[Nek5000-users] 2 and a half dimentions with nekton?

[nek5000-users at lists.mcs.anl.gov]

Dear Antonios,


Your suggestion to use two perturbation modes to represent
the real and imaginary parts is an excellent one - I think
you could code this in a fairly std way, particularly if you
are not using the characteristics time stepping (i.e., if you
are using the BDF/EXT scheme, which is standard).  In that case,
one would only need to add to ffx and ffy the additional
terms associated with the interactions of the sin/cosine
terms.   The timestepper treats ffx and ffy w/ exactly the
same extrapolation as the nonlinear terms, so everything should
go through w/o much effort.

Best regards,

Paul


On Thu, 1 Apr 2010, nek5000-users at lists.mcs.anl.gov wrote:

> Dear Paul & Stefar,
>
> One question: In the case of the perturbation mode if one has a base
> flow with one homogeneous direction the perturbation equation for three
> dimensional disturbances (perturbation fields) can be solved in Fourier
> space with one fourier mode in that direction and then only one point is
> necessary instead of 3 X N (the polynomial order) and it becomes as
> expensive as a 2D simulation. I wonder if a feature like that exists in
> the current version of the code or maybe in an older one.
>
> hint(?) : Maybe one could use two separate perturbation fields to store
> the "real" and "imaginary" part of the perturbation.
>
>
> Regards & happy Easter!
> Antonios
>
> ps: This procedure is often termed 2.5D, hence the subject text.
>
> -- 
> ---------------------------------------------------------------------------------------------
> Antonios Monokrousos
> Department of Mechanics                 email:    antonios at mech.kth.se
> Royal Institute of Technology (KTH)     phone:    +46 8 790 68 76
> Osquars Backe 18                        telefax:  +46 8 796 98 50
> SE-100 44 Stockholm, SWEDEN
>
>
>
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