Accuracy setting for calculating pressure vessel atmospheric release time

[Kitazawa_sgk]

Using CFA, I am trying to set the initial condition of a pressure vessel filled with gas at high pressure,
set the outlet pressure to atmospheric pressure, and measure the time it takes for the entire vessel to reach atmospheric pressure.

The time it takes for the pressure to drop is almost the same as the simulation time (required time).
Specifically,
if the simulation time is set to 5 seconds, it will take about 5 seconds to reach atmospheric pressure,
and if the simulation time is set to 10 seconds, it will take about 10 seconds to reach atmospheric pressure.

Is there something wrong with my settings?
For example, maybe there aren't enough iterations.
I would appreciate some advice on the settings when performing calculations like this.

[tmoser · Accepted solution]

Do you have this set up as a transient solution (time dependent)? The initial release of the gas will be at a high rate but will slow down as the internal pressure drops as a function of time. 

[Kitazawa_sgk]

Thank you for your reply.
That's right, I am calculating in a transient solution (time-dependent). One calculation takes more than 30 hours, so I am currently trying to reduce the calculation time by using fewer iterations and time steps.
I'm not sure whether I should increase the iterations or the time step to improve accuracy, and I've tried various things but still don't know.
It would be nice if the time step in the latter half of the calculation could be automatically reduced, but I heard from TS that this is not possible. (I would like an automatic step like Creo Simulate.)

[Kitazawa_sgk]

As expected, a good solution was obtained by increasing the number of iterations.
The effect of the calculation steps on the results is small; for example, for a 60-second calculation, 60 steps, or one step per second, seems to be sufficient. I think I have solved the problem myself, but if you have any other useful information, please comment.