topic Re: Calculate Simulation Time in CFD Forum

Calculate Simulation Time

Anonymous — Tue, 28 Mar 2017 06:19:36 GMT

Hello Guys!

I have simple question, How to calculate simulation time based on Time Step Size, Time Steps to Run and Inner Iterations?

Here is my print screen :

Regards
Hasan,

Re: Calculate Simulation Time

Jon.Wilde — Tue, 28 Mar 2017 06:40:39 GMT

The time run is just (time step size x time steps run).

You do need to be sure to turn of Intelligent Solution Control (in Solution Control) though, so CFD keeps the same time step sizes.

A better way might be to set a fixed stop time and just set 100,000 iterations to run. Then CFD will simply stop at the time you have assigned (in seconds).

Thanks,

Jon

Re: Calculate Simulation Time

Anonymous — Tue, 28 Mar 2017 09:00:29 GMT

Do you mean "turn off" Intelligent Solution Control ?

I dont need to turn off since Intelligent Solution Control has turned off
as default. You can see in my print screen, I set time step size 0.1 and
time steps to run 5500, why is simulation time 15 seconds??

Regards,
Hasan

Re: Calculate Simulation Time

Jon.Wilde — Tue, 28 Mar 2017 09:05:48 GMT

That is the question 🙂

Right now I am not sure, are you running free surface or anything?

You might need to share your model... (CFZ file).

Re: Calculate Simulation Time

Anonymous — Tue, 28 Mar 2017 09:27:03 GMT

Yes I am using Free Surface.

This is my CFZ file:

Regards
Hasan

Re: Calculate Simulation Time

Anonymous — Tue, 28 Mar 2017 09:27:04 GMT

Yes I am using Free Surface.

This is my CFZ file:

Regards
Hasan

Re: Calculate Simulation Time

Jon.Wilde — Tue, 28 Mar 2017 10:47:07 GMT

OK, that is the issue then. Free Surface will change the time step size to suit, so that it does not diverge.

It usually decreases it for stability.

This is why the numbers do not appear to match up.

Does that answer your question?

Kind regards,

Jon

Re: Calculate Simulation Time

Anonymous — Tue, 28 Mar 2017 11:18:22 GMT

Thank you very much John.

Since I conducted free surface simulation and got some (not all) fails. Do I need to turn on Intelligent Solution Control in free surface simulation? Error message informed that divergence

Regards,
Hasan.

Here is print screen.

Re: Calculate Simulation Time

Jon.Wilde — Tue, 28 Mar 2017 11:28:58 GMT

I would leave everything as the default that is selected when you enable free surface 🙂

(ISC = ON)

Re: Calculate Simulation Time

Anonymous — Tue, 28 Mar 2017 13:40:03 GMT

I have assigned stop time 14 but the simulation stopped at 5s. What do you
think about it?

FYI, free surface and ISC on.

Regards,
Hasan

Re: Calculate Simulation Time

Anonymous — Tue, 28 Mar 2017 13:40:04 GMT

I have assigned stop time 14 but the simulation stopped at 5s. What do you
think about it?

FYI, free surface and ISC on.

Regards,
Hasan

Re: Calculate Simulation Time

Jon.Wilde — Tue, 28 Mar 2017 13:45:38 GMT

Did CFD say that it was converged?

Maybe you need to turn off the convergence assessment so it will just keep running?

Re: Calculate Simulation Time

Anonymous — Fri, 31 Mar 2017 14:03:34 GMT

Hello John, How are you?

I am still not able to catch water hammer phenomenon as I can not see the
oscillating water level in surge tank. I hope you have a nice trick to
solve this problem since this is my final project. FYI the x velocity
changed to zero is at 15.3 s. Thank you John

this is my cfz file :