<div dir="ltr">OK. I tried clipping and it seems to run atleast. I need to see the results tomorrow in office.<div><br></div><div style>There is an option to do filtering in nek. If I understood it correctly, on each element, you first interpolate solution to lower degree polynomial and then interpolate it back to higher degree. This kills highly oscillatory components in the solution. Is this implemented for passive scalars also if I enable the filtering in rea file ?</div>
<div style><br></div><div style>I implemented clipping passive scalar like this in userchk but is there a better way to do the loops</div><div style><br></div><div style><div> do e=1,nelv</div><div> do k=1,nz1</div>
<div> do j=1,ny1</div><div> do i=1,nx1</div><div> t(i,j,k,e,2) = max(0.0, t(i,j,k,e,2))</div><div> t(i,j,k,e,2) = min(1.0, t(i,j,k,e,2))</div><div> enddo</div><div> enddo</div><div> enddo</div>
<div> enddo</div><div><br></div><div style>Thanks</div><div style>praveen</div></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Sun, Oct 13, 2013 at 7:38 PM, <span dir="ltr"><<a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.gov</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><br>
With such a small diffusion coefficient you typically<br>
are going to need very fine resolution in space.<br>
<br>
Maintaining monotonicity (i.e., no over- / undershoots) in<br>
an under-resolved scenario is a current research topic.<br>
For the time being, I typically simply clip when monotonicity<br>
is critical.<br>
<br>
Paul<div class="HOEnZb"><div class="h5"><br>
<br>
<br>
On Sun, 13 Oct 2013, <a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.<u></u>gov</a> wrote:<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I am not sure that what you are solving for c is a normalized scalar like a mass fraction Y for example<br>
If c is not normalized May be the formulation is equivalent to<br>
C= rho* Y where y is a normalized scalar and rho is the total density..<br>
<br>
Finally check mass conservation<br>
By integrating over the volume of the channel, the density equation<br>
d/dt integral(rho) + integral (u. Grad rho) =error<br>
And see how error changes over time<br>
<br>
Ammar<br>
<br>
Sent from my iPhone<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On Oct 13, 2013, at 1:46 AM, <a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.<u></u>gov</a> wrote:<br>
<br>
<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
On Sun, Oct 13, 2013 at 10:35 AM, <<a href="mailto:nek5000-users@lists.mcs.anl.gov" target="_blank">nek5000-users@lists.mcs.anl.<u></u>gov</a>> wrote:<br>
You can also try error function like profile with 0 value at the inlet and increases to a peak somewhere and stays constant up to the exit so gradient is0 at the exit<br>
Insulation normally refers to the diffusive flux (first form)<br>
Ammar<br>
</blockquote>
<br>
Thanks for the tips. I am using a smoothed initial condition for scalar now. However after some time the scalar does not stay within [0,1] which is important. My time step is already small with cfl ~= 0.1. What can I do to get better behaviour of the scalar ?<br>
<br>
The diffusion coefficient for my scalar is quite small, D = 5*10^(-5).<br>
<br>
Regards<br>
praveen<br>
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