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difference in results when the duration of the model was changed
Posted 16 nov. 2012, 12:33 UTC−5 Computational Fluid Dynamics (CFD), Results & Visualization, Studies & Solvers Version 4.3a 1 Reply
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Hi!
I ran the same model for a longer time (Rotating Machinery, Laminar Flow module) and the resulting velocity and pressure are different. Which one should I trust? Why does this happen?
For the 2 s duration model at 2 s:
Volume velocity range: 0 to 0.5801 m/s
Volume pressure range: -99.33 to 365.86 Pa
For the 5 s duration model at 2 s:
Volume velocity range: 0 to 0.5364 m/s
Volume pressure range: -114.64 to 294.14 Pa
The mesh is the same, as well as the time step and everything else in the model. The only difference was the total duration of the model.
Thank you,
Sylvana
I ran the same model for a longer time (Rotating Machinery, Laminar Flow module) and the resulting velocity and pressure are different. Which one should I trust? Why does this happen?
For the 2 s duration model at 2 s:
Volume velocity range: 0 to 0.5801 m/s
Volume pressure range: -99.33 to 365.86 Pa
For the 5 s duration model at 2 s:
Volume velocity range: 0 to 0.5364 m/s
Volume pressure range: -114.64 to 294.14 Pa
The mesh is the same, as well as the time step and everything else in the model. The only difference was the total duration of the model.
Thank you,
Sylvana
1 Reply Last Post 16 nov. 2012, 15:22 UTC−5
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Posted:
1 decade ago
Hi
check the time stepping, often COMSOL assumes regular progressing/decaying solutions, and the automatic default stepper algorithm can easily tak too large steps. So check the log, how many solver steps there are between each "out" saved step, normally if the solution is still changing and you have many "- out" adjacent without any solver step in between, there are chances that the solver is taking shortcuts (frequent for periodic BCs). Then try to change the time stepping from automatic or free, to strict or intermediate, and be sure you have a time setting that resolve correctly the time evolution
--
Good luck
Ivar
check the time stepping, often COMSOL assumes regular progressing/decaying solutions, and the automatic default stepper algorithm can easily tak too large steps. So check the log, how many solver steps there are between each "out" saved step, normally if the solution is still changing and you have many "- out" adjacent without any solver step in between, there are chances that the solver is taking shortcuts (frequent for periodic BCs). Then try to change the time stepping from automatic or free, to strict or intermediate, and be sure you have a time setting that resolve correctly the time evolution
--
Good luck
Ivar