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<div>Dear Michiel,</div>
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<div>On your second question: are you sure that you’re not setting up a cylindrical blast wave, rather than a spherical one? A 2D, slab symmetric, point explosion is effectively that of an infinite line charge, rather than a spherical, point explosion. The
line charge indeed expands faster. There is, of course, an exact analytic solution for this. For an analogous case with a constant energy input, see eqs. 5-7 of Mac Low, McCray, & Norman, ApJ (1989). Therefore, you may be fine sticking with your Cartesian
grid, so perhaps you don’t need to solve your first problem.</div>
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<div>Best,</div>
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<div>Mordecai-Mark Mac Low</div>
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<div>--<br class="">
Mordecai-Mark Mac Low <span class="Apple-tab-span" style="white-space: pre;"> </span>
Curator & Professor<br class="">
+1-212-496-3443 <span class="Apple-tab-span" style="white-space: pre;"> </span>
Department of Astrophysics<br class="">
+1-212-769-5007 (fax) <span class="Apple-tab-span" style="white-space: pre;"> </span>
American Museum of Natural History<br class="">
mmaclow (Skype, Hangout) <span class="Apple-tab-span" style="white-space: pre;">
</span>79th St at CPW, NY, NY, 10024-5192, USA<br class="">
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<div class="">On Sep 23, 2016, at 08:50, Michiel Bustraan <<a href="mailto:michiel.bustraan@astro.su.se" class="">michiel.bustraan@astro.su.se</a>> wrote:</div>
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Hello all,<br class="">
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I have two things that I could really use some help with, and I haven't been able to figure it out by myself.<br class="">
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Firstly, I've been trying to run a simulation in 2D with a spherical geometry, but a few steps after starting the simulation the code crashes due to a negative dt.<br class="">
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I set the density and temperature constant in the simulation, and the velocity to 0, so nothing should be happening (just as a test case).<br class="">
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I'm attaching a plot of the density just before the crash. <span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);" class="">I</span><span style="font-family: Calibri, Arial, Helvetica, sans-serif; font-size: 16px; background-color: rgb(255, 255, 255);" class="">'m
guessing the problem lies in the grid somewhere, but I have no idea how to fix it.</span><br class="">
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Have any of you encountered something like this before?<br class="">
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Secondly, and the reason I've been wanting to switch to a spherical geometry, is the results of simulating shocks in 2D using a Cartesian geometry.<br class="">
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I ran some simulations with a spherical shock (outward radial velocity from a dense region), and found that the shock doesn't develop the same way in 2D as it does in<br class="">
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3D Cartesian. The shock tends to move much faster, as if it is encountering less resistance or has too much kinetic energy.<br class="">
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Shouldn't it be possible to have a 2D Cartesian slice of a spherical outward shock? Are these issues simply due to the geometry or from an error in setting up the problem?<br class="">
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I would really love some help on this, since I've just been trying unsuccessfully to fix it on my own.<br class="">
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Kind Regards,<br class="">
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Michiel Bustraan<br class="">
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<span id="cid:F05972CF-9702-45F6-9D4E-74CD8648C75B@domain.actdsltmp"><SphericalIssues.png></span></div>
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