[Nek5000-users] Restarting simulation from instantenous & average velocity field files

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

Hi Paul,

Thanks for your info. on how to find the rms quantities. This will
certainly save me a lot of computing time.

Regards,

Harish.

On Sat, 1 May 2010 nek5000-users at lists.mcs.anl.gov wrote:

>
>
> If you're trying to compute the rms quantities, you can do
> these directly from the data generated by avg_all, which
> produces
>
>    <u>  <v> <w>
>
> and <u^2> <v^2> <w^2>  <uv>  <vw> etc.
>
>
> Given these, you have
>
>
>     <u'2> = <u^2> - <u>^2
>
> etc., so no need to rerun if you're after those statistics.
>
> Paul
>
>
>
> On Sat, 1 May 2010, nek5000-users at lists.mcs.anl.gov wrote:
>
> > Hi Paul & Stefan,
> >
> > Thanks for your replies.
> >
> > I read through the routine avg_all() and I am using that to compute
> > averages. I am also using userchk subroutine in turbChannel case as a
> > guideline.
> >
> > I am sorry for not being very clear about my simulations. For the DNS
> > simulation I ran it for 10 flow throughs till quasi-stationary state is
> > achieved. Then compute averages over 5 more flow throughs and finally
> > compute fluctuations over 10 more flow throughs.
> >
> > Right now I am computing averages by setting up the simulation for all the
> > 5 flow throughs at one time. At the end of 5 flow throughs I will end up
> > with 2 fld* files. One for instantaneous (blah.fld*) and other for
> > averages (avgblah.fld*).
> >
> > To continue with calculating fluctuations over the next 10 flow throughs.
> > I need to read in the instantaneous and average field values to calculate
> > fluctuations. Is there is possible to do this with the RESTART OPTIONS.
> > Something like this,
> >
> >         2 PRESOLVE/RESTART OPTIONS  *****
> > blah.fld01 X U P
> > avgblah.fld01 Uavg Pavg
> >
> > I think there is one way around this. To calculate fluctuations, start
> > from fresh averaging for next 10 flow throughs and not use the averages
> > calculated from previous 5 flow throughs. I am not sure if this is the
> > right way to go about it.
> >
> > Thanks for your help. I will test some cases out and will post any
> > questions I have.
> >
> > Regards,
> >
> > Harish.
> >
> >
> > On Fri, April 30, 2010 7:37 am, nek5000-users at lists.mcs.anl.gov wrote:
> >> Harish,
> >>
> >> you can compute mean and variances based on the averages we computed in
> >> avg_all().
> >> The averages E(X), E(X*X), E(X*Y) are stored in the common blocks defined
> >> in AVG (make sure you set lxa in SIZE correct).
> >>
> >> The averages are dumped into different files (I/O freq can be adjusted
> >> with param(68):
> >> *.avg -- E(X)
> >> *.rms -- E(X*X)
> >> *.rm2 -- E(X*Y)
> >>
> >> If you have want to compute the mean and variance of multiple files, run
> >> Nek in postprocessing mode and read the *.avg files and the *.rms files
> >> using load_fld() and sum up the averages for every variable (you need some
> >> temporary arrays for that).
> >>
> >> Then compute the variance as
> >>
> >> var(X) := E(X^X) - E(X)*E(X)
> >>
> >> Finally just dump the final arrays containing your mean and/or variances.
> >>
> >> hth,
> >> Stefan
> >>
> >>
> >>
> >>
> >>
> >>
> >> On Apr 30, 2010, at 2:16 PM, nek5000-users at lists.mcs.anl.gov wrote:
> >>
> >>> Hello Paul & Stefan,
> >>>
> >>> I am running a DNS simulation of backward facing simulation (BFS) at
> >>> Re=3000. The Reynolds # is based on step height (h=1) & free stream
> >>> velocity (ux = 1.0). The BFS geometry has 5184 elements and
> >>> lx1=ly1=lz1=8.
> >>>
> >>> After running for about 10 flow throughs, we started computing averages.
> >>> I
> >>> want to restart simulation after 2 flow throughs, but I have 2 field
> >>> files
> >>> one for instantaneous (blah.fld01) and the other for average
> >>> (avgblah.fld01). To continue computing averages I need to read in both
> >>> the
> >>> velocity field files. Is there an option to restart from 2 field files?
> >>> Or
> >>> how else can I do this? I will also require this option later for
> >>> computing "rms" velocities.
> >>>
> >>> Thanks,
> >>>
> >>> Harish.
> >>>
> >>>
> >>>
> >>>
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> >>
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> >
> >
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