11,493 research outputs found
Computational fluid dynamics
An overview of computational fluid dynamics (CFD) activities at the Langley Research Center is given. The role of supercomputers in CFD research, algorithm development, multigrid approaches to computational fluid flows, aerodynamics computer programs, computational grid generation, turbulence research, and studies of rarefied gas flows are among the topics that are briefly surveyed
Newtonian dynamics in the plane corresponding to straight and cyclic motions on the hyperelliptic curve : ergodicity, isochrony, periodicity and fractals
We study the complexification of the one-dimensional Newtonian particle in a
monomial potential. We discuss two classes of motions on the associated Riemann
surface: the rectilinear and the cyclic motions, corresponding to two different
classes of real and autonomous Newtonian dynamics in the plane. The rectilinear
motion has been studied in a number of papers, while the cyclic motion is much
less understood. For small data, the cyclic time trajectories lead to
isochronous dynamics. For bigger data the situation is quite complicated;
computer experiments show that, for sufficiently small degree of the monomial,
the motion is generically periodic with integer period, which depends in a
quite sensitive way on the initial data. If the degree of the monomial is
sufficiently high, computer experiments show essentially chaotic behaviour. We
suggest a possible theoretical explanation of these different behaviours. We
also introduce a one-parameter family of 2-dimensional mappings, describing the
motion of the center of the circle, as a convenient representation of the
cyclic dynamics; we call such mapping the center map. Computer experiments for
the center map show a typical multi-fractal behaviour with periodicity islands.
Therefore the above complexification procedure generates dynamics amenable to
analytic treatment and possessing a high degree of complexity.Comment: LaTex, 28 pages, 10 figure
On the enumeration of closures and environments with an application to random generation
Environments and closures are two of the main ingredients of evaluation in
lambda-calculus. A closure is a pair consisting of a lambda-term and an
environment, whereas an environment is a list of lambda-terms assigned to free
variables. In this paper we investigate some dynamic aspects of evaluation in
lambda-calculus considering the quantitative, combinatorial properties of
environments and closures. Focusing on two classes of environments and
closures, namely the so-called plain and closed ones, we consider the problem
of their asymptotic counting and effective random generation. We provide an
asymptotic approximation of the number of both plain environments and closures
of size . Using the associated generating functions, we construct effective
samplers for both classes of combinatorial structures. Finally, we discuss the
related problem of asymptotic counting and random generation of closed
environemnts and closures
Institute for Computational Mechanics in Propulsion (ICOMP)
The Institute for Computational Mechanics in Propulsion (ICOMP) is a combined activity of Case Western Reserve University, Ohio Aerospace Institute (OAI) and NASA Lewis. The purpose of ICOMP is to develop techniques to improve problem solving capabilities in all aspects of computational mechanics related to propulsion. The activities at ICOMP during 1991 are described
Institute for Computational Mechanics in Propulsion (ICOMP) fourth annual review, 1989
The Institute for Computational Mechanics in Propulsion (ICOMP) is operated jointly by Case Western Reserve University and the NASA Lewis Research Center. The purpose of ICOMP is to develop techniques to improve problem solving capabilities in all aspects of computational mechanics related to propulsion. The activities at ICOMP during 1989 are described
Hydrodynamic Flows on Curved Surfaces: Spectral Numerical Methods for Radial Manifold Shapes
We formulate hydrodynamic equations and spectrally accurate numerical methods
for investigating the role of geometry in flows within two-dimensional fluid
interfaces. To achieve numerical approximations having high precision and level
of symmetry for radial manifold shapes, we develop spectral Galerkin methods
based on hyperinterpolation with Lebedev quadratures for -projection to
spherical harmonics. We demonstrate our methods by investigating hydrodynamic
responses as the surface geometry is varied. Relative to the case of a sphere,
we find significant changes can occur in the observed hydrodynamic flow
responses as exhibited by quantitative and topological transitions in the
structure of the flow. We present numerical results based on the
Rayleigh-Dissipation principle to gain further insights into these flow
responses. We investigate the roles played by the geometry especially
concerning the positive and negative Gaussian curvature of the interface. We
provide general approaches for taking geometric effects into account for
investigations of hydrodynamic phenomena within curved fluid interfaces.Comment: 14 figure
Summary of research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics, numerical analysis and computer science
Research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics, numerical analysis, and computer science during the period October 1, 1988 through March 31, 1989 is summarized
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