Change Timestep

FrankW · February 12, 2021, 05:40

I have a transient simulation where a parameter changes at a certain time. The whole thing runs with adaptive time steps. How can I reduce the time step in a defined manner shortly before changing the parameter in order to better capture the change.

AtoHM · February 12, 2021, 09:13

I don't know for sure if its impossible, but I think it is. Wouldn't that defeat the purpose of adaptive timestepping?
However, you can still check the timestep cfx takes on its own, make a new simulation with that time step and then you can change it with an expression however you like.

ghorrocks · February 12, 2021, 19:35

Yes, AtoHM is right. It sounds like you want to change from adaptive time steps to your own time step as you approach the change. This means you need to stop the simulation and restart with adaptive time stepping removed and your defined time stepping used instead.

FrankW · February 15, 2021, 04:13

Ok, thanks for the hints. I'll see how I can best implement it.

February 12, 2021, 05:40	Change Timestep	#1
FrankW Member Frank Weise Join Date: Mar 2009 Location: Germany Posts: 55 Rep Power: 17	I have a transient simulation where a parameter changes at a certain time. The whole thing runs with adaptive time steps. How can I reduce the time step in a defined manner shortly before changing the parameter in order to better capture the change.

February 12, 2021, 09:13		#2
AtoHM Senior Member M Join Date: Dec 2017 Posts: 645 Rep Power: 12	I don't know for sure if its impossible, but I think it is. Wouldn't that defeat the purpose of adaptive timestepping? However, you can still check the timestep cfx takes on its own, make a new simulation with that time step and then you can change it with an expression however you like. aero_head likes this.

February 12, 2021, 19:35		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,732 Rep Power: 143	Yes, AtoHM is right. It sounds like you want to change from adaptive time steps to your own time step as you approach the change. This means you need to stop the simulation and restart with adaptive time stepping removed and your defined time stepping used instead. aero_head likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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February 15, 2021, 04:13		#4
FrankW Member Frank Weise Join Date: Mar 2009 Location: Germany Posts: 55 Rep Power: 17	Ok, thanks for the hints. I'll see how I can best implement it.