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July 6, 2017, 05:46 |
Star ccm+Unsteady residuals
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#1 |
New Member
gemxx
Join Date: Feb 2015
Posts: 28
Rep Power: 11 |
Hi all,
I simulate the flow around a submerged body for acoustic analysis. The analysis converges during steady state, but the residuals, especially x-y-z momentum residuals, are changing rapidly when the unsteady state analysis starts . I attach some pictures about residuals and physical models which I selected. Please advise as to what the reason of this change on residuals. What can I do to reduce the residuals at the beginning of the unsteady state ? |
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July 6, 2017, 11:10 |
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#2 | |
Senior Member
Lane Carasik
Join Date: Aug 2014
Posts: 692
Rep Power: 14 |
Quote:
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July 6, 2017, 11:17 |
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#3 | |
New Member
gemxx
Join Date: Feb 2015
Posts: 28
Rep Power: 11 |
Quote:
residuals are not dropping significantly between each time step. After 100-200 steps , they remains constant. I think that is the problem. |
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July 6, 2017, 11:53 |
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#4 |
Senior Member
Matt
Join Date: Aug 2014
Posts: 947
Rep Power: 17 |
It could also be a product of your time step. Either too large or too small of a time step and your residuals will fail to converge. You will still see the so called 'sawtooth' pattern but your residual magnitudes should be reducing at least 3 orders of magnitude as well. I suspect if you fix your time step you will get better convergence on residuals.
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July 10, 2017, 14:13 |
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#5 |
New Member
Vincent
Join Date: Jul 2017
Posts: 9
Rep Power: 8 |
You should not pay lots of attention to the residuals, I think your residuals looks fine. Its the relative error that is important.
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July 10, 2017, 15:49 |
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#6 | |
New Member
gemxx
Join Date: Feb 2015
Posts: 28
Rep Power: 11 |
Quote:
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July 10, 2017, 15:56 |
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#7 |
New Member
Vincent
Join Date: Jul 2017
Posts: 9
Rep Power: 8 |
Don't focus so much on the residuals. It is better to create reports and monitors, from that you can determine if the results are reasonable. Also in the monitor settings set the setting from auto to off. That gives a better understanding of the residuals.
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July 11, 2017, 02:34 |
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#8 | |
New Member
gemxx
Join Date: Feb 2015
Posts: 28
Rep Power: 11 |
Quote:
I also wonder the mesh structure is appropriate at the sharp bodies. I added two mesh picture and I marked the complex parts of the geometry. Do you think that the mesh structure is good especially at the marked parts ? How can I generate continuous prism layer layers along the geometry ? |
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July 11, 2017, 02:37 |
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#9 | |
New Member
gemxx
Join Date: Feb 2015
Posts: 28
Rep Power: 11 |
Quote:
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July 11, 2017, 03:08 |
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#10 | |
New Member
gemxx
Join Date: Feb 2015
Posts: 28
Rep Power: 11 |
Quote:
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