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# NX Thermal-Flow Time to reach steady state temperatures

Creator

I built up a coupled flow and thermal analysis model on an electronic assembly using NX 11 and Simcenter Thermal/Flow Solver (Solution Type: Steady State). Calculated temperature results seem reasonable to me, but it would also be interesting to see how long it takes to reach steady state conditions. Is there a way to look up the time necessary to reach steady state conditions directly from a steady state solution?

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# Re: NX Thermal-Flow Time to reach steady state temperatures

Pioneer

By definition, a steady state condition gives you the resulting temperatures after a infinite time. The best method to precisely evaluate the evolution of the temperature in function of the time is... to run a transient analysis, isn't it ?

# Re: NX Thermal-Flow Time to reach steady state temperatures

Creator

You are absolutely right. Let me underline that I do not need a precise evolution of all single temperatures within my assembly as function of time, an integral estimation for the time to reach steady state conditions would be sufficient. I am just asking if it is really necessary to re-run my whole analysis (changing solution type "steady state" to "transient") in order to find out an estimation of the time necessary to reach near steady state. If this is the case, I will need to use a very high value for the "End Time" in the "Transient Solution Time Interval" settings since I have no clue about the order of magnitude of time to reach steady state (could be seconds, minutes, hours). So I understand there is no way to get a first idea from any simulation data / log files / ...?

# Re: NX Thermal-Flow Time to reach steady state temperatures

Siemens Phenom

Yes, it is necessary to run a transient analysis to determine the time needed to reach steady state.

A steady state solution is simpler/faster because transient terms have been removed. As indicated in the previous response, this is a fundamental assumption. As such, a steady state analysis cannot give any type of time estimate.

# Re: NX Thermal-Flow Time to reach steady state temperatures

Creator

Say I have a transient simulation 60s long. After the simulation has completed, I find out that I need to extend the simulation end time another 30s. Is there a way to continue the simulation where it left off while keeping everything the same? Or do I have to re-run the whole transient analysis from zero?

Siemens Phenom