[Nek5000-users] Nek5000-users Digest, Vol 56, Issue 27
nek5000-users at lists.mcs.anl.gov
nek5000-users at lists.mcs.anl.gov
Thu Oct 24 07:31:40 CDT 2013
Hi Vincent,
You simply need to fill userdiv... typically this would be done
in userchk.
grep div */*usr from the /examples directory would illustrate
some use cases.
It'd be a good idea to run a few tests to make certain it's
working in the way that you think it should.
Paul
----- Original Message -----
From: nek5000-users at lists.mcs.anl.gov
To: nek5000-users at lists.mcs.anl.gov
Sent: Thursday, October 24, 2013 6:32:17 AM
Subject: Re: [Nek5000-users] Nek5000-users Digest, Vol 56, Issue 27
Hi Paul,
Thank you very much for your answer.
It should be okay with the forcing term and the param(107) flag for most
of what I want to do. By the way in the equations I wrote yesterday
(divergence + momentum) I forgot the pressure gradient in the momentum
equations, i.e. dphat/dx, dphat/dy and k*phat for the x, y and z
components respectively.
One difficulty that I did not mention yesterday is that although I want
to use a 2D mesh, I need to compute the third velocity component like if
I was in 3D. But I guess I can do that by adding a passive scalar to
play that role since the equation for the third velocity component is of
the diffusion/convection type (with the pressure gradient term though
but I can add that through the forcing).
However the problem that remains is for the divergence operator which
reads (d/dx, d/dy, k) in 3D while it is only (d/dx, d/dy) in 2D, so the
k*what term is missing if I run 2D simulations. How can I add the k term
there ?
I have seen that there is the possibility of a user defined divergence
operator in navier4.f but I don't see how to use it ?
Thanks again,
Vincent.
Le 24/10/2013 03:37, nek5000-users-request at lists.mcs.anl.gov a écrit :
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> Today's Topics:
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> 1. 2D simulation for 3D perturbation mode with a 2D baseflow
> (nek5000-users at lists.mcs.anl.gov)
> 2. Re: 2D simulation for 3D perturbation mode with a 2D baseflow
> (nek5000-users at lists.mcs.anl.gov)
> 3. Re: Extruding 2D .fld file to 3D (nek5000-users at lists.mcs.anl.gov)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 23 Oct 2013 19:06:13 +0200
> From: nek5000-users at lists.mcs.anl.gov
> To: nek5000-users at lists.mcs.anl.gov
> Subject: [Nek5000-users] 2D simulation for 3D perturbation mode with a
> 2D baseflow
> Message-ID:
> <mailman.3484.1382547977.3278.nek5000-users at lists.mcs.anl.gov>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> Hi Neks,
>
> I have a 2D baseflow and I am doing 3D perturbation mode calculation at
> a prescribed spatial wavelength lambda=2pi/k (k the wavenumber) in the
> third direction. The baseflow is assumed to be invariant in this third
> direction therefore the perturbation can be chosen in the form
> u=uhat(x,y,t) e(ikz) where z is the third direction and u=(u,v,w) and
> the baseflow is in the form (U,V)(x,y) (in particular W=0).
>
> In this case the 3D linearized equations simplify to the following form
> duhat/dx+dvhat/dy+kwhat=0
> duhat/dt + U duhat/dx + V duhat/dy = -uhat dU/dx - vhat dU/dy + nu (
> d^2uhat/dxx+d^2uhat/dyy-k^2uhat )
> dvhat/dt + U dvhat/dx + V dvhat/dy = -uhat dV/dx - vhat dV/dy + nu (
> d^2vhat/dxx+d^2vhat/dyy-k^2vhat )
> dwhat/dt + U dwhat/dx + V dwhat/dy = nu ( d^2what/dxx+d^2what/dyy-k^2what )
>
> I am currently doing 3D perturbation simulations with the box dimension
> in the third dimension set to lambda but I was wondering if Nek offers
> the possibility to run 2D simulations instead to solve for uhat(x,y,t).
>
> Indeed in the above equations, one does not need any mesh in the z
> direction. A 2D mesh is enough but this means modifying slightly the
> linearized equations to insert the k terms.
>
> I have been looking in the source files and I have found nothing like
> that so I guess this is not currently in Nek.
> Any idea if that would be possible/easy to implement?
>
> Thanks a lot,
>
> Vincent.
>
>
>
>
> ------------------------------
>
> Message: 2
> Date: Wed, 23 Oct 2013 19:39:49 -0500 (CDT)
> From: nek5000-users at lists.mcs.anl.gov
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] 2D simulation for 3D perturbation mode
> with a 2D baseflow
> Message-ID:
> <mailman.3537.1382575189.3278.nek5000-users at lists.mcs.anl.gov>
> Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
>
>
> Hi Vincent,
>
> Yes - this should be easy to implement.
>
> For one thing, you have the option of inserting any forcing
> in the rhs via ffx and ffy.
>
> I've only glanced at the equations but am certain that they
> can be inserted.
>
> If it's an additional part that should be treated implicitly
> in the Helmholtz solve there is a flag for that as well. If
> the multiplier is constant (w.r.t. space) then you can set
> that term using param(107).
>
> Paul
>
>
> On Wed, 23 Oct 2013, nek5000-users at lists.mcs.anl.gov wrote:
>
>> Hi Neks,
>>
>> I have a 2D baseflow and I am doing 3D perturbation mode calculation at a
>> prescribed spatial wavelength lambda=2pi/k (k the wavenumber) in the third
>> direction. The baseflow is assumed to be invariant in this third direction
>> therefore the perturbation can be chosen in the form u=uhat(x,y,t) e(ikz)
>> where z is the third direction and u=(u,v,w) and the baseflow is in the form
>> (U,V)(x,y) (in particular W=0).
>>
>> In this case the 3D linearized equations simplify to the following form
>> duhat/dx+dvhat/dy+kwhat=0
>> duhat/dt + U duhat/dx + V duhat/dy = -uhat dU/dx - vhat dU/dy + nu (
>> d^2uhat/dxx+d^2uhat/dyy-k^2uhat )
>> dvhat/dt + U dvhat/dx + V dvhat/dy = -uhat dV/dx - vhat dV/dy + nu (
>> d^2vhat/dxx+d^2vhat/dyy-k^2vhat )
>> dwhat/dt + U dwhat/dx + V dwhat/dy = nu ( d^2what/dxx+d^2what/dyy-k^2what )
>>
>> I am currently doing 3D perturbation simulations with the box dimension in
>> the third dimension set to lambda but I was wondering if Nek offers the
>> possibility to run 2D simulations instead to solve for uhat(x,y,t).
>>
>> Indeed in the above equations, one does not need any mesh in the z direction.
>> A 2D mesh is enough but this means modifying slightly the linearized
>> equations to insert the k terms.
>>
>> I have been looking in the source files and I have found nothing like that so
>> I guess this is not currently in Nek.
>> Any idea if that would be possible/easy to implement?
>>
>> Thanks a lot,
>>
>> Vincent.
>>
>>
>> _______________________________________________
>> Nek5000-users mailing list
>> Nek5000-users at lists.mcs.anl.gov
>> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>>
>
> ------------------------------
>
> Message: 3
> Date: Wed, 23 Oct 2013 19:52:45 -0500 (CDT)
> From: nek5000-users at lists.mcs.anl.gov
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] Extruding 2D .fld file to 3D
> Message-ID:
> <mailman.3546.1382578645.3278.nek5000-users at lists.mcs.anl.gov>
> Content-Type: text/plain; charset="x-unknown"; Format="flowed"
>
>
> Hi Holly,
>
>
> I would likely do this in usrdat2().
>
> Suppose my 2D problem had 70 elements. The the following
> should work:
>
> In SIZE, set lelx=70,lely=1, and lelz=# of levels in your extruded geometry.
>
> In usrdat2() in the .usr file, set nelx=lelx,nely=lely,nelz=lelz.
>
> Then:
> parameter (l2d=lx1*ly1*lelx) ! Number of points in 2D field
> common /mystuff/ u2d(l2d),v2d(l2d)
>
> if (nid.eq.0) then
> open(33,file='my2dfile.dat')
> do i=1,l2d
> read(33,*) u2d(i),v2d(i)
> enddo
> close(33)
> endif
> nbytes = 8*l2d
> call bcast(u2d,nbytes)
> call bcast(v2d,nbytes)
>
> Once you load your 2D data you can use
>
> call z_average_transpose(vx,u2d)
> call z_average_transpose(vy,v2d)
>
> to map this to 3D.
>
> After that, I would just dump the 3D results and exit:
>
> call outpost(vx,vy,vz,pr,t,' ')
> call exitti('Quit in usrdat2.$',nelgt)
>
> This _should_ work, but probably needs a couple iterations
> to get everything correct.
>
> To generate myfile2d.dat, I would do the following:
>
> 1) Run the 2D code and dump an ascii .fld file by setting
> param(66)=0 in usrdat2 or userchk prior to output the fld file.
>
> 2) Edit the resultant .fld file and get rid of the first few
> line at the top of that file so that your u,v data is all
> that it holds. (Look both at the top and bottom of the file
> when you're ready -- they should have the same column format.)
>
>
> Hope this helps.
>
> Paul
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