11,808 research outputs found
The MOLDY short-range molecular dynamics package
We describe a parallelised version of the MOLDY molecular dynamics program.
This Fortran code is aimed at systems which may be described by short-range
potentials and specifically those which may be addressed with the embedded atom
method. This includes a wide range of transition metals and alloys. MOLDY
provides a range of options in terms of the molecular dynamics ensemble used
and the boundary conditions which may be applied. A number of standard
potentials are provided, and the modular structure of the code allows new
potentials to be added easily. The code is parallelised using OpenMP and can
therefore be run on shared memory systems, including modern multicore
processors. Particular attention is paid to the updates required in the main
force loop, where synchronisation is often required in OpenMP implementations
of molecular dynamics. We examine the performance of the parallel code in
detail and give some examples of applications to realistic problems, including
the dynamic compression of copper and carbon migration in an iron-carbon alloy
Segregation effects during solidification in weightless melts
The generalized problem of determining the temperature and solute concentration profiles during directional solidification of binary alloys with surface evaporation was mathematically formulated. Realistic initial and boundary conditions were defined, and a computer program was developed and checked out. The programs computes the positions of two moving boundaries, evaporation and solidification, and their velocities. Temperature and solute concentration profiles in the semiinfinite material body at selected instances of time are also computed
Program in electro-physical studies - Microcircuit models and diagnostic techniques for environmental failure mode prediction
Microcircuit models and computer program for predicting failure modes under adverse environmental condition
Combustion of hydrogen-air jets in local chemical equilibrium: A guide to the CHARNAL computer program
A guide to a computer program, written in FORTRAN 4, for predicting the flow properties of turbulent mixing with combustion of a circular jet of hydrogen into a co-flowing stream of air is presented. The program, which is based upon the Imperial College group's PASSA series, solves differential equations for diffusion and dissipation of turbulent kinetic energy and also of the R.M.S. fluctuation of hydrogen concentration. The effective turbulent viscosity for use in the shear stress equation is computed. Chemical equilibrium is assumed throughout the flow
kmos: A lattice kinetic Monte Carlo framework
Kinetic Monte Carlo (kMC) simulations have emerged as a key tool for
microkinetic modeling in heterogeneous catalysis and other materials
applications. Systems, where site-specificity of all elementary reactions
allows a mapping onto a lattice of discrete active sites, can be addressed
within the particularly efficient lattice kMC approach. To this end we describe
the versatile kmos software package, which offers a most user-friendly
implementation, execution, and evaluation of lattice kMC models of arbitrary
complexity in one- to three-dimensional lattice systems, involving multiple
active sites in periodic or aperiodic arrangements, as well as site-resolved
pairwise and higher-order lateral interactions. Conceptually, kmos achieves a
maximum runtime performance which is essentially independent of lattice size by
generating code for the efficiency-determining local update of available events
that is optimized for a defined kMC model. For this model definition and the
control of all runtime and evaluation aspects kmos offers a high-level
application programming interface. Usage proceeds interactively, via scripts,
or a graphical user interface, which visualizes the model geometry, the lattice
occupations and rates of selected elementary reactions, while allowing
on-the-fly changes of simulation parameters. We demonstrate the performance and
scaling of kmos with the application to kMC models for surface catalytic
processes, where for given operation conditions (temperature and partial
pressures of all reactants) central simulation outcomes are catalytic activity
and selectivities, surface composition, and mechanistic insight into the
occurrence of individual elementary processes in the reaction network.Comment: 21 pages, 12 figure
Boundary layer integral matrix procedure: Verification of models
The three turbulent models currently available in the JANNAF version of the Aerotherm Boundary Layer Integral Matrix Procedure (BLIMP-J) code were studied. The BLIMP-J program is the standard prediction method for boundary layer effects in liquid rocket engine thrust chambers. Experimental data from flow fields with large edge-to-wall temperature ratios are compared to the predictions of the three turbulence models contained in BLIMP-J. In addition, test conditions necessary to generate additional data on a flat plate or in a nozzle are given. It is concluded that the Cebeci-Smith turbulence model be the recommended model for the prediction of boundary layer effects in liquid rocket engines. In addition, the effects of homogeneous chemical reaction kinetics were examined for a hydrogen/oxygen system. Results show that for most flows, kinetics are probably only significant for stoichiometric mixture ratios
Numerical modeling tools for chemical vapor deposition
Development of general numerical simulation tools for chemical vapor deposition (CVD) was the objective of this study. Physical models of important CVD phenomena were developed and implemented into the commercial computational fluid dynamics software FLUENT. The resulting software can address general geometries as well as the most important phenomena occurring with CVD reactors: fluid flow patterns, temperature and chemical species distribution, gas phase and surface deposition. The physical models are documented which are available and examples are provided of CVD simulation capabilities
Analytical modeling of operating characteristics of premixing-prevaporizing fuel-air mixing passages. Volume 2: User's manual
A user's manual describing the operation of three computer codes (ADD code, PTRAK code, and VAPDIF code) is presented. The general features of the computer codes, the input/output formats, run streams, and sample input cases are described
Microscopic diffusion of partly ionized metals in the Sun and metal-poor stars
An improved microscopic diffusion in stars is presented considering in detail
the partly ionized stages of metals. Besides,the influence of degenerate
electron-gas and of the contribution of radiation to the total pressure has
been accounted for. The solution of the diffusion equations is then performed
following the scheme of Thoul et al. (1994). By defining one mean charged ion
per element very few modifications are necessary to solve the improved
diffusion scheme. (A portable FORTRAN routine is provided.) The change in the
sound-speed profile of a solar model obtained with the new diffusion
description is at most about 25% at r=0.6 R(sun). The biggest effect on
low-mass stars is expected near the turn-off, where the convective envelope is
shallowest. However, only a difference of at most 40 K in the effective
temperature could be observed when assuming either fully or partly ionized
metals in the diffusion equation. Nevertheless, the surface metal distribution
is strongly altered.Comment: 12 pages, 10 figures, A&A accepte
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