[Nek5000-users] Problem in obtaining eigenvalues through Arnoldi (using NEK5000 with the ARPACK library)

nek5000-users at lists.mcs.anl.gov nek5000-users at lists.mcs.anl.gov
Fri Jul 13 05:00:28 CDT 2018


Hi Adam,
Thanks for your reply.


 0.100000E-09 p021 DIVERGENCE
  0.100000E-09 p022 HELMHOLTZ
  0.100000E-09 p024 TOLREL
  0.100000E-04 p025 TOLABS
  1.00000E-06 p113 : ARNOLDI: arpack tolerance
Number of mesh element for entire domain is 1200.
 The resolution in cylinder vicinity


On Thu, Jul 12, 2018 at 9:41 PM, <nek5000-users at lists.mcs.anl.gov> wrote:

> Hi;
> What is your tolerance for eigenvalue convergence? I'm unable to answer
> your question directly, as there can be number of problems. One of the
> obvious ones could be mesh resolution. You have pretty big mesh. What is
> the resolution in cylinder vicinity? What is the polynomial order? You have
> number of eigenvalues converged to machine accuracy and a few of the order
> 10**-4 in between. Those could be some spurious modes related to
> insufficient resolution.  What is your Reynolds number?
> Regards
> Adam
>
>
> On 12/07/18 10:07, nek5000-users at lists.mcs.anl.gov wrote:
>
> Hi Neks
>
>     I am running a 3D simulation for a flow over a cylinder. My domain
> size for simulation is 100Dx100D. where D is the diameter of a cylinder. We
> have obtained the base flow through SFD. The base flow is used to calculate
> the stability analysis through NEK5000 with the ARPACK library (Implemented
> by A.  Peplinski).
>
> we have used the following parameters.....
>
>   90.0000     p111 : ARNOLDI: size of Krylov space
>    30.0000     p112 : ARNOLDI: number of eigenvectors
>
> We have run the Arnoldi with restart but we are not able to get the output
> file (eigenvalues.txt and egvext_cyl0.f0..) even after almost 20 restarts.
> Also, we tried to run with increasing the size of Krylov space but the
> eigenvalues are not converging.
>
> The log file shows no changes in converged ritz values after around 20-22
> values.
>
> The part of the log file is shown below...........
>
> Kindly,  help me out and let me know where I am going wrong.....
>
> Alok Mishra
>
>
>
> ------------------------------------------------------------
> ---------------------------------------------------
>
> ARNOLDI: after  520 stepper phase
>
>  _naup2: Corresponding B-norm of the residual
>  --------------------------------------------
>     1 -    1:   6.623D-01
>
>
>  _naup2: no. of "converged" Ritz values at this iter.
>  ----------------------------------------------------
>     1 -    1:    22
>
>
>  _naup2: NEV and NP are
>  ----------------------
>     1 -    2:    52   128
>
>
>  _naup2: "wanted" Ritz values -- real part
>  -----------------------------------------
>     1 -    5:   9.905D-01   9.905D-01   9.854D-01   9.854D-01   9.855D-01
>     6 -   10:   9.855D-01   9.897D-01   9.897D-01   9.924D-01   9.930D-01
>    11 -   15:   9.930D-01   9.905D-01   9.905D-01   9.943D-01   9.943D-01
>    16 -   20:   9.938D-01   9.938D-01   9.948D-01   9.948D-01   9.949D-01
>    21 -   25:   9.949D-01   9.951D-01   9.958D-01   9.960D-01   9.962D-01
>    26 -   30:   9.962D-01   9.966D-01   9.970D-01   9.970D-01   9.969D-01
>    31 -   35:   9.969D-01   9.973D-01   9.974D-01   9.975D-01   9.976D-01
>    36 -   40:   9.976D-01   9.971D-01   9.971D-01   9.978D-01   9.979D-01
>    41 -   45:   9.979D-01   9.982D-01   9.982D-01   1.000D+00   9.908D-01
>    46 -   50:   9.908D-01   1.004D+00   1.004D+00   1.005D+00   1.005D+00
>    51 -   52:   1.006D+00   1.006D+00
>
>
>  _naup2: "wanted" Ritz values -- imag part
>  -----------------------------------------
>     1 -    5:   5.038D-02  -5.038D-02  -1.127D-01   1.127D-01  -1.119D-01
>     6 -   10:   1.119D-01   6.954D-02  -6.954D-02   0.000D+00   3.705D-03
>    11 -   15:  -3.705D-03  -7.103D-02   7.103D-02  -9.233D-04   9.233D-04
>    16 -   20:   4.345D-02  -4.345D-02   6.799D-04  -6.799D-04  -1.821D-02
>    21 -   25:   1.821D-02   0.000D+00   0.000D+00   0.000D+00  -2.047D-03
>    26 -   30:   2.047D-03   0.000D+00   7.200D-05  -7.200D-05   2.386D-02
>    31 -   35:  -2.386D-02   0.000D+00   0.000D+00   0.000D+00  -1.140D-04
>    36 -   40:   1.140D-04   3.125D-02  -3.125D-02   0.000D+00  -1.248D-04
>    41 -   45:   1.248D-04  -1.673D-03   1.673D-03   0.000D+00  -1.508D-01
>    46 -   50:   1.508D-01  -1.863D-02   1.863D-02  -2.109D-02   2.109D-02
>    51 -   52:  -1.152D-02   1.152D-02
>
>
>  _naup2: Ritz estimates of the "wanted" values
>  ----------------------------------------------
>     1 -    5:   3.315D-02   3.315D-02   3.244D-05   3.244D-05   7.035D-05
>     6 -   10:   7.035D-05   6.072D-11   6.072D-11   1.314D-02   2.772D-06
>    11 -   15:   2.772D-06   6.796D-15   6.796D-15   9.719D-04   9.719D-04
>    16 -   20:   7.467D-17   7.467D-17   5.506D-04   5.506D-04   2.437D-16
>    21 -   25:   2.437D-16   2.977D-03   7.238D-04   6.054D-04   3.914D-11
>    26 -   30:   3.914D-11   1.827D-04   1.138D-04   1.138D-04   1.048D-16
>    31 -   35:   1.048D-16   1.198D-04   6.358D-05   3.013D-05   3.490D-07
>    36 -   40:   3.490D-07   9.960D-18   9.960D-18   1.340D-07   2.518D-10
>    41 -   45:   2.518D-10   1.827D-16   1.827D-16   1.781D-16   7.278D-17
>    46 -   50:   7.278D-17   0.000D+00   0.000D+00   0.000D+00   0.000D+00
>    51 -   52:   0.000D+00   0.000D+00
>
>  Reached max iteration number; settingido=-2 for checkpointing.
>  ARNOLDI:
>  IDOARP  =           -2
>  Writing checkpoint
>        0      40 OPEN: ARPm11800.f00002
>        0      40 OPEN: ARVm11800.f00002
>
>        40  2.0000E-01 done :: Write checkpoint
>                               file size =     621.E+00MB
>                               avg data-throughput =   624.1MB/s
>                               io-nodes =     1
>
>
>  ARNOLDI: finalize
>     Number of stepper cycles            520
>     Time spent in ARNOLDI         60.3302609920502
>     Average stepper phase time    10.9141681075096
>  call outfld: ifpsco: F
>
>        40  2.0000E-01 Write checkpoint:
>        0      40 OPEN: m11800.f00001
>
>        40  2.0000E-01 done :: Write checkpoint
>                               file size =      4.0    MB
>                               avg data-throughput =   303.2MB/s
>                               io-nodes =     1
>
>
> end of time-step loop
>
>
>
>
>
>
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>
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-- 
Alok Mishra
Research Scholar
Computational Propulsion Lab
Aerospace Department IIT Kanpur
+91-8795844555
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