# UDF for ANSYS Fluent and Runge Kutta Method

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 November 17, 2014, 10:27 UDF for ANSYS Fluent and Runge Kutta Method #1 New Member     Cagri Metin Join Date: Jul 2013 Location: İzmir/Turkey Posts: 14 Rep Power: 12 Hello everybody, I need to manage a boundary conditiıon that pressure change with time. On the other hand I have to solve a differential equation for this boundary condition. Solving the diffrential equation decided Runge-Kutta Method. Am I write another code to solve this equation or write Runge Kutta Method inside UDF. What is your idea ?, thank you all attention.

 November 20, 2014, 19:23 #2 Senior Member   Michael Prinkey Join Date: Mar 2009 Location: Pittsburgh PA Posts: 363 Rep Power: 24 This is not too hard do. Declare a global variable to hold your pressure boundary condition. Use a DEFINE_BOUNDARY to set it where needed using that variable. Then use a DEFINE_ADJUST to do the RK. Declare the variables in the DEFINE_ADJUST as static so the values remain. You will need to check the simulation time (CURRENT_TIME) at the beginning of the define adjust. Store the old value in a static variable. At the beginning of the DEFINE_ADJUST if the current solution time is different from the old value, then update the old and do your RK step(s) to get to the new time and update the global pressure variable. aroma likes this.

December 8, 2016, 03:18
#3
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Hamed
Join Date: Jul 2012
Posts: 16
Rep Power: 13
Quote:
 Originally Posted by mprinkey This is not too hard do. Declare a global variable to hold your pressure boundary condition. Use a DEFINE_BOUNDARY to set it where needed using that variable. Then use a DEFINE_ADJUST to do the RK. Declare the variables in the DEFINE_ADJUST as static so the values remain. You will need to check the simulation time (CURRENT_TIME) at the beginning of the define adjust. Store the old value in a static variable. At the beginning of the DEFINE_ADJUST if the current solution time is different from the old value, then update the old and do your RK step(s) to get to the new time and update the global pressure variable.
Do you have any template for that? Tnx

January 24, 2020, 04:46
Runge kutta
#4
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FDE
Join Date: Feb 2012
Posts: 4
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Quote:
 Originally Posted by aroma Do you have any template for that? Tnx
Hi,
I need a UDF code to solve the ODE equation (for example: y'=y(y-1), y(0)=...) in FLUENT.
I know that the ADJUST macro must be used. But, I have some problems in writing this code.
Thanks.