55,286 research outputs found
DNS of compressible multiphase flows through the Eulerian approach
In this paper we present three multiphase flow models suitable for the study
of the dynamics of compressible dispersed multiphase flows. We adopt the
Eulerian approach because we focus our attention to dispersed (concentration
smaller than 0.001) and small particles (the Stokes number has to be smaller
than 0.2). We apply these models to the compressible ()
homogeneous and isotropic decaying turbulence inside a periodic
three-dimensional box ( cells) using a numerical solver based on the
OpenFOAM C++ libraries. In order to validate our simulations in the
single-phase case we compare the energy spectrum obtained with our code with
the one computed by an eighth order scheme getting a very good result (the
relative error is very small ). Moving to the bi-phase case,
initially we insert inside the box an homogeneous distribution of particles
leaving unchanged the initial velocity field. Because of the centrifugal force,
turbulence induce particle preferential concentration and we study the
evolution of the solid-phase density. Moreover, we do an {\em a-priori} test on
the new sub-grid term of the multiphase equations comparing them with the
standard sub-grid scale term of the Navier-Stokes equations.Comment: 10 pages, 5 figures, preprint. Direct and Large Eddy Simulations 9,
201
A grid-enabled problem solving environment for parallel computational engineering design
This paper describes the development and application of a piece of engineering software that provides a problem solving environment (PSE) capable of launching, and interfacing with, computational jobs executing on remote resources on a computational grid. In particular it is demonstrated how a complex, serial, engineering optimisation code may be efficiently parallelised, grid-enabled and embedded within a PSE.
The environment is highly flexible, allowing remote users from different sites to collaborate, and permitting computational tasks to be executed in parallel across multiple grid resources, each of which may be a parallel architecture. A full working prototype has been built and successfully applied to a computationally demanding engineering optimisation problem. This particular problem stems from elastohydrodynamic lubrication and involves optimising the computational model for a lubricant based on the match between simulation results and experimentally observed data
The Parma Polyhedra Library: Toward a Complete Set of Numerical Abstractions for the Analysis and Verification of Hardware and Software Systems
Since its inception as a student project in 2001, initially just for the
handling (as the name implies) of convex polyhedra, the Parma Polyhedra Library
has been continuously improved and extended by joining scrupulous research on
the theoretical foundations of (possibly non-convex) numerical abstractions to
a total adherence to the best available practices in software development. Even
though it is still not fully mature and functionally complete, the Parma
Polyhedra Library already offers a combination of functionality, reliability,
usability and performance that is not matched by similar, freely available
libraries. In this paper, we present the main features of the current version
of the library, emphasizing those that distinguish it from other similar
libraries and those that are important for applications in the field of
analysis and verification of hardware and software systems.Comment: 38 pages, 2 figures, 3 listings, 3 table
Computing the demagnetizing tensor for finite difference micromagnetic simulations via numerical integration
In the finite difference method which is commonly used in computational
micromagnetics, the demagnetizing field is usually computed as a convolution of
the magnetization vector field with the demagnetizing tensor that describes the
magnetostatic field of a cuboidal cell with constant magnetization. An
analytical expression for the demagnetizing tensor is available, however at
distances far from the cuboidal cell, the numerical evaluation of the
analytical expression can be very inaccurate.
Due to this large-distance inaccuracy numerical packages such as OOMMF
compute the demagnetizing tensor using the explicit formula at distances close
to the originating cell, but at distances far from the originating cell a
formula based on an asymptotic expansion has to be used. In this work, we
describe a method to calculate the demagnetizing field by numerical evaluation
of the multidimensional integral in the demagnetization tensor terms using a
sparse grid integration scheme. This method improves the accuracy of
computation at intermediate distances from the origin.
We compute and report the accuracy of (i) the numerical evaluation of the
exact tensor expression which is best for short distances, (ii) the asymptotic
expansion best suited for large distances, and (iii) the new method based on
numerical integration, which is superior to methods (i) and (ii) for
intermediate distances. For all three methods, we show the measurements of
accuracy and execution time as a function of distance, for calculations using
single precision (4-byte) and double precision (8-byte) floating point
arithmetic. We make recommendations for the choice of scheme order and
integrating coefficients for the numerical integration method (iii)
CalcHEP 3.4 for collider physics within and beyond the Standard Model
We present version 3.4 of the CalcHEP software package which is designed for
effective evaluation and simulation of high energy physics collider processes
at parton level.
The main features of CalcHEP are the computation of Feynman diagrams,
integration over multi-particle phase space and event simulation at parton
level. The principle attractive key-points along these lines are that it has:
a) an easy startup even for those who are not familiar with CalcHEP; b) a
friendly and convenient graphical user interface; c) the option for a user to
easily modify a model or introduce a new model by either using the graphical
interface or by using an external package with the possibility of cross
checking the results in different gauges; d) a batch interface which allows to
perform very complicated and tedious calculations connecting production and
decay modes for processes with many particles in the final state.
With this features set, CalcHEP can efficiently perform calculations with a
high level of automation from a theory in the form of a Lagrangian down to
phenomenology in the form of cross sections, parton level event simulation and
various kinematical distributions.
In this paper we report on the new features of CalcHEP 3.4 which improves the
power of our package to be an effective tool for the study of modern collider
phenomenology.Comment: 82 pages, elsarticle LaTeX, 7 Figures. Changes from v1: 1) updated
reference list and Acknowledgments; 2) 2->1 processes added to CalcHEP; 3)
particles decay (i.e. Higgs boson) into virtual W/Z decays added together
with comparison to results from Hdecay package; 4) added interface with Root
packag
A Parallel Mesh-Adaptive Framework for Hyperbolic Conservation Laws
We report on the development of a computational framework for the parallel,
mesh-adaptive solution of systems of hyperbolic conservation laws like the
time-dependent Euler equations in compressible gas dynamics or
Magneto-Hydrodynamics (MHD) and similar models in plasma physics. Local mesh
refinement is realized by the recursive bisection of grid blocks along each
spatial dimension, implemented numerical schemes include standard
finite-differences as well as shock-capturing central schemes, both in
connection with Runge-Kutta type integrators. Parallel execution is achieved
through a configurable hybrid of POSIX-multi-threading and MPI-distribution
with dynamic load balancing. One- two- and three-dimensional test computations
for the Euler equations have been carried out and show good parallel scaling
behavior. The Racoon framework is currently used to study the formation of
singularities in plasmas and fluids.Comment: late submissio
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