HI Matt,

As Abishek has suggested finding 20 modes is very challenging since there is pollution from the leading modes which makes converging this type of problem very difficult. In an ideal world you could shift the problem to a local region around the 20th eigenvalue but not sure that is currently setup for the adjoint mode. It might be possible with the coupled solvers on the forward problem.

Cheers,
Spencer.


On 13 Mar 2022, at 23:48, Abhishek Kumar <abhishek.kir@gmail.com> wrote:

Dear Matt,

I think waiting for 20 modes with the Arnoldi method is too much. I suggest seeking one mode and keeping the Krylov space of 16. You can do something like following :

          <P> kdim          = 16        </P>
          <P> nvec          = 1         </P>
          <P> nits          = 500       </P>
          <P> evtol         = 1e-06     </P>

With regards
Abhishek 

---------------------------------------------------------------------------------------
Abhishek Kumar
Assistant Professor (Research)
Centre for Fluid and Complex Systems
Coventry University, Coventry CV15FB, UK
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On Sun, Mar 13, 2022 at 10:18 PM Matt Duran <matt.duran60@gmail.com> wrote:
This email from matt.duran60@gmail.com originates from outside Imperial. Do not click on links and attachments unless you recognise the sender. If you trust the sender, add them to your safe senders list to disable email stamping for this address.
 
Hello Nektar++ community,

 

I recently have been running an adjoint stability simulation and am interested in the vortex shedding mode.

 

From the Strouhal number found in the literature I know the eigenmode of interest is the one highlighted below with a magnitude of 0.97 and a frequency of 0.731.

 

<image.png><image.png>

I have tried using a Krylov space of 40 and instructing Nektar to wait for the 20 modes with the highest magnitude to converge but I have no luck in getting the specific mode of interest to converge.

 

I was wondering whether there was some way I could narrow down the convergence criteria so the specific mode I need will converge, rather than these other 20 modes I’m getting. I have tried to also converge modes by the highest imaginary part but I can’t seem to get the specific mode I need.

 

 

Thank you,
Matt Duran
PhD student
University of Central Florida
 

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