20 research outputs found
RIACS
Topics considered include: high-performance computing; cognitive and perceptual prostheses (computational aids designed to leverage human abilities); autonomous systems. Also included: development of a 3D unstructured grid code based on a finite volume formulation and applied to the Navier-stokes equations; Cartesian grid methods for complex geometry; multigrid methods for solving elliptic problems on unstructured grids; algebraic non-overlapping domain decomposition methods for compressible fluid flow problems on unstructured meshes; numerical methods for the compressible navier-stokes equations with application to aerodynamic flows; research in aerodynamic shape optimization; S-HARP: a parallel dynamic spectral partitioner; numerical schemes for the Hamilton-Jacobi and level set equations on triangulated domains; application of high-order shock capturing schemes to direct simulation of turbulence; multicast technology; network testbeds; supercomputer consolidation project
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Optimising subdomain aspect ratios for parallel load balancing
In parallel adaptive Finite Element simulations the work load 011the individual processors can change frequently. To (re)distribute the load evenly over the processors a load balancing heuristic is needed. Common strategies try to minimise subdomain dependencies by minimising the number of cut edges in the partition. For many solvers this is the most influential factor. However for example, for certain preconditioned Conjugate Gradient solvers this cutsize can play only a minor role, but their convergence can be highly dependent on the subdomain shapes. Degenerated subdomain shapes can cause them to need significantly more iterations to converge. Common heuristics often fail to address these requirements. In this thesis a new strategy is introduced which directly addresses the problem of generating and conserving reasonably good subdomain shapes while balancing the load in a dynamically changing Finite Element Simulation. A new definition of Aspect Ratio is presented which assesses subdomain shapes. The common methodology of using adjacency information to select the best elements to be migrated is not considered since it is not necessarily related to the subdomain shapes. Instead, geometric data is used to formulate several cost functions to rate elements in terms of their suitability to be migrated. The well known diffusive and Generalised Dimension Exchange methods which calculate the necessary load flow are enhanced by weighting the subdomain edges in order to influence their impact on the resulting partition positively. The results of comprehensive tests are presented and demonstrate that the proposed methods are competitive with state-of-the-art load balancing tools
Unstructured Grid Generation Techniques and Software
The Workshop on Unstructured Grid Generation Techniques and Software was conducted for NASA to assess its unstructured grid activities, improve the coordination among NASA centers, and promote technology transfer to industry. The proceedings represent contributions from Ames, Langley, and Lewis Research Centers, and the Johnson and Marshall Space Flight Centers. This report is a compilation of the presentations made at the workshop
Cumulative reports and publications through December 31, 1990
This document contains a complete list of ICASE reports. Since ICASE reports are intended to be preprints of articles that will appear in journals or conference proceedings, the published reference is included when it is available
Parallel algorithms for the solution of elliptic and parabolic problems on transputer networks
This thesis is a study of the implementation of parallel algorithms for solving
elliptic and parabolic partial differential equations on a network of transputers.
The thesis commences with a general introduction to parallel processing. Here a
discussion of the various ways of introducing parallelism in computer systems and the
classification of parallel architectures is presented.
In chapter 2, the transputer architecture and the associated language OCCAM are
described. The transputer development system (TDS) is also described as well as a
short account of other transputer programming languages. Also, a brief description of
the methodologies for programming transputer networks is given. The chapter is
concluded by a detailed description of the hardware used for the research. [Continues.
ICASE
This report summarizes research conducted at the Institute for Computer Applications in Science and Engineering in the areas of (1) applied and numerical mathematics, including numerical analysis and algorithm development; (2) theoretical and computational research in fluid mechanics in selected areas of interest, including acoustics and combustion; (3) experimental research in transition and turbulence and aerodynamics involving Langley facilities and scientists; and (4) computer science
Finite elements software and applications
The contents of this thesis are a detailed study of the software
for the finite element method. In the text, the finite element method
is introduced from both the engineering and mathematical points of view.
The computer implementation of the method is explained with samples of
mainframe, mini- and micro-computer implementations. A solution is
presented for the problem of limited stack size for both mini- and
micro-computers which possess stack architecture.
Several finite element programs are presented. Special purpose
programs to solve problems in structural analysis and groundwater flow
are discussed. However, an efficient easy-to-use finite element program
for general two-dimensional problems is presented. Several problems in
groundwater flow are considered that include steady, unsteady flows in
different types of aquifers. Different cases of sinks and sources in
the flow domain are also considered. The performance of finite element
methods is studied for the chosen problems by comparing the numerical
solutions of test problems with analytical solutions (if they exist) or
with solutions obtained by other numerical methods. The polynomial
refinement of the finite elements is studied for the presented problems
in order to offer some evidence as to which finite element simulation
is best to use under a variety of circumstances
An Interactive Framework For Meshless Methods Analysis In Computational Mechanics And Thermofluids
In recent history, the area of physics-based engineering simulation has seen rapid increases in both computer workstation performance as well as common model complexity, both driven largely in part by advances in memory density and availability of clusters and multi-core processors. While the increase in computation time due to model complexity has been largely offset by the increased performance of modern workstations, the increase in model setup time due to model complexity has continued to rise. As such, the major time requirement for solving an engineering model has transitioned from computation time to problem setup time. This is due to the fact that developing the required mesh for complex geometry can be an extremely complicated and time consuming task. Consequently, new solution techniques which are capable of reducing the required amount of human interaction are desirable. The subject of this thesis is the development of a novel meshless method that promises to eliminate the need for structured meshes, and thus, the need for complicated meshing procedures. Although the savings gain due to eliminating the meshing process would be more than sufficient to warrant further study, the proposed method is also capable of reducing the computation time and memory footprint compared to similar models solved using more traditional finite element, finite difference, finite volume, or boundary element methods. In particular, this thesis will outline the development of an interactive, meshless, physically accurate modeling environment that provides an extensible framework which can be applied to a multitude of governing equations encountered in computational mechanics and thermofluids. Additionally, through the development of tailored preprocessing routines, efficiency and accuracy of the proposed meshless algorithms can be tested in a more realistic and flexible environment. Examples are provided in the areas of elasticity, heat transfer and computational fluid dynamics
Lewis Structures Technology, 1988. Volume 1: Structural Dynamics
The specific purpose of the symposium was to familiarize the engineering structures community with the depth and range of research performed by the Structures Division of the Lewis Research Center and its academic and industrial partners. Sessions covered vibration control, fracture mechanics, ceramic component reliability, parallel computing, nondestructive testing, dynamical systems, fatigue and damage, wind turbines, hot section technology, structural mechanics codes, computational methods for dynamics, structural optimization, and applications of structural dynamics
Finite element solution for elliptic partial differential equations
The contents of this thesis are a detailed study of the implementation
of Finite Element method for solving linear and non-linear elliptic
partial differential equations. It commences with a description and
classification of partial differential equations, the related matrix and
eigenvalue theory and the related matrix methods to solve the linear and
non-linear systems of equations.
In Chapter Three, we discuss the development of the, finite element
method and its application with a full description of an orderly step-by-step
process. In Chapter Four, we discuss the implementation of developing
an efficient easy-to-use finite element program for the general two-dimensional
problem along with the capability of handling problems for
different domains and boundary conditions and with a fully automated mesh
generation and refinement technique along with a description of generalised
pre- and post-processors for the Finite Element Method. [Continues.