# Time step size, number of time steps and max iterations per time step

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 December 4, 2009, 06:07 Time step size, number of time steps and max iterations per time step #1 New Member   Guido Join Date: Dec 2009 Posts: 17 Rep Power: 7 I'm modeling a flow in an open-open pipe with a sinusoidal UDF. My frequency is 2000 Hz. How I can set time step size, number of time steps and max iterations per time step ? I want that it resonate so i find that it has to be 8.43cm long and 1cm of diameter

 December 4, 2009, 13:34 #2 Senior Member   karine Join Date: Nov 2009 Posts: 158 Rep Power: 8 Hi Time step = 1/2*2000. Number of time steps: u must continue ure simulation untill u obtain a steady (oscillatory of course) solution. U will need at least that ure fluid traverse the pipe for 2 times , i mean 2*V/L Max iteration by time step: try to monitor variables...choose the max iter. as the number of iterations after what ure solution does not change anymore within a time step....(u can also add 1 iteration for security, this ure unsteadiness is not uniform) If those condirtions are so strict (take a lot of time to finish ure simulation), use NITA solver: it will give u fairly accurate solution within 1 iter by time step P.S be4 asking a question, u can say hello and at the end, u can say thanks no?

 December 4, 2009, 13:40 #3 New Member   Guido Join Date: Dec 2009 Posts: 17 Rep Power: 7 Thanks a lot,you're absolutely right ! I'll try to follow your suggestions, thanks again !

 December 4, 2009, 14:11 #4 Senior Member   karine Join Date: Nov 2009 Posts: 158 Rep Power: 8 No problem comrade Anyway i forgot to tell u, for the time step i told u 1/4000 to stay conform to shannon theorem...but if u have more unsteadiness, u must use a smaller time step. URANS models are not sensible to high frequencies, so this will not be a big problem but if u are performing DNS or LES, u will need maybe to refine ure time step... There is no universal formula: the best way is to perform ure simulations with 2 different time steps and compare so u can be sure. With smaller time step, u will need less ietrations by time step. Sometimes using a smaller time step only influences rms values without influencing the mean field... Good Luck

 August 30, 2012, 14:49 how to calculate time steps required in a transient analysis #5 New Member   abdul khader Join Date: Dec 2010 Posts: 19 Rep Power: 7 I am performing FSI analysis on a elastic tube. Total time is 0.8sec and I am using timestep of 0.005sec. How can we calculate the required no. of time steps for a total time. is there any thumb rule for this ..? or its always a guess..? kindly reply

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