overflow

rasool motamedi · April 23, 2013, 14:36

hello
I am simulating a channel in micro scale with two fluids.
I have two problem
1-my outlet must be opening or static pres.?
because i have overflow error
i reduced my time step to 0.0001 but still i have error
is giving backup of solution useful then i do solution with final backup again?
can i do it?how?
number of my elements 37297
what are your Proposals to Resolve the overflow?
thanks
q.jpg

ghorrocks · April 23, 2013, 19:10

Your outlet can be whatever matches the conditions you are modelling. If you are modelling the vorticies coming off the plate in your picture then I suspect you could use either. I tend to use outlets when possible as they are a bit easier to converge.

What makes you think 0.0001 [unknown units] is the correct time step? My recommendation is to use adaptive time stepping, homing in on 3-5 coeff loops per iteration. Then the solver finds the best time step by itself.

For transient simulations it is better to save transient results files. If you want to use them to restart the simulation then just make sure you include all the parameters required to restart a simulation.

The overflow is probably due to too large a time step.

April 23, 2013, 14:36	overflow	#1
rasool motamedi Member rasool Join Date: Apr 2013 Posts: 41 Rep Power: 13	hello I am simulating a channel in micro scale with two fluids. I have two problem 1-my outlet must be opening or static pres.? because i have overflow error i reduced my time step to 0.0001 but still i have error is giving backup of solution useful then i do solution with final backup again? can i do it?how? number of my elements 37297 what are your Proposals to Resolve the overflow? thanks q.jpg

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April 23, 2013, 19:10		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	Your outlet can be whatever matches the conditions you are modelling. If you are modelling the vorticies coming off the plate in your picture then I suspect you could use either. I tend to use outlets when possible as they are a bit easier to converge. What makes you think 0.0001 [unknown units] is the correct time step? My recommendation is to use adaptive time stepping, homing in on 3-5 coeff loops per iteration. Then the solver finds the best time step by itself. For transient simulations it is better to save transient results files. If you want to use them to restart the simulation then just make sure you include all the parameters required to restart a simulation. The overflow is probably due to too large a time step.