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<font size="+1"><font face="monospace">Andy -<br>
<br>
I would think that with that many cells per scale height the
mesh resolution is adequate.<br>
</font></font><br>
<font size="+1"><font face="monospace"><font size="+1"><font face="monospace">I have a sense something happens near the
lower-left boundary (perhaps across the equatorial plane),
and a perturbation from that region sweeps through the rest
of the domain.<br>
<br>
</font></font>Whatever happens breaks the assumed radial
symmetry and lateral uniformity. I would be more interested in
lateral (momentum, pressure gradients, field gradients) rather
than radial components as the former should nominally remain
zero at all times. You could try to suppress lateral fluxes and
see whether any particular part of the domain eventually becomes
a source of perturbations. In either case, the simulation is in
trouble as soon as lateral perturbations develop and their
source is not controlled.<br>
<br>
I assume the mesh is uniform, correct?<br>
<br>
In the plots, is the symmetry axis at the left and equatorial
plane at the bottom?<br>
<br>
Not sure if assuming reflecting boundary at Rmax is justified?
Depending how it is implemented in the code, there might be a
jump in some magnetic field components. I would think that zero
gradient/outflow conditions might be safer as any perturbations
will likely feed back into the domain, and one would want to
avoid that. (It seems Tummel et al. actually stress that
particular point.)<br>
<br>
Have you tried a 1D version of this setup?<br>
<br>
Which version of FLASH are you using?<br>
<br>
Tomek<br>
--</font></font><br>
<div class="moz-cite-prefix">On 4/8/21 11:12 AM, Andy Sha Liao
wrote:<br>
</div>
<blockquote type="cite" cite="mid:CAKfEzWCQmVf6VetR4_a711HULuoKjEDoY8zaNs1YQ9fTY-EQ-w@mail.gmail.com">
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<div dir="ltr">
<div dir="ltr">
<div dir="ltr">Tomasz,
<div><br>
</div>
<div><br>
</div>
<div>Thanks for taking interest in our problem. Let me
send you a few movies from my GDrive so you have a
better picture.</div>
<div><br>
</div>
<div>First, the movie from which the stills were sent to
you previously:</div>
<div><br>
</div>
<div><a href="https://urldefense.com/v3/__https://drive.google.com/file/d/1pKKQzVHn8Qm9RVMNpX0CINJlqULoIfzw/view?usp=sharing__;!!PhOWcWs!nWLN84YtVshbYV71fKfEPMDMQ9Jrl6lAUw98Vz8sWBW6dtvRjvzPqMCWBYUCXQ$" target="_blank" moz-do-not-send="true">https://drive.google.com/file/d/1pKKQzVHn8Qm9RVMNpX0CINJlqULoIfzw/view?usp=sharing</a><br>
</div>
<div><br>
</div>
<div>The movie shows density, radial momentum, and
azimuthal magnetic field.</div>
<div><br>
</div>
<div>Next, a movie of the radial lineout near the
equatorial plane of the domain, of radial velocity as a
fraction of the characteristic alfven speed ~240 km/s. I
show results from two different interpolation orders,
olive is 3rd order, magenta is 2nd order:</div>
<div><br>
</div>
<div><a href="https://urldefense.com/v3/__https://drive.google.com/file/d/1pCh_Lb4P6TbBWxNOItLotb7-SoWLqvmq/view?usp=sharing__;!!PhOWcWs!nWLN84YtVshbYV71fKfEPMDMQ9Jrl6lAUw98Vz8sWBW6dtvRjvzPqMDM5Tj5lA$" target="_blank" moz-do-not-send="true">https://drive.google.com/file/d/1pCh_Lb4P6TbBWxNOItLotb7-SoWLqvmq/view?usp=sharing</a><br>
</div>
<div><br>
</div>
<div>The problem is not the long waves, but the sawteeth
oscillations. In other simulations, I suppressed the
long waves, but the sawteeth still came in on
schedule. </div>
<div><br>
</div>
<div>To answer your questions, the scale height, or
characteristic length of the pinch is 0.0910 cm, as
found in the reference in the previous message, and the
resolution is 32 cells per characteristic length. We
also ran up to 256 cells per characteristic length, but
the problem doesn't go away.</div>
<div><br>
</div>
<div><br>
</div>
<div>Andy</div>
</div>
</div>
</div>
</div>
</blockquote>
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