[Nek5000-users] perturbation mode

[Antonios Monokrousos]

Hi Paul,
Thank you for you answer. As I see it the best it to have a switch to
deactivate the solver for the base flow. This would make the computation
cheaper. Is that implemented? Can one just add an if statement in the
nek_solve subroutine of the form:

----------------------------------------
if(jp.ne.0) then
   call nek_advance
   call prepost (.false.,'his')
    ...
    ...
end if	
----------------------------------------

Would something like that work?

Antonios



Paul Fischer wrote:
> 
> Hi Antonios,
> 
> I'll look into this.
> 
> One key thing is that the perturbation code is designed
> to solve for perturbations about an evolving base flow,
> so that one can compute Lyapunov exponents....
> 
> You should be able to override this by continually resetting
> the base flow to the desired steady state base flow.
> 
> We could also likely modify the code to work in the mode
> that you desire (i.e., by simply turning off the evolution
> of the base flow).
> 
> Paul
> 
> 
> On Fri, 15 May 2009, Antonios Monokrousos wrote:
> 
>> Hello!
>> I have a question about the pertubation mode of the code.
>>
>> First I computed the base flow using the full non-linear solver and
>> letting it run until I get a steady solution. This worked fine.
>> Then I construct a perturbation which I add on the steady solution I got
>> before (base flow) with a very small amplitude, around 0.1%. The
>> solution, after I subtract the base flow looks good. (I'm comparing to a
>> different code).
>>
>> Next I try to use perturbation mode since I want to use the exact
>> linearised Navier-Stokes and the problems appear.
>> I have the base flow and the perturbation in two different restart
>> files, which I specify in .rea file like this:
>> ------------------------------------------------------
>>            2 PRESOLVE/RESTART OPTIONS  *****
>> meanflow.u
>> ic_pert_field.fld
>> ------------------------------------------------------
>> I activate the perturbation mode (option 31 in .rea).
>>
>> I damp both the solution of the base-flow and of the pertubation. I can
>> see that the code is solving for the base-flow (which it shouldn't) but
>> also has as initial condition the one that is supposed to be for the
>> The simulation blows-up after a few time steps.
>>
>> I'm not sure I use the perturbation mode in the right manner.
>> Thanks in advance for any feedback or help.
>> Antonios
>>
>>
>> -- 
>> ---------------------------------------------------------------------------------------------
>>
>> 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
>> _______________________________________________
>> Nek5000-users mailing list
>> Nek5000-users at lists.mcs.anl.gov
>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>>


-- 
---------------------------------------------------------------------------------------------
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