[Nek5000-users] proj_ortho error in pipe flow

Fri Apr 7 12:54:32 CDT 2017

Hi Steffen,

It looks like your solution is hitting a steady-state condition and that the
projection onto prior solutions is thus projecting in to a set of linearly-dependent
vectors.

In principle, the code is supposed to correct for this condition but apparently
it is not doing so correctly.

I see you're running at Re > 5000, so presumably you are interested in turbulence,
rather than laminar steady state.   I would recommend adding a random perturbation
to the initial condition or, better still, adding something with bound vorticity near the
walls that will get stretched and bring about a more rapid transition.

I find that something like the attached works well with channel flow (snap through within
about 10 convective time units).  I was disappointed that it didn't work as well with pipe
flow, where I had to go up to Re=40k to get the thing started and then bring it down.
I assume this has something to do with the lack of linear transition in Hagen-Poiseuille flow.
If you find a better mechanism to speed transition, I'd be interested to find out about it.

Best,

Paul

________________________________________
From: nek5000-users-bounces at lists.mcs.anl.gov [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
Sent: Friday, April 07, 2017 10:18 AM
To: nek5000-users at lists.mcs.anl.gov
Subject: [Nek5000-users] proj_ortho error in pipe flow

Dear Nek users,

I am running a simple pipe flow on a Cray XC40 (Hazel Hen). After 32
steps, I get this problem (see attachment for complete logfile):

Step     32, t= 3.2000000E-02, DT= 1.0000000E-03, C=  0.025 3.2660E-01
1.0526E-02
              Solving for fluid
          32  Project velx           6.6444E-09   2.4759E-09
2.6836E+00   8   0
          32  Hmholtz velx       1   3.9238E-09   6.7918E-07 1.0000E-08
          32  Project vely           6.8730E-09   2.1046E-09
3.2656E+00   8   0
          32  Hmholtz vely       1   3.6166E-09   5.9974E-07 1.0000E-08
          32  Project velz           5.2396E-03   2.5121E-06
2.0858E+03   8   0
          32  Hmholtz velz       3   7.6028E-10   9.3795E-04 1.0000E-08
        32proj_ortho:    2   8 velz   Detect rank deficiency: NaN
1.0000E+00
        32proj_ortho:    1   8 velz   Detect rank deficiency: NaN
1.0000E+00
          32  U-PRES gmres      29   9.9376E-09   5.2213E-04
1.0000E-08   8.7926E-03   1.7780E-02
           32  DNORM, DIVEX  2.704668739973178E-005 9.937641774554489E-009
       32 0.3200000E-01  1.61568E-01  6.88948E-05  7.85330E-01
7.85399E-01 volflow Z
          32  Fluid done  3.2000E-02  2.4042E-02

In the next step I get CFL, CTarg! and the simulation exits.

This problem does neither show up on my local machine nor on another
smaller cluster. Moreover, when I set either parameter 94 or 95 to 0, I
do not see this error. It only appears when p94 and p95 are both unequal
0. In my case I set them to 9.

Do you know what might be causing this issue and how to solve it for the
Cray XC40 system?

Best Regards
Steffen
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