[Nek5000-users] Guidelines for Tolerances
nek5000-users at lists.mcs.anl.gov
nek5000-users at lists.mcs.anl.gov
Sat Mar 31 04:20:06 CDT 2018
Your tolerances look good to me. Typically 1e-5 for pressure is accurate enough. Note, in the Pn/Pn-2 formulation the tolerance is equivalent to the desired divergence error. This is in contract to Pn/Pn where such a relation does not exists. In most cases the divergence error is dominated by the spatial resolution. That's something you can try - just lower the tol to say 1e-5. If you'll get a similiar divergence error (compared to 1e-8) try to lower it even further.
--
Stefan
-----Original message-----
> From:nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov>
> Sent: Saturday 31st March 2018 11:07
> To: nek5000-users at lists.mcs.anl.gov
> Subject: [Nek5000-users] Guidelines for Tolerances
>
> 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
>
> Send Nek5000-users mailing list submissions to
> nek5000-users at lists.mcs.anl.gov
>
> To subscribe or unsubscribe via the World Wide Web, visit
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
> or, via email, send a message with subject or body 'help' to
> nek5000-users-request at lists.mcs.anl.gov
>
> You can reach the person managing the list at
> nek5000-users-owner at lists.mcs.anl.gov
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Nek5000-users digest..."
>
>
> 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
> > >>>
> > >> _______________________________________________
> > >> Nek5000-users mailing list
> > >> Nek5000-users at lists.mcs.anl.gov
> > >> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
> > > _______________________________________________
> > > Nek5000-users mailing list
> > > Nek5000-users at lists.mcs.anl.gov
> > > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
> > >
> > > _______________________________________________
> > > Nek5000-users mailing list
> > > Nek5000-users at lists.mcs.anl.gov
> > > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
> > >
> > _______________________________________________
> > Nek5000-users mailing list
> > Nek5000-users at lists.mcs.anl.gov
> > https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
> >
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>
More information about the Nek5000-users
mailing list