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

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

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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