Transient analysis with variable time step AcuConsole

Andrea_Formartis · November 29, 2016, 03:06

Hey guys,

I am new to this forum and I would like to know if anyone has ever used AcuConsole for some CFD analysis.
Is it possible to setup a transient simulation with a variable time step?
I ask because I am facing the problem of an opening valve: the first few instants of the simulation are very important and I would need a very small time step to reach a good time resolution.
However, after few seconds, such a small time step becomes useless and I would like to increase it, in order to save space disk and simulation time.
The AcuConsole interface does not seem to support this function, has anyone ever done anything similar with it?

Thanks in advance for your help.

Best Regards,

Andrea

hellorishi · November 30, 2016, 01:41

Hi Andreas,
One option here would be run the first part of the simulation with small time steps. Then use a restart for the second part with coarser time steps.
Another option is to use automatic time steps. I would prefer the first option.

iancmlositano · July 18, 2017, 11:17

Mr. Rishi, changing from small to bigger time steps, will the simulation run time be significantly reduced? And I would like to follow up asking if the more refine the time step - more decimal places to the right - the slower the computation, thus longer computing time?

Sent from my HUAWEI TIT-U02 using CFD Online Forum mobile app

hellorishi · July 19, 2017, 07:57

Yes that is correct.
With small time step (e.g. 0.01 sec) you will need substantial amount of time for the entire simulation.
With larger time step (e.g. 10 sec) simulation time will be drastically reduced.

Although AcuSolve is stable at higher CFL numbers and does not need CFL<1 for stability, you have to also take into consideration, what kind of physics is involved and whether the time stepping is making sense for the phenomenon you would like to capture.

November 29, 2016, 03:06	Transient analysis with variable time step AcuConsole	#1
Andrea_Formartis New Member Andrea Join Date: Nov 2016 Posts: 3 Rep Power: 9	Hey guys, I am new to this forum and I would like to know if anyone has ever used AcuConsole for some CFD analysis. Is it possible to setup a transient simulation with a variable time step? I ask because I am facing the problem of an opening valve: the first few instants of the simulation are very important and I would need a very small time step to reach a good time resolution. However, after few seconds, such a small time step becomes useless and I would like to increase it, in order to save space disk and simulation time. The AcuConsole interface does not seem to support this function, has anyone ever done anything similar with it? Thanks in advance for your help. Best Regards, Andrea

November 30, 2016, 01:41		#2
hellorishi Senior Member Rishi . Join Date: Mar 2009 Posts: 149 Rep Power: 17	Hi Andreas, One option here would be run the first part of the simulation with small time steps. Then use a restart for the second part with coarser time steps. Another option is to use automatic time steps. I would prefer the first option. iancmlositano likes this.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Multiple floating objects	CKH	OpenFOAM Running, Solving & CFD	14	February 20, 2019 09:08
High Courant Number @ icoFoam	Artex85	OpenFOAM Running, Solving & CFD	11	February 16, 2017 13:40
Stuck in a Rut- interDyMFoam!	xoitx	OpenFOAM Running, Solving & CFD	14	March 25, 2016 07:09
Help for the small implementation in turbulence model	shipman	OpenFOAM Programming & Development	25	March 19, 2014 10:08
plot over time	fferroni	OpenFOAM Post-Processing	7	June 8, 2012 07:56

July 18, 2017, 11:17		#3
iancmlositano New Member Ian Carlo M. Lositaño Join Date: Mar 2017 Location: Legazpi City, Philippines Posts: 14 Rep Power: 9	Mr. Rishi, changing from small to bigger time steps, will the simulation run time be significantly reduced? And I would like to follow up asking if the more refine the time step - more decimal places to the right - the slower the computation, thus longer computing time? Sent from my HUAWEI TIT-U02 using CFD Online Forum mobile app

July 19, 2017, 07:57		#4
hellorishi Senior Member Rishi . Join Date: Mar 2009 Posts: 149 Rep Power: 17	Yes that is correct. With small time step (e.g. 0.01 sec) you will need substantial amount of time for the entire simulation. With larger time step (e.g. 10 sec) simulation time will be drastically reduced. Although AcuSolve is stable at higher CFL numbers and does not need CFL<1 for stability, you have to also take into consideration, what kind of physics is involved and whether the time stepping is making sense for the phenomenon you would like to capture.