UDF with data-output to file

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I am writing a UFD to simulate a dynamic mesh in Fluent.
The function itself works fine. But I want to include a data output, so I can work with the values (e.g. in Matlab). Besides, it's important for me to have a feedback what the function does because I'm still learning C / UDFs and need to understand the language.

#include "udf.h"
#include

DEFINE_CG_MOTION(movement,dt,vel,omega,time,dtime)
real t = CURRENT_TIME;
real a,w;
a=1.6;
w=1.5;
NV_S(vel, =, 0.0);
if (!Data_Valid_P())
return;

vel[0]=1;
vel[1] = a * sin(w*t);

printf("x-Vel: %f, y-Vel: %f",vel[0],vel[1]);

// Works till here!
// Data output:

FILE *str;
str = fopen ("Output.txt","w");

fprintf (str,"x-vel: %f , y-vel: %f \n", vel[0], vel[1]);
fclose (str);
>

The last part SHOULD create a "Output.txt" file and save all the velocities line by line in it. I hoped that the \n would work but it doesn't.
The file appears and the LAST velocity entry is in line one.

Here is my question: How can I make this UDF write each entry in a new line?

I really hope you guys can help me.

This happens because you used
str = fopen ("Output.txt","w");
This tells Fluent to open the file "Output.txt" for writing, and if the file already exists to remove the content.

Replace this by
str = fopen ("Output.txt","a");
then you only append information to this file.

you are the lucky winner of the biggest "Thank you" that i have.
Everything works fine now.

Hello Pakk，
I have the same problem with Deepblack,Accroding to you method, i successfully compile my udf.but i don't find output date file. Where should i find it.
I really hope you can help me. thk!

Hello Pakk，
I have the same problem with Deepblack,Accroding to you method, i successfully compile my udf.but i don't find output date file. Where should i find it.
I really hope you can help me. thk!

I think it should be in the working directory, which you choose when you start fluent.
Usually it has to be where your cas dat files are.

I can find my cas and date file ,bu don't find the output date file.
This my udf
#include "udf.h"
#include "math.h"
#include
#define pi 3.1415926

DEFINE_CG_MOTION(velocity,dt,vel,omega,time,dtime)
Thread *t;
cell_t c;
real N=1000.0;
real r=0.03765;
real alpa=10;
real X[ND_ND];
real x,y,z,p;
real flow_time=RP_Get_Real("flow-time");
t=DT_THREAD(dt);
vel[2]=r*2*pi*(N/60)*tan((alpa*pi)/180)*sin(2*pi*(N/60.0)*time+pi/9);
omega[2]=2;
begin_c_loop(c,t)
C_CENTROID(X,c,t);
x=X[0];x=X[1];x=X[2];
p=C_P(c,t);
>
end_c_loop(c,t)

FILE *str;
str = fopen("OutPut.txt","a");
if(str==NULL)
printf("Error\n");
>
fprintf (str,"x %f , y %f ,z %f,p %f\n", X[0], X[1],X[2],p);
fclose (str);
>

If you want to know which folder you are using in Fluent, then in the text input box of Fluent you can type:

Fluent might have a problem with creating the file. I see that in your code you tried to show an error message in that case, but you did it slightly wrong: instead of

printf("Error\n");

Message("Error\n");

Then this warning should be shown in Fluent if it is unable to open the file.

A reason why your code does not do what you expect could be the location where you declare

FILE *str;

These declarations should happen at the top of the function (so before "t=DT_THREAD(dt);" in your case). I would expect the compiler to complain about it.

Hello,Pakk.
I modify the udf as you have told me.My work floder is G:\Simulation\Workbench\YM\YM_files\dp0\FLU-3\Fluent.I still can't find .txt file.

Hi,pakk.I am very willing to share with you a good news.Following with you proposal,my udf can work successfully.I wrote the udf with c & c++.At the first time ,I compiled the udf write with c ,it pointed out that there was some syntax errors.So I write the same code with c++,thus it can compiled successfully in fluent.But couldn't find any output files in my working directory.Today,I found that though the c++ code can compile successfully,I could't find the code file in "G:\Simulation\Workbench\YM\YM_files\dp0\FLU-3\Fluent\libudf\src". So I understood why always can't find output file.At the last ,I modified the c code as you told me, this time,it compiled successfully and worked very well.
Thanks for you patience with my problem!Good luck to you.

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