[Nek5000-users] Infinite Prandtlnumber with Nek5000

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

Hi,
thanks for the advice. I found that one also has to comment the line
IF (.NOT.IFTRAN) NSTEPS=1
in setvar in drive2.f and use a fixed timestep so that the timeloop does 
not stop too soon.

Thanks again,
Jan

On 08/05/2015 02:30 PM, nek5000-users at lists.mcs.anl.gov wrote:
> Hello, Jan,
>
> We have in fact solved a similar problem as you face now. In our case, 
> we have steady Stokes equation at each time step,
> in the absence of time derivative and convection term. However we have 
> time-dependent volume forcing and boundary
> conditions, as we solve for fluid-structure interactions in the Stokes 
> regime.
>
> You only need to change the source code for one thing. By changing the 
> flags in the .rea file, you can easily turn
> off the two terms. However, the code only runs for 1 time step even if 
> you specify for example 10 total time steps, which makes sense
> as NEK realizes this is a steady problem. NEK5000 does not see that 
> the next time step, BCs and forcing will be changed, and so
> as the flow.
>
> So I remember I only commented two lines of the source code to achieve 
> this, in the file 'connect2.f', subroutine 'rdparam',
> this is what I have done (i am using a quite old version of the NEK, 
> so...)
>
>       IF (.NOT.IFTRAN) THEN
> c         PARAM(11) = 1.0 !lailai comment for steady stokes
> c         PARAM(12) = 1.0 !lailai comment for steady stokes
>          PARAM(19) = 0.0
>       ENDIF
>
> Of course you need to set the flags right in .rea file, which you can 
> find the details on the webpage. You also need to
> solve for heat equations to get T. Then in the userchk subroutine, you 
> calculate the T-dependent buoyancy forcing at each time step.
> Solve the flow with new forcing terms. This should be all manageable.
>
> cheers and good luck,
>
> lailai
>
>
>
> On 2015/8/5 12:15, nek5000-users at lists.mcs.anl.gov wrote:
>> Hi all,
>> I was wondering if it is possible to use Nek5000 for simulations in 
>> the infinite Prandtlnumber regime (e.g. planetary mantles). This 
>> would require to solve the NS Stokes equation without the time 
>> derivative and advection term and the heat equation for T:
>>
>> 1) Solve visc * laplace u - grad p + buoyancy = 0 and div u = 0, 
>> where bouyancy depends on a given T field and a Rayleigh number
>> 2) Update T by solving dT/dt + u grad T = diff * laplace T (+ other 
>> sources)
>> 3) go back to 1 with the new T field, repeat
>>
>> More realistic models would then use a varying viscosity.
>> I looked at the steady state example (kov_st_state), but this is 
>> missing the time depencence via the Temperature. Any hints on the 
>> possibility would be much appreciated.
>>
>> Thanks,
>> Jan
>>
>> _______________________________________________
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>> Nek5000-users at lists.mcs.anl.gov
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>
> -- 
> Lailai Zhu
> Laboratory of Fluid Mechanics and Instabilities LFMI
> EPFL STI IGM LFMI ME A2 408 (Bâtiment ME) Station 9
> CH-1015 Lausanne Switzerland
>
>
>
> _______________________________________________
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> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users

-- 
----------------------
Jan Vormann
Institut für Geophysik
Corrensstr. 24
D-48149 Münster

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