that it is giving a constant velocity at the inlet that is 7.36. I think that probably it is not taking the coordinate into the equation.

pls help me. its urgent
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Old   September 9, 2011, 09:10
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Laurent B
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Hi,
You can add after F_CENTROID line :
printf("x-coord = %f y-coord = %f", x[0], x[1]);
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Old   September 9, 2011, 09:46
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Mohammad
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hi,
check if you are hooking udf in correct boundary. does the boundary have variable y-coordinate?
your case is 2d or 3d?
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Old   September 11, 2011, 00:45
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Harpreet
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my case is 2d, and i am hooking it in velocity inlet boundary condition.Another thing i noticed that, if i scale my in unit of 'm', the variation in velocity is obserable, but the same is not the case when it is scaled in 'mm' units.
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Old   September 12, 2011, 07:06
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the UDF takes units of your mesh scaled in Fluent interface, just check in SCALE panel.
Further, check whether your position in UDF is y position or x position. If it is x, you have to write x = x[0]. If it is y, you write y=x[1]
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