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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:
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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>
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