[Nek5000-users] Projection technique's parameters

[nek5000-users at lists.mcs.anl.gov]

Hi Andrew,

The projection routines are currently being overhauled, but the general strategy is:

   Number of projections controlled by p93 and mxprev in SIZE.

   p94 > 0:   start projecting velocity/temp after step p94

   p95 > 0:   start projecting pressure after step 95

I typically set p94 and p95 to 5

I set mxprev and p93 to 20, but sometimes to a higher value.

I used to occasionally to to much higher than 20 (say, 80), but in a recent
rewrite and effort to make projection more robust I slowed the projection
step down with too much work, so another rewrite is due soon.

Paul

PS - note that certain combinations of run parameters don't support
projection or potentially blow up.  Set p94=0 in this case and retry.
There was a bug that was fixed about 6 weeks back---it may have cured
some of the cases that users were running into.


________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
Sent: Monday, June 27, 2016 3:17 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: [Nek5000-users] Projection technique's parameters

Hi Neks,

My question is about the parameters which manage the projection method in the NEK5000: p93, p94 and p95. How can the correct values be selected for these parameters to obtain the better performance depending on the nature of simulation: laminar / turbulent, convection / diffusion, time step?

Thank you for any suggestion,
Andrew
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