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

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

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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>>> Nek5000-users at lists.mcs.anl.gov
>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>>
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