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

Thu Jul 12 11:11:05 CDT 2018

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
>
>
>
>
>
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/nek5000-users/attachments/20180712/1e80b52f/attachment-0001.html>