steady to unsteady

wlt_1985 · November 23, 2010, 03:48

how to implement the results obtained from steady state modeling to unsteady state modeling? is it just switch the steady state condition to unsteady state condition in solver after the steady state condition has been converged?

Thanks

KristianEtienne · November 23, 2010, 04:46

Yes, the solution method you sketch should work without any problems; switch to the unsteady solver and continue your calculations from where the steady one stopped.

Cheers!

wlt_1985 · November 23, 2010, 06:34

Quote:

Originally Posted by KristianEtienne

Yes, the solution method you sketch should work without any problems; switch to the unsteady solver and continue your calculations from where the steady one stopped.

Cheers!

Thanks for help.

wlt_1985 · November 24, 2010, 03:10

Quote:

Originally Posted by KristianEtienne

Yes, the solution method you sketch should work without any problems; switch to the unsteady solver and continue your calculations from where the steady one stopped.

Cheers!

should i reinitialize before unsteady state modeling?

KristianEtienne · November 24, 2010, 04:06

No, why would you want to do that?

That will reset your solution to what it was before you started the steady simulation..

wlt_1985 · November 24, 2010, 04:43

Quote:

Originally Posted by KristianEtienne

No, why would you want to do that?

That will reset your solution to what it was before you started the steady simulation..

Thanks for help

Ozgur_ · December 4, 2010, 17:17

Hey everyone,

I wanted to ask a couple of stuff related to unsteady modelling: I'm doing the exact same thing you discussed; I first get a converged steady-state solution, then I run it unsteady. Here's what happens though:

- I'm analyzing the wake of a 3D cylinder in cross flow. Since for most Re numbers (including mine) the wake is unsteady, so the contour plots of variables oscillate inside the wake.
The funny thing is, for the first 90 - 100 time steps, the wake oscillates, but after that point, and even when the residuals go down and flatten out at low levels, the wake oscillation disappears. The wake looks symmetric, like the average, mean version of all the oscillations.

Any idea why this is happening? Could it be related to the size of the time step and/or the number of pseudo-time iterations at each time step? Or could it be related to the boundary conditions?

Cheers,

Ozgur

November 23, 2010, 03:48	steady to unsteady	#1
wlt_1985 Senior Member raymond Join Date: Nov 2009 Posts: 149 Rep Power: 17	how to implement the results obtained from steady state modeling to unsteady state modeling? is it just switch the steady state condition to unsteady state condition in solver after the steady state condition has been converged? Thanks

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November 23, 2010, 04:46		#2
KristianEtienne New Member Kristian Etienne Einarsrud Join Date: Oct 2010 Location: Trondheim Posts: 29 Rep Power: 16	Yes, the solution method you sketch should work without any problems; switch to the unsteady solver and continue your calculations from where the steady one stopped. Cheers!

November 24, 2010, 04:06		#5
KristianEtienne New Member Kristian Etienne Einarsrud Join Date: Oct 2010 Location: Trondheim Posts: 29 Rep Power: 16	No, why would you want to do that? That will reset your solution to what it was before you started the steady simulation..

December 4, 2010, 17:17		#7
Ozgur_ New Member Join Date: Mar 2010 Posts: 6 Rep Power: 16	Hey everyone, I wanted to ask a couple of stuff related to unsteady modelling: I'm doing the exact same thing you discussed; I first get a converged steady-state solution, then I run it unsteady. Here's what happens though: - I'm analyzing the wake of a 3D cylinder in cross flow. Since for most Re numbers (including mine) the wake is unsteady, so the contour plots of variables oscillate inside the wake. The funny thing is, for the first 90 - 100 time steps, the wake oscillates, but after that point, and even when the residuals go down and flatten out at low levels, the wake oscillation disappears. The wake looks symmetric, like the average, mean version of all the oscillations. Any idea why this is happening? Could it be related to the size of the time step and/or the number of pseudo-time iterations at each time step? Or could it be related to the boundary conditions? Cheers, Ozgur