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<p>Hi Francesco,</p>
<p>BCNEUSC computes the contribution of Robin boundary condition to
the diagonal components of the matrix (if ITYPE=-1), and to the
RHS (if ITYPE=1). You can read the nek5000 manual about Newton
cooling BC, and you will understand immediately what is being
done.</p>
<p>In your specific case, you do not have an RHS contribution. You
can see that this subroutine BCNEUSC computes matrix "S" which is
added to "H2" (see subroutine CDSCAL). In your case, you need to
do the same thing for Navier-Stokes. If you have Robin BC for vx
and other BC for vy, you need to define H2 for each direction. <br>
</p>
<p>Note that this works only when IFSTRS=false your rea file. Hope
this helps!</p>
<p>Sudhakar.<br>
</p>
<br>
<div class="moz-cite-prefix">On 04/24/2017 05:20 PM,
<a class="moz-txt-link-abbreviated" href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.gov</a> wrote:<br>
</div>
<blockquote
cite="mid:mailman.5532.1493047270.2967.nek5000-users@lists.mcs.anl.gov"
type="cite">
<div dir="ltr">Hi <span style="font-size:12.8px">Sudhakar,</span>
<div><span style="font-size:12.8px">thank you for your reply. </span></div>
<div><span style="font-size:12.8px"><br>
</span></div>
<div><span style="font-size:12.8px">It seems to me that
subroutine BCNEUSC is in charge of reading the "HC" value
for all element faces withstanding the "c " boundary
condition.</span></div>
<div><span style="font-size:12.8px">Nevertheless there is no
info about how to Robin boundary condition is effectively
implemented within the solver.</span></div>
<div><span style="font-size:12.8px"><br>
</span></div>
<div><span style="font-size:12.8px">May I ask you to give me
some more suggestions, in order to implement such BC on a
velocity component?</span></div>
<div><br>
</div>
<div><span style="font-size:12.8px">Best regards,</span></div>
<div><span style="font-size:12.8px"><br>
</span></div>
<div><span style="font-size:12.8px">Francesco</span></div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">2017-04-22 12:36 GMT+02:00 <span
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1. Robin boundary condition on velocity<br>
(<a moz-do-not-send="true"
href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>)<br>
2. Re: Robin boundary condition on velocity<br>
(<a moz-do-not-send="true"
href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>)<br>
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------------------------------<wbr>------------------------------<wbr>----------<br>
<br>
Message: 1<br>
Date: Fri, 21 Apr 2017 20:35:23 +0200<br>
From: <a moz-do-not-send="true"
href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
To: <a moz-do-not-send="true"
href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a><br>
Subject: [Nek5000-users] Robin boundary condition on
velocity<br>
Message-ID:<br>
<<a moz-do-not-send="true"
href="mailto:mailman.5414.1492799726.2967.nek5000-users@lists.mcs.anl.gov">mailman.5414.1492799726.2967.<wbr>nek5000-users@lists.mcs.anl.<wbr>gov</a>><br>
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<br>
Hi Neks<br>
I'm trying to implement a slip-length (Robin) as boundary
condition for a<br>
plane channel flow, namely:<br>
(u+du/dy)_{wall}=0<br>
where x and y are the streamwise and wall normal directions
respectively.<br>
<br>
Following the latter post:<br>
<a moz-do-not-send="true"
href="http://lists.mcs.anl.gov/pipermail/nek5000-users/2011-April/001313.html"
rel="noreferrer" target="_blank">http://lists.mcs.anl.gov/<wbr>pipermail/nek5000-users/2011-<wbr>April/001313.html</a><br>
<br>
here there's what I came up with:<br>
<br>
c-----------------------------<wbr>------------------------------<wbr>------------<br>
subroutine userchk<br>
include 'SIZE'<br>
include 'TOTAL'<br>
common /my_DEBUG/ rmodulate<br>
common /my_ROBIN/ ROBIN_mask(lx1,ly1,lz1,lelt)<br>
$ , work1(lx1,ly1,lz1,lelt)<br>
$ , work2(lx1,ly1,lz1,lelt)<br>
$ , graduy(lx1,ly1,lz1,lelt)<br>
n = nx1*ny1*nz1*nelv<br>
!!!Build Up MASKS!<br>
if (istep.eq.0) then<br>
do i=1,n<br>
x=xm1(i,1,1,1)<br>
y=ym1(i,1,1,1)<br>
if(x.gt.3.and.x.lt.4)then<br>
ROBIN_mask(i,1,1,1)=1.0<br>
else<br>
ROBIN_mask(i,1,1,1)=0.0<br>
endif<br>
enddo<br>
endif<br>
!Compute velocity gradient<br>
call rzero(graduy,n)<br>
call gradm1(work1,graduy,work2,vx)<br>
call dsavg(graduy)<br>
! call outpost(work1,graduy,work2,pr,<wbr>t,'GRD')<br>
!Da aggiungere l'eventualit? del 3D...<br>
rmodulate = 0.5*(tanh(0.25*time-10)+1)<br>
if (nid.eq.0) write(6,*)"MODULATE", rmodulate,time<br>
return<br>
end<br>
c-----------------------------<wbr>------------------------------<wbr>------------<br>
c-----------------------------<wbr>------------------------------<wbr>------------<br>
subroutine userbc (ix,iy,iz,iside,eg)<br>
c NOTE ::: This subroutine MAY NOT be called by every
process<br>
include 'SIZE'<br>
include 'TOTAL'<br>
include 'NEKUSE'<br>
integer e, eg<br>
!Imposing Fancy Boundary Conditions...<br>
![Nek5000-users] Robin boundary conditions for the velocity<br>
common /my_ROBIN/ ROBIN_mask(lx1,ly1,lz1,lelt)<br>
$ , work1(lx1,ly1,lz1,lelt)<br>
$ , work2(lx1,ly1,lz1,lelt)<br>
$ , graduy(lx1,ly1,lz1,lelt)<br>
common /my_DEBUG/ rmodulate<br>
e=gllel(eg) ! global element number to processor-local
el. #<br>
ux=1*graduy(ix,iy,iz,e)*<wbr>rmodulate<br>
uy=0.0<br>
uz=0.0<br>
return<br>
end<br>
c-----------------------------<wbr>------------------------------<wbr>------------<br>
subroutine useric (ix,iy,iz,ieg)<br>
include 'SIZE'<br>
include 'TOTAL'<br>
include 'NEKUSE'<br>
ux=1.0*y**2<br>
uy=0.0<br>
uz=0.0<br>
temp=0<br>
return<br>
end<br>
c-----------------------------<wbr>------------------------------<wbr>------------<br>
<br>
The code becomes unstable in the gradient computation due to
some<br>
point-to-point oscillations.<br>
As you can see I've also tried to use a ramp function in
order to make the<br>
onset of Robin condition more gentle,<br>
but at a given "slip-length amplitude" oscillations
deteriorates the<br>
solution.<br>
I use ROBIN_mask in order to chose where to have such BC,
but it seems that<br>
I'm still missing something in computing the velocity
gradient GRD.<br>
<br>
By the way, this is my box.BOX file:<br>
<br>
base.rea<br>
2 spatial dimension ( < 0 -->
generate .rea/.re2 pair)<br>
1 number of fields<br>
#=============================<wbr>==============================<wbr>============<br>
#<br>
# Example of .box file for channel flow<br>
#<br>
# If nelx (y or z) < 0, then genbox automatically
generates the<br>
# grid spacing in the x (y or z)
direction<br>
# with a geometric ratio given by
"ratio".<br>
# ( ratio=1 implies uniform spacing
)<br>
#<br>
# Note that the character bcs _must_ have 3 spaces.<br>
#<br>
#=============================<wbr>==============================<wbr>============<br>
#<br>
Box<br>
-32 -16
nelx,nely,nelz for Box<br>
0 6.2832 1.
x0,x1,gain<br>
-1 1 1.
y0,y1,gain<br>
P ,P ,v ,v , , bc's (3
chars each!)<br>
<br>
<br>
I was wondering if you might be able to give me some advice.<br>
<br>
Best regards,<br>
<br>
Francesco<br>
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Message: 2<br>
Date: Sat, 22 Apr 2017 12:35:45 +0200<br>
From: <a moz-do-not-send="true"
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To: <a moz-do-not-send="true"
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Subject: Re: [Nek5000-users] Robin boundary condition on
velocity<br>
Message-ID:<br>
<<a moz-do-not-send="true"
href="mailto:mailman.5458.1492857360.2967.nek5000-users@lists.mcs.anl.gov">mailman.5458.1492857360.2967.<wbr>nek5000-users@lists.mcs.anl.<wbr>gov</a>><br>
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<br>
Hi Francesco,<br>
<br>
Robin boundary condition is implemented already for the
passive scalar, in the form of Newton cooling boundary
condition. You can see how this is implemented in subroutine
BCNEUSC. In your case ITYPE=-1 and CB=?c ' in the
subroutine, and you need to only set ?HC? accordingly. We
tested this and even our turbulent simulations are stable
with Robin BC.<br>
<br>
Best regards,<br>
Sudhakar.<br>
<br>
> On 21 Apr 2017, at 20:35, <a moz-do-not-send="true"
href="mailto:nek5000-users@lists.mcs.anl.gov">nek5000-users@lists.mcs.anl.<wbr>gov</a>
wrote:<br>
><br>
> Hi Neks<br>
> I'm trying to implement a slip-length (Robin) as
boundary condition for a plane channel flow, namely:<br>
> (u+du/dy)_{wall}=0<br>
> where x and y are the streamwise and wall normal
directions respectively.<br>
><br>
> Following the latter post:<br>
> <a moz-do-not-send="true"
href="http://lists.mcs.anl.gov/pipermail/nek5000-users/2011-April/001313.html"
rel="noreferrer" target="_blank">http://lists.mcs.anl.gov/<wbr>pipermail/nek5000-users/2011-<wbr>April/001313.html</a>
<<a moz-do-not-send="true"
href="http://lists.mcs.anl.gov/pipermail/nek5000-users/2011-April/001313.html"
rel="noreferrer" target="_blank">http://lists.mcs.anl.gov/<wbr>pipermail/nek5000-users/2011-<wbr>April/001313.html</a>><br>
><br>
> here there's what I came up with:<br>
><br>
> c-----------------------------<wbr>------------------------------<wbr>------------<br>
> subroutine userchk<br>
> include 'SIZE'<br>
> include 'TOTAL'<br>
> common /my_DEBUG/ rmodulate<br>
> common /my_ROBIN/ ROBIN_mask(lx1,ly1,lz1,lelt)<br>
> $ , work1(lx1,ly1,lz1,lelt)<br>
> $ , work2(lx1,ly1,lz1,lelt)<br>
> $ , graduy(lx1,ly1,lz1,lelt)<br>
> n = nx1*ny1*nz1*nelv<br>
> !!!Build Up MASKS!<br>
> if (istep.eq.0) then<br>
> do i=1,n<br>
> x=xm1(i,1,1,1)<br>
> y=ym1(i,1,1,1)<br>
> if(x.gt.3.and.x.lt.4)then<br>
> ROBIN_mask(i,1,1,1)=1.0<br>
> else<br>
> ROBIN_mask(i,1,1,1)=0.0<br>
> endif<br>
> enddo<br>
> endif<br>
> !Compute velocity gradient<br>
> call rzero(graduy,n)<br>
> call gradm1(work1,graduy,work2,vx)<br>
> call dsavg(graduy)<br>
> ! call outpost(work1,graduy,work2,pr,<wbr>t,'GRD')<br>
> !Da aggiungere l'eventualit? del 3D...<br>
> rmodulate = 0.5*(tanh(0.25*time-10)+1)<br>
> if (nid.eq.0) write(6,*)"MODULATE",
rmodulate,time<br>
> return<br>
> end<br>
> c-----------------------------<wbr>------------------------------<wbr>------------<br>
> c-----------------------------<wbr>------------------------------<wbr>------------<br>
> subroutine userbc (ix,iy,iz,iside,eg)<br>
> c NOTE ::: This subroutine MAY NOT be called by
every process<br>
> include 'SIZE'<br>
> include 'TOTAL'<br>
> include 'NEKUSE'<br>
> integer e, eg<br>
> !Imposing Fancy Boundary Conditions...<br>
> ![Nek5000-users] Robin boundary conditions for the
velocity<br>
> common /my_ROBIN/ ROBIN_mask(lx1,ly1,lz1,lelt)<br>
> $ , work1(lx1,ly1,lz1,lelt)<br>
> $ , work2(lx1,ly1,lz1,lelt)<br>
> $ , graduy(lx1,ly1,lz1,lelt)<br>
> common /my_DEBUG/ rmodulate<br>
> e=gllel(eg) ! global element number to
processor-local el. #<br>
> ux=1*graduy(ix,iy,iz,e)*<wbr>rmodulate<br>
> uy=0.0<br>
> uz=0.0<br>
> return<br>
> end<br>
> c-----------------------------<wbr>------------------------------<wbr>------------<br>
> subroutine useric (ix,iy,iz,ieg)<br>
> include 'SIZE'<br>
> include 'TOTAL'<br>
> include 'NEKUSE'<br>
> ux=1.0*y**2<br>
> uy=0.0<br>
> uz=0.0<br>
> temp=0<br>
> return<br>
> end<br>
> c-----------------------------<wbr>------------------------------<wbr>------------<br>
><br>
> The code becomes unstable in the gradient computation
due to some point-to-point oscillations.<br>
> As you can see I've also tried to use a ramp function
in order to make the onset of Robin condition more gentle,<br>
> but at a given "slip-length amplitude" oscillations
deteriorates the solution.<br>
> I use ROBIN_mask in order to chose where to have such
BC, but it seems that I'm still missing something in
computing the velocity gradient GRD.<br>
><br>
> By the way, this is my box.BOX file:<br>
><br>
> base.rea<br>
> 2 spatial dimension ( < 0
--> generate .rea/.re2 pair)<br>
> 1 number of fields<br>
> #=============================<wbr>==============================<wbr>============<br>
> #<br>
> # Example of .box file for channel flow<br>
> #<br>
> # If nelx (y or z) < 0, then genbox automatically
generates the<br>
> # grid spacing in the x (y or
z) direction<br>
> # with a geometric ratio given
by "ratio".<br>
> # ( ratio=1 implies uniform
spacing )<br>
> #<br>
> # Note that the character bcs _must_ have 3 spaces.<br>
> #<br>
> #=============================<wbr>==============================<wbr>============<br>
> #<br>
> Box<br>
> -32 -16
nelx,nely,nelz for Box<br>
> 0 6.2832 1.
x0,x1,gain<br>
> -1 1 1.
y0,y1,gain<br>
> P ,P ,v ,v , ,
bc's (3 chars each!)<br>
><br>
><br>
> I was wondering if you might be able to give me some
advice.<br>
><br>
> Best regards,<br>
><br>
> Francesco<br>
> ______________________________<wbr>_________________<br>
> Nek5000-users mailing list<br>
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