[Nek5000-users] Nek5000-users Digest, Vol 109, Issue 32

Sat Mar 31 03:45:05 CDT 2018

Dear Nek experts,

I am simulating turbulent pipe flow with 6 thermal fields treated as passive scalars.
The first three thermal fields use Pr=0.71 and the remaining three use Pr=0.025. 

________________________________________
Von: Nek5000-users <nek5000-users-bounces at lists.mcs.anl.gov> im Auftrag von nek5000-users-request at lists.mcs.anl.gov <nek5000-users-request at lists.mcs.anl.gov>
Gesendet: Freitag, 30. März 2018 17:02
An: nek5000-users at lists.mcs.anl.gov
Betreff: Nek5000-users Digest, Vol 109, Issue 32

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Today's Topics:

   1. Re: logfile (nek5000-users at lists.mcs.anl.gov)
   2. Re: logfile (nek5000-users at lists.mcs.anl.gov)
   3. Re: logfile (nek5000-users at lists.mcs.anl.gov)
   4. Re: logfile (nek5000-users at lists.mcs.anl.gov)

----------------------------------------------------------------------

Message: 1
Date: Fri, 30 Mar 2018 15:34:49 +0200
From: nek5000-users at lists.mcs.anl.gov
To: nek5000-users at lists.mcs.anl.gov     <nek5000-users at lists.mcs.anl.gov>
Subject: Re: [Nek5000-users] logfile
Message-ID:
        <mailman.12194.1522416912.19102.nek5000-users at lists.mcs.anl.gov>
Content-Type: text/plain; charset=utf-8

That par file doesn't currently support a relative and absolute tolerance for the Helmholtz solver. I think there are two options to tackle your tolerance problem:

* Specify the parameters below in usrdat3 of your usr file.
* Solve a non-dimensional problem and use a residual tolerance of e.g. 1e-8 (for velocity and temp) and 1e-5 for pressure

--
Stefan

-----Original message-----
> From:nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov>
> Sent: Friday 30th March 2018 14:19
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] logfile
>
> Thanks, Paul,
>     Could you please tell me the parameters in terms of ###.par file.
> I am using the latest version.
>
> Thank you
>
> On Fri, Mar 30, 2018 at 5:35 PM,  <nek5000-users at lists.mcs.anl.gov> wrote:
> >
> >
> >        1520  Hmholtz TEMP      12   3.8789E-11   4.5120E+07   1.0000E-10
> >
> >
> > On Step 1520, it took 12 iterations to reach a residual of 3.8e-11, starting
> > with a residual of 4.5e7, with target residual 1.e-10.
> >
> >
> > [ This is actually too tight of a tolerance, since you are asking for 17
> > orders of magnitude reduction in residual and are working only with 16
> > significant digits. It seems like you might need to change your .rea file in
> > the following way:
> >
> >
> >        set p21 and p22 to 0
> >
> >
> >        set p24, tolrel , to 1.e-3
> >
> >        set p25, tolabs, to 1.e-3
> >
> >
> > The only time you'll need tolrel/abs tighter than this is if you're doing an
> > analytic convergence study where you know the answer to an infinite number
> > of digits.   For engineering calculations, 1.e-2 to 1.e-3 is fine.   The
> > residual tolerances are set conservatively based on these input values.
> >
> >
> >   1520  Helmh3 fluid      17   3.6594E-11   4.7524E-01   1.0000E-10
> >        1520  U-PRES gmres     120   1.3494E-08   4.5675E-06
> > 1.0000E-10   7.8799E-01   3.0171E+00
> >
> >
> > You have 17 iterations for the moment equations.
> >
> >
> > You have 120 iterations for pressure.   Again, your tolerances are too tight
> > for engineering calculations -- you do not need 1.e-10 for divergence (i.e.,
> > for the pressure residual tolerance).
> >
> >
> > hth,
> >
> > Paul
> >
> >
> > ________________________________
> > From: Nek5000-users <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: Friday, March 30, 2018 4:52:26 AM
> > To: nek5000-users at lists.mcs.anl.gov
> > Subject: Re: [Nek5000-users] logfile
> >
> > The following is my logfile entry (sample lines). The first line is
> > understandable. What do the values in the third and following lines
> > denote?
> >
> >
> > ------------------------------------------------------
> > Step   1520, t= 7.6000000E-02, DT= 5.0000000E-05, C=  0.072 5.3831E+03
> > 3.5403E+00
> >              Solving for Hmholtz scalars
> >        1520  Hmholtz TEMP      12   3.8789E-11   4.5120E+07   1.0000E-10
> >        1520  Scalars done  7.6000E-02  8.3823E-02
> >              Solving for fluid
> >        1520  Helmh3 fluid      17   3.6594E-11   4.7524E-01   1.0000E-10
> >        1520  U-PRES gmres     120   1.3494E-08   4.5675E-06
> > 1.0000E-10   7.8799E-01   3.0171E+00
> >        1520  Fluid done  7.6000E-02  3.3650E+00
> > --------------------------------------------------------
> >
> > On Fri, Mar 30, 2018 at 3:05 PM,  <nek5000-users at lists.mcs.anl.gov> wrote:
> >> I am not sure what you are talking about?
> >>
> >> -----Original message-----
> >>> From:nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov>
> >>> Sent: Friday 30th March 2018 10:30
> >>> To: nek5000-users at lists.mcs.anl.gov
> >>> Subject: [Nek5000-users] logfile
> >>>
> >>> Hi Neks,
> >>>
> >>>      What are the entries in the logfile that is output from running
> >>> the code.  Please let me know where the entries are determined in the
> >>> code.
> >>>
> >>> Thanks
> >>> Swarandeep
> >>> _______________________________________________
> >>> Nek5000-users mailing list
> >>> Nek5000-users at lists.mcs.anl.gov
> >>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
> >>>
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> >
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