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UDF to read a set of data?

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Old   November 7, 2019, 06:40
Default UDF to read a set of data?
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Josh
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Hi everyone,

I have a txt document like this:

time velocity
0 0
0.1 1.3
0.2 1.7
0.3 2.5

..and so on.
My dataset unfortunately is not so easy, in fact I have a periodic function that has a pretty irregular velocity in time. The problem is that I have to impose this velocity as a UDF on a wall of my domain but I cannot find a function to properly fits those data. So my question: is there a way to write a UDF to read this dataset to impose the value of velocity for the timestep?

Thanks
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Old   November 7, 2019, 06:54
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You need to load your data into a C array and use a search function to get them.
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Old   November 7, 2019, 07:02
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Quote:
Originally Posted by Large Epic Simulations View Post
You need to load your data into a C array and use a search function to get them.
Could you write an example?
I am not so experienced with UDF...
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Old   November 7, 2019, 07:20
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https://stackoverflow.com/questions/...nto-array-in-c
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Old   November 7, 2019, 07:24
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Quote:
Originally Posted by Large Epic Simulations View Post
Thanks, but I know how to use C.
The problem is to write in the udf language. I have the udf manual but I cannot do it...
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Old   November 7, 2019, 07:46
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You should be aware that UDF is a C code in which you load the udf header to access some of the Fluent utilities.



What I want to say is that that you can write a dummy C function which reads your file and transfers the values to a global defined array:


Code:
#include "udf.h"

double** data;
void build_table()
{
 // code to allocate data from file to the variable "data" 
}
You need to run this function just one time before you start your simulation. In the UDF context you can do:



Code:
DEFINE_ON_DEMAND(read_file)
{
 build_table();
}

This creates you an "execute on demand" function that allows the remaining part of your code to read the values in the array.
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