[Nek5000-users] Guidelines for Tolerances
nek5000-users at lists.mcs.anl.gov
nek5000-users at lists.mcs.anl.gov
Sat Mar 31 04:06:58 CDT 2018
Dear Nek experts,
sorry, my first mail was incomplete. I will start again.
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.
In the par file, I set residualTol = 1e-08 for pressure velocity and all thermal fields. Having read the recent discussion about another logfile, I was wondering whether these settings might be too tight.
The log for one timestep is given below (sorry about the formatting).
As you can see, I need 16 - 21 iterations for the scalar fields of Pr=0.025.
Do you think I could reduce the residualTol for the low Pr fields to speedup the simulation?
Best regards,
Steffen
Step 99999, t= 8.4999900E+02, DT= 1.0000000E-03, C= 0.291 3.3389E+04 3.2523E-01
Solving for Hmholtz scalars
99999 Project TEMP 9.7160E-08 5.5444E+00 5.7064E+07 8 8
99999 Hmholtz TEMP 6 8.0673E-09 3.1410E-05 1.0000E-08
99999 Project PS 1 1.9038E-07 6.6127E+00 3.4734E+07 8 8
99999 Hmholtz PS 1 7 6.2818E-09 6.1081E-05 1.0000E-08
99999 Project PS 2 5.7194E-06 1.1100E+01 1.9408E+06 7 8
99999 Hmholtz PS 2 8 4.7345E-09 1.5839E-03 1.0000E-08
99999 Project PS 3 1.6110E-09 2.0874E-01 1.2958E+08 8 8
99999 Hmholtz PS 3 16 8.1941E-09 6.8549E-07 1.0000E-08
99999 Project PS 4 1.8743E-09 2.5528E-01 1.3620E+08 8 8
99999 Hmholtz PS 4 16 9.3461E-09 7.7774E-07 1.0000E-08
99999 Project PS 5 4.9138E-08 4.4469E-01 9.0499E+06 7 8
99999 Hmholtz PS 5 21 8.2110E-09 1.3142E-05 1.0000E-08
99999 Scalars done 8.5000E+02 1.7601E-01
Solving for fluid
99999 Project VELX 5.5774E-09 6.9874E-03 1.2528E+06 8 8
99999 Hmholtz VELX 4 2.7784E-09 1.7303E-06 1.0000E-08
99999 Project VELY 5.4643E-09 6.9118E-03 1.2649E+06 8 8
99999 Hmholtz VELY 4 2.7477E-09 1.6969E-06 1.0000E-08
99999 Project VELZ 5.0326E-09 6.9213E-03 1.3753E+06 8 8
99999 Hmholtz VELZ 4 6.0439E-09 2.0347E-06 1.0000E-08
99999 Project PRES 1.5397E-04 9.8607E-02 6.4043E+02 14 20
99999 U-PRES gmres 13 9.9860E-09 8.3983E-08 1.0000E-08 4.3257E-02 7.0065E-02
99999 volflow Z 1.8796E-02 8.0416E-06 7.8539E-01 7.8540E-01
99999 Fluid done 8.5000E+02 1.2875E-01
________________________________________
Von: Straub, Steffen (ISTM)
Gesendet: Samstag, 31. März 2018 10:45
An: nek5000-users at lists.mcs.anl.gov
Betreff: AW: Nek5000-users Digest, Vol 109, Issue 32
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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