20,509 research outputs found
A New Multi-Energy Neutrino Radiation-Hydrodynamics Code in Full General Relativity and Its Application to Gravitational Collapse of Massive Stars
We present a new multi-dimensional radiation-hydrodynamics code for massive
stellar core-collapse in full general relativity (GR). Employing an M1
analytical closure scheme, we solve spectral neutrino transport of the
radiation energy and momentum based on a truncated moment formalism. Regarding
neutrino opacities, we take into account a baseline set in state-of-the-art
simulations, in which inelastic neutrinoelectron scattering, thermal neutrino
production via pair annihilation and nucleonnucleon bremsstrahlung are
included. While the Einstein field equations and the spatial advection terms in
the radiation-hydrodynamics equations are evolved explicitly, the source terms
due to neutrino-matter interactions and energy shift in the radiation moment
equations are integrated implicitly by an iteration method. To verify our code,
we first perform a series of standard radiation tests with analytical solutions
that include the check of gravitational redshift and Doppler shift. A good
agreement in these tests supports the reliability of the GR multi-energy
neutrino transport scheme. We then conduct several test simulations of
core-collapse, bounce, and shock-stall of a 15Msun star in the Cartesian
coordinates and make a detailed comparison with published results. Our code
performs quite well to reproduce the results of full-Boltzmann neutrino
transport especially before bounce. In the postbounce phase, our code basically
performs well, however, there are several differences that are most likely to
come from the insufficient spatial resolution in our current 3D-GR models. For
clarifying the resolution dependence and extending the code comparison in the
late postbounce phase, we discuss that next-generation Exaflops-class
supercomputers are at least needed.Comment: 61 pages, 20 figures, accepted for publication in ApJ
The 1999 Center for Simulation of Dynamic Response in Materials Annual Technical Report
Introduction:
This annual report describes research accomplishments for FY 99 of the Center
for Simulation of Dynamic Response of Materials. The Center is constructing a
virtual shock physics facility in which the full three dimensional response of a
variety of target materials can be computed for a wide range of compressive, ten-
sional, and shear loadings, including those produced by detonation of energetic
materials. The goals are to facilitate computation of a variety of experiments
in which strong shock and detonation waves are made to impinge on targets
consisting of various combinations of materials, compute the subsequent dy-
namic response of the target materials, and validate these computations against
experimental data
ORB5: a global electromagnetic gyrokinetic code using the PIC approach in toroidal geometry
This paper presents the current state of the global gyrokinetic code ORB5 as
an update of the previous reference [Jolliet et al., Comp. Phys. Commun. 177
409 (2007)]. The ORB5 code solves the electromagnetic Vlasov-Maxwell system of
equations using a PIC scheme and also includes collisions and strong flows. The
code assumes multiple gyrokinetic ion species at all wavelengths for the
polarization density and drift-kinetic electrons. Variants of the physical
model can be selected for electrons such as assuming an adiabatic response or a
``hybrid'' model in which passing electrons are assumed adiabatic and trapped
electrons are drift-kinetic. A Fourier filter as well as various control
variates and noise reduction techniques enable simulations with good
signal-to-noise ratios at a limited numerical cost. They are completed with
different momentum and zonal flow-conserving heat sources allowing for
temperature-gradient and flux-driven simulations. The code, which runs on both
CPUs and GPUs, is well benchmarked against other similar codes and analytical
predictions, and shows good scalability up to thousands of nodes
GPU accelerated Monte Carlo simulation of Brownian motors dynamics with CUDA
This work presents an updated and extended guide on methods of a proper
acceleration of the Monte Carlo integration of stochastic differential
equations with the commonly available NVIDIA Graphics Processing Units using
the CUDA programming environment. We outline the general aspects of the
scientific computing on graphics cards and demonstrate them with two models of
a well known phenomenon of the noise induced transport of Brownian motors in
periodic structures. As a source of fluctuations in the considered systems we
selected the three most commonly occurring noises: the Gaussian white noise,
the white Poissonian noise and the dichotomous process also known as a random
telegraph signal. The detailed discussion on various aspects of the applied
numerical schemes is also presented. The measured speedup can be of the
astonishing order of about 3000 when compared to a typical CPU. This number
significantly expands the range of problems solvable by use of stochastic
simulations, allowing even an interactive research in some cases.Comment: 21 pages, 5 figures; Comput. Phys. Commun., accepted, 201
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