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<div class="moz-cite-prefix">Hi,</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">What is your time step? I calculated
the spectrum of the cylinder flow a while ago at Re=44 and I got
an angular frequency of 0.7278, which corresponds to a period of
8.63.<br>
</div>
<div class="moz-cite-prefix">It is possible that 40 time steps per
Arnoldi iteration is too small; a good start is to integrate for
1/10th of the period, so dt*p109 = 0.8 approximately. I used 120
time steps at dt=4.2e-3 but it may be faster with more steps.<br>
</div>
<div class="moz-cite-prefix">It depends on which frequencies you
want to resolve; if you integrate for a short time your operator
is close to identity and all eigenvalues are close to 1, but if
you integrate for too long then the frequencies of the eigenvalues
you are interested in will be aliased.</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">I think you could try decreasing p021
and p022 to maybe 1e-10 or 1e-12 and see if helps, too.<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">Best,</div>
<div class="moz-cite-prefix">Guillaume<br>
</div>
<div class="moz-cite-prefix"><br>
</div>
<div class="moz-cite-prefix">On 03/10/2018 07:24,
<a class="moz-txt-link-abbreviated" href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a> wrote:<br>
</div>
<blockquote type="cite"
cite="mid:mailman.11962.1538547898.86639.nek5000-users@lists.mcs.anl.gov">
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<div dir="ltr"><span class="gmail-im"
style="color:rgb(80,0,80)">Hi Guillaume,
<div><br>
</div>
<div>Thanks for your reply. My reply to your
queries is as below:-</div>
<div><br>
</div>
</span>
<div>1) I am getting unstable pair of Eigen values
with growth rate around 0.02.</div>
<span class="gmail-im" style="color:rgb(80,0,80)">
<div>2) Solver tolerance that I used are ;</div>
<div>
<div> 7.00000 p020 NORDER</div>
<div> 0.100000E-09 p021 DIVERGENCE</div>
<div> 0.100000E-09. p022 HELMHOLTZ</div>
<div> 0.00000 p023 NPSCAL</div>
<div> 0.100000E-09 p024 TOLREL</div>
<div> 0.100000E-04 p025 TOLABS</div>
</div>
</span>
<div>1.00000E-05. p113 : ARNOLDI: arpack
tolerance</div>
<div><br>
</div>
<div><br>
</div>
<div>3) Boundary conditions are :</div>
<div><br>
</div>
<div>I am using sponge strength at inlet and outlet
with following details in .rea file</div>
<div>
<div> 1.00000 p119 : SPONGE STRENGTH</div>
<div> 25.0000 p120 : SPONGE TOTAL WIDTH</div>
<div> 3.00000 p121 : SPONGE DROP WIDTH
(INFLOW)</div>
<div> 5.00000 p122 : SPONGE RISE WIDTH
(OUTFLOW) </div>
</div>
<div>the sponge function and its cal is detailed in
userf subroutine of .usr file</div>
<div><br>
</div>
<div>Also following is defined in .usr file</div>
<div>
<div>c-----------------------------------------------------------------------</div>
<div> subroutine userbc (ix,iy,iz,iside,eg)</div>
<div><br>
</div>
<div> include 'SIZE'</div>
<div> include 'NEKUSE' ! UX, UY, UZ,
TEMP, X, Y</div>
<div> include 'PARALLEL' ! GLLEL</div>
<div><br>
</div>
<div><br>
</div>
<div> integer e,eg</div>
<div><br>
</div>
<div>c velocity</div>
<div>c e = GLLEL(eg)</div>
<div> UX = 0.0</div>
<div> UY = 0.0</div>
<div> UZ = 0.0</div>
<div><br>
</div>
<div>c t</div>
<div> TEMP=0.0</div>
<div><br>
</div>
<div> return</div>
<div> end</div>
<div>c-----------------------------------------------------------------------</div>
<div> subroutine useric (ix,iy,iz,ieg)</div>
<div><br>
</div>
<div> include 'SIZE'</div>
<div> include 'NEKUSE' ! UX, UY, UZ,
TEMP, Z</div>
<div> </div>
<div> integer idum</div>
<div> save idum </div>
<div> data idum / 0 /</div>
<div><br>
</div>
<div> real eps</div>
<div><br>
</div>
<div> if (idum.eq.0) idum = 99 + nid</div>
<div> eps = 0.1</div>
<div><br>
</div>
<div>c velocity</div>
<div>c random distribution</div>
<div> UX = eps*(ran1(idum)-0.50)</div>
<div> UY = eps*(ran1(idum)-0.50)</div>
<div> UZ = eps*(ran1(idum)-0.50)</div>
<div><br>
</div>
<div>c t</div>
<div> TEMP=0</div>
<div><br>
</div>
<div> return</div>
<div> end</div>
</div>
<div><br>
</div>
<div><br>
</div>
<div>
<div>40.0000 p109 : ARNOLDI: frequency of
calling arn_solve</div>
<div> 4.00000 p110 : ARNOLDI: maximal number
of arnoldi cycles</div>
<div> 90.0000 p111 : ARNOLDI: size of Krylov
space</div>
<div> 30.0000 p112 : ARNOLDI: number of
eigenvectors</div>
</div>
<div><br>
</div>
<div><br>
</div>
<div>If I am increasing the Krylov subspace then
will I get Eigen values at lesser restart ?</div>
<div><br>
</div>
<div>Kindly help please as I am new to this. Thanks
in advance.</div>
<div><br>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">
<div dir="ltr">
<div>
<div dir="ltr">Alok Mishra
<div>Research Scholar </div>
<div>Computational Propulsion Lab </div>
<div>Aerospace Department IIT Kanpur</div>
<div>+91-8795844555</div>
</div>
</div>
</div>
</div>
</div>
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