[Nek5000-users] proj_ortho error in pipe flow

Mon Apr 10 07:32:33 CDT 2017

Hi Paul & Philipp,

thanks for your quick replies and suggestions. I started the simulation 
again with a slightly perturbed laminar flow field as initial conditions 
and there are no proj_ortho errors anymore.
For now, this perturbation is more or less random and probably not ideal 
for tripping the laminar flow to turbulence. Therefore, I might try to 
implement a more effective numerical tripping method in the future. I 
can let you know when (and if) I succeed.

The parameters p94 and p95 are set to "9" just because I have found that 
in another simulation somewhere. Do you suggest trying different values 
here?
The Nek5000 version was downloaded as a zip file on 21/03/2017 so I 
suppose it is the commit 95b42f08c960d522679e0f0881d284ec841ae09

\Steffen

On 09/04/17 19:00, nek5000-users-request at lists.mcs.anl.gov wrote:
> Message: 1
> Date: Sat, 8 Apr 2017 19:55:36 +0200
> From: nek5000-users at lists.mcs.anl.gov
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] proj_ortho error in pipe flow
> Message-ID:
> 	<mailman.4792.1491674149.2967.nek5000-users at lists.mcs.anl.gov>
> Content-Type: text/plain; charset=windows-1252; format=flowed
>
> 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
>>
>>
>>
>> _______________________________________________
>> Nek5000-users mailing list
>> Nek5000-users at lists.mcs.anl.gov
>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>>
>>