[Nek5000-users] Perturbation mode

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

PS -- It appears that

    p93 = 20    (and mxprev=20 in SIZE)
    p94 = 0
    p95 = 5

(say) is a good combination -- this still allows projection of
the pressure onto the prior solutions, which gives important
savings in many cases.



On Wed, 16 Feb 2011, nek5000-users at lists.mcs.anl.gov wrote:

>
> Hi JC,
>
> There may also be an issue with having the projection turned on.
> (This is a common source of NaN...).   I suggest setting p93-95 to 0
> in the .rea file.  (We can subsequently fix the problem correctly.)
>
> Are you trying to run with a steady-state base flow, or an evolving
> base flow?
>
> I'm out of the office today but can hopefully look into this in
> the next day or two.   To date I've not done a lot of perturbation
> cases, so there are likely a few issues to resolve.  Several groups
> have had some success, however.
>
> Regards,
>
> Paul
>
>
> On Wed, 16 Feb 2011, nek5000-users at lists.mcs.anl.gov wrote:
>
>> Hi Jean-Christophe,
>> 
>> I think the restart option does not work properly in the perturbation
>> mode. That means, in the rea-file you can just give the base flow under
>> RESOLVE/RESTART OPTIONS.
>> I usually do the restart of the perturbation manually in the user-file.
>> Another way is to change that in the source code.
>> 
>> David
>> 
>> nek5000-users at lists.mcs.anl.gov wrote:
>>> Hi Nek's,
>>> 
>>> I am still struggling with the perturbation mode.
>>> Cavity_20x20x10_6x6x6_R1000_25D0.f00001 contains my base flow. It is a
>>> 2D lid-driven cavity extruded in the third direction (z).
>>> Perturbation_20x20x10_6x6x6_25D0.f00001 contains my divergence-free
>>> perturbation. It is subject to no-slip conditions at the walls and
>>> periodic BC at zmin and zmax.
>>> 
>>> Following is how I set it up.
>>> 
>>> **********************************************
>>> 
>>> In my blah.rea
>>> 
>>> -1.           p31 NPERT: #perturbation modes
>>> 
>>> [...]
>>> 
>>> 2 PRESOLVE/RESTART OPTIONS *****
>>> Cavity_20x20x10_6x6x6_R1000_25D0.f00001
>>> Perturbation_20x20x10_6x6x6_25D0.f00001
>>> 
>>> **********************************************
>>> 
>>> In SIZE:
>>> 
>>> parameter (lpelv=lelv,lpelt=lelt,lpert=1) ! perturbation
>>> parameter (lpx1=lx1,lpy1=ly1,lpz1=lz1) ! array sizes
>>> parameter (lpx2=lx2,lpy2=ly2,lpz2=lz2)
>>> 
>>> **********************************************
>>> 
>>> I have tried with various initial amplitude for the perturbation, and
>>> various time steps. However, I always have a very small CFL and after
>>> six timesteps I get:
>>>
>>>     Failed in HMHOLTZ: VELX NAN
>>> 
>>> 
>>> Same for vely and velz. I may have missed a key point but being not
>>> particularly familiar with Nek numerics yet I'm not sure where I
>>> missed it.
>>> 
>>> Best regards,
>>> --
>>> Jean-Christophe
>>> ------------------------------------------------------------------------
>>> 
>>> _______________________________________________
>>> Nek5000-users mailing list
>>> Nek5000-users at lists.mcs.anl.gov
>>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>>> 
>> 
>> 
>> -- 
>> David Tempelmann
>> Linné Flow Center, Mechanics KTH
>> SE-100 44, Stockholm, Sweden
>> Phone: +46 8 7907161
>> E-mail: david at mech.kth.se
>> 
>> _______________________________________________
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>