[Nek5000-users] Specifying boundary condition for Annulus Geometry in box file

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

Hi Ravi,

You are correct, for annulus geometry, the BC's used correspond to

r_0, r_nelr, theta0, theta1

You don't see theta0 and theta1 when the geometry is a full cylinder
(theta0=0 to theta1=1) since the theta edges will connect to one another
and essential be 'E  ' BC.  However, if you were working with a half or
quarter cylinder, these would be relevant and visible in prex.

Similarly, if you run genbox for a full cylinder and put a BC that is not
'E  ' or blank ('   ') for theta0 or theta1, genbox will put this BC in the
.rea file.  This could then result in an incorrect BC.

I can look at setting up a warning message within genbox for this situation.

Best,
Katie




On Fri, Mar 14, 2014 at 3:21 AM, <nek5000-users at lists.mcs.anl.gov> wrote:

> Hi Ravi,
>
> I came across this issue recently as well. I found that you are correct
> about the first and second BC. However, the third and the fourth, I do not
> know what they are. I tried to find it with prex, but nothing turns out.
>
> However, when I merged it with another mesh, it played a role, which
> modified the whole mesh BC, so I have a bad global BC. I do not see where
> is the problem. I think there is some isssue with pretex.
>
> Cheers,
>
> Tubois
>
> On Fri, Mar 14, 2014 at 2:43 AM, <nek5000-users at lists.mcs.anl.gov> wrote:
>
>> Hi All,
>>
>> We are trying to build a mesh to simulate external cylinder flow, similar
>> to the one given in the example "ext_cyl". Searching though the
>> documentation, we understand that it is possible to generate several boxes
>> of mesh using genbox and combine using pretex to get the final mesh.
>>
>> We are having difficulty in interpreting the boundary condition (BC)
>> strings in the input to files to genbox. It is clear for a rectangular box,
>> the BC string follows the order West, East, South, and North in 2D. What is
>> the analogous interpretation for a circular annulus geometry? such as for
>> the one defined by the box files given in "primer.pdf" (
>> http://www.mcs.anl.gov/~fischer/primer.pdf), which is repeated below:
>>
>> x2d.rea
>> 2 spatial dimension
>> 1 number of fields
>> #
>> # comments
>> #
>> #
>> #========================================================
>> #
>> Y         cYlinder
>> 3 -24 1     nelr,nel_theta,nelz
>> .5 .3         x0,y0 - center of cylinder
>> ccbb         descriptors: c-cyl, o-oct, b-box (1 character + space)
>> .5 .55 .7 .8     r0 r1 ... r_nelr
>> 0 1 1         theta0/2pi theta1/2pi ratio
>> v ,W ,E ,E ,     bc's (3 characters + comma)
>>
>>
>> Does "v" corresponds to BC at r0 and W correspond to BC at r_nelr in
>> r-direction and the two E's correspond to BC at theta0 and theta1?
>>
>> Thanks in advance for your help.
>>
>> Regards,
>> Ravi
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> --
>> Ravi Kumar T R
>>
>> University of Illinois at Urbana-Champaign
>> ph : +1 217 778 7538
>> http://lndvl.mechse.illinois.edu/
>>
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>
>
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