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Author name code: ustyugov
ADS astronomy entries on 2022-09-14
author:"Ustyugov, Sergey D."
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Title: Dust-Polarization Maps for Local Interstellar Turbulence
Authors: Kritsuk, Alexei G.; Flauger, Raphael; Ustyugov, Sergey D.
2018PhRvL.121b1104K Altcode: 2017arXiv171111108K
We show that simulations of magnetohydrodynamic turbulence in the
multiphase interstellar medium yield an E /B ratio for polarized
emission from Galactic dust in broad agreement with recent Planck
measurements. In addition, the B -mode spectra display a scale
dependence that is consistent with observations over the range of scales
resolved in the simulations. The simulations present an opportunity to
understand the physical origin of the E /B ratio and a starting point
for more refined models of Galactic emission of use for both current
and future cosmic microwave background experiments.
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Title: The structure and statistics of interstellar turbulence
Authors: Kritsuk, A. G.; Ustyugov, S. D.; Norman, M. L.
2017NJPh...19f5003K Altcode: 2017arXiv170501912K
We explore the structure and statistics of multiphase, magnetized
ISM turbulence in the local Milky Way by means of driven periodic
box numerical MHD simulations. Using the higher order-accurate
piecewise-parabolic method on a local stencil (PPML), we carry out a
small parameter survey varying the mean magnetic field strength and
density while fixing the rms velocity to observed values. We quantify
numerous characteristics of the transient and steady-state turbulence,
including its thermodynamics and phase structure, kinetic and magnetic
energy power spectra, structure functions, and distribution functions
of density, column density, pressure, and magnetic field strength. The
simulations reproduce many observables of the local ISM, including
molecular clouds, such as the ratio of turbulent to mean magnetic
field at 100 pc scale, the mass and volume fractions of thermally
stable Hi, the lognormal distribution of column densities, the
mass-weighted distribution of thermal pressure, and the linewidth-size
relationship for molecular clouds. Our models predict the shape of
magnetic field probability density functions (PDFs), which are strongly
non-Gaussian, and the relative alignment of magnetic field and density
structures. Finally, our models show how the observed low rates of
star formation per free-fall time are controlled by the multiphase
thermodynamics and large-scale turbulence.
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Title: Realistic Magnetohydrodynamical Simulation of Solar Local
Supergranulation
Authors: Ustyugov, S. D.
2012ASPC..454...73U Altcode:
Three-dimensional numerical simulations of solar surface
magnetoconvection using realistic model physics are conducted. The
thermal structure of convective motions into the upper radiative
layers of the photosphere, the main scales of convective cells and
the penetration depths of convection are investigated. We take part of
the solar photosphere with size of 60×60 Mm in horizontal direction
and by depth 20 Mm from level of the visible solar surface. We use
a realistic initial model of the Sun and apply equation of state
and opacities of stellar matter. The equations of fully compressible
radiation magnetohydrodynamics with dynamical viscosity and gravity are
solved. We apply: <P />1) Piecewise Parabolic Method on a Local Stecil
(PPML) for the magnetohydrodynamics, <P />2) conservative method of
characteristic for the radiative transfer, <P />3) dynamical viscosity
from subgrid scale modeling. <P />In simulation we take uniform
two-dimesional grid in gorizontal plane and nonuniform grid in vertical
direction with number of cells 600×600×204. We use 512 processors
with distributed memory multiprocessors on supercomputer MVS-100k in
the Joint Computational Centre of the Russian Academy of Sciences.
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Title: The Two States of Star-forming Clouds
Authors: Collins, David C.; Kritsuk, Alexei G.; Padoan, Paolo; Li,
Hui; Xu, Hao; Ustyugov, Sergey D.; Norman, Michael L.
2012ApJ...750...13C Altcode: 2012arXiv1202.2594C
We examine the effects of self-gravity and magnetic fields on supersonic
turbulence in isothermal molecular clouds with high-resolution
simulations and adaptive mesh refinement. These simulations use large
root grids (512<SUP>3</SUP>) to capture turbulence and four levels of
refinement to follow the collapse to high densities, for an effective
resolution of 8192<SUP>3</SUP>. Three Mach 9 simulations are performed,
two super-Alfvénic and one trans-Alfvénic. We find that gravity
splits the clouds into two populations, one low-density turbulent
state and one high-density collapsing state. The low-density state
exhibits properties similar to non-self-gravitating in this regime,
and we examine the effects of varied magnetic field strength on
statistical properties: the density probability distribution function
is approximately lognormal, the velocity power spectral slopes decrease
with decreasing mean field strength, the alignment between velocity
and magnetic field increases with the field, and the magnetic field
probability distribution can be fitted to a stretched exponential. The
high-density state is well characterized by self-similar spheres:
the density probability distribution is a power law, collapse rate
decreases with increasing mean field, density power spectra have
positive slopes, P(ρ, k)vpropk, thermal-to-magnetic pressure ratios
are roughly unity for all mean field strengths, dynamic-to-magnetic
pressure ratios are larger than unity for all mean field strengths,
the magnetic field distribution follows a power-law distribution. The
high Alfvén Mach numbers in collapsing regions explain the recent
observations of magnetic influence decreasing with density. We also find
that the high-density state is typically found in filaments formed by
converging flows, consistent with recent Herschel observations. Possible
modifications to existing star formation theories are explored. The
overall trans-Alfvénic nature of star-forming clouds is discussed.
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Title: Comparing Numerical Methods for Isothermal Magnetized
Supersonic Turbulence
Authors: Kritsuk, Alexei G.; Nordlund, Åke; Collins, David; Padoan,
Paolo; Norman, Michael L.; Abel, Tom; Banerjee, Robi; Federrath,
Christoph; Flock, Mario; Lee, Dongwook; Li, Pak Shing; Müller,
Wolf-Christian; Teyssier, Romain; Ustyugov, Sergey D.; Vogel,
Christian; Xu, Hao
2011ApJ...737...13K Altcode: 2011arXiv1103.5525K
Many astrophysical applications involve magnetized turbulent flows
with shock waves. Ab initio star formation simulations require a robust
representation of supersonic turbulence in molecular clouds on a wide
range of scales imposing stringent demands on the quality of numerical
algorithms. We employ simulations of supersonic super-Alfvénic
turbulence decay as a benchmark test problem to assess and compare
the performance of nine popular astrophysical MHD methods actively
used to model star formation. The set of nine codes includes: ENZO,
FLASH, KT-MHD, LL-MHD, PLUTO, PPML, RAMSES, STAGGER, and ZEUS. These
applications employ a variety of numerical approaches, including both
split and unsplit, finite difference and finite volume, divergence
preserving and divergence cleaning, a variety of Riemann solvers, and
a range of spatial reconstruction and time integration techniques. We
present a comprehensive set of statistical measures designed to quantify
the effects of numerical dissipation in these MHD solvers. We compare
power spectra for basic fields to determine the effective spectral
bandwidth of the methods and rank them based on their relative effective
Reynolds numbers. We also compare numerical dissipation for solenoidal
and dilatational velocity components to check for possible impacts of
the numerics on small-scale density statistics. Finally, we discuss the
convergence of various characteristics for the turbulence decay test and
the impact of various components of numerical schemes on the accuracy
of solutions. The nine codes gave qualitatively the same results,
implying that they are all performing reasonably well and are useful
for scientific applications. We show that the best performing codes
employ a consistently high order of accuracy for spatial reconstruction
of the evolved fields, transverse gradient interpolation, conservation
law update step, and Lorentz force computation. The best results are
achieved with divergence-free evolution of the magnetic field using
the constrained transport method and using little to no explicit
artificial viscosity. Codes that fall short in one or more of these
areas are still useful, but they must compensate for higher numerical
dissipation with higher numerical resolution. This paper is the largest,
most comprehensive MHD code comparison on an application-like test
problem to date. We hope this work will help developers improve their
numerical algorithms while helping users to make informed choices about
choosing optimal applications for their specific astrophysical problems.
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Title: Magnetic Fields in Molecular Clouds
Authors: Padoan, Paolo; Lunttila, Tuomas; Juvela, Mika; Nordlund, Åke;
Collins, David; Kritsuk, Alexei; Normal, Michael; Ustyugov, Sergey
2011IAUS..271..187P Altcode:
Supersonic magneto-hydrodynamic (MHD) turbulence in molecular clouds
(MCs) plays an important role in the process of star formation. The
effect of the turbulence on the cloud fragmentation process depends
on the magnetic field strength. In this work we discuss the idea
that the turbulence is super-Alfvénic, at least with respect to
the cloud mean magnetic field. We argue that MCs are likely to be
born super-Alfvénic. We then support this scenario based on a recent
simulation of the large-scale warm interstellar medium turbulence. Using
small-scale isothermal MHD turbulence simulation, we also show that
MCs may remain super-Alfvénic even with respect to their rms magnetic
field strength, amplified by the turbulence. Finally, we briefly discuss
the comparison with the observations, suggesting that super-Alfvénic
turbulence successfully reproduces the Zeeman measurements of the
magnetic field strength in dense MC clouds.
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Title: Validated helioseismic inversions for 3D vector flows
Authors: Švanda, M.; Gizon, L.; Hanasoge, S. M.; Ustyugov, S. D.
2011A&A...530A.148S Altcode: 2011arXiv1104.4083S
Context. According to time-distance helioseismology, information
about internal fluid motions is encoded in the travel times of solar
waves. The inverse problem consists of inferring three-dimensional
vector flows from a set of travel-time measurements. While only few
tests of the inversions have been done, it is known that the retrieval
of the small-amplitude vertical flow velocities is problematic. A
thorough study of biases and noise has not been carried out in
realistic conditions. <BR /> Aims: Here we investigate the potential
of time-distance helioseismology to infer three-dimensional convective
velocities in the near-surface layers of the Sun. We developed a new
subtractive optimally localised averaging (SOLA) code suitable for
pipeline pseudo-automatic processing. Compared to its predecessor,
the code was improved by accounting for additional constraints in
order to get the right answer within a given noise level. The main
aim of this study is to validate results obtained by our inversion
code. <BR /> Methods: We simulate travel-time maps using a snapshot
from a numerical simulation of solar convective flows, realistic Born
travel-time sensitivity kernels, and a realistic model of travel-time
noise. These synthetic travel times are inverted for flows and the
results compared with the known input flow field. Additional constraints
are implemented in the inversion: cross-talk minimization between flow
components and spatial localization of inversion coefficients. <BR />
Results: Using modes f, p<SUB>1</SUB> through p<SUB>4</SUB>, we show
that horizontal convective flow velocities can be inferred without
bias, at a signal-to-noise ratio greater than one in the top 3.5 Mm,
provided that observations span at least four days. The vertical
component of velocity (v<SUB>z</SUB>), if it were to be weak, is
more difficult to infer and is seriously affected by cross-talk from
horizontal velocity components. We emphasise that this cross-talk
must be explicitly minimised in order to retrieve v<SUB>z</SUB>
in the top 1 Mm. We also show that statistical averaging over many
different areas of the Sun allows for reliably measuring of average
properties of all three flow components in the top 5.5 Mm of the
convection zone. <P />Figures 16-28 are available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Interstellar Turbulence and Star Formation
Authors: Kritsuk, Alexei G.; Ustyugov, Sergey D.; Norman, Michael L.
2011IAUS..270..179K Altcode: 2010arXiv1011.2177K
We provide a brief overview of recent advances and outstanding issues
in simulations of interstellar turbulence, including isothermal models
for interior structure of molecular clouds and larger-scale multiphase
models designed to simulate the formation of molecular clouds. We show
how self-organization in highly compressible magnetized turbulence
in the multiphase ISM can be exploited in simple numerical models to
generate realistic initial conditions for star formation.
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Title: Realistic magnetohydrodynamical simulation of solar local
supergranulation
Authors: Ustyugov, Sergey D.
2010PhST..142a4031U Altcode: 2009arXiv0906.5232U
Three-dimensional numerical simulations of solar surface
magnetoconvection using realistic model physics are conducted. The
thermal structure of convective motions into the upper radiative
layers of the photosphere, the main scales of convective cells and
the penetration depths of convection are investigated. We take part
of the solar photosphere with a size of 60×60 Mm<SUP>2</SUP> in
the horizontal direction and of depth 20 Mm from the level of the
visible solar surface. We use a realistic initial model of the sun
and apply the equation of state and opacities of stellar matter. The
equations of fully compressible radiation magnetohydrodynamics
(MHD) with dynamical viscosity and gravity are solved. We apply (i)
the conservative total variation diminishing (TVD) difference scheme
for MHD, (ii) the diffusion approximation for radiative transfer and
(iii) dynamical viscosity from subgrid-scale modeling. In simulation,
we take a uniform two-dimensional grid in the horizontal plane and a
nonuniform grid in the vertical direction with the number of cells
being 600×600×204. We use 512 processors with distributed memory
multiprocessors on the supercomputer MVS-100k at the Joint Computational
Centre of the Russian Academy of Sciences.
---------------------------------------------------------
Title: Self-organization in Turbulent Molecular Clouds: Compressional
Versus Solenoidal Modes
Authors: Kritsuk, A. G.; Ustyugov, S. D.; Norman, M. L.; Padoan, P.
2010ASPC..429...15K Altcode: 2009arXiv0912.0546K
We use three-dimensional numerical simulations to study
self-organization in supersonic turbulence in molecular clouds. Our
numerical experiments describe decaying and driven turbulent flows
with an isothermal equation of state, sonic Mach numbers from 2 to
10, and various degrees of magnetization. We focus on properties of
the velocity field and, specifically, on the level of its potential
(dilatational) component as a function of turbulent Mach number,
magnetic field strength, and scale. We show how extreme choices of
either purely solenoidal or purely potential forcing can reduce the
extent of the inertial range in the context of periodic box models
for molecular cloud turbulence. We suggest an optimized forcing to
maximize the effective Reynolds number in numerical models.
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Title: MHD Turbulence In Star-Forming Clouds
Authors: Padoan, P.; Kritsuk, A. G.; Lunttila, T.; Juvela, M.;
Nordlund, A.; Norman, M. L.; Ustyugov, S. D.
2010AIPC.1242..219P Altcode:
Supersonic magneto-hydrodynamic (MHD) turbulence in molecular clouds
(MCs) plays an important role in the process of star formation. The
effect of the turbulence on the cloud fragmentation process depends
on the magnetic field strength. In this work we discuss the idea
that the turbulence is super-Alfvénic, at least with respect to
the cloud mean magnetic field. We argue that MCs are likely to be
born super-Alfvénic. We then support this scenario based on a recent
simulation of the large-scale warm interstellar medium turbulence. Using
small-scale isothermal MHD turbulence simulation, we also show that
MCs may remain super-Alfvénic even with respect to their rms magnetic
field strength, amplified by the turbulence. Finally, we briefly discuss
the comparison with the observations, suggesting that super-Alfvénic
turbulence successfully reproduces the Zeeman measurements of the
magnetic field strength in dense MC clouds.
---------------------------------------------------------
Title: Realistic Magnetohydrodynamical Simulations of Local Solar
Supergranulation
Authors: Ustyugov, S. D.
2009ASPC..416..427U Altcode:
Three-dimensional numerical simulations of solar surface
magnetoconvection using realistic model physics are conducted. The
thermal structure of convective motions into the upper radiative
layers of the photosphere, the main scales of convective cells and the
penetration depths of convection are investigated. We take a part of
the solar photosphere with horizontal size 60 × 60 Mm by depth 20
Mm from the level of the visible solar surface. We use a realistic
initial model of the Sun and apply the equation of state with the
opacities of stellar matter. The equations of fully compressible
radiative magnetohydrodynamics with dynamical viscosity and gravity
are solved. We apply 1) a conservative TVD difference scheme for the
magnetohydrodynamics, 2) the diffusion approximation for radiative
transfer, and 3) dynamical viscosity from subgrid-scale modeling. In
the simulations, we take a uniform two-dimensional grid in the
horizontal plane and a nonuniform grid in depth with 600 × 600 × 204
pixels. We use 512 processors with distributed-memory multiprocessors
on supercomputer MVS-100k in the Joint Computational Center of the
Russian Academy of Sciences.
---------------------------------------------------------
Title: Piecewise parabolic method on a local stencil for magnetized
supersonic turbulence simulation
Authors: Ustyugov, Sergey D.; Popov, Mikhail V.; Kritsuk, Alexei G.;
Norman, Michael L.
2009JCoPh.228.7614U Altcode: 2009arXiv0905.2960U
Stable, accurate, divergence-free simulation of magnetized supersonic
turbulence is a severe test of numerical MHD schemes and has been
surprisingly difficult to achieve due to the range of flow conditions
present. Here we present a new, higher order-accurate, low dissipation
numerical method which requires no additional dissipation or local
“fixes” for stable execution. We describe PPML, a local stencil
variant of the popular PPM algorithm for solving the equations of
compressible ideal magnetohydrodynamics. The principal difference
between PPML and PPM is that cell interface states are evolved
rather that reconstructed at every timestep, resulting in a compact
stencil. Interface states are evolved using Riemann invariants
containing all transverse derivative information. The conservation
laws are updated in an unsplit fashion, making the scheme fully
multidimensional. Divergence-free evolution of the magnetic field
is maintained using the higher order-accurate constrained transport
technique of Gardiner and Stone. The accuracy and stability of the
scheme is documented against a bank of standard test problems drawn
from the literature. The method is applied to numerical simulation
of supersonic MHD turbulence, which is important for many problems in
astrophysics, including star formation in dark molecular clouds. PPML
accurately reproduces in three-dimensions a transition to turbulence
in highly compressible isothermal gas in a molecular cloud model. The
low dissipation and wide spectral bandwidth of this method make it an
ideal candidate for direct turbulence simulations.
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Title: Simulating supersonic turbulence in magnetized molecular clouds
Authors: Kritsuk, Alexei G.; Ustyugov, Sergey D.; Norman, Michael L.;
Padoan, Paolo
2009JPhCS.180a2020K Altcode: 2009arXiv0908.0378K
We present results of large-scale three-dimensional weakly magnetized
supersonic turbulence simulations with an isothermal equation of state
at grid resolutions up to 1024<SUP>3</SUP> cells with the Piecewise
Parabolic Method on a Local Stencil. The turbulence is driven by a
large-scale isotropic solenoidal force in a periodic computational
domain and fully develops in a few flow crossing times. We then evolve
the flow for a number of flow crossing times and analyze various
statistical properties of the saturated turbulent state. We show that
the energy transfer rate in the inertial range of scales is surprisingly
close to a constant, indicating that Kolmogorov's phenomenology for
incompressible turbulence can be extended to magnetized supersonic
flows. We also discuss numerical dissipation effects and convergence
of different turbulence diagnostics as grid resolution refines from
256<SUP>3</SUP> to 1024<SUP>3</SUP> cells.
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Title: Simulations of Supersonic Turbulence in Molecular Clouds:
Evidence for a New Universality
Authors: Kritsuk, A. G.; Ustyugov, S. D.; Norman, M. L.; Padoan, P.
2009ASPC..406...15K Altcode: 2009arXiv0902.3222K
We use three-dimensional simulations to study the statistics of
supersonic turbulence in molecular clouds. Our numerical experiments
describe driven turbulent flows with an isothermal equation of state,
Mach numbers around 10, and various degrees of magnetization. We first
support the so-called 1/3-rule of \cite{kritsuk...07a} with our new
data from a larger 2048<SUP>3</SUP> simulation. We then attempt to
extend the 1/3-rule to supersonic MHD turbulence and get encouraging
preliminary results based on a set of 512<SUP>3</SUP> simulations. Our
results suggest an interesting new approach to tackle universal scaling
relations and intermittency in supersonic MHD turbulence.
---------------------------------------------------------
Title: Simulations of Supersonic Turbulence in Magnetized Molecular
Clouds
Authors: Kritsuk, Alexei; Ustyugov, S. D.; Norman, M. L.; Padoan, P.
2009AAS...21348510K Altcode: 2009BAAS...41R.457K
We report first results from three-dimensional numerical simulations
of supersonic magnetohydrodynamic (MHD) turbulence with the Piecewise
Parabolic Method on Local Stencil (PPML, Popov & Ustyugov
2008). PPML is a multi-dimensional higher-order Godunov scheme
that preserves monotonicity of solutions in the vicinity of strong
discontinuities, and maintains zero divergence of the magnetic field
through a constrained transport approach. The method is very accurate,
extremely low-dissipation, and perfectly stable for super-Alfv'enic
turbulence, where many other MHD schemes experience difficulties. <P
/>We solve the equations of ideal MHD in a periodic domain on Cartesian
grids of up to 1024^3 points. Our models describe driven turbulence
at Mach 10 and assume an isothermal equation of state to mimic the
conditions in molecular clouds. We start with uniform gas density and
uniform magnetic field aligned with one of the coordinate directions
and apply large-scale solenoidal force to develop a saturated turbulent
state in a statistical equilibrium. Depending on the initial field
strength, B_0, a saturation is reached within three-to-six dynamical
times of driving. We then collect the turbulence statistics and
compare those for different models. <P />As predicted by Kritsuk
et al. (2007), for weak initial fields we get Kolmogorov spectra
for the density-weighted velocities ρ^{1/3}u. With stronger fields,
the spectra tend to get shallower, but the -5/3 scaling still appears
to hold (even in these highly compressible, magnetized flows) for a
combination of kinetic and magnetic variables constructed in the spirit
of Politano & Pouquet (1998). We compare PDFs, structure functions,
and power spectra from runs with different B_0 and discuss the signature
of magnetic field in the statistical properties of molecular cloud
turbulence and their role in overall flow dynamics. <P />This research
was partially supported by NSF grants AST0607675, AST0808184, and by
NRAC allocation MCA07S014. We utilized computing resources provided
by NICS, TACC, and SDSC.
---------------------------------------------------------
Title: Realistic Simulation of Local Solar Supergranulation
Authors: Ustyugov, Sergey D.
2008AIPC.1043..234U Altcode: 2008arXiv0806.1337U
I represent results three-dimensional numerical simulation of solar
surface convection on scales local supergranulation with realistic
model physics. I study thermal structure of convective motions in
photosphere, the range of convection cell sizes and the penetration
depths of convection. A portion of the solar photosphere extending
100×100 Mm horizontally and from 0 Mm down to 20 Mm below the visible
surface is considered. I take equation of state and opacities of stellar
matter and distribution with radius of all physical variables from
Solar Standard Model. The equations of fully compressible radiation
hydrodynamics with dynamical viscosity and gravity are solved. The
high order conservative PPML difference scheme for the hydrodynamics,
the method of characteristic for the radiative transfer and dynamical
viscosity from subgrid scale modeling are applied. The simulations
are conducted on a uniform horizontal grid of 1000×1000, with 168
nonuniformly spaced vertical grid points, on 256 processors with
distributed memory multiprocessors on supercomputer MVS5000 in
Computational Center of Russian Academy of Sciences.
---------------------------------------------------------
Title: Large Eddy Simulation of Solar Photosphere Convection with
Realistic Physics
Authors: Ustyugov, S. D.
2008ASPC..383...43U Altcode: 2007arXiv0710.3023U
Three-dimensional large eddy simulations of solar surface convection
using realistic model physics are conducted. The thermal structure of
convective motions into the upper radiative layers of the photosphere,
the range of convection cell sizes, and the penetration depths of
convection are investigated. A portion of the solar photosphere and
the upper layers of the convection zone, a region extending 60× 60
Mm horizontally from 0 Mm down to 20 Mm below the visible surface,
is considered. We start from a realistic initial model of the Sun with
an equation of state and opacities of stellar matter. The equations of
fully compressible radiation hydrodynamics with dynamical viscosity and
gravity are solved. We use: 1) a high order conservative TVD scheme for
the hydrodynamics, 2) the diffusion approximation for the radiative
transfer, 3) dynamical viscosity from subgrid scale modeling. The
simulations are conducted on a uniform horizontal grid of 600× 600,
with 168 nonuniformly spaced vertical grid points, on 144 processors
with distributed memory multiprocessors on supercomputer MBC-1500 in
the Computational Centre of the Russian Academy of Sciences.
---------------------------------------------------------
Title: Numerical Simulation of Solar Magnetoconvection with Realistic
Physics
Authors: Ustyugov, Sergey D.
2007AIPC..895..109U Altcode:
Three-dimensional magnetohydrodynamics numerical simulation of solar
surface convection on scale of supergranulation using realistic
model physics is conducted. The effects of magnetic fields on
thermal structure of convective motions into radiative layers, the
range of convection cell sizes and penetration depths of convection
are investigated. We simulate a part of the solar photosphere and
the upper layers of the convection zone, a region extending on
30 × 30 Mm horizontally from 0 Mm down to 18 Mm below the visible
surface. Equations of the compressible radiation magnetohydrodynamics
with dynamical viscosity and gravity are solved. We used: 1)
distribution by radius of all variables from realistic model
of Sun, 2) equation of state and opacities of matter for stellar
conditions, 3) high order conservative TVD scheme for solution of the
magnetohydrodynamics equations, 4) diffusion approximation for radiative
transfer solution, 5) calculation dynamical viscosity applying subgrid
scale modelling. Simulations are conducted on horizontal uniform grid
of 320 × 320 and with 144 nonuniformly spaced vertical grid points
on the 128 processors of super-computer with distributed memory
multiprocessors in Russian Academy of Sciences in Moscow.
---------------------------------------------------------
Title: Mechanisms of supernova explosions
Authors: Chechetkin, V. M.; Popov, M. V.; Ustyugov, S. D.
2007acag.conf..179C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetohydrodynamic Simulation of Solar Supergranulation
Authors: Ustyugov, S. D.
2006ASPC..359..226U Altcode: 2006astro.ph..5627U
Three-dimensional magnetohydrodynamical large eddy simulations of solar
surface convection using realistic model physics are conducted. The
effects of magnetic fields on the thermal structure of convective
motions into radiative layers, the range of convection cell sizes
and penetration depths of convection are investigated. We simulate a
portion of the solar photosphere and the upper layers of the convection
zone, a region extending 30× 30 Mm horizontally from 0 Mm down to
18 Mm below the visible surface. We solve equations of the fully
compressible radiation magnetohydrodynamics with dynamical viscosity
and gravity. For numerical simulation we use: 1) realistic initial
model of Sun and equation of state and opacities of stellar matter, 2)
high order conservative TVD scheme for solution magnetohydrodynamics, 3)
diffusion approximation for radiative transfer 4) dynamical viscosity
from subgrid scale modeling. Simulations are conducted on a horizontal
uniform grid of 320 × 320 and with 144 nonuniformly spaced vertical
grid points on 128 processors of a supercomputer MBC-1500 with
distributed memory multiprocessors in Russian Academy of Sciences.
---------------------------------------------------------
Title: Three Dimensional Numerical Simulation of MHD Solar Convection
on Multiproccesor Supercomputer Systems
Authors: Ustyugov, S. D.
2006ASPC..354..115U Altcode:
Three-dimensional magnetohydrodynamical large eddy simulations of solar
surface convection using realistic model physics are conducted. The
effects of magnetic fields on the thermal structure of convective
motions into radiative layers, the range of convection cell sizes and
the penetration depths of convection are investigated. We simulate a
portion of the solar photosphere and the upper layers of the convection
zone, a region extending 18 × 18 Mm horizontally from 0 Mm down
to 18 Mm below the visible surface. We solve the equations of fully
compressible radiation magnetohydrodynamics with dynamical viscosity
and gravity. We use: 1) a high order conservative TVD scheme for the
magnetohydrodynamics, 2) the diffusion approximation for the radiative
transfer, 3) dynamical viscosity from subgrid scale modeling. We start
from a realistic initial model of Sun with an equation of state and
opacities of stellar matter. The simulations are conducted on a uniform
horizontal grid of 192 × 192, with 144 nonuniformly spaced vertical
grid points, on 64 processors with distributed memory multiprocessors.
---------------------------------------------------------
Title: Subsurface flows from numerical simulations compared with
flows from ring analysis
Authors: Ustyugov, S.; Komm, R.; Burtseva, O.; Howe, R.; Kholikov, S.
2006ESASP.624E..54U Altcode: 2006soho...18E..54U
No abstract at ADS
---------------------------------------------------------
Title: Three Dimensional Numerical Simulation of Solar Convection
on Multiproccesors Supercomputer Systems
Authors: Ustyugov, S. D.
2005ASPC..346..357U Altcode:
Three-dimensional large eddy simulations of solar surface convection
using realistic model physics is conducted. Thermal structure
of convective motions into radiative layers and the range of
convection cell sizes is investigated. We simulate a some portion
of the solar photosphere and the upper layers of the convection
zone, a region extending 18 x 18 Mm horizontally from 0 Mm down to
18 Mm below the visible surface. We solve equations of the fully
compressible radiation hydrodynamics with dynamical viscosity and
gravity. For numerical simulation we use: 1) realistic initial model
of Sun and equation of state and opacities of stellar matter, 2)
high order conservative TVD scheme for solution hydrodynamics, 3)
diffusion approximation for solution radiative transfer in convective
layers of Sun, 4) calculation dynamical viscosity from subgrid scale
modelling. Simulations are conducted on horizontal uniform grid of 192
x 192 and with 144 non-uniformly spaced vertical grid points on the 64
processors of supercomputer with distributed memory multiprocesseres
(two Alpha 21264/667 MHz in node, memory 1 Gb in node, SAN Myrinet to
communication, 512 nodes).
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Title: Boundary Conditions for Simulations of the Thermal Outburst
of a Type Ia Supernova
Authors: Popov, M. V.; Ustyugov, S. D.; Chechetkin, V. M.
2005ARep...49..450P Altcode:
We present a technique to calculate the boundary conditions for
simulations of the development of large-scale convective instability in
the cores of rotating white-dwarf progenitors of type Ia supernovae. The
hydrodynamical equations describing this situation are analyzed. We
also study the impact of the boundary conditions on the development
of the thermal outburst.
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Title: Numerical Simulation of Hydrodynamic Instability in a Rotating
Protoneutron Star by Supernova Explosion II Type
Authors: Ustyugov, S. D.
2005tsra.conf..567U Altcode:
Large-scale convective instability owing to the neutronization of matter
in a protoneutron star during the collapse of star with low initial
entropy are considered. The 3D hydrodynamic calculation on nested
grids with three level shows that large-scale bubbles of hot matter
with size 106 cm arise to surface neutrinosphere. When the bubbles
reaches low density, the neutrinos contained in matter freely escape
from it in the regime of volume radiation. The characteristic time of
this process is equalled to 3.5 ms. The shock from the initial bounce
when the collapse in the stellar core stops will then be supported by
the neutrino emission, resulting in the ejection of an envelope. In
rotating protoneutron star the large scale bubbles come to the surface
of the stellar core along the axis of rotation. Neutrino with energy
30-50 MeV are contained in the bubbles. Calculations shows that time
of neutrino emission form such bubble is equal near 1 ms with mean
energy of neutrino 30-40 MeV.
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Title: Development of the Geometric Structure of the
Thermonuclear-Deflagration Front in Type Ia Supernovae
Authors: Popov, M. V.; Ustyugov, S. D.; Chechetkin, V. M.
2004ARep...48..921P Altcode:
Three-dimensional hydrodynamical simulations of the development of
a large-scale instability accompanying deflagration in the degenerate
cores of rotating white dwarfs—progenitors of type-Ia supernovae—are
presented. The numerical algorithm used is described in detail. An
explicit, conservative, Godunov-type TVD difference scheme was employed
for the computations. Large-scale convective processes are important as
the deflagration front propagates. The supernova explosion is strongly
nonspherically symmetric; a large-scale front structure emerges and
propagates most rapidly along the rotational axis. The arrival of
fresh thermonuclear fuel to the central region of the core can result
in flares and the destruction of the core.
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Title: Three Dimensional Numerical Simulations of Near Surface Solar
Convection with Realistic Physics
Authors: Ustyugov, S. D.
2004ESASP.559..660U Altcode: 2004soho...14..660U
No abstract at ADS
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Title: Numerical simulation of large-scale convection in type-II
supernovae explosion
Authors: Chechetkin, V. M.; Popov, M. V.; Ustyugov, S. D.
2002NCimB.117.1027C Altcode:
No abstract at ADS
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Title: Simulation of Neutrino Transport by Large-Scale Convective
Instability in a Proto-Neutron Star
Authors: Suslin, V. M.; Ustyugov, S. D.; Chechetkin, V. M.; Churkina,
G. P.
2001ARep...45..241S Altcode:
Neutrino transfer via convective flow to the surface of a
proto-neutron star is numerically simulated. The evolution of the
neutrino distribution in a heated region rising from the center of
the proto-neutron star to its surface is simulated using a kinetic
equation with a Uehling-Uhlenbeck collision integral in a uniform,
isotropic approximation. The composition of the matter in the region
under consideration changes due to the “burning” of electrons and
protons by beta processes. The simulation results enable the estimation
of the characteristic time required for the rising medium to become
optically thin to neutrinos and the characteristic spectrum of the
neutrinos that are emitted.
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Title: Supernovae explosions in the presence of large-scale convective
instability in a rotating protoneutron star
Authors: Ustyugov, S. D.; Chechetkin, V. M.
1999ARep...43..718U Altcode:
No abstract at ADS
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Title: Gravitational radiation from a rotating protoneutron star
Authors: Sazhin, M. V.; Ustyugov, S. D.; Chechetkin, V. M.
1998JETP...86..629S Altcode:
No abstract at ADS
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Title: On the neutrino mechanism of supernova explosions
Authors: Chechetkin, V. M.; Ustyugov, S. D.; Gorbunov, A. A.;
Polezhaev, V. I.
1997AstL...23...30C Altcode: 1997PAZh...23...34C
No abstract at ADS
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Title: Gravity waves accompanying supernova explosions
Authors: Sazhin, M. V.; Ustyugov, S. D.; Chechetkin, V. M.
1996JETPL..64..871S Altcode:
No abstract at ADS
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Title: Gravity waves accompanying supernova explosions
Authors: Sazhin, M. V.; Ustyugov, S. D.; Chechetkin, V. M.
1996ZhPmR..64..817S Altcode:
No abstract at ADS
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Title: On the Minimal Critical Mass of Magnetic Interstellar Clouds
Authors: Dudorov, A. E.; Ustyugov, S. D.
1990ATsir1546....7D Altcode:
No abstract at ADS
