<div dir="ltr"><div>Hello Dongwook,</div><div><br></div>That's correct, I did not have this same problem using FLASH3. I have not run this same exact setup under FLASH3, but I have run many very similar setups (same mass/energy blastwaves in similar environment). Unfortunately it would take some effort to back-port this particular setup to FLASH3. The primary difference in our setup between FLASH3 and FLASH4 is the move from the split to the unsplit solver, but I don't know if that is causing the issue here. The basic setup is a spherical blast wave with 10^51 erg kinetic energy started in the free-expansion phase inside an HII region, where we have zoomed in from a cosmological simulation. There are 128-256 cells across the diameter of the blast wave. <div><br></div><div>I've tried different Riemann solvers (Roe, HLLC, and hybrid), with and without shock detection and lowering the CFL. I've tried different masses/velocities for the blastwaves. They all eventually run into this problem at some point, usually after a few hundred years. I wonder if I don't have some incorrect choices in flash.par? Below are the relevant values from the Hydro section of my flash.par. </div><div><br><div>Cheers,</div><div>-Jeremy</div><div><br></div><div><br></div><div><div># Hydro ---------------------------------------------------</div><div>useHydro<span style="white-space:pre"> </span>= .true.</div><div>updateHydroFluxes<span style="white-space:pre"> </span>= .true.</div><div>ppm_modifystates<span style="white-space:pre"> </span>= .false.</div><div>use_auxEintEqn<span style="white-space:pre"> </span>= .false.</div><div><br></div><div>eintSwitch<span style="white-space:pre"> </span>= 1.0e-4</div><div>gamma<span style="white-space:pre"> </span>= 1.66666666667</div><div>cfl<span style="white-space:pre"> </span>= 0.8</div><div>cvisc<span style="white-space:pre"> </span>= 0.1</div><div>nriem<span style="white-space:pre"> </span>= 25</div><div><br></div><div>small<span style="white-space:pre"> </span>= 1.0E-40</div><div>smlrho<span style="white-space:pre"> </span>= 1.0E-40</div><div>smallp<span style="white-space:pre"> </span>= 1.0E-40</div><div>smalle<span style="white-space:pre"> </span>= 1.E8</div><div>smallt<span style="white-space:pre"> </span>= 1.</div><div>smallu<span style="white-space:pre"> </span>= 1.0E-40</div><div>smallx<span style="white-space:pre"> </span>= 1.0E-40</div><div><br></div><div>## SWITCHES SPECIFIC TO THE UNSPLIT HYDRO SOLVER ##</div><div>#interpol_order<span style="white-space:pre"> </span>= 2</div><div>order<span style="white-space:pre"> </span>= 3<span style="white-space:pre"> </span># 3rd PPM</div><div>slopeLimiter<span style="white-space:pre"> </span>= "mc"<span style="white-space:pre"> </span># Slope limiters (minmod, mc, vanLeer, hybrid, limited)</div><div>LimitedSlopeBeta<span style="white-space:pre"> </span>= 1.<span style="white-space:pre"> </span># Slope parameter for the "limited" slope by Toro</div><div>charLimiting<span style="white-space:pre"> </span>= .true.<span style="white-space:pre"> </span># Characteristic limiting vs.Primitive limiting</div><div><br></div><div>use_avisc<span style="white-space:pre"> </span>= .true.<span style="white-space:pre"> </span># use artificial viscosity (originally for PPM)</div><div>use_flattening<span style="white-space:pre"> </span>= .false.<span style="white-space:pre"> </span># use flattening (dissipative) (originally for PPM)</div><div>use_steepening<span style="white-space:pre"> </span>= .false.<span style="white-space:pre"> </span># use contact steepening (originally for PPM)</div><div>use_upwindTVD<span style="white-space:pre"> </span>= .false.<span style="white-space:pre"> </span># use upwind biased TVD slope for PPM (need nguard=6)</div><div><br></div><div>flux_correct<span style="white-space:pre"> </span>= .true.</div><div>shockDetect<span style="white-space:pre"> </span>= .true.</div><div>shockLowerCFL<span style="white-space:pre"> </span>= .true.</div><div><br></div><div># II. RIEMANN SOLVERS: </div><div>RiemannSolver<span style="white-space:pre"> </span>= "hybrid" # Roe, HLL, HLLC, LLF, Marquina</div><div>entropy<span style="white-space:pre"> </span>= .false.</div><div><br></div><div>use_gravHalfUpdate<span style="white-space:pre"> </span>= .true.</div><div><br></div><div>#convertToConsvdInMeshInterp<span style="white-space:pre"> </span>= .false.</div><div><br></div><div><br></div><div># apply gr_smalle and don't print anything</div><div>#enableMaskedGCFill<span style="white-space:pre"> </span>= .true.</div><div>gr_sanitizeDataMode<span style="white-space:pre"> </span>= 3</div><div>gr_sanitizeVerbosity<span style="white-space:pre"> </span>= 0</div></div><div><br></div><div><br></div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Feb 20, 2018 at 2:40 PM, Dongwook Lee <span dir="ltr"><<a href="mailto:dongwook@flash.uchicago.edu" target="_blank">dongwook@flash.uchicago.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Dear Jeremy,<div><br></div><div>Do you see this instability issue only with FLASH4, but NOT with FLASH3? More specifically, I wonder what happens if you run the exact same problem with FLASH3. Have you tried this type of FLASH3 and FLASH4 comparison tests?</div><div><br></div><div>Cheers,</div><div>Dongwook</div></div><div class="gmail_extra"><div><div class="gmail-h5"><br><div class="gmail_quote">On Sun, Feb 18, 2018 at 10:41 AM, Jeremy S Ritter <span dir="ltr"><<a href="mailto:jritter@mail.utexas.edu" target="_blank">jritter@mail.utexas.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Hello Flash Users,<div><br></div><div>I have been using FLASH since version 3 to run simulations of supernova blastwaves in cosmological simulations. Since updating to version 4 I have had a lot of stability problems with the unsplit solver and strong shocks. The setup is similar to a Sedov example, with a spherical blastwave inserted into a realistic cosmological environment. We zoom in to high resolution to insert the blastwaves with radii of ~1 pc and 16-32 grid blocks across the diameter. The background density/temperature/pressure in the vicinity of the blastwaves is effectively constant when zoomed in to this scale. We refine a large volume around the blastwave so that the entirety of it is kept at the same refinement level while expanding.</div><div><br></div><div>The blastwaves will evolve as they should for many years, doubling or more in radius, and then suddenly within 1 step the solution will break down. This happens in the free expansion phase, before the reverse shock. The timestep dt will drop from ~1 year to 10^-7 seconds, tracer particles in the blastwave will be flung outside of the simulation box, gas density in some cells will drop by 20 orders of magnitude, etc. </div><div><br></div><div>I have tried both the HLLC and the hybrid HLLC solver with shock detection and shock lower CFL. By lowering the CFL even further, to 0.1, I was able to push the simulation further but eventually it breaks down too. I never had any similar issues in FLASH3. I was wondering if anybody has dealt with anything similar in FLASH4?</div><div><br></div><div>Cheers,</div><div>-Jeremy</div><div><br></div></div>
</blockquote></div><br><br clear="all"><div><br></div></div></div><span class="gmail-HOEnZb"><font color="#888888">-- <br><div class="gmail-m_-1207754710095964481gmail_signature"><div dir="ltr"><div style="font-size:12.8px"><font color="#000000" size="2" face="arial, helvetica, sans-serif"><br>==============================<wbr>===========</font></div><div style="font-size:12.8px"><font color="#000000" size="2" face="arial, helvetica, sans-serif">Dongwook Lee, Ph.D., Assistant Professor</font></div><div style="font-size:12.8px"><font color="#000000" size="2" face="arial, helvetica, sans-serif">Applied Mathematics and Statistics<br></font></div><div style="font-size:12.8px"><font color="#000000" size="2" face="arial, helvetica, sans-serif">University of California, Santa Cruz</font></div><div style="font-size:12.8px"><font color="#000000" size="2" face="arial, helvetica, sans-serif">Baskin Engineering, Room 353C</font></div><div style="font-size:12.8px"><font color="#000000" size="2" face="arial, helvetica, sans-serif"><a href="https://maps.google.com/?q=1156+High+Street,+Santa+Cruz,+CA+95064&entry=gmail&source=g">1156 High Street, Santa Cruz, CA 95064</a></font></div><div style="font-size:12.8px"><font color="#000000" size="2" face="arial, helvetica, sans-serif"><a href="https://users.soe.ucsc.edu/~dongwook/" target="_blank">https://users.soe.ucsc.edu/~<wbr>dongwook/</a></font></div><div><br></div></div></div>
</font></span></div>
</blockquote></div><br></div></div>