[Nek5000-users] proj_ortho error in pipe flow

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

Hi Steffen,
which revision of the code are you using? Is the initial field you are 
using already turbulent, or are you going through transition? Any 
special reason why you have 9 for p94/95?

Philipp

On 2017-04-07 19:54, nek5000-users at lists.mcs.anl.gov wrote:
>
> 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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