[Nek5000-users] Restarting with PNPN using PNPN-2 results

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

Hi,

In principle, you can do a Navier-Stokes restart without pressure field. 
For PnPn-2 you can for instance do one step with Uzawa (nested 
iterations) to have a good pressure. So usually, when we do a restart of 
a solution wi
thout pressure (e.g. when doing Arnoldi or Newton) then one Uzawa step 
fixes everything. I am not too familiar with PnPn, but I guess that 
there is a flavour that is not dependent on a previous pressure 
solution. Perhaps a PnPn-expert has some opinion on a Uzawa-like method?

Best regards,
Philipp

On 2016-06-13 21:15, nek5000-users at lists.mcs.anl.gov wrote:
> Hi Phil,
>
> The regularity of the pressure field is much larger for Pn-Pn as
> compared to Pn-Pn-2 so it should take some time to readjust to the
> larger resolution.
>
> Aleks
> ------------------------------------------------------------------------
> *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 13, 2016 2:09 PM
> *To:* nek5000-users at lists.mcs.anl.gov
> *Subject:* [Nek5000-users] Restarting with PNPN using PNPN-2 results
>
> Hello neks,
>
> I have a DNS simulation that I was running as PNPN-2 and I would like to
> run it as PNPN without starting back at the initial conditions.
> I am curious if anyone has experience running a PNPN case with initial
> conditions from a PNPN-2 simulation?  I have tried this and the
> simulation runs okay, except the pressure term never seems to converge
> when running the PNPN simulation.  This dramatically increases runtime
> and makes the results questionable.  It seems to me that restarting with
> PNPN-2 results should be doable, and that it should only take a few
> iterations for the pressure term to start converging.  However, my
> simulation is still not converging after 100+ iterations, but it was
> converging fine when I was running PNPN-2.
>
> Any suggestions for things I should look for that might cause the
> problem, or potential fixes?
>
> Thanks
> --
> Phil Sakievich
>
> PhD Candidate - Mechanical Engineering
> Arizona State University - Ira A. Fulton School for Engineering of
> Matter Transport and Energy
> Tempe, Arizona
>
>
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