[LinW]

Hey,

I've spent a few hours trying to set up a UDF for a 2D velocity inlet.
Nothing special but as im relatively new to fluent and completely new to C im facing some errors.

I wan't to do a transient simulation of water flow where the u (x-velocity) inlet profile is a time and space dependent sinus.

The formula it should solve looks like this: u(y,t)=2*sin(5*t+0.1*y). Im not sure whether the following code is suitable to solve this equation for every node (centroid?) and adds a node-specific phase angle phi(y) where y is the number of the node. (Position in the Array)
I shloud propably mention, that the specific u-profile is supposed to only be "active" in a specified time.

Starting with zero C knowledge a few hours ago, but with the help of this forum and the manual, i've put together the following code.

I hope there arent too many mistakes left. I tried to let fluent interpret the UDF but it keeps failing at line 25 saying: parse error.

The encoding can't be the cause as i chose ANSI.

P.S.: Is there a way to read out the amount of entrys in the x[ND_ND] array?

Thanks a lot already.

My UDF:

#include "udf.h"
#define PI 3.141592654
#define N 600 //Amount of nodes
#define Y_max 0.3 //Max. amplitude
#define U_inf 1.2 //Base velocity
#define W 0.502654825 //Angular velocity

DEFINE_PROFILE(inlet_u_velocity,thread,position)
{
float x[ND_ND];
float y; //?

face_t f;

double t = CURRENT_TIME; //Time

begin_f_loop(f,thread) //here the "parse-error" occurs
{

F_CENTROID(x, f, thread);

y=x[1]; //gives y-coordinate

if(t >= 0 && t <= 1) //Base velocity at beginning
F_PROFILE(f,thread,position) = 1,2);

if(t > 1 && t <= 13.5) //Varying velocity
F_PROFILE(f,thread,position) = Y_max*sin(W*t+(2*PI*y/N)); //For every timestep this equation has to be solved for every centroid y

else if(t > 13.5) //Base velocity for the rest of the time
F_PROFILE(f,thread,position) = 1,2;

}
end_f_loop(f,thread)
}

[obscureed]

Hi LinW

Are you sure you're counting lines correctly? Because one line that looks bad to me is
F_PROFILE(f,thread,position) = 1,2);
which could easily be line 25. Lines are counted from the top of the text file. Line 31 is also bad. You cannot supply a vector here -- you can only supply one component.

Your "if" statements hang together fairly well, but the neatest structure (without repeating values, for example) is

if(t < 1.0) {
   //...
} else if (t < 13.5) {
   //...
} else {
   // ...
}

I would always recommend compiling UDFs rather than interpreting. M_PI is built-in and needs no definition; if you run in double precision, it will be more accurate than your value (not that this matters much).

Good luck!
Ed

[LinW]

Thanks a lot!

You're right... i added the comment in the wrong line.

The Solution for the Problem was the brace in line 25 and the commas in Line 25 and 31. Additionally i changed the y in Line 25 against x[1] and deleted Line 11.

Now it seems to work.