47,067 research outputs found
Radiation hydrodynamics including irradiation and adaptive mesh refinement with AZEuS. I. Methods
Aims. The importance of radiation to the physical structure of protoplanetary
disks cannot be understated. However, protoplanetary disks evolve with time,
and so to understand disk evolution and by association, disk structure, one
should solve the combined and time-dependent equations of radiation
hydrodynamics.
Methods. We implement a new implicit radiation solver in the AZEuS adaptive
mesh refinement magnetohydrodynamics fluid code. Based on a hybrid approach
that combines frequency-dependent ray-tracing for stellar irradiation with
non-equilibrium flux limited diffusion, we solve the equations of radiation
hydrodynamics while preserving the directionality of the stellar irradiation.
The implementation permits simulations in Cartesian, cylindrical, and spherical
coordinates, on both uniform and adaptive grids.
Results. We present several hydrostatic and hydrodynamic radiation tests
which validate our implementation on uniform and adaptive grids as appropriate,
including benchmarks specifically designed for protoplanetary disks. Our
results demonstrate that the combination of a hybrid radiation algorithm with
AZEuS is an effective tool for radiation hydrodynamics studies, and produces
results which are competitive with other astrophysical radiation hydrodynamics
codes.Comment: 15 pages, 10 figures, accepted for publication in A&
Cosmological Radiation Hydrodynamics with ENZO
We describe an extension of the cosmological hydrodynamics code ENZO to
include the self-consistent transport of ionizing radiation modeled in the
flux-limited diffusion approximation. A novel feature of our algorithm is a
coupled implicit solution of radiation transport, ionization kinetics, and gas
photoheating, making the timestepping for this portion of the calculation
resolution independent. The implicit system is coupled to the explicit
cosmological hydrodynamics through operator splitting and solved with scalable
multigrid methods. We summarize the numerical method, present a verification
test on cosmological Stromgren spheres, and then apply it to the problem of
cosmological hydrogen reionization.Comment: 14 pages, 3 figures, to appear in Recent Directions in Astrophysical
Quantitative Spectroscopy and Radiation Hydrodynamics, Ed. I. Hubeny,
American Institute of Physics (2009
Radiation hydrodynamics integrated in the code PLUTO
The transport of energy through radiation is very important in many
astrophysical phenomena. In dynamical problems the time-dependent equations of
radiation hydrodynamics have to be solved. We present a newly developed
radiation-hydrodynamics module specifically designed for the versatile MHD code
PLUTO. The solver is based on the flux-limited diffusion approximation in the
two-temperature approach. All equations are solved in the co-moving frame in
the frequency independent (grey) approximation. The hydrodynamics is solved by
the different Godunov schemes implemented in PLUTO, and for the radiation
transport we use a fully implicit scheme. The resulting system of linear
equations is solved either using the successive over-relaxation (SOR) method
(for testing purposes), or matrix solvers that are available in the PETSc
library. We state in detail the methodology and describe several test cases in
order to verify the correctness of our implementation. The solver works in
standard coordinate systems, such as Cartesian, cylindrical and spherical, and
also for non-equidistant grids. We have presented a new radiation-hydrodynamics
solver coupled to the MHD-code \PLUTO that is a modern, versatile and efficient
new module for treating complex radiation hydrodynamical problems in
astrophysics. As test cases, either purely radiative situations, or full
radiation-hydrodynamical setups (including radiative shocks and convection in
accretion discs) have been studied successfully. The new module scales very
well on parallel computers using MPI. For problems in star or planet formation,
we have added the possibility of irradiation by a central source.Comment: 13 pages, 11 figures, accepted by Astronomy & Astrophysic
Fornax: a Flexible Code for Multiphysics Astrophysical Simulations
This paper describes the design and implementation of our new multi-group,
multi-dimensional radiation hydrodynamics (RHD) code Fornax and provides a
suite of code tests to validate its application in a wide range of physical
regimes. Instead of focusing exclusively on tests of neutrino radiation
hydrodynamics relevant to the core-collapse supernova problem for which Fornax
is primarily intended, we present here classical and rigorous demonstrations of
code performance relevant to a broad range of multi-dimensional hydrodynamic
and multi-group radiation hydrodynamic problems. Our code solves the
comoving-frame radiation moment equations using the M1 closure, utilizes
conservative high-order reconstruction, employs semi-explicit matter and
radiation transport via a high-order time stepping scheme, and is suitable for
application to a wide range of astrophysical problems. To this end, we first
describe the philosophy, algorithms, and methodologies of Fornax and then
perform numerous stringent code tests, that collectively and vigorously
exercise the code, demonstrate the excellent numerical fidelity with which it
captures the many physical effects of radiation hydrodynamics, and show
excellent strong scaling well above 100k MPI tasks.Comment: Accepted to the Astrophysical Journal Supplement Series; A few more
textual and reference updates; As before, one additional code test include
Truncated Moment Formalism for Radiation Hydrodynamics in Numerical Relativity
A truncated moment formalism for general relativistic radiation
hydrodynamics, based on the Thorne's moment formalism, is derived. The fluid
rest frame is chosen to be the fiducial frame for defining the radiation
moments. Then, zeroth-, first-, and second-rank radiation moments are defined
from the distribution function with a physically reasonable assumption for it
in the optically thin and thick limits. The source terms are written, focusing
specifically on the neutrino transfer and neglecting higher harmonic angular
dependence of the reaction angle. Finally, basic equations for a truncated
moment formalism for general relativistic radiation hydrodynamics in a closed
covariant form are derived assuming a closure relation among the radiation
stress tensor, energy density, and energy flux, and a variable Eddington
factor, which works well.Comment: 33 pages, 2 figures, to be published in Prog. Theor. Phy
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
Model for an optically thick torus in local thermodynamic equilibrium around a black hole
We propose a simple model for an optically thick radiative torus in local
thermodynamic equilibrium around a Kerr black hole. The hydrodynamics
structure, which is not affected by the radiation field, is the same as for the
so--called polish doughnuts. Under the assumption of isentropic fluid and
polytropic equation of state, a simple stationary and axisymmetric solution to
the relativistic radiation hydrodynamics equations is possible, for which the
temperature of the torus scales like the specific enthalpy. The astrophysical
relevance of the model is briefly discussed.Comment: With updated bibliographyc informatio
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