194 research outputs found
Realistic Magnetohydrodynamical Simulation of Solar Local Supergranulation
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 60x60 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: 1) conservative TVD difference scheme for the magnetohydrodynamics,
2) the diffusion approximation for the radiative transfer, 3) dynamical
viscosity from subgrid scale modeling. In simulation we take uniform
two-dimesional grid in gorizontal plane and nonuniform grid in vertical
direction with number of cells 600x600x204. We use 512 processors with
distributed memory multiprocessors on supercomputer MVS-100k in the Joint
Computational Centre of the Russian Academy of Sciences.Comment: 6 pages, 5 figures, submitted to the proceedings of the GONG 2008 /
SOHO XXI conferenc
Realistic Simulation of Local Solar Supergranulation
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 x 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 x 1000, with 168 nonuniformly spaced vertical
grid points, on 256 processors with distributed memory multiprocessors on
supercomputer MVS5000 in Computational Centre of Russian Academy of Sciences.Comment: 4 pages, 3 figures. To appear in AIP Conference Proceedings,
"Exploring the Solar System and the Universe", Apr 8-12 2008, Bucharest,
Romania, eds. Vasile Mioc, Cristiana Dumitrache & Nedelia A. Popesc
Interstellar Turbulence and Star Formation
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.Comment: 8 pages, 5 color figures; submitted to Proceedings of IAU Symposium
270 "Computational Star Formation" held in Barcelona, May 31 - June 4, 201
Influence of cosmic factors on mud volcanic activity of the Earth
In this work, the influence of various cosmic factors (gravitational influence of the Moon and the Sun, solar activity, the Earth’s rotation) on mud volcanic activity was analyzed for the first time. The analysis was carried out mainly on the example of mud volcanoes in Azerbaijan, for which there is the largest and most complete catalog of eruptions (431 events over almost 210 years). It has been found that the activity of mud volcanoes can increase after syzygial tides, when the Earth is in line with the Moon and the Sun (their tidal forces are summed up in this case). The response of mud volcanoes to the tidal influence of the Moon is delayed by 5–10 days. It is also found that the number of mud volcanic eruptions is distributed unevenly throughout the year with maximums in March–June and September–October. The presence of these maximums may be due to a change in the distance between the Sun and the Earth and variations in solar tidal forces during the periods of perihelion and aphelion. At the same time, the response of mud volcanoes to the tidal influence of the Sun is delayed by several months and is quite strongly extended in time. It was revealed that there are fluctuations in mud volcanic activity with a period of 14–20 years, which do not coincide with the cycles of solar activity (with periods of 11 and 22 years), although some researchers talk about a connection between solar and mud volcanic activity. It is possible that the indicated fluctuations in mud volcanic activity are related to the main harmonic of the Earth’s nutation (18.6 years). It is shown that the maximum number of mud volcanoes on the Earth falls on the latitudinal belts of 30–45° N and 10–15° N (about 22 and 46 % of the total number of volcanoes, respectively). In the southern hemisphere, the largest number of volcanoes (about 3 % of their total number) is located within the boundaries of 5–10° S
Simulating Supersonic Turbulence in Magnetized Molecular Clouds
We present results of large-scale three-dimensional simulations of weakly
magnetized supersonic turbulence at grid resolutions up to 1024^3 cells. Our
numerical experiments are carried out with the Piecewise Parabolic Method on a
Local Stencil and assume an isothermal equation of state. 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
256^3 to 1024^3 cells.Comment: 10 pages, 3 figures, to appear in the proceedings of the DOE/SciDAC
2009 conferenc
- …