[Nek5000-users] perturbing interior variables

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

Hi Frank,

Boundary values will be set by userbc().

There is no opportunity to intercede between userbc() being called
and the solver.  (In effect, userbc() _is_ the opportunity to
intercede.)

userchk is called at the end of each step and therefore effectively
at the beginning of the next.  Perturbing there will work - you can
perturb all values and rest assured that values on Dirichlet surfaces
will be overwritten by userbc.   Values on Neumann surfaces, however,
would not be reset by userbc.

hth,

Paul

On Tue, 11 May 2010, nek5000-users at lists.mcs.anl.gov wrote:

> Thanks for the replies, Aleks and Stefan.  I am still not clear on one
point though.  Are changes made to temperature or velocity on boundaries
in "userchk" at each time step irrelevant since they are overwritten by
calls to "userbc"?

Cheers,
Frank


On Mon, 2010-05-10 at 18:15 +0200, nek5000-users at lists.mcs.anl.gov
wrote:
> The heat solver calls BCDIRSC which will apply Dirichlet bcs. All 't  ' boundary points call userbc so you have the full control over the values at the boundary.
> 
> Stefan
>
> 
> 
> 
> On May 10, 2010, at 6:00 PM, nek5000-users at lists.mcs.anl.gov wrote:
> 
> > 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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-- 
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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