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Simulation stopping without error message

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Message 1 of 2
Emily.I
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Simulation stopping without error message

Hi,

 

I was getting unphysical results in my model (negative Kelvin), so I made the mesh finer in an attempt to make it more physical (as I was told in a previous problem), however now it verifies the model and then stops before analysing anything. No error message comes up at all. I attached my simulation.

 

Thank you,

Emily

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Message 2 of 2
John_Holtz
in reply to: Emily.I

Hi Emily,

 

How do you know that stopped? I'm sure that sounds like a stupid question, but here's why I ask. I changed your model to create fewer body to body radiation "elements". After the verification phase, the analysis was running but only showed 3 or 4 lines in the log file for a long, long time. Two hours after "starting" the analysis, it finished loading in all of those radiation elements and really began solving the problem. So, I think you just need to let it run for a long time.

 

I highly suggest that you consider making some changes to the model. The reason is that every element you define in the body to body radiation radiates to every other element. So even though you only have about 5000 elements in the model, 5000^2 is a lot of elements!

 

Because of the body to body radiation, you cannot run the analysis on a half symmetry model. But I wonder if using a fine mesh in half of the model and a coarser mesh on the other "symmetry" half would give reasonable results. Something to test in a smaller model.

 

To optimize the body to body radiation, you should only include the elements that will radiate to each other. (see "bowl-suggestions.png") For example:

 

a) the top of the flange (surface 4 in my sketch) does not need to be included in body to body radiation because those elements do not see any other elements in the bowl. The amount of heat received is known (1400 W/m^2, projected onto the surface).

 

b) The "Sun" can barely see any of the outside of the bowl, so it may be possible to ignore that heat flux entirely.

 

c) The bottom of the flange (surface 1) can see just the upper half of the bowl (surface 2). So if you split the bowl into different surfaces, you can define the body to body radiation between 1 and 2.

 

d) The bottom half of the outside radiates to the ambient. This can be modeled with surface radiation instead of body to body radiation.

 

e) Use body to body radiation between the sun and the inside of the bowl (surface 5).

 

Finally, it appears that the rim of the bowl is not attached to the bowl itself. Is that intentional? I did not notice this until the analysis was finished, and it does not seem correct to me. See attached image.

 



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


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