Revision as of 14:47, 14 May 2021 view source Pavlina Monhartova (talk \| contribs) Bureaucrats, Administrators 5,343 edits →Why is my HPC model getting unstable? And why are my control numbers lower than they could be? ← Older edit		Revision as of 15:09, 14 May 2021 view source Pavlina Monhartova (talk \| contribs) Bureaucrats, Administrators 5,343 edits →Why is my HPC model getting unstable? And why are my control numbers lower than they could be? Newer edit →
Line 89: * The solver can't reduce the big timestep to a sufficiently small timestep within the ten default trials, the simulation gets unstable and the model is stopped with an error. * The solver is able to reduce the timestep to a sufficient timestep within the ten default trials and the simulation continues running. This however comes with a price of slower run time: Warning 2550 - instability timestep corrections might be recorded for some or all of the cells in the model at the end of the simulation. If a wave celerity or courant control number exceed its target by up to 20% or diffusion number by 10%, the step is still accepted, but the next timestep is factored down by the same percentage. ** If there are NaNs or control number exceeds its target by more than 20% or 10% respectively, the step is rejected, the timestep is cut to half, a repeat step is performed and the control number will be cut to 90% of the previous value. The control number is then allowed to increase only by 0.001% per timestep. It will take 10,000 timesteps to creep back up to the original value if there are no other reduced timesteps, keeping the model running slower than it could.

HPC FAQ: Difference between revisions