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I also have artifacts in my moving (orbiting) molecular magnetized
cloud, especially in the wake of the cloud. But I still like it.<br>
My first impression of the unsplit solver is that it is more
diffusive, unfortunately. Everything seems to be more smooth. Can
anybody confirm?<br>
<br>
Seyit<br>
<br>
<br>
<br>
<br>
On 02/10/2012 06:55 PM, david arnett wrote:
<blockquote
cite="mid:CAGpgfQEUXVOdhu9xkLRS0h+T1L9xZNV-KFipTFshuD5ruZ4ARA@mail.gmail.com"
type="cite">The prime failing of the un-split solver, that I know
of, is that it produces poor results for high electron degeneracy;
errors due to grid artifacts appear. This is an ancient problem;
are there more recent ones?
<div><br>
</div>
<div>Dave</div>
<div><br>
</div>
<div><br>
<br>
<div class="gmail_quote">On Fri, Feb 10, 2012 at 10:45 AM, Seyit
Hocuk <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:seyit@astro.rug.nl">seyit@astro.rug.nl</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt
0.8ex; border-left: 1px solid rgb(204, 204, 204);
padding-left: 1ex;">
<div bgcolor="#ffffff" text="#000000"> Those are all good
questions. I'd like to hear them myself as well.<br>
You should come to the FLASH workshop in Hamburg/Germany
next week.<br>
<br>
Seyit<br>
<br>
<br>
On 02/10/2012 06:36 PM, Massimo Gaspari wrote:
<blockquote type="cite">
<div dir="ltr"> Dear FLASH users/developers,
<div><br>
</div>
<div>I write this email in order to open a discussion
on the unsplit hydro solver.</div>
<div>A preamble.</div>
<div>I have mostly used the basic split PPM module and
I think it works pretty well.</div>
<div>The only real "issue" is the splitting, which
complicates the implementation of several physical
modules.</div>
<div>Therefore, I am right now testing the unsplit
module (FLASH 4b).</div>
<div>However... there are endless options! This is
certainly a good thing. On the other hand, it is
pretty daunting to test every single option/solver,
plus several different combinations, even for a
single problem.</div>
<div><br>
</div>
<div>I am thus wondering if you (developers and
users) may kindly provide more comments/experiences
on the methods used in the unsplit solver. I don't
want to know how the solver is written (I have
Toro's book for that), but *when* and *why* we have
to use a particular solver/option, and *which are
the pros and cons/risks*?</div>
<div><br>
</div>
<div>For instance, ...</div>
<div>1) Using PPM (order=3) over Godunov (order=1) is
pretty trivial, but why and when using MUSCL
(order=2) over PPM?</div>
<div><br>
</div>
<div>2) I also do not understand the default value of
several options... shouldn't be the default value
the best (in theory) option? If so why transOrder=1?
transOrder=2 seems to me a more appropriate choice,
in general.</div>
<div>When do you use transOrder=3? The same can be
said for the half gravity update: if it is second
order, why the first order is set to be the default?</div>
<div><br>
</div>
<div>3) I am puzzled by the several Riemann solvers.
What is the hybrid solver? Why should I use hybrid,
LLF or Marquina solver over the more standard Roe or
HLLC?</div>
<div><br>
</div>
<div>4) The same can be asked about the different
slope limiters...</div>
<div><br>
</div>
<div>5) ... or use_upwindTVD and use_3dFullCTU.</div>
<div><br>
</div>
<div>Summarizing:</div>
<div>a) what are your - general and specific -
suggestions?</div>
<div>b) why should I avoid or use a specific
solver/option over other standard implementations?</div>
<div><br>
</div>
<div>I think the unsplit module is a great part of
FLASH, but all the parameters/options/solvers need
to be better clarified. I hope you can help in that
direction.</div>
<div>Thank you in advance.</div>
<div>Best,</div>
<div><br>
</div>
<div><br>
</div>
<div> Max</div>
<div><br>
</div>
</div>
</blockquote>
<br>
</div>
</blockquote>
</div>
<br>
<br clear="all">
<div><br>
</div>
-- <br>
David Arnett<br>
Regents Professor<br>
Steward Observatory<br>
University of Arizona<br>
</div>
</blockquote>
<br>
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