View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0003030 | OpenFOAM | Feature | public | 2018-08-07 07:56 | 2018-12-18 09:40 |
| Reporter | akidess | Assigned To | henry | ||
| Priority | low | Severity | feature | Reproducibility | N/A |
| Status | closed | Resolution | suspended | ||
| Summary | 0003030: Restrict minimum timestep for simulations with adaptive time step | ||||
| Description | Sometimes, OpenFOAM manages to hang on to a blown up simulation by reducing the time step to very small values. This is not desirable, since it leads to the blocking of computational resources without producing a meaningful result. I thus suggest the introduction of an optional minimum allowed timestep. | ||||
| Additional Information | Changes required: 1. Addition of minDeltaT in createTimeControls.H - runTime.controlDict().lookupOrDefault<scalar>("minDeltaT", 0.0) 2. In setDeltaT.H, change the setting of new timestep to runTime.setDeltaT ( max ( min ( deltaTFact*runTime.deltaTValue(), maxDeltaT ), minDeltaT ) ); | ||||
| Tags | No tags attached. | ||||
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I don't think this is a good approach as the time-step control is usually used for cases in which the Courant number must be strictly limited, i.e. will crash due to unboundedness if this limit is violated. A better approach would be to simply stop the run if the time-step falls below some limit. |
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Indeed that would be nicer than crashing. In this case, I guess we should add something like the following to setDeltaT.H? scalar newDeltaT = min(deltaTFact*runTime.deltaTValue(), maxDeltaT); if (newDeltaT < minDeltaT) runTime.writeAndEnd(); |
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We have considered this several times and not really converged on the best approach. It could be done in setDeltaT.H but that would require maintaining several implementations, or in Time::setDeltaT which would be good if you also want options on writing because it could reset the endTime so that functionObjects etc. could execute. Another option would be to write a functionObject to stop the run. |
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Tricky. Setting in setDeltaT.H seems to be the least desirable option considering maintenance, but on the other hand I think a minimum timestep criterion should be enforced at the same location where it is done for the maximum timestep. The maxCo/maxDeltaT setting is essential for transient runs with adaptive timestepping, so I wouldn't move it into a function object. This leaves moving maxDeltaT into Time::setDeltaT or adding minDeltaT to every setDeltaT.H |
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Stopping the run if the time-step becomes lower than some level could by done in a functionObject. The big difference to setting the maximum is that it has serious side effects, in particular stopping then run and you want a (optional) write. So it cannot really be done in setDeltaT.H, it has to be in Time or a functionObject. Either way this is a significant effort and would need funding via maintenance: https://openfoam.org/maintenance/ |
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I'll try to submit a patch. |
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Suspended pending a patch and maintenance funding. |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2018-08-07 07:56 | akidess | New Issue | |
| 2018-08-07 08:10 | henry | Note Added: 0009907 | |
| 2018-08-07 08:38 | akidess | Note Added: 0009908 | |
| 2018-08-07 09:15 | henry | Note Added: 0009909 | |
| 2018-08-07 18:07 | akidess | Note Added: 0009912 | |
| 2018-08-07 18:22 | henry | Note Added: 0009913 | |
| 2018-08-08 07:17 | akidess | Note Added: 0009919 | |
| 2018-08-14 17:25 | henry | Assigned To | => henry |
| 2018-08-14 17:25 | henry | Status | new => closed |
| 2018-08-14 17:25 | henry | Resolution | open => suspended |
| 2018-08-14 17:25 | henry | Note Added: 0009951 |
