Troubleshooting
Indexed by the message you can see. Somebody stuck pastes the error into a search box, so the heading is the literal string rather than a description of the category it belongs to.
Every message below is a real one from the application or the solver. If you hit something not listed, [email protected].
Before the run
Section titled “Before the run”The Problems tab in the bottom dock reports these before you start solving. It is the single most useful part of the interface and the easiest to ignore. A red entry means the run will fail or produce nonsense; an amber one means it will run but something is worth knowing.
“A two-phase case needs gravity”
Section titled ““A two-phase case needs gravity””A free-surface or multiphase case with gravity left at zero has nothing to separate the phases. There is no interface without it — the two fluids simply diffuse into each other.
Set gravity in the case. For a normal orientation that is −9.81 m/s² on the axis pointing up.
“An axisymmetric case needs exactly two wedge patches, one either side”
Section titled ““An axisymmetric case needs exactly two wedge patches, one either side””Axisymmetric cases in OpenFOAM are a single wedge of small angle, with the two
cut faces as wedge patches facing each other across the axis. Two is the only
valid number: one is an open domain and three does not describe a wedge.
Set both faces to Wedge (axisymmetric) in Boundary conditions.
“A case cannot be both two-dimensional and axisymmetric”
Section titled ““A case cannot be both two-dimensional and axisymmetric””These are two different ways of reducing a 3-D problem and they use different
patch types — 2-D uses empty on the front and back, axisymmetric uses wedge.
Choose one.
“A reacting case needs at least a fuel and an oxidiser”
Section titled ““A reacting case needs at least a fuel and an oxidiser””A combustion case with only one species has nothing to react. Add both to the mixture.
“A patch name cannot start with a digit”
Section titled ““A patch name cannot start with a digit””An OpenFOAM restriction rather than ours. Rename the patch.
“Cell zones and multi-region cases are not part of the free tier”
Section titled ““Cell zones and multi-region cases are not part of the free tier””The free tier runs every analysis type but not every concept. Cell zones — MRF, AMI, overset, porous media, sources — and multi-region cases need a paid licence. Nothing is lost: the case is still there when the licence is.
Import and geometry
Section titled “Import and geometry”“No converter in this build can read …”
Section titled ““No converter in this build can read …””The format is not supported by the converters bundled with this build. Every polygon format is supported, plus STEP, IGES and BREP through OCCT.
Re-export from your CAD system as STEP if you can — it is the most reliable route and carries real units.
“Could not read the geometry to split it”
Section titled ““Could not read the geometry to split it””The file loaded but could not be divided into patches, usually because it is a single unnamed surface with no distinguishable regions, or because it is not watertight.
Check the geometry is closed. A surface with holes cannot be split reliably and will not mesh well either.
“DAT aerofoil — a 2-D profile, so it needs a …”
Section titled ““DAT aerofoil — a 2-D profile, so it needs a …””An aerofoil .dat file is a 2-D coordinate list, not a solid. It has to be
extruded to a span before it can be meshed.
During the run
Section titled “During the run”The residuals rise instead of falling
Section titled “The residuals rise instead of falling”The run is diverging. It will not recover on its own — stop it.
In rough order of likelihood:
- The time step is too large. Check the Courant number in Simulation control. For most transient cases it wants to stay below 1.
- The mesh is poor where the flow is interesting. Check Quality: non-orthogonality above roughly 70 and skewness above roughly 4 are where trouble starts.
- A boundary condition is unphysical. A pressure outlet on the inlet side, or a velocity specified into a wall, will not settle.
- Relaxation is too aggressive for the case. Numerics.
The residuals go flat, well above convergence
Section titled “The residuals go flat, well above convergence”It has stopped improving rather than diverged. Usually the mesh is too coarse to resolve what is happening, or the case is genuinely unsteady and is being solved as steady. A steady solver applied to vortex shedding will sit at a plateau forever, because there is no steady answer to find.
“Unable to set reference cell for field p”
Section titled ““Unable to set reference cell for field p””A sealed domain — a cavity, a tank, a closed vessel — has no pressure outlet, so the absolute pressure level is undetermined and the solver needs a reference cell and value to pin it.
This was a real defect in the application, found by building the lid-driven cavity benchmark: every sealed case stopped here because nothing wrote those entries. It is fixed. If you see it on a current build, it is a case setup that the application has not recognised as closed — report it, because that is a rule gap rather than your mistake.
The solver stops immediately with no useful output
Section titled “The solver stops immediately with no useful output”Check the log in the bottom dock rather than the summary. Most immediate stops are a missing dictionary entry, and OpenFOAM names the entry it wanted on the last line.
Results
Section titled “Results”The answer changes a lot when I refine the mesh
Section titled “The answer changes a lot when I refine the mesh”Then the first answer was not an answer — it was a property of the mesh.
This is normal and expected, and it is why the Comparison node exists. Keep refining until the quantity you care about stops moving. That point is mesh independence, and until you have found it you do not have a result you can defend.
Two turbulence models give different answers
Section titled “Two turbulence models give different answers”Also normal. It tells you the result depends on the model, which is a fact about your problem rather than a fault in the software. Report it as a range, or justify the model choice against data.
The forces look wrong by a factor I recognise
Section titled “The forces look wrong by a factor I recognise”Check units and reference values first. Density in the wrong units, or a reference area that is half the model because the case is symmetric, accounts for most factor-of-two and factor-of-ten errors.
Licensing
Section titled “Licensing”The application dropped to the free tier
Section titled “The application dropped to the free tier”The licence could not be revalidated within the 14-day offline grace period, or the subscription lapsed. Your cases are untouched — nothing is locked, read-only, or deleted.
Reconnect and sign in, or check the subscription at account.shd-sim.com.
A seat is held by a machine I no longer have
Section titled “A seat is held by a machine I no longer have”Deactivate it from the Devices screen in your account. You do not need the machine to release its seat.