[Nek5000-users] perturbing interior variables

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

Hi Frank,


I assume that you refer to t(i,j,k,iel) as temperature -- to be safe it 
should be t(i,j,k,iel,1)...


In timestepping loop, subroutine userchk is called last by one -- right 
before the last one -- prepost which dumps field files .f or .fld -- see 
nek5_svn/trunk/nek/drive1.f:

       DO ISTEP=1,NSTEPS
          call nek_advance
          call userchk
          call prepost (.false.,'his')
          if (lastep .eq. 1) goto 1001B
       ENDDO

while, as I can see, userbc for a passive scalar is called from a chain of 
subroutines nek_advance > heat > cdscal > BCNEUSC/BCDIRSC

This means that perturbation of temperature at the boundary won't be 
overwritten in userbc.


One way to apply perturbation everywhere including the element faces that 
are not on the boundary of your domain is simply to multiply your 
perturbation factor by a function that goes to zero on the boundaries, 
e.g.:

    t(i,j,k,iel,1)=.99*t(i,j,k,iel,1)*(xm1(i,j,k,iel)**2.-1.)

in case the boundary surface plane is at x=1 & x=-1

Best,
Aleks






On Mon, 10 May 2010, nek5000-users at lists.mcs.anl.gov wrote:

> Hello all,

I am trying to perturb the temperature in a small part of the flow.
However, I only wish to perturb in the interior and not on a boundary.
I have the following in "userchk".  If I instead looped from "k=1,nz1"
instead of "k=2,nz1-1", would this change the BC's?  The general
question would be, does changing uvw & T in "userchk" change BC's or
does "userbc" override what is done in "userchk"?

Cheers,
Frank

         do 100 iel=1,nelv
         do 100 k=2,nz1-1
         do 100 j=2,ny1-1
         do 100 i=2,nx1-1
         if(((xm1(i,j,k,iel)-1.1)**2
      &    + (ym1(i,j,k,iel)-1.1)**2
      &    + (zm1(i,j,k,iel)-.45)**2)**.5.le..25)then
            t(i,j,k,iel)=.99*t(i,j,k,iel)
         endif
           enddo !n
100     continue




-- 
Frank Herbert Muldoon, Ph.D. Mechanical Engineering
Technische Universität Wien (Technical University of Vienna)
Inst. f. Strömungsmechanik und Wärmeübertragung (Institute of Fluid
Mechanics and Heat Transfer)
Resselgasse 3
1040 Wien
Tel: +4315880132232
Fax: +4315880132299 
Cell:+436765203470
fmuldoo (skype)
http://tetra.fluid.tuwien.ac.at/fmuldoo/public_html/webpage/frank-muldoon.html

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