Hybrid Adaptive Ray-Moment Method (HARM2): A highly parallel method for radiation hydrodynamics on adaptive grids

Abstract

We present a highly-parallel multi-frequency hybrid radiation hydrodynamics algorithm that combines a spatially-adaptive long characteristics method for the radiation field from point sources with a moment method that handles the diffuse radiation field produced by a volumefilling fluid. Our Hybrid Adaptive Ray-Moment Method (HARM 2 ) operates on patch-based adaptive grids, is compatible with asynchronous time stepping, and works with any moment method. In comparison to previous long characteristics methods, we have greatly improved the parallel performance of the adaptive long-characteristics method by developing a new completely asynchronous and non-blocking communication algorithm. As a result of this improvement, our implementation achieves near-perfect scaling up to O(10 3 ) processors on distributed memory machines. We present a series of tests to demonstrate the accuracy and performance of the method.

Synthetic observations of star formation and the interstellar medium

“…In a hybrid method, the radiation from the central point source is followed using ray-tracing, while the cooler extended emission is modelled using a cheaper but more diffusive technique, such as flux-limited diffusion (see e.g. Kuiper et al, 2010a;Rosen et al, 2017).…”

Massive-star Formation via the Collapse of Subvirial and Virialized Turbulent Massive Cores

“…Each star particle includes a model for protostellar evolution used to represent them as radiating protostars with frequency dependent stellar luminosities (Lejeune et al 1997;Hosokawa & Omukai 2009;Offner et al 2009;Rosen et al 2016). In order to properly model both the direct and indirect radiation pressure we use the HARM 2 algorithm presented in Rosen et al (2017). HARM 2 uses a frequency-dependent adaptive long-characteristics ray-tracing scheme that accurately solves the radiative transfer equation along rays to model the radial stellar radiation field from stars that is absorbed by dust and is coupled to a grey moment method, in our case FLD, which models the dust reprocessed thermal radiation field intrinsic to the dusty fluid.…”

“…To reduce the computational cost, the rays adaptively split to conserve solid angle as they propagate radially away from their sources. We refer the reader to , Paper I, and Rosen et al (2017) for a complete description of our treatment of the direct and indirect radiation pressures modeled in this work. For each simulation we begin with a base grid with volume (0.4 pc) 3 discretized by 128 3 cells and allow for five levels of refinement resulting in a maximum resolution of 20 AU.…”

Numerical Methods for Simulating Star Formation

“…The simpler sub-grid models use a gray FLD model for the radiation transport where the protostellar luminosity is simply a source term in the radiative energy equation (Krumholz et al, 2007a;Offner et al, 2009;Stamatellos et al, 2011;Fontani et al, 2018;Jones and Bate, 2018). Frequency dependent protostellar irradiation modules have been developed using ray-tracing to compute the radiation fields, combined with moment models for radiation hydrodynamics (Kuiper et al, 2010a;Wise and Abel, 2011;Klassen et al, 2014;Ramsey and Dullemond, 2015;Buntemeyer et al, 2016;Rosen et al, 2017). These frequency dependent modules have been used primarily in the context of massive star formation Rosen et al, 2016).…”