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

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

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.
>>
>>
>>
>>
>> _______________________________________________
>> 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
>