[Nek5000-users] perturbation mode

[Paul Fischer]

Hi Antonios,

I think it would work if you were to simply comment out
the call to "call fluid" in drive1.f and then run your
perturbation simulation.

Do you have a small test case on which you can try this?

I'll also try to make a small test here, but unfortunately
am very busy with visitors this week.

Paul



On Mon, 18 May 2009, Antonios Monokrousos wrote:

> 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
>