Speeding up time-dependent solver

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Hi!

I want to simulate air convection generated by Joule Effect. Using an input source of 1 V (constant over all times except for t=0, where there's a quick rising phase from 0 to 1 in order to have consistent initial conditions), I can simulate pretty good results on a time window of one minute, with a CPU time of about a hour.

When I try to simulate larger timespans, the reciprocal of step size tend to grow more and more until COMSOL warns that a singularity is likely hit, and the simulation is inturrepted (see image attached).

How can I prevent this and at the same time increase time durations to hours/days with a reasonable CPU time running? I use an Intel Core(TM) i5-7500 CPU and 16 GB RAM. The model is rather simple and the figure above refers to a 2D model with a simple geometry ~29k DOF.



1 Reply Last Post Jan 15, 2021, 3:04 PM EST
Jeff Hiller COMSOL Employee

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Posted: 2 weeks ago Jan 15, 2021, 3:04 PM EST

Hello Luca,

If I understand you correctly, you have some sort electric conductor that's exposed to a DC current; it heats up, and as a result some fluid nearby heat up to and starts moving. If I got that right (and if there is no feedback loop from the thermal and fluid flow problems into the DC problem), then one suggestion to speed up your calculations would be to solve the DC problem as a first solution step using a stationary solver, and then solving the heat transfer and fluid flow poblem as a second solution step using a transient solver. This may or may not be related to the singularity error, but it will not hurt to do what I just described. The singularity could come from a number of possible reasons, for instance maybe the flow becomes turbulent when the temperature gets too high, it's hard to tell from your post.

Best,

Jeff

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Jeff Hiller
Hello Luca, If I understand you correctly, you have some sort electric conductor that's exposed to a DC current; it heats up, and as a result some fluid nearby heat up to and starts moving. If I got that right (and if there is no feedback loop from the thermal and fluid flow problems into the DC problem), then one suggestion to speed up your calculations would be to solve the DC problem as a first solution step using a stationary solver, and then solving the heat transfer and fluid flow poblem as a second solution step using a transient solver. This may or may not be related to the singularity error, but it will not hurt to do what I just described. The singularity could come from a number of possible reasons, for instance maybe the flow becomes turbulent when the temperature gets too high, it's hard to tell from your post. Best, Jeff

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