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Hi,<br>
<br>
I use:<br>
<br>
order=3<br>
transorder=4<br>
rimannsolver=HLLD<br>
slopelimiter=mc<br>
eosforrieman=.true.<br>
<br>
Default for the rest<br>
<br>
I use order=3, because I want similar results with the simulations I
did with PPM. <br>
TransOrder seems less important in my runs. I've played around with
that, but I don't think it's a critical parameter. TrOr=3 seemd to
produce less artifacts. As I understand, it's kind of averaging
method, like 'A-B' or '4A-3B-C' or '6A-3B-C-2D' or
minmod('6A-3B-C-2D','A-B').<br>
I think the Riemannsolver is quite important. 'Roe' never worked for
me. I've seen several papers where they say that 'HLLD' is one of
the best, so I use that one as well. Slopelimiter was a suggestion
by Dongwook.<br>
<br>
<br>
On 02/12/2012 04:27 PM, Massimo Gaspari wrote:
<blockquote cite="mid:DUB105-W66A55B5421DB515647AC9BE7E0@phx.gbl"
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<div>Hi guys,</div>
<div><br>
</div>
<div>I am glad that you share my interest on such an important
topic, i.e. pros and cons of the unsplit hydro solver.</div>
<div><br>
</div>
<div>Seyit:</div>
<div>The workshop would be really interesting, but unfortunately
I am unavailable for that date.</div>
<div>When you say more diffusive ... which order/riemann/slope
are you using? (and why?)</div>
<div>In theory I should expect the unsplit solver to produce
*less* artifacts compared to the split formulation </div>
<div>(otherwise why bothering with a more complex scheme?).</div>
<div><br>
</div>
<div>Tomek:</div>
<div>Can you elaborate more on the "artifacts linked only to
PPM"... this is kind of new for me (any reference?).</div>
<div>I totally agree for the database of the verification tests,
in particular comparing all the options of the unsplit module.</div>
<div><br>
</div>
<div>Paul/Sean:</div>
<div>The <font class="Apple-style-span" face="monospace"
size="3"><span class="Apple-style-span" style="white-space:
pre;">"FLASH knowledge base" s</span></font>eems a great
idea.</div>
<div>I do not totally agree about "in general they depend on the
flow problem". I think that some kind</div>
<div>of quality must be *independent* of the specific problem
solved, leading to a solver better than another, also in
general.</div>
<div>Evidently some detail will be different, but I think we
must find one (or more) scale to properly evaluate them.</div>
<div><br>
</div>
<div>Dongwook:</div>
<div>A verification paper would be really great, certainly more
than the method paper, at least for the community.</div>
<div>In particular the split vs unsplit comparison, testing
different options.</div>
<div>I totally agree with you that providing in advance a
summary document with the *when & why*</div>
<div>is really necessary. Can't wait to read that.</div>
<div>I think in fact that only the FLASH developers of the
unsplit module really know the behaviour of all the
solvers/options</div>
<div>and perhaps they have already a scale of preferences.</div>
<div>In the meantime, what is *your* best hydro setup? </div>
<div>Dongwook, what do you suggest to normally avoid? </div>
<div><br>
</div>
<div>All:</div>
<div>Thanks again for all your positive interest. On the other
hand, may you kindly provide some specific example of your
current unsplit setup?</div>
<div>For instance:</div>
<div>order=</div>
<div>transOrder=</div>
<div>RiemannSolver= </div>
<div>...</div>
<div>2 lines of explanation (e.g., seems more stable... seems
more precise... less artifacts... I don't know, I like it!)</div>
<div><br>
</div>
<div>Sadly, I am just starting to test the module, so I do not
have much experience to share, aside that I've found this
setup to be rather stable:</div>
<div>order=3</div>
<div>transOrder=2</div>
<div>RiemannSolver=Roe</div>
<div><br>
</div>
<div>TransOrder seems to be a critical switch in order to
loose/gain stability. It is strange that with transOrder 1
crashes more than 2.... but I need further tests.</div>
<div>I am particularly interested in hydro simulations with
multiphase gas in it (i.e., very dense and cold clumps inside
hot and diffuse regions). Hope you have some experience in
that direction. Strong gradients in density (and temp) usually
make the code suddenly unstable. Any hint?</div>
<div><br>
</div>
<div><br>
</div>
<div>Until next time,</div>
<div><br>
</div>
<div> </div>
<div> Max</div>
<div><br>
</div>
<div><span class="Apple-style-span" style="text-indent: 0px !
important; font-family: 'Times New Roman';"><br>
</span></div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<br>
<br>
<div>> Subject: Re: [FLASH-USERS] Unsplit Hydro Solvers: Why
and When?<br>
> From: <a class="moz-txt-link-abbreviated" href="mailto:smc@flash.uchicago.edu">smc@flash.uchicago.edu</a><br>
> Date: Fri, 10 Feb 2012 16:22:07 -0600<br>
> CC: <a class="moz-txt-link-abbreviated" href="mailto:dongwook@flash.uchicago.edu">dongwook@flash.uchicago.edu</a>;
<a class="moz-txt-link-abbreviated" href="mailto:flash-users@flash.uchicago.edu">flash-users@flash.uchicago.edu</a>; <a class="moz-txt-link-abbreviated" href="mailto:gaspmax@hotmail.com">gaspmax@hotmail.com</a><br>
> To: <a class="moz-txt-link-abbreviated" href="mailto:pmricker@illinois.edu">pmricker@illinois.edu</a><br>
> <br>
> Paul,<br>
> <br>
> I love this idea. One word: FLASHBook. Unfortunately,
that domain name is already occupied (and for something far
less unsavory than I would have guessed). But we can work
around that.<br>
> <br>
> Sean<br>
> <br>
> On Feb 10, 2012, at 2:00 PM, Paul M. Ricker wrote:<br>
> <br>
> > Dongwook,<br>
> > <br>
> > I'd like to add my support for something like what
Massimo is requesting. The answers to his questions can be
obtained from textbooks and the applied math literature, or
informally from experienced algorithm developers, but in
general they depend on the flow problem being solved.
Documenting a group of test problems that demonstrate the pros
and cons of the different switches would therefore be very
useful. Perhaps the most feasible way to obtain this end,
given limited resources, would be to create an online space of
some type to allow users to submit this kind of information
from their own experience. A FLASH Knowledge Base, if you
will.<br>
> > <br>
> > Paul<br>
> > <br>
> > <br>
> > <br>
> > On 02/10/2012 01:20 PM, <a class="moz-txt-link-abbreviated" href="mailto:dongwook@flash.uchicago.edu">dongwook@flash.uchicago.edu</a>
wrote:<br>
> >> Dear Massimo,<br>
> >> <br>
> >> This is a really good case I can provide more
useful information on the<br>
> >> unsplit hydro/MHD solvers.<br>
> >> I understand that, ultimately, it will be ideal
to have a couple of useful<br>
> >> reference papers including at least:<br>
> >> <br>
> >> (a) a method paper, and<br>
> >> (b) a verification paper along with comparisons
with other methods<br>
> >> (e.g., split vs unsplit; FLASH vs other codes)<br>
> >> <br>
> >> And unfortunately, these papers are in
preparation and one of my todo list<br>
> >> in a near future.<br>
> >> <br>
> >> In the meantime, I think it will be a good idea
for FLASH users that I<br>
> >> provide a summary document that describe several
key features/usages<br>
> >> (e.g., answering when& why) in more detail
(that what's done in the FLASH<br>
> >> users guide) and make that available to
community.<br>
> >> <br>
> >> I will think about coming up with an idea how to
provide such an useful<br>
> >> information in order to help users to use the
FLASH's unsplit hydro/MHD<br>
> >> solvers for their research.<br>
> >> <br>
> >> Thank you for your interest in using the FLASH's
unsplit solvers!<br>
> >> <br>
> >> Best,<br>
> >> Dongwook<br>
> >> <br>
> >> =========================================<br>
> >> Dongwook Lee, Ph.D., Research Scientist<br>
> >> FLASH Center for Computational Science<br>
> >> University of Chicago<br>
> >> 5747 S. Ellis Ave., Room 319<br>
> >> (773) 834-6830<br>
> >> <br>
> >>> <br>
> >>> Dear FLASH users/developers,<br>
> >>> I write this email in order to open a
discussion on the unsplit hydro<br>
> >>> solver.A preamble.I have mostly used the
basic split PPM module and I<br>
> >>> think it works pretty well.The only real
"issue" is the splitting, which<br>
> >>> complicates the implementation of several
physical modules.Therefore, I am<br>
> >>> right now testing the unsplit module (FLASH
4b).However... there are<br>
> >>> endless options! This is certainly a good
thing. On the other hand, it is<br>
> >>> pretty daunting to test every single
option/solver, plus several different<br>
> >>> combinations, even for a single problem.<br>
> >>> I am thus wondering if you (developers and
users) may kindly provide more<br>
> >>> comments/experiences on the methods used in
the unsplit solver. I don't<br>
> >>> want to know how the solver is written (I
have Toro's book for that), but<br>
> >>> *when* and *why* we have to use a particular
solver/option, and *which are<br>
> >>> the pros and cons/risks*?<br>
> >>> For instance, ...1) Using PPM (order=3) over
Godunov (order=1) is pretty<br>
> >>> trivial, but why and when using MUSCL
(order=2) over PPM?<br>
> >>> 2) I also do not understand the default
value of several options...<br>
> >>> shouldn't be the default value the best (in
theory) option? If so why<br>
> >>> transOrder=1? transOrder=2 seems to me a
more appropriate choice, in<br>
> >>> general.When do you use transOrder=3? The
same can be said for the half<br>
> >>> gravity update: if it is second order, why
the first order is set to be<br>
> >>> the default?<br>
> >>> 3) I am puzzled by the several Riemann
solvers. What is the hybrid solver?<br>
> >>> Why should I use hybrid, LLF or Marquina
solver over the more standard Roe<br>
> >>> or HLLC?<br>
> >>> 4) The same can be asked about the different
slope limiters...<br>
> >>> 5) ... or use_upwindTVD and use_3dFullCTU.<br>
> >>> Summarizing:a) what are your - general and
specific - suggestions?b) why<br>
> >>> should I avoid or use a specific
solver/option over other standard<br>
> >>> implementations?<br>
> >>> I think the unsplit module is a great part
of FLASH, but all the<br>
> >>> parameters/options/solvers need to be better
clarified. I hope you can<br>
> >>> help in that direction.Thank you in
advance.Best,<br>
> >>> <br>
> >>> Max<br>
> >>> <br>
> >> <br>
> > <br>
> > -- <br>
> > Paul M. Ricker<br>
> > Associate Professor of Astronomy<br>
> > University of Illinois<br>
> > <a class="moz-txt-link-abbreviated" href="mailto:pmricker@illinois.edu">pmricker@illinois.edu</a> / 217-244-1187<br>
> <br>
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