## Simulation CFD

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# Transient Natural Convection Model

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I am trying to carry out a transient thermal model but I am having trouble getting it to make sense and running the proper number of time steps.I am trying to conduct a transient model where I have steady state conditions at a low power and then have a transient model that uses that as an initial conditon and monitor the temperature increase to max power over a certain period of time. Unfortunately there are no initial heat generation conditions it only allows me to choose temperatures.

My first approach was I ran my model as steady state using the low power until it converged. In the same scenario since it kept the results I switched the BCs from steady state to transient and set each component to its max power using the constant setting. I then wanted to run a 10min transient so I told it to run 600 time steps at 1 second each with 4 inner iterations. I am also incorporating raditation in my analyses and for the transient run I am disabling the intelligent solver. My transient model will only run for about 15 time steps and then say analysis completed successfully and when I hit solve again to finish the total time steps it will only run 1 more time step and then complete. I am not sure why I cannot get the transient model it initialize from a steady state model and then conduct a transient solve for a certain number of time steps.

Should I run my transient for several iterations at low power to initialize and then switch to high power for the rest of my analysis time? This just seems it will take a lot of computing time and a lot of memory.

Thanks.

# Re: Transient Natural Convection Model

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Hi,

Is the Output Bar reporting flatlines in the convergence?

If so, perhaps there is something not quite right with the setup, is this conduction only?

**Jon Wilde**