Run in parallel

Decompose the case across cores so the solver uses the whole machine.

The free tier solves on one core. Everything below can be set, and the case is written correctly, but the run is clamped to the licensed core count and the Problems tab says so. Check what your licence allows under Settings → Licence.

Steps

1. Select Simulation control.
2. Under Parallel, pick Cores. It is a combo over a fixed ladder, not a number you type: the list stops at what the licence allows and, on a local run, at what the machine has.
3. Read the block below it. It reports cells per core and states the efficient range as 30–100 k. It turns amber above 120 k or below 10 k — the two limits are not symmetric. Too few cells per core spends the run on communication rather than solving.
4. Set Decomposition if the default does not suit: scotch, hierarchical, simple, kahip, multiLevel or manual.
5. hierarchical and simple add Split x, Split y and Split z, and hierarchical also Split order. Zero for x means every rank along x, which is right for a long channel and wrong for a tall or square domain — otherwise the three should multiply to the core count, and decomposePar says so itself if they do not.
6. Run as normal.

The application runs decomposePar, then the solver under mpirun, then reconstructPar, so what you get back is an ordinary reconstructed case. You do not decompose or reconstruct by hand.

Choosing a core count

Set it from the cell count, not from the machine. Divide the cells by a figure in the efficient range and use that many cores; more than the mesh can feed makes the run slower, not faster. The read-out on the pane does this arithmetic for you.

The pane's advice above the read-out follows the executor rather than this machine. A local run over-subscribed against the hardware is warned about; a remote machine with no recorded core count says the check was skipped rather than implying approval; and on SHD Cloud the hardware is provisioned to match, so cores set the bill rather than the contention — see run on SHD Cloud.

Check it worked

• The Simulation runs pane's status line shows the solver, the core count and the executor.
• The Log tab shows the decomposition and then the parallel solver starting.
• The Problems tab carries no core-count warning. If it does, the run is proceeding on fewer cores than you asked for.