How to write an UDF programming inside FLUENT?
I have a brick region..the front surface i make it as inlet and i would like to write a UDF programme for the inlet velocity which is parabolic shape.. eg: at the center of the inlet is the highest velociy. (a parabolic shape)
secondly, left, right and behind surface i make it as pressure outlet and write a UDF programme for pressure different. Due to the brick region as a sea. and the lower surface is a seabed.. therefore if from top surface to lower surface(deeper) , the pressure will increase..(a triangle shape) May I know how to write a UDF programme for this..THX 
There is a detailed example of a parabolic velocity profile in the UDF manual (chapter 8). Once you learn how to do it, the pressure BCs would be easy to add.

ya..i saw it be4..but then i got the result that doesnt make sense..for example: i put X=0 , Y=1, Z=0..inside the grapgh, ya i get the parabolic shape which is 'u' shape..OR is it suppose a 'n' shape.
But for the pressure difference is it necessary use this function?F_CENTROID(x,f,thread) regards 
yes, probably. f_centroid will return the position vector of the cell in 'x'. The solver should produce the pressure profile throughout your domain given appropriate initial and boundary conditions.

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and if the using of the cell will return the vector of it,what will return if we use face instead? O(∩_∩)O~ thx in advance 
UDF for derivatives if fluctuating velocities
Hello,
Does anyone know how to calculate 1st derivatives (partial derivative) of the fluctuating velocities in UDF? Appreciate any help. Thanks, 
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Bruno Machado,
Thank you for your reply. I really appreciate your help. I never tried a UDF and UDS before. Could you please give me some more help on this? I have added an image file of the equation that I am trying to define in Fluent. Thank you, 
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The macro C_UDSI_G(c,t,i)[0] is the derivative with respect of X, whilst C_UDSI_G(c,t,i)[1] is in the Y direction and C_UDSI_G(c,t,i)[2] is with respect of Z direction. What you gotta do is to define a UDS (fluctuating velocity) and then using the macros previous mentioned, you can easily reproduce the equation you attached. 
nested if statement in udf
Respected members
I am using udf for defining transient temperature at inlet boundary of my model in fluent. I am writing nested if statement, but model keeps on using the same equation after 180 seconds, and does not move to the next if else statement. My udf is as follows: #include"udf.h" DEFINE_PROFILE(inlet_temperature,thread,position ) { face_t f; begin_f_loop(f,thread) { real t = RP_Get_Real("flowtime"); if ( t <= 100.0 ) F_PROFILE(f,thread,position) = 379.48 + 0.0004*t; else if (100.0 < t <= 180.0 ) F_PROFILE(f,thread,position) = 1.0624*t + 352.0; else if (180.0 < t <= 200.0 ) F_PROFILE(f,thread,position) = 0.2716*t + 494.4; else if (200.0 < t <= 400.0 ) F_PROFILE(f,thread,position) = 328.14*pow(t,0.097); else F_PROFILE(f,thread,position) = 727.82; } end_f_loop(f,thread) } sorry for my poor knowledge of programming. please help me on this error. Thanks. 
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