[hajott]

Hello,
what is the recommended way to repeat a time step in time dependent solvers, when a given accuracy criterion is not met at the end of the actual time step?

The existing solvers, which can work with "adjustableTimeStep yes;" in controlDict, set the FUTURE time step based on the courant number or other criteria and don't care if the courant number is too large AFTER the time step has been solved.

But what if my solver decides that the actual step has been calculated with a too large deltaT, and I have to dismiss the latest solution, and start over with a smaller deltaT? My idea is to implement something like this:

while(runTime.run()){
  runTime++;
  solve();
  while (!isAccurate()){
    undoSolve();
    runTime.setDeltaT(0.5*runTime.deltaTValue();
    solve();
  }
}

But how do I implement "undoSolve()"? All fields, their values stored from previous timesteps and all other conditions must be reset as if the last "solve()" didn't happen. Does OpenFOAM offer an easy solution for this, or do I have to backup and possibly restore all fields?

Regards