[cedame]

Hello,

[Using Converge 2.2.0]

I am simulating hot flow in a cylindric tube to study heat flow in the radial direction of the tube.
I am doing some kind of parametric study, where I have one fully working case setup.
No problems occured during setup, calculation and results interpretation of this first case.
In a second case I changed thermal conductivity of the tube material.
When I try to run this calculation, Converge gives me the line that I described in the title of this thread.

As I merely changed 1 parameter (the thermal conductivity of the tube material), I don't know where to start to debug my case setup.

Moreover, at every cycle Converge writes something like:
ncyc= 770, time= 9.625000000e-04, dt= 1.250000000e-06, time-step limit =dt_min forced by dt_recover

Where dt = 1.250000000e-06 is the minimum time step.
I see that Converge uses some kind of recovered time step, but I don't see where it gets it. Is the dt_recover the time step of the previous cycle ?

Converge continues running, but writes that it is extrapolating for temperature calculation, so I guess that this calculation is not exact enough.

Thanks in advance,
Cedric

[xieshengbai]

Dear Cedric,

There might be many reasons to cause this warning message. Basically, it means something is wrong in the temperature calculation (either too high or too low). For example, maybe you changed the thermal conductivity too much such that the temperature drops or increases drastically falling out of the reasonable range.

The appearance of dt_recover means that the solver doesn't converge well. When the solver doesn't converge, CONVERGE has to go back to the last cycle and reduces the time-step size and retry it until it reaches the minimum time-step limit you set. It seems to me that the temperature is not converged in your case, as a response to the change of conductivity.

Hope it helps.

Shengbai

[cedame]

Hello Shengbai,

Indeed, the sudden change in thermal conductivity was the problem.
I chose another value, closer to my initial case setup, and it works now.

Thank you for your help,

Cedric