35,635 research outputs found
Fast and accurate frequency-dependent radiation transport for hydrodynamics simulations in massive star formation
Context: Radiative feedback plays a crucial role in the formation of massive
stars. The implementation of a fast and accurate description of the proceeding
thermodynamics in pre-stellar cores and evolving accretion disks is therefore a
main effort in current hydrodynamics simulations.
Aims: We introduce our newly implemented three-dimensional frequency
dependent radiation transport algorithm for hydrodynamics simulations of
spatial configurations with a dominant central source.
Methods: The module combines the advantage of the speed of an approximate
Flux Limited Diffusion (FLD) solver with the high accuracy of a frequency
dependent first order ray-tracing routine.
Results: We prove the viability of the scheme in a standard radiation
benchmark test compared to a full frequency dependent Monte-Carlo based
radiative transfer code. The setup includes a central star, a circumstellar
flared disk, as well as an envelope. The test is performed for different
optical depths. Considering the frequency dependence of the stellar
irradiation, the temperature distributions can be described precisely in the
optically thin, thick, and irradiated transition regions. Resulting radiative
forces onto dust grains are reproduced with high accuracy. The achievable
parallel speedup of the method imposes no restriction on further radiative
(magneto-) hydrodynamics simulations.
Conclusions: The proposed approximate radiation transport method enables
frequency dependent radiation hydrodynamics studies of the evolution of
pre-stellar cores and circumstellar accretion disks around an evolving massive
star in a highly efficient and accurate manner.Comment: 16 pages, 11 figure
Hierarchical fractional-step approximations and parallel kinetic Monte Carlo algorithms
We present a mathematical framework for constructing and analyzing parallel
algorithms for lattice Kinetic Monte Carlo (KMC) simulations. The resulting
algorithms have the capacity to simulate a wide range of spatio-temporal scales
in spatially distributed, non-equilibrium physiochemical processes with complex
chemistry and transport micro-mechanisms. The algorithms can be tailored to
specific hierarchical parallel architectures such as multi-core processors or
clusters of Graphical Processing Units (GPUs). The proposed parallel algorithms
are controlled-error approximations of kinetic Monte Carlo algorithms,
departing from the predominant paradigm of creating parallel KMC algorithms
with exactly the same master equation as the serial one.
Our methodology relies on a spatial decomposition of the Markov operator
underlying the KMC algorithm into a hierarchy of operators corresponding to the
processors' structure in the parallel architecture. Based on this operator
decomposition, we formulate Fractional Step Approximation schemes by employing
the Trotter Theorem and its random variants; these schemes, (a) determine the
communication schedule} between processors, and (b) are run independently on
each processor through a serial KMC simulation, called a kernel, on each
fractional step time-window.
Furthermore, the proposed mathematical framework allows us to rigorously
justify the numerical and statistical consistency of the proposed algorithms,
showing the convergence of our approximating schemes to the original serial
KMC. The approach also provides a systematic evaluation of different processor
communicating schedules.Comment: 34 pages, 9 figure
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