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Hi Dongwook,<br>
<br>
I'm using the HLLC Riemann solver. I've attached a recent log file
from a short run.<br>
<br>
Thanks!<br>
<br>
Best,<br>
Rukmani<br>
<br>
<br>
<div class="moz-cite-prefix">On 02/18/2016 10:31 PM, Dongwook Lee
wrote:<br>
</div>
<blockquote
cite="mid:7690B0E9-99A8-4F91-B1E5-59A5F5849056@gmail.com"
type="cite">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<div>Dear Rukmani,</div>
<div><br>
</div>
<div>What kind of Riemann solver are you using?</div>
<div>Can you send me a log file or flash.par?</div>
<div><br>
</div>
<div>Thanks,</div>
<div>Dongwook</div>
<div><br>
On Feb 18, 2016, at 6:59 PM, Rukmani Vijayaraghavan <<a
moz-do-not-send="true" href="mailto:rukmani@virginia.edu"><a class="moz-txt-link-abbreviated" href="mailto:rukmani@virginia.edu">rukmani@virginia.edu</a></a>>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div>
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Hi Jason, Klaus,<br>
<br>
This block-by-block variation is correlated with similar
variation in other fluid variables (density, pressure), and
this persists even where there is a zero velocity inflow, as
well as with a uniform grid, and with both USM and PPM (pure
hydro) solvers. Modifying the gravity solver from Multigrid to
Multipole doesn't make a difference either. I'm using the
FLASH Gamma EOS unit. As far as I've seen, there is no
variation in B-field across grid cells adjacent to block /
refinement boundaries, this only happens at the inflow edge. <br>
<br>
I also update the magnetic field face variables (MAG_FACE_VAR
and/or MAGI_FACE_VAR), with no effect. Div(B) still seems to
be 0. <br>
<br>
Any other suggestions would be great!<br>
<br>
Thanks,<br>
Rukmani<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 02/18/2016 01:30 PM, Jason
Galyardt wrote:<br>
</div>
<blockquote
cite="mid:CABdF9uevM2PyrdYd_1Lz1Ofx11u0mTKEjCRHxboEA9aB6_YFKA@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div>
<div>
<div>
<div>Hi Rukmani,<br>
<br>
</div>
I used a spatially varying wind; the velocity of
the wind varies along the boundary, but it has a
well-defined, time-independent form. I've also
seen problems with more realistic B-field
geometries which (to my horror) included step
functions in the domain interior. I had to smooth
these out to avoid unphysical evolution in those
regions. <br>
<br>
I've also seen some modest increase in B-field
magnitude for the cells adjacent to a refinement
boundary. I haven't reported the latter previously
because I haven't had time to figure out what's
going on there. You might try setting lrefine_min
= lrefine_max to get uniform refinement and see
whether that helps (some of our group's
simulations do this).<br>
<br>
</div>
The block by block variation does seem strange. I
would expect this kind of variation to be correlated
with variation in another variable. How do the other
variables look in the problem region?<br>
<br>
</div>
Another idea: could this variation be tied to the
equation of state? If you're using one of the
supported FLASH EOS units, you're probably fine.<br>
<br>
</div>
Regards,<br>
</div>
Jason<br>
<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Feb 18, 2016 at 11:07 AM,
Rukmani Vijayaraghavan <span dir="ltr"><<a
moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:rukmani@virginia.edu"><a class="moz-txt-link-abbreviated" href="mailto:rukmani@virginia.edu">rukmani@virginia.edu</a></a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF"> Hi Jason,<br>
<br>
Thanks! I'm using FLASH 4.2, I'll try using 4.3 to
see if that makes a difference. I haven't tried
refining on the magnetic variables yet.<br>
<br>
For the different runtime parameters -- <br>
<br>
1. I've tried cfl = 0.5 and 0.8, but nothing lower
yet. I'll check to see if that works.<br>
<br>
2. For the Riemann Solver, I've found HLLC to be a
bit more dissipative than HLLD, and therefore
marginally better at smoothing out the magnetic
field at the edges. Ditto with second order
MUSCL-Hancock over third order PPM.<br>
<br>
3. All the other runtime parameters are mostly the
same. I don't refine on the magnetic variables, but
I tried higher overall lrefine_min (to make sure the
outer edges get further refined) and it didn't help
-- the same block-based discontinuity persists.<br>
<br>
4. I'm using a constant wind inflow for this
particular run. One thing I checked to see was if
there was a round off error in reading my input
variables into double precision arrays, and this
tiny "seed" instability might grow, but it doesn't
seem to be an issue. What is strange is that the
value (and sign) of the initial instability varies
block-by-block. In your simulations, did you use a
constant wind?<br>
<br>
Thanks,<br>
Rukmani
<div>
<div class="h5"><br>
<br>
<div>On 02/18/2016 09:38 AM, Jason Galyardt
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>
<div>
<div>
<div>Hi Rukmani,<br>
<br>
</div>
I've had some similar issues with MHD
runs. You didn't mention which version
of FLASH you're using, but I've found
the latest (v4.3) to be a bit more
stable than v4.2 or v2.5. As for
runtime parameters, found the
following combination to be helpful:<br>
<br>
#~~~~<br>
</div>
<div># Refine on the magnetic variables:<br>
</div>
<div>refine_var_1 = "dens"<br>
refine_var_2 = "magp"<br>
</div>
<div># -OR-<br>
</div>
<div># refine_var_2 = "magx"<br>
</div>
<div># refine_var_3 = "magy"<br>
</div>
<div># refine_var_4 = "magz"<br>
</div>
<div># prefer higher refinement,
according to magp (default
refine_cutoff_X = 0.8)<br>
refine_cutoff_2 = 0.7<br>
# refine_cutoff_3 = 0.7<br>
# refine_cutoff_4 = 0.7<br>
<br>
</div>
<div># Lower CFL: between 0.25 and 0.5<br>
</div>
<div>cfl = 0.5<br>
<br>
</div>
<div># Use second order MUSCL-Hancock
reconstruction scheme<br>
</div>
<div>order = 2<br>
</div>
<div><br>
# I've mostly used the "hybrid" slope
limiter, but occasionally I've found
the "minmod" useful in particularly
difficult situations <br>
</div>
<div>slopeLimiter = "hybrid"<br>
<br>
# use flattening (dissipative)
(originally for PPM)<br>
use_flattening = .true. <br>
<br>
# Use high order algorithm for E-field
construction<br>
E_modification = .true.<br>
<br>
# Update magnetic energy using
staggered B-fields<br>
energyFix = .true.<br>
<br>
# Prolongation method (injecton_prol,
balsara_prol) -- Using Balsara's
method is particularly critical, in my
experience.<br>
prolMethod = "BALSARA_PROL"<br>
<br>
</div>
<div># For the Riemann solver, I use
HLLD for MHD runs, and HLLC for pure
hydro runs.<br>
</div>
<div>RiemannSolver = "HLLD"<br>
</div>
<div>#~~~~<br>
</div>
<br>
<div>What sort of inflow conditions have
you implemented? Small non-linearities
in the inflow can grow into large
unphysical features over time (I've
seen this happen in my own
simulations). So, it's worth checking
your boundary condition code for
undesirable features. In any case, I
hope this helps.<br>
</div>
<br>
Sean: is the E_upwind option available
for the unsplit MHD solver in FLASH 4.3?
My recollection is that it caused some
problems in previous versions....<br>
<br>
</div>
Regards,<br>
</div>
Jason<br>
<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Wed, Feb 17,
2016 at 9:22 PM, Rukmani Vijayaraghavan <span
dir="ltr"><<a moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:rukmani@virginia.edu">rukmani@virginia.edu</a>></span>
wrote:<br>
<blockquote class="gmail_quote"
style="margin:0 0 0 .8ex;border-left:1px
#ccc solid;padding-left:1ex">Hi
everyone,<br>
<br>
I've come across an error when updating
fluid variables at the inflow edge of a
wind tunnel simulation. I'm running a
simulation of a galaxy (with active dark
matter particles, gas, and passive
particles) in a box, whose fluid is
initialized to be identical to the
incoming wind (with vx, vy, vz = 600
km/s, 0, 0). There is a small error (on
the order of 1%) when updating grid
cells near the inflow boundary (with
both USM and PPM solvers), and this
error is spatially correlated with
block boundaries. While this error
itself is tolerable as far as the
density and pressure go, this has bad
consequences for the magnetic field
which grows as the wind propagates
through the box (see attached figure,
xl_boundary). This figure shows slices
of Bx at two timesteps (annotated with
block boundaries and magnetic field
vectors). The dynamic range of Bx in
this image has been reduced to highlight
these discontinuities. At the timesteps
shown in the attached image, the
fluctuations in Bx are ~1%, but grow
with time up to order unity. I've tried
a variety of Riemann solvers (HLLC,
HLLD, Roe, Hybrid), slope limiters (mc,
minmod, etc.), interpolation orders,
prolongation methods, turning on and off
specific USM switches, but nothing seems
to solve this issue so far. Has anybody
else dealt with and/or successfully
solved this issue?<br>
<br>
Thanks,<br>
Rukmani<span><font color="#888888"><br>
<br>
-- <br>
Rukmani Vijayaraghavan<br>
NSF Astronomy & Astrophysics
Postdoctoral Fellow<br>
University of Virginia<br>
<a moz-do-not-send="true"
href="mailto:rukmani@virginia.edu"
target="_blank">rukmani@virginia.edu</a><br>
<br>
</font></span></blockquote>
</div>
<br>
</div>
</blockquote>
<br>
<pre cols="72">--
Rukmani Vijayaraghavan
NSF Astronomy & Astrophysics Postdoctoral Fellow
University of Virginia
<a moz-do-not-send="true" href="mailto:rukmani@virginia.edu" target="_blank">rukmani@virginia.edu</a></pre>
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</blockquote>
</div>
<br>
</div>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Rukmani Vijayaraghavan
NSF Astronomy & Astrophysics Postdoctoral Fellow
University of Virginia
<a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="mailto:rukmani@virginia.edu">rukmani@virginia.edu</a></pre>
</div>
</blockquote>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Rukmani Vijayaraghavan
NSF Astronomy & Astrophysics Postdoctoral Fellow
University of Virginia
<a class="moz-txt-link-abbreviated" href="mailto:rukmani@virginia.edu">rukmani@virginia.edu</a></pre>
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