[Nek5000-users] Selective frequency damping

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

It indeed solved my problems.
Thanks a lot.

On 13 September 2011 16:56, <nek5000-users at lists.mcs.anl.gov> wrote:

> Hi Jean-Christophe,
>
> A couple of comments.
>
> 1). I would use declaration of arrays vxold,...,qxold,...,f_x,...
> similar to declaration of vx, vy,... in
>
> nek5_svn/trunk/nek/SOLN :
>
>
>   COMMON /VPTSOL/
> ...
>     $               , VX     (LX1,LY1,LZ1,LELV)
> ...
>
>
> 2). To set an array on velocity mesh to zero, please use
>
>      ntot = nx1*ny1*nz1*nelv
>      call rzero(vxold,ntot)
>
> instead of
>
>      vxold = 0.0D+00
>
>
> 3). You do need local element number for setting the forcing in userf,
> namely
>
>      e   = gllel(eg)
>      ffx = f_x(ix,iy,iz,e)
>
> Otherwise it will work correctly only on one core.
>
>
> Let me know if it helps.
> Best,
> Aleks
>
>
>
>
>
> On Tue, 13 Sep 2011, nek5000-users at lists.mcs.anl.**gov<nek5000-users at lists.mcs.anl.gov>wrote:
>
>  Hi Nek's,
>>
>> I've been trying to implement the selective frequency damping (Akervik E.,
>> Brandt L., Henningson D.S., Hoepffner J., Marxen O., Schlatter P. 2006.
>> *Steady
>> solutions of the Navier-Stokes equations by selective frequency
>> damping.*Physics of fluids
>> *18*) which enables to compute stationnary solution. Here is what I have
>> written in my .usr file:
>>
>> In userchk:
>>
>>      common /vxold/ vxold(size(vx,1),size(vx,2),**size(vx,3),size(vx,4))
>>      common /vyold/ vyold(size(vy,1),size(vy,2),**size(vy,3),size(vy,4))
>>      common /vzold/ vzold(size(vz,1),size(vz,2),**size(vz,3),size(vz,4))
>>
>>      common /qxold/ qxold(size(vx,1),size(vx,2),**size(vx,3),size(vx,4))
>>      common /qyold/ qyold(size(vy,1),size(vy,2),**size(vy,3),size(vy,4))
>>      common /qzold/ qzold(size(vz,1),size(vz,2),**size(vz,3),size(vz,4))
>>
>>      common /for_x/ f_x(size(vx,1),size(vx,2),**size(vx,3),size(vx,4))
>>      common /for_y/ f_y(size(vy,1),size(vy,2),**size(vy,3),size(vy,4))
>>      common /for_z/ f_z(size(vz,1),size(vz,2),**size(vz,3),size(vz,4))
>>
>>      real chi, omega_c
>>      integer step_filtr
>>
>>
>>      chi = .25
>>      omega_c = .1
>>      step_filtr = 020000
>>
>>      if(istep.EQ.step_filtr.AND.**nid.EQ.0) write(*,*) 'Filtrage'
>>
>>      if(istep.EQ.0) then
>>      vxold = 0.0D+00
>>      vyold = 0.0D+00
>>      vzold = 0.0D+00
>>      endif
>>
>>      if(istep.LT.step_filtr) then
>>      qxold = 0.0D+00
>>      qyold = 0.0D+00
>>      qzold = 0.0D+00
>>
>>      f_x = 0.0D+00
>>      f_y = 0.0D+00
>>      f_z = 0.0D+00
>>
>>      call opcopy(vxold,vyold,vzold,vx,**vy,vz)
>>      endif
>>
>>      if(istep.GE.step_filtr) then
>>      qxold = qxold + dt*omega_c * (vxold - qxold)
>>      qyold = qyold + dt*omega_c * (vyold - qyold)
>>      qzold = qzold + dt*omega_c * (vzold - qzold)
>>
>>      f_x = -chi * (vxold - qxold)
>>      f_y = -chi * (vyold - qyold)
>>      f_z = -chi * (vzold - qzold)
>>
>>      call opcopy(vxxold,vyyold,vzzold,**vxold,vyold,vzold)
>>      call opcopy(vxold,vyold,vzold,vx,**vy,vz)
>>      endif
>>
>> and in userf:
>>
>>      common /for_x/ f_x(size(vx,1),size(vx,2),**size(vx,3),size(vx,4))
>>      common /for_y/ f_y(size(vx,1),size(vx,2),**size(vx,3),size(vx,4))
>>      common /for_z/ f_z(size(vx,1),size(vx,2),**size(vx,3),size(vx,4))
>>
>>
>>     integer e,f,eg
>> c     e = gllel(eg)
>>
>>
>> c     Note: this is an acceleration term, NOT a force!
>> c     Thus, ffx will subsequently be multiplied by rho(x,t).
>>
>>
>>    ffx = f_x(ix,iy,iz,eg)
>>    ffy = f_y(ix,iy,iz,eg)
>>    ffz = f_z(ix,iy,iz,eg)
>>
>>
>> I have tried to compute with such routines the base flow for a 2D
>> lid-driven
>> cavity flow at Re = 8500, however depending on the number of spectral
>> elements I use, I sometimes get a stationnary solution that looks slightly
>> as the one I'm looking for (but some differences near the lid) and
>> sometimes
>> I get one which is actually not stationnary. I applied the same algorithm
>> for a finite-difference code and encountered no problem, so I was
>> wondering
>> then if I missed something specific to spectral elements or Nek 5000 (such
>> as a mass matrix multplication for instance) or to F77 (which I'm not at
>> ease with, see my definition of the common for instance)?
>>
>> Sincerely yours,
>>
>> --
>> Jean-Christophe
>>
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-- 
Jean-Christophe
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