Restart from an existing solution

Start a run from fields that already exist rather than from a uniform guess. There are two different things people mean by this and the application does both.

Carry on the same run and Potential flow run on the free tier. Map from another case does not: an Initialise command beginning mapFields: is reported as an error on the Problems tab against Simulation control until the licence allows it. The run itself is not limited, only the head start.

Carry on the same run

The run converged or you stopped it, and you want more iterations.

1. Select Simulation runs.
2. Under After the run, press Continue for 1000 more iterations.

That section is drawn only for a run that converged or was stopped. A run that diverged or failed can still be continued, from the ribbon: Model → RUN → Continue, which is enabled for all four finished states. A diverged run is exactly the one somebody wants to continue with a smaller step.

The end iteration is extended, the dictionaries are rewritten, and the solver restarts from the latest written time. Nothing is re-meshed and nothing is lost.

A running solver cannot be paused — stop it, and it ends at the next write. Stop gracefully writes the current step out first; Kill does not.

Map from another case

A different mesh, a different model, or a coarse run seeding a fine one.

1. Select Initial conditions.
2. Set Initialise to From an existing run.
3. Give the Source case — the case directory to map from. Its latest time is used. Use this case's own run fills in this simulation's own run directory, which is what a mesh-refinement study wants.
4. Run.

mapFields runs before the solver, in series. The line under the control names what will run.

If Source case is left empty the run starts from 0/ as written, and the pane says so rather than silently ignoring the choice.

The cheaper middle option

If there is no previous solution to map from, set Initialise to Potential flow. It runs potentialFoam first to seed the velocity field, costs seconds, and removes the worst of the initial transient. Track the inlet seeds the domain from the inlet's velocity and turbulence instead, and keeps the two consistent when the inlet changes.

Check it worked

• The Log tab shows mapFields (or potentialFoam) completing before the solver starts.
• The first residuals are orders of magnitude below what a cold start gives.
• For a continued run, the iteration counter on Simulation runs resumes from where it stopped rather than from zero.