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-   -   Random function UDF for boundary condition (http://www.cfd-online.com/Forums/fluent/31162-random-function-udf-boundary-condition.html)

Chris March 28, 2003 13:10

Random function UDF for boundary condition
 
Hi,

Does anyone know what to write in the UDF if I would like to generate a randomly varying pressure input? Is the command

rand()

or something?

Thanks in advance

Chris March 28, 2003 14:08

Re: Random function UDF for boundary condition
 
Actually, I want to do this because I would like to obtain a frequency response of a probe that I am modeling...

I figured that if I subject the system to a random input, and generate some output files, I can process the data in MATLAB or something to plot the frequency response curve...

I hope this bit of background information helps whoever's able to give me advice!

Gracias!

Alex Munoz March 28, 2003 14:28

Re: Random function UDF for boundary condition
 
Hi Chris

I have not used a random function in a UDF, however, you must be careful rand() function in C provides a uniform random number betweem 0 to RAND_MAX=32767 (always integer). Therefore I you want to generate a random number between 0 to 1 you have to divide the rand()/RAND_MAX. Don't know forget to feed somehow a seed generator for the random number srand()

In addition if you want to generate a normal distribution function a "bell" shape, you must to use another function, which potentially you could download.

Regards

Alex


Chris March 28, 2003 14:39

Re: Random function UDF for boundary condition
 
Thanks Alex. Where could I get the "potential" download? :)

Alex Munoz March 28, 2003 16:38

Re: Random function UDF for boundary condition
 
My friend

type on google "random number generation in C" or something related to the type of distributio that you need gauss, binomial, poisson etc.

Regards

Alex


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