# Variable Time Steps in transient CFX simulation

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 November 15, 2019, 06:09 Variable Time Steps in transient CFX simulation #1 New Member   M S Join Date: Nov 2019 Posts: 8 Rep Power: 6 Dear all, Iam developing a pipe model a steam flow. For my Simulation runs, i plan a transient Simulation over a 3600 s period. For the inital Startup it is necessary to start with very short time steps (0.1-0.5s) but after the first minutes this solution wont be necessary. So, my Question: Iam Looking for a solution to Change the time steps in the Simulation or Setting a timestep profile. So from second 0 - 120 Timestep size = 0.5s From 120 to end Timestep size = 20s Is there any possibility to do that (i have seen i can add functions to the timestep but iam not sure About the Syntax) Thanks and best regards

 November 15, 2019, 08:45 #2 Senior Member   M Join Date: Dec 2017 Posts: 642 Rep Power: 12 There are dozen threads about achieving something like this, so instead of doing all the work for you, here are some keywords to look for: cfx expression language, cfx step function, cfx step syntax Good luck

 November 18, 2019, 01:19 #3 Senior Member   urosgrivc Join Date: Dec 2015 Location: Slovenija Posts: 365 Rep Power: 11 This can be done in two ways: First one is a simple expression like: if(t<120[s], 0.5[s], 20[s]) The other way is a table input under user functions: slide 12 here... https://www.slideshare.net/al11429964/cfx12-11-cel create a table of values which will map [s] to [s] folowed by expresionuserfunction(t) t stands for time or time dependant The first way is far simpler for what you want to achieve just be careful when jumping from 0,5 to 20 as it is better to ramp the value unless you know that this jump won't cause any failure of the solver

 November 19, 2019, 01:59 #4 New Member   M S Join Date: Nov 2019 Posts: 8 Rep Power: 6 Thank you very much, it worked

 Tags cfx, transient simulation