Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session F08: Numerical Methods I |
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Sponsoring Units: DGRAV Chair: David Neilsen, Brigham Young University Room: Symphony III - 2nd Floor |
Sunday, April 16, 2023 8:30AM - 8:42AM |
F08.00001: GRHayL: an open-source, modular, extensible library for GRMHD simulations Samuel D Cupp, Leonardo Werneck, Terrence Jacques, Zachariah B Etienne Most current general relativistic magnetohydrodynamic codes exist as monolithic blocks of code with limited code separation and modularity. This makes improvements and extensions to these codes difficult and lengthens the new user/contributor pipeline. These monoliths also work against the native benefits of open-source programming, as research groups have far less capability to use and interoperate with other groups' work. These problems are exacerbated by the underlying differences of different code infrastructures, which further limit the ability to share code between groups. Our new open-source General Relativistic Hydrodynamic Library (GRHayL) aims to resolve this by providing a modular, extensible, infrastructure-agnostic library of functions with standardized interfaces. This code is the successor to the IllinoisGRMHD code, inheriting and extending that code while compartmentalizing it into self-contained modules ("gems"). I discuss the motivations, design philosophies, and general structure of the GRHayL library. I also describe the methodology of unit and integration testing used for continuous code validation. |
Sunday, April 16, 2023 8:42AM - 8:54AM |
F08.00002: IllinoisGRMHD: Recent Developments and Future Plans Leonardo Werneck, Zachariah B Etienne, Ariadna Murguia-Berthier, Roland Haas, Federico Cipolletta, Scott C Noble, Lorenzo Ennoggi, Federico G Lopez Armengol, Bruno Giacomazzo, Thiago Assumpcao, Joshua A Faber, Tanmayee Gupte, Bernard J Kelly, Julian H Krolik, Samuel D Cupp, Terrence Jacques We have recently added support for finite-temperature, microphysical equations of state and neutrino physics (via a leakage scheme) to IllinoisGRMHD, an open-source Einstein Toolkit module that solves the General Relativistic Magnetohydrodynamics equations. First, we describe the two new open-source NRPy+-based codes that implement these new features: NRPyEOS and NRPyLeakage. Second, we present results of magnetized BNS simulations that leverage these improvements. Third, we discuss the modularization of these new features and their implementation in the open-source, infrastructure-agnostic General Relativistic Hydrodynamic Library (GRHayL), which is currently under development. Finally, we report on ongoing efforts, such as a new M1 closure scheme for neutrino radiation transport. |
Sunday, April 16, 2023 8:54AM - 9:06AM |
F08.00003: A new code to solve the equations of general relativistic hydrodynamics in singular curvilinear coordinates using GRHayL Terrence Jacques, Zachariah B Etienne, Maria C Hamilton, Mew-Bing Wan, Samuel D Cupp, Leonardo Werneck We report on the development of a new open-source code that solves the equations of general relativistic hydrodynamics (GRHD) in singular curvilinear coordinates. This code extends the General Relativistic Hydrodynamic Library (GRHayL) to support reference-metric-based formulations of the GRHD equations within the NRPy+ framework. Building on the existing capabilities within GRHayL, this extension will enable us to exploit near symmetries to perform extremely efficient simulations of systems of astrophysical interest, including neutron stars (nearly spherically symmetric or axisymmetric), black hole accretion disks (nearly axisymmetric), etc. As GRHayL already provides robust implementations of reconstruction algorithms, conservative-to-primitive solvers, finite-temperature microphysical equations of state, and neutrino physics, this code will be capable of state-of-the-art simulations. Here we present our progress and multi-dimensional tests validating our code. |
Sunday, April 16, 2023 9:06AM - 9:18AM |
F08.00004: Initial data for extreme binary black holes with the NRPyElliptic solver Thiago Assumpcao, Zachariah B Etienne Numerical relativity simulations of binary black holes (BBHs) form the foundation for gravitational wave (GW) data analysis. A great majority of these simulations cover zero- to moderate-spin scenarios. Modeling high to near-extremal spins is essential to the field of GW science, but is far more difficult. One challenge stems from the requirement that generating simulation initial data (ID) involves solving the (elliptic PDE) ADM Hamiltonian and momentum constraint equations for two superposed, conformally curved, boosted single-BH solutions. NRPyElliptic solves these constraint equations via a fast hyperbolic relaxation method. In its first version, it supported conformally flat, binary puncture ID. I will report on our new implementation of conformally curved BBH ID relaxations, as well as on infrastructure updates that make NRPyElliptic both faster and more flexible. |
Sunday, April 16, 2023 9:18AM - 9:30AM |
F08.00005: Implementation of Monte-Carlo radiation transport for the treatment of neutrinos in the SpEC merger code Francois V Foucart, Matthew Duez, Francois Hebert, Lawrence E Kidder, Phillip J Kovarik, Harald P Pfeiffer, Mark A Scheel Neutrino radiation transport plays an important role in the simulation of compact binary mergers involving neutron stars. Neutrinos are the main source of cooling of the post-merger remnant. Additionally, neutrino-matter interactions in the matter ejected during and after merger are crucial in determining the properties of the UV/optical/infrared transients following many neutron star mergers, as well as the outcome of nucleosynthesis in the ejecta. Properly evolving Boltzmann's equations for radiation transport remains however a difficult technical challenge. In this talk, I will review a significant step towards performing full transport in merger simulations: the implementation in the SpEC code of a Monte-Carlo algorithm. I will discuss the overall structure of a Monte-Carlo transport code, its advantages in the merger context, as well as the approximations that still have to be performed in order to keep simulations computationally affordable. |
Sunday, April 16, 2023 9:30AM - 9:42AM |
F08.00006: A new approach to isometric embedding of 2-surfaces, with applications in numerical relativity Robert P Owen, Iago Braz Mendes, Hengrui Zhu The isometric embedding of 2-surfaces such as apparent horizons in flat geometry is useful both for visualizing horizon structure and for computing quasilocal charges such as mass, energy, and angular momentum. Despite a very long history of approaches, the problem still remains difficult, particularly for the highly deformed horizons that occur when numerical relativity simulations are most interesting. Here we will introduce a radically new approach to the problem that factors the solving of the highly nonlinear embedding PDEs into a sequence of quasilinear and fully linear PDEs that are much more straightforward to handle. We will present an implementation of this method in the SpEC code and compare it with more conventional approaches. |
Sunday, April 16, 2023 9:42AM - 9:54AM |
F08.00007: Local Accretion Disk Dynamo Models from Azimuthally Averaged 3D Simulations Courtney L Cadenhead, Matt D Duez Magnetized turbulent systems such as accretion disks can be numerically evolved for long times much more cheaply if axisymmetry is assumed. However, the field in such 2D simulations unphysically decays unless dynamo terms, representing the underlying nonaxisymmetry, are explicitly added to the induction equation. Thus far, such simulations have commonly assumed simple, isotropic forms of the dynamo coefficient tensors. While this does yield magnetic fields that do not die off, it is unclear that it is necessarily correct. We test this assumption by azimuthally averaging data from a 3D black hole accretion simulation carried out by the IllinoisGRMHD code. Multiple local models, in which the dynamo electromotive force is a linear function of the local azimuthally averaged magnetic field and current, are tested, but no statistically reliable model could be attained. However, we do find that most of the turbulent kinetic and magnetic energy in the disk is not in the azimuthal mean, but in the RMS deviation, although the jet is mostly axisymmetric. As such, we conclude by discussing more general models that incorporate turbulent energy, dynamo electromotive force and momentum transport. |
Sunday, April 16, 2023 9:54AM - 10:06AM |
F08.00008: AsterX: a new open-source GPU-accelerated GRMHD code for dynamical spacetimes Jay V Kalinani, Steven Brandt, Manuela Campanelli, Riccardo Ciolfi, Lorenzo Ennoggi, Bruno Giacomazzo, Roland Haas, liwei Ji, Federico G Lopez Armengol, Erik Schnetter, Yosef Zlochower With an increasing demand of extensive parallel computing in numerical simulations addressing various astrophysical problems, codes which can efficiently work on GPUs are the need of the hour. In this talk, I will discuss the salient features of a new open-source general relativistic magnetohydrodynamic (GRMHD) code AsterX, which is built upon CarpetX, a new driver for the Einstein Toolkit. AsterX is based on the flux-conservative Valencia formulation, considering staggered vector potential evolution. It designed to work on GPUs and also takes advantage of the block-structured adaptive mesh refinement provided by CarpetX through the AMReX framework. AsterX is still under development, and currently being tested on the Frontera cluster, passing some of the stringent GRMHD tests. |
Sunday, April 16, 2023 10:06AM - 10:18AM |
F08.00009: Dynamical perturbations of black-hole punctures: effects of slicing conditions Sean E Li, Thomas W Baumgarte, Kenneth A Dennison, Henrique P de Oliveira While numerous numerical relativity simulations adopt a 1+log slicing condition, shock-avoiding slicing conditions form a viable and sometimes advantageous alternative. Despite both conditions satisfying similar equations, recent numerical experiments point to a qualitative difference in the behavior of the lapse in the vicinity of the black-hole puncture: for 1+log slicing, the lapse appears to decay approximately exponentially, while for shock-avoiding slices it performs approximately harmonic oscillation. Motivated by this observation, we consider dynamical coordinate transformations of the Schwarzschild spacetime to describe small perturbations of static trumpet geometries analytically. We identify the mean curvature at the unperturbed puncture as causing the qualitative differences seen in dynamical evolutions. |
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