<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;"><div>Dear FLASH users,</div><div><br></div><div>I am currently getting started with FLASH. I am trying to reproduce the radiation-inhibited Bondi accretion test problem of the RadFLAH scheme. The problem corresponds to spherical accretion of matter onto a central luminous object modeled as a point-like source of radiation. The problem is described in detail in Section 4.6 of Chatzopoulos & Weide (2019), the paper about the implementation of the RadFLAH scheme in FLASH.</div><div><br></div><div>I am using the latest release of FLASH, and the simulation files under Simulation/SimulationMain/radflaHD/BondiAccretion. My setup command is the one provided in the flash.par file of the simulation directory: </div><div><br></div><div><p style="margin: 0px; font-style: normal; font-variant-caps: normal; font-stretch: normal; line-height: normal; font-family: Menlo; font-size-adjust: none; font-kerning: auto; font-variant-alternates: normal; font-variant-ligatures: normal; font-variant-numeric: normal; font-variant-east-asian: normal; font-variant-position: normal; font-feature-settings: normal; font-optical-sizing: auto; font-variation-settings: normal; color: rgb(0, 0, 0);"><span style="font-variant-ligatures: no-common-ligatures;"><font size="2">./setup radflaHD/BondiAccretion -1d -auto +spherical -nxb=16 mgd_meshgroups=1 +parallelio +uhd3Tr IgnoreSpecies=True</font></span></p></div><div><br></div>When I run the code using the parameter values in the flash.par file as they are (using the physical parameters detailed in the paper), the code crashes before reaching a stationary state (and the analytical solution of the problem). The issue seems to arise due to high-frequency oscillations at the outer boundary which lead to negative internal energies. S<span style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0);">ee the first attached figure below for illustration</span>. For reference, I also attached the log files of this simulation.<div><br></div><div>On the other hand, I ran another simulation increasing the rho_vac parameter (vacuum density) from its default value (1.0e-18) to 1.0e-16, and the simulation ended successfully, reaching a stationary state, and matching the analytic solution nearly everywhere (aside from a few small features). You can see this final state in the second attached figure.</div><div><br></div><div>I also tried initializing the variables from the analytic solution but the high-frequency oscillations at the boundary still apear and make the simulation crash (see the third figure). Lowering the CFL factor down to 0.4 does not help either in any case.</div><div><br></div><div>I am a bit lost now as to what could be the source of the problem. <span style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0);">I would greatly appreciate any insights or suggestions about things I could try. </span><span style="caret-color: rgb(0, 0, 0); color: rgb(0, 0, 0);">Please let me know if you would like me to provide any further details that may be useful to diagnose the issue (for example, any other plots or animations).</span></div><div><br></div><div>Thank you very much in advance. </div><div><div><br></div><div>Best wishes,</div><div>Joaquin.</div><div><p style="caret-color: rgb(0, 0, 0);"><font color="#000000"><span class="gmail_signature_prefix" style="caret-color: rgb(34, 34, 34); background-color: rgb(255, 255, 255);">-- </span><br style="caret-color: rgb(34, 34, 34); background-color: rgb(255, 255, 255);"></font></p><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><b style="caret-color: rgb(34, 34, 34);"><font color="#000000" style="background-color: rgba(255, 255, 255, 0);">Dr. Joaquin Pelle</font></b><div style="caret-color: rgb(34, 34, 34);"><div><font color="#000000" style="background-color: rgba(255, 255, 255, 0);">Max Planck Institute for Gravitational Physics (Albert Einstein Institute) <br>Am Mühlenberg 1, 14476 Potsdam</font></div><div><font color="#000000" style="background-color: rgba(255, 255, 255, 0);">Phone: +49 331 567-7168 <br>Office: 0.28 <br>Personal website: <a href="https://joaquinpelle.github.io/" target="_blank">https://joaquinpelle.github.io/</a></font></div></div><div style="caret-color: rgb(34, 34, 34);"><font color="#000000" style="background-color: rgba(255, 255, 255, 0);">Institutional website: <a href="https://www.aei.mpg.de/person/137090/25873">https://www.aei.mpg.de/person/137090/25873</a></font></div><div style="caret-color: rgb(34, 34, 34);"><br></div><div style="caret-color: rgb(34, 34, 34);"></div></div></div></div></div></div></div></div></div></div></body></html>