[Nek5000-users] New Recycling BC based on interpolation

Fri Jul 16 17:30:41 CDT 2010

Hi Michael,

Thanks for the suggestion --- I think it's a good one, but we're
not quite there yet.   I have a couple of comments -

Technically "R  " is the same as "v  " --- because it is a time-space
varying prescribed Dirichlet condition.

Why not simply populate bc(4,f,e,1) with 1,2,3,...  to indicate 
that it is a Recycle bc of type 1,2,3,... ?   For every cbc, there
are 6 bc() entries (i.e, bc(k,f,e,1) for k=1 to 6).  For "v  ", the 
first one of these (k=1) is reserved.

That being said, genmap doesn't care about any bc other than "O  " and
"P  " (in fact, only "P  " at this point), so you could in fact do what
you propose right now, as long as you replace in usrdat or usrdat2 with
the functionally correct "v  " bc.

At present I'm a bit reluctant to make a change to the repo that is
still in flux w.r.t. development -- There are a few issues to resolve.
Presumably what one wants to be able to specify is the translation
distance -- with respect to what? -- and the scale factor as a function
of time.  We have selected w.r.t. to the unit normal on the R face.  In
exact arithmetic there's no difficulty - but in some tricky situations
there will be problems.  Rather than try to engineer a solution for all
possible scenarios I think it's best to handle this on a case-by-case
basis until we get a handle on what works and what doesn't.

There are also performance issues to be investigated, particularly at
high processor counts.

In a few months I expect we'll have a consolidated code team such
that we can implement changes (at least the mechanics of them)
without much difficulty.  Right now (through the summer) we're
a bit saturated.

Paul

On Fri, 16 Jul 2010, nek5000-users at lists.mcs.anl.gov wrote:

> Oh ok.
>
> Let's say that I leave one inlet as 'v ', but then change the other
> inlet to some other variable 'v1 ' or 'X ' or whatever. Would this be
> ok, without interfering with other routines?
>
> I suppose where this discussion is heading is: What is the possibility
> of adding a recycling boundary condition explicity in Nek, such that
> you can apply it like any other boundary condition, say R for example.
> So, in the routine you now search for this recycling flag 'R', and
> then run through the setup, rescale etc...?
>
> -Michael
>
> ----- Original Message -----
> From: nek5000-users at lists.mcs.anl.gov
> To: nek5000-users at lists.mcs.anl.gov
> Sent: Friday, July 16, 2010 4:47:11 PM GMT -06:00 US/Canada Central
> Subject: Re: [Nek5000-users] New Recycling BC based on interpolation
>
>
> Hi Michael,
>
> Use whatever discrimination you like --- I would not suggest
> modifying the character bcs, however, save that you can enter
> values in bc(k,f,e,1) for k > 1, for any cbc(f,e,1) = 'v '
>
> The reason for this is that nek checks explicitly for cbc='v '
> (v, followed by two spaces) in many locations.
>
> The correct place for discriminating parameters is in the
> arracy bc().
>
> Normally I discriminate by geometry --- e.g., x < x0, or
> something similar, occasionally involving the unit normals on
> the face in question - as that can be a stronger discriminator.
>
> Paul
>
>
> On Fri, 16 Jul 2010, nek5000-users at lists.mcs.anl.gov wrote:
>
>> Hi Aleks,
>>
>> Thank you very much for looking into this. I already have a question; I noticed that you marked several notes dealing with "RBC single inlet -- modify for other cases". I am assuming this means that you have one inlet that you want to recycle, but another inlet that you do not want to recycle, which just happens to be my case.
>>
>> Can I distinguish in the rea between the two by "v1 " and "v2 " without giving genmap any problems, and then modify the checks in the usr file accordingly? Also, the subroutine rescale_inflow mentions to modify for multiple inlets as well but I do not see where any modification could/needs to be done for it.
>>
>> - Michael
>>
>> ----- Original Message -----
>> From: nek5000-users at lists.mcs.anl.gov
>> To: nek5000-users at lists.mcs.anl.gov
>> Sent: Friday, July 16, 2010 3:03:52 PM GMT -06:00 US/Canada Central
>> Subject: [Nek5000-users] New Recycling BC based on interpolation
>>
>> Hi Michael and Markus,
>>
>> Here is a test case for an unsteady pipe flow with Michael's GambitPipe.rea file which sets inlet Recycling BCs based on interpolation from a cross-section downstream that you specify by a multiple of the inlet normal:
>>
>> http://www.mcs.anl.gov/~obabko/z4.tgz
>>
>>
>> Let me know if you have any questions.
>> Best,
>> Aleks
>>
>>
>>
>>
>> ----- Original Message -----
>> From: nek5000-users at lists.mcs.anl.gov
>> To: nek5000-users at lists.mcs.anl.gov
>> Sent: Thursday, July 8, 2010 5:06:48 PM GMT -06:00 US/Canada Central
>> Subject: Re: [Nek5000-users] New Recycling BC method?
>>
>>
>>
>>
>>
>> No worries, just checkin in to see how it was going, thanks for the update! Look forward to trying it out!
>>
>>
>>
>> - Michael
>>
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