<div dir="ltr">Hi Zach and Samuel,<div><br></div><div>Thank you both for the great tips. To comment on some of the suggestions:</div><div><br></div><div>1. Resolution: I tested with a higher amount of resolution when I first encountered the problem, but for that particular case I still found the eccentricity. However, I do agree that resolution could not be ruled out as it might still not be high enough.<br><br></div><div>2. NS tracking grids: I used VisIt to visualize the grids following the two stars and they seem to cover most of the stars until they are tidally disrupted. The boxes are only slightly (1.2x) bigger than the star so I will increase the radius to what Zach recommended.<br><br></div><div>3. Initial data being too close: I was also wondering if 45 km was too close as it is about 3 * R_star. It is reassuring to hear from Samuel's test with FUKA that ADM angular momentum is consistent with PN results for a nearly same case.</div><div><br></div><div>In summary, I will try a few simulations with much higher resolution, bigger tracking grids to see if the problem persists. I will also make sure that I am measuring the ADM angular momentum correctly when comparing the PN and Lorene ID.</div><div><br></div><div>Again, thanks for the help. I will keep this thread updated whether it works out or not.</div><div><br></div><div>Best,</div><div>Johnny Tsao</div><div><br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Oct 6, 2022 at 12:21 PM Samuel Tootle <<a href="mailto:tootle@itp.uni-frankfurt.de">tootle@itp.uni-frankfurt.de</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<span dir="ltr" style="margin-top:0px;margin-bottom:0px">Hi Johnny,</span> <br> <br> <span dir="ltr" style="margin-top:0px;margin-bottom:0px">This is quite interesting given my understanding is that the inspiral for equal mass Lorene ID is usually quite reasonable. Specifically your note regarding the 20% difference between ADM Angular momentum for quasi-equilibrium and that resulting from your PN estimate ID seems quite wrong. Maybe the Lorene ID is at a poor resolution?</span> <br> <br> <span dir="ltr" style="margin-top:0px;margin-bottom:0px">I did a test with the FUKA BNS code for a 1.4-1.4 BNS using a polytope at 45km and the difference in the ADM Angular momentum between a coarse solution using quasi-equilibrium and 3.5PN estimates was < 1%.</span> <br> <br> <span dir="ltr" style="margin-top:0px;margin-bottom:0px">Cheers,</span> <br> <span dir="ltr" style="margin-top:0px;margin-bottom:0px">Samuel Tootle</span> <br> <span dir="ltr" style="margin-top:0px;margin-bottom:0px">Goethe Universität Frankfurt </span> <br>
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<p><strong>From: </strong>Zach Etienne <<a href="mailto:zachetie@gmail.com" target="_blank">zachetie@gmail.com</a>><br><strong>To: </strong>Bing-Jyun Tsao <<a href="mailto:johnny.tsao.880724@gmail.com" target="_blank">johnny.tsao.880724@gmail.com</a>><br><strong>CC: </strong><a href="mailto:users@einsteintoolkit.org" target="_blank">users@einsteintoolkit.org</a><br><strong>Date: </strong>Oct 5, 2022 21:02:01<br><strong>Subject: </strong>Re: [Users] Eccentricity in BNS evolution with Lorene<br></p>
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Hi Johnny,
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ADMBase::initial_shift = "zero"<br>
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so you eliminated one possible contributor to coordinate eccentricity (Lorene's initial shift condition results in significant eccentricity). Good choice.
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I don't use GRHydro/ML_BSSN, so I cannot comment on your choices there. Generic advice:
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* Resolution may be too low -- try higher resolution & see if your eccentricity reduces.
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* Initial data is too close (Lorene assumes a helical Killing vector, which is violated more and more as the initial separation of the stars decreases)
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* Check that you are properly tracking the NSs such that they are centered within high-resolution AMR boxes, and that the radius of the AMR boxes is at least 1.5x the radius of each NS. A movie visualizing the density of the stars in the orbital plane would be very very useful.
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Hope this helps!
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-Zach
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</div><span style="font-size:12.8px">* * *</span><br style="font-size:12.8px"><span style="font-size:12.8px">Zachariah Etienne</span>
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<div><a href="https://etienneresearch.com" target="_blank">https://etienneresearch.com</a>
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<div><a href="https://blackholesathome.net/" target="_blank">https://blackholesathome.net</a><br>
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On Wed, Oct 5, 2022 at 11:41 AM Bing-Jyun Tsao <<a href="mailto:johnny.tsao.880724@gmail.com" target="_blank">johnny.tsao.880724@gmail.com</a>> wrote:<br>
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Dear Einstein Toolkit community,
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I am Bing-Jyun (Johnny) Tsao, a graduate student at University of Texas at Austin. I am currently working on a project comparing our local version of BNS initial data (M. Clark, P. Laguna, 2016 Physical Review D 94 064058) with Lorene.
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When using Lorene, I found that the trajectory of the stars is showing eccentricity (as shown in the plot below), and this occurred when I ran Lorene with equal-mass BNS with ADM mass = 1.4 Msun, and with the publicly available Lorene data on their website "G2_I14vs14_D4R33_45km", both of which have an initial separation of 45 km. I use VolumeIntegral_GRMHD to track the stars, and GRHydro + ML_BSSN to evolve. Additionally, I also found that the ADM angular momentum from Lorene is about 20% smaller than that from our code which uses post-Newtonian calculations.
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My question is:
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From my understanding, Lorene gives quasi-circular initial data. Thus, is it abnormal to see eccentricity, or is it a physical artifact, perhaps from tidal deformation, that always shows up when the stars are very close to each other?
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Here I attached my parfile and the trajectory for a run using the Lorene publicly available data "G2_I14vs14_D4R33_45km".
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Thanks in advance.
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Best,
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Johnny Tsao
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