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Hi Jon,<br>
<br>
Thanks for the quick response. I too have a sudden increase/decrease
in temperature and internal energy in a single cell (I assume that
E_int --> T --> P). It is possible that there is a single
origin to this problem. Let us notify one another about any progress
on this matter, and anyone else from the community.<br>
<br>
Best wishes,<br>
Seyit<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 06/02/17 19:24, Slavin, Jonathan
wrote:<br>
</div>
<blockquote
cite="mid:CACcRS=cmfbGynWCo+Fzog4HHnVuhgCCfWxELiQkhKvDVgRBEhg@mail.gmail.com"
type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;font-size:small">Hi
Seyit,</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;font-size:small">I
have had to put that problem aside for a while, though I
hope to get back to it soon. I have not solved the problem
that leads to negative or zero timesteps. What I found was
that what leads to the problem is that suddenly in a single
grid zone/pixel the thermal pressure jumps to a very high
value, which thus leads to a very small timestep. I plan to
probe the problem further as soon as I can.</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;font-size:small"><br>
</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;font-size:small">Regards,</div>
<div class="gmail_default"
style="font-family:arial,helvetica,sans-serif;font-size:small">Jon</div>
<br>
<div class="gmail_quote">On Mon, Feb 6, 2017 at 1:00 PM, <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:flash-users-request@flash.uchicago.edu"
target="_blank">flash-users-request@flash.uchicago.edu</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div id=":1ew" class="a3s aXjCH m15a14952389b85ad">From: Seyit
Hocuk <<a moz-do-not-send="true"
href="mailto:seyit@mpe.mpg.de">seyit@mpe.mpg.de</a>><br>
To: "<a moz-do-not-send="true"
href="mailto:flash-users@flash.uchicago.edu">flash-users@flash.uchicago.edu</a>"
<<a moz-do-not-send="true"
href="mailto:flash-users@flash.uchicago.edu">flash-users@flash.uchicago.edu</a>><br>
Cc: <br>
Date: Mon, 6 Feb 2017 10:56:22 +0100<br>
Subject: [FLASH-USERS] MHD simulations Eint=0 problem<br>
Hi community,<br>
<br>
Has anyone else encountered this problem before?<br>
<br>
Whenever I run MHD simulations with the USM solver
(Flash4.4), I occasionally get Eint=0. This seems to
occur only when I put a B-field > 0 (I often simulate
mass-to-flux ratio of 2). The problem is bigger with
higher magnetic field strength. I have played around
with the "eintswitch" parameter, thereby reducing
reducing the issue it as much as I can (eintswitch =<
1e-4), but the problem still persists. A high
eintswitch, on the other hand, thereby reverting to an
independent internal energy calculation was giving me
crazy values. It is as if the magnetic energy is not
considered for the internal energy calculations when
derived from the total energy (Eint = E_tot - Ekin -
Emag), or something along those lines, but this is just
guessing.<br>
<br>
Optimizing the parameters helped a little. See parameter
choices below. My initial guess was that the solver has
a hard time solving, because the problem is stiff on
occasion. Playing with these options and relaxing the
solver still did not completely remove this issue.<br>
<br>
I initially thought that this happens after new cells
are created, however, the problem does still occur when
lrefine_min=lrefine_max.<br>
<br>
The problem also seems to persist if:<br>
ForceHydroLimit = .True. (but the B-field is not set to
zero; in the tested case it is 10.0e-6)<br>
So, forcing hydrolimit did not help! This while when the
B = 0 (+Forcehydrolimit=true), the Eint does not become
0, but very low instead (which is a different issue?).
While with B=0, I also get a different refinement.
Therefore, I am not entirely sure what forcehydrolimit
does actually. Clearly, there is still impact by the
B-field.<br>
<br>
Another funny thing is enableMaskedGCFill. I usually
have<br>
enableMaskedGCFill = .True.<br>
but the module that made use of this is turned off.
Setting this to true or false gives me somewhat
different kind of errors. With .False. I also get
negative values, i.e., WARNING after gc filling: min.
unk(EINT_VAR)=-1487770975.0815<wbr>08<br>
<br>
The end results is sometimes (especially if I don't
constrain by "small" variables, i.e., make the "small"
values really small):<br>
DRIVER_ABORT: Computed new time step smaller than
dr_dtMinContinue!<br>
similar to a problem mentioned recently "dt not positive
in MHD simulations" by Jon Slavin. Was any solution
fouond for that?<br>
<br>
What does help is:<br>
cfl = crazy low, but normally lowering cfl only delays
the issue.<br>
<br>
What doesn't help is:<br>
Turning off gravity<br>
Turning off particles<br>
Turning off refinement<br>
Turning of all my modules (Heating/Cooling/Chemistry/Col<wbr>mndensities...)<br>
Changing boundaries from periodic/isolated to outflow<br>
Viscosity<br>
And many other things<br>
<br>
With kind regards,<br>
Seyit<br>
<br>
<br>
Normal conditions (but I tested them all):<br>
mfieldstrength = 5.0e-6<br>
killdivb = .True.<br>
E_upwind = .True.<br>
energyFix = .True.<br>
RiemannSolver = "HYBRID"<br>
slopeLimiter = "HYBRID"<br>
order = 3<br>
use_steepening = .False.<br>
use_flattening = .True.<br>
use_avisc = .True.<br>
shockDetect = .True.<br>
cfl = 0.6<br>
<br>
Libraries/Compilers:<br>
hdf5-serial/1.8.15<br>
ifort: intel/15.0<br>
impi/5.0.3<br>
x86_64 x86_64 x86_64 GNU/Linux<br>
<br>
<br>
-- <br>
Dr. Seyit Hocuk<br>
Post-doctoral researcher<br>
Center for Astrochemical Studies (CAS)<br>
Max-Planck-Institute for Extraterrestrial physics (MPE)<br>
Giessenbachstrasse 1, 85748 Garching bei Munchen<br>
Phone: <a moz-do-not-send="true"
href="tel:%2B49-8930000-3012" value="+4989300003012"
target="_blank">+49-8930000-3012</a> | Fax: <a
moz-do-not-send="true" href="tel:%2B49-8930000-3569"
value="+4989300003569" target="_blank">+49-8930000-3569</a><br>
Web : <a moz-do-not-send="true"
href="http://www.mpe.mpg.de/%7Eseyit" rel="noreferrer"
target="_blank">www.mpe.mpg.de/~seyit</a><br>
<br>
</div>
</blockquote>
</div>
<br>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
<div class="gmail_signature" data-smartmail="gmail_signature">
<div dir="ltr">
<div>
<div dir="ltr">________________________________________________________<br>
Jonathan D. Slavin Harvard-Smithsonian
CfA<br>
<a moz-do-not-send="true"
href="mailto:jslavin@cfa.harvard.edu"
target="_blank">jslavin@cfa.harvard.edu</a> 60
Garden Street, MS 83<br>
phone: (617) 496-7981 Cambridge, MA 02138-1516<br>
cell: (781) 363-0035 USA<br>
________________________________________________________<br>
<br>
</div>
</div>
</div>
</div>
</div>
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</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Dr. Seyit Hocuk
Post-doctoral researcher
Center for Astrochemical Studies (CAS)
Max-Planck-Institute for Extraterrestrial physics (MPE)
Giessenbachstrasse 1, 85748 Garching bei Munchen
Phone: +49-8930000-3012 | Fax: +49-8930000-3569
Web : <a class="moz-txt-link-abbreviated" href="http://www.mpe.mpg.de/~seyit">www.mpe.mpg.de/~seyit</a></pre>
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