3,993 research outputs found
SAPPORO: A way to turn your graphics cards into a GRAPE-6
We present Sapporo, a library for performing high-precision gravitational
N-body simulations on NVIDIA Graphical Processing Units (GPUs). Our library
mimics the GRAPE-6 library, and N-body codes currently running on GRAPE-6 can
switch to Sapporo by a simple relinking of the library. The precision of our
library is comparable to that of GRAPE-6, even though internally the GPU
hardware is limited to single precision arithmetics. This limitation is
effectively overcome by emulating double precision for calculating the distance
between particles. The performance loss of this operation is small (< 20%)
compared to the advantage of being able to run at high precision. We tested the
library using several GRAPE-6-enabled N-body codes, in particular with Starlab
and phiGRAPE. We measured peak performance of 800 Gflop/s for running with 10^6
particles on a PC with four commercial G92 architecture GPUs (two GeForce
9800GX2). As a production test, we simulated a 32k Plummer model with equal
mass stars well beyond core collapse. The simulation took 41 days, during which
the mean performance was 113 Gflop/s. The GPU did not show any problems from
running in a production environment for such an extended period of time.Comment: 13 pages, 9 figures, accepted to New Astronom
Dynamical Processes in Globular Clusters
Globular clusters are among the most congested stellar systems in the
Universe. Internal dynamical evolution drives them toward states of high
central density, while simultaneously concentrating the most massive stars and
binary systems in their cores. As a result, these clusters are expected to be
sites of frequent close encounters and physical collisions between stars and
binaries, making them efficient factories for the production of interesting and
observable astrophysical exotica. I describe some elements of the competition
among stellar dynamics, stellar evolution, and other processes that control
globular cluster dynamics, with particular emphasis on pathways that may lead
to the formation of blue stragglers.Comment: Chapter 10, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
SPH modeling of water-related natural hazards
This paper collects some recent smoothed particle hydrodynamic (SPH) applications in the field of natural hazards connected to rapidly varied flows of both water and dense granular mixtures including sediment erosion and bed load transport. The paper gathers together and outlines the basic aspects of some relevant works dealing with flooding on complex topography, sediment scouring, fast landslide dynamics, and induced surge wave. Additionally, the preliminary results of a new study regarding the post-failure dynamics of rainfall-induced shallow landslide are presented. The paper also shows the latest advances in the use of high performance computing (HPC) techniques to accelerate computational fluid dynamic (CFD) codes through the efficient use of current computational resources. This aspect is extremely important when simulating complex three-dimensional problems that require a high computational cost and are generally involved in the modeling of water-related natural hazards of practical interest. The paper provides an overview of some widespread SPH free open source software (FOSS) codes applied to multiphase problems of theoretical and practical interest in the field of hydraulic engineering. The paper aims to provide insight into the SPH modeling of some relevant physical aspects involved in water-related natural hazards (e.g., sediment erosion and non-Newtonian rheology). The future perspectives of SPH in this application field are finally pointed out
Swarm-NG: a CUDA Library for Parallel n-body Integrations with focus on Simulations of Planetary Systems
We present Swarm-NG, a C++ library for the efficient direct integration of
many n-body systems using highly-parallel Graphics Processing Unit (GPU), such
as NVIDIA's Tesla T10 and M2070 GPUs. While previous studies have demonstrated
the benefit of GPUs for n-body simulations with thousands to millions of
bodies, Swarm-NG focuses on many few-body systems, e.g., thousands of systems
with 3...15 bodies each, as is typical for the study of planetary systems.
Swarm-NG parallelizes the simulation, including both the numerical integration
of the equations of motion and the evaluation of forces using NVIDIA's "Compute
Unified Device Architecture" (CUDA) on the GPU. Swarm-NG includes optimized
implementations of 4th order time-symmetrized Hermite integration and mixed
variable symplectic integration, as well as several sample codes for other
algorithms to illustrate how non-CUDA-savvy users may themselves introduce
customized integrators into the Swarm-NG framework. To optimize performance, we
analyze the effect of GPU-specific parameters on performance under double
precision.
Applications of Swarm-NG include studying the late stages of planet
formation, testing the stability of planetary systems and evaluating the
goodness-of-fit between many planetary system models and observations of
extrasolar planet host stars (e.g., radial velocity, astrometry, transit
timing). While Swarm-NG focuses on the parallel integration of many planetary
systems,the underlying integrators could be applied to a wide variety of
problems that require repeatedly integrating a set of ordinary differential
equations many times using different initial conditions and/or parameter
values.Comment: Submitted to New Astronom
Visionless TRAC
This final report documents the activities during a sabbatical. Leo Monford was the principal NASA contact for this work. The work supported a flight experiment planned by the Space Research Consortium which investigated the potential of using a Targeting Reflective Alignment Concept (TRAC) sensor to automatically rendezvous satellites. Other work supported the Explorer flight experiment by providing TRAC reflectors for future rendezvous experiments. The third project initiated was a visionless TRAC sensing concept called the PSD concept
Exploration of Reaction Pathways and Chemical Transformation Networks
For the investigation of chemical reaction networks, the identification of
all relevant intermediates and elementary reactions is mandatory. Many
algorithmic approaches exist that perform explorations efficiently and
automatedly. These approaches differ in their application range, the level of
completeness of the exploration, as well as the amount of heuristics and human
intervention required. Here, we describe and compare the different approaches
based on these criteria. Future directions leveraging the strengths of chemical
heuristics, human interaction, and physical rigor are discussed.Comment: 48 pages, 4 figure
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