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goldschmidt.mp4 (1,641,906 bytes) |
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goldschmidt_noFlow.mp4 (1,860,351 bytes) |
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Do you see this with version 7? The cyclone tutorial has stopped working since version 7, and I don't know why. Might these be related? |
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Oh, yes. There's a bug in dev. Look at the difference in the column case. column.png (54,752 bytes) |
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Yes there is a considerable difference. I see this with version 7 as well. This packing behaviour made me think that there is something to do with the averaging method but I am not sure though. It is hard to track this bug. For me, column case without the isotropy model hangs at about 0.28s and the same happens with cellPointWallModified interpolation for U.air. There happens to be overpacking which is not usual with the implicit method. On the other hand if the drag force is disabled, the simulation runs till the end but then there is excessive scattering. This should be irrelevant to the averaging method. |
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The image I posted is the difference between 7 and dev. If you see your problem in 7, too, then that is a different issue. MPPIC has stability issues. Mostly this is when the parcels are too large relative to the cells, meaning a reliable average cannot be computed. There are other issues, too, though. When we wrote this, doing MPPIC reliably on polyhedral meshes wasn't a solved problem, and the only references we had when we first did the implementation were structured-mesh codes (Barracuda and Mfix) in which stability was achieved by various staggering procedures only possible on structured meshes. That situation may have changed now, I don't know. There has been zero funding for improvement or extension of MPPIC since it's first release in 2013. If the basic limitations of our implementation of MPPIC is the issue here, then that will require someone to pay for additional research and development work to resolve it. I'll find the bug that is causing the difference between 7 and dev. That's clearly a bug that has been introduced since version 7, and we have funding available (https://openfoam.org/maintenance) to do maintenance work of this sort. Removing drag and isotropy will cause more scattering. Both act to reduce relative velocities within the system. Both will, in all likelihood, be necessary to get a physical solution. Damping, too, is important, as it is the only mechanism by which the sub-grid collision modelling dissipates energy. However, it can interact badly with the packing models. Again, limitations that we have never had the opportunity to fix. |
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Thank you for the clarification and detailed explanation. I understand that the other issue is clearly a matter of funding. I just think that OpenFOAM is a great platform for MP-PIC too and could be quite unique with further developments which obviously require funding. I wish the big players in this field would be interested in it. Thanks in advance for your effort to find the bug that causes the difference between version 7 and dev. |
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The issue with the staggering has been resolved by commit 43d66b5e. See https://bugs.openfoam.org/view.php?id=3385#c11442 for explanation. The issue regarding instability in the absence of the isotropy model is suspended pending funding. |
- Anonymous
