[Nek5000-users] boundary condition issue?

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

I check the first time step, the pressure is more or less correct. From the
second step, the singular point starts to show up.

I changed the Cartesian mesh of the example back, I have the same problem.
So the problem looks like to produced during the generation of the mesh
around the cylinder.

I used the import.rea from the ext_cyl example, so that I won't introduced
any other problem.
After several tests, I isolated the problem to two potential issues:
1, genbox to generate the mesh around cylinder, the script is below
2, prex, after importing the geometry and boundaries conditions, there is
only the boundary condition of the cylinder left, which I imposed as 'wall'
by using the script below

I feel that it is very probably caused by prex, but I do not see where is
the bug? I attached all scripts in the mail as well.

Thank you!

Tubois

pretex << EOF
new
   1 READ PREVIOUS PARAMETERS
box
   1 BUILD FROM FILE
box
  10 IMPORT MESH
toto
y Would you like to displace existing elements in box?
   1 END    ELEMENTS
   1 ACCEPT MATL,QVOL
   1 SET BCs
  11 SET ENTIRE LEVEL
   3 WALL
n Is this a lattice for hex-close-packed spheres?:
1 END  LEVEL
1 ACCEPT B.C.'s
1 EXIT
EOF
genmap << EOF
new
.1
EOF




import.rea
#========================================================
2             spatial dimension
1             number of fields
#
# comments
#
#
#========================================================
#
Y             cylinder
4 -40 1         nelr,nel_theta,nelz
.0 .0             x0,y0 - center of cylinder
cccbb             descriptors: c-cyl, o-oct, b-box (1 character + space)
.5 .6 .7 .8 1.          r0 r1 ... r_nelr
0 1 1             theta0/2pi theta1/2pi ratio
E  ,E  ,E  ,E  ,             bc's (3 characters + comma)






On Wed, Mar 5, 2014 at 7:29 PM, <nek5000-users at lists.mcs.anl.gov> wrote:

> Hi nek users,
>
> I am encountering a strange issue. Build on the example of cylinder flow,
> I write a matlab script to generate the Cartesian mesh and a genbox script
> to generate the mesh around the cylinder. When the domain is small, the
> code runs. When I increases the domain size and cell numbers, the
> calculation blows up after several steps?
>
> See the picture attached here, there is a singular point on the boundary
> for the pressure. But the velociy is ok, since I imposed a uniform flow for
> inlet and top bottom.
>
> It also sometimes shows another error, the problem size is too large, even
> I run them in 32 procs instead of 4 as usual.
>
> Here attached the output of nek.
>
> Does someone have an idea?
>
> Best regards
>
> Tubois
>
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>
>


-- 
Université Pierre et Marie Curie
CNRS-LIMSI
Campus d'Orsay
91403 ORSAY
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