8,290 research outputs found
Nonlinear potential analysis techniques for supersonic-hypersonic configuration design
Approximate nonlinear inviscid theoretical techniques for predicting aerodynamic characteristics and surface pressures for relatively slender vehicles at moderate hypersonic speeds were developed. Emphasis was placed on approaches that would be responsive to preliminary configuration design level of effort. Second order small disturbance and full potential theory was utilized to meet this objective. Numerical pilot codes were developed for relatively general three dimensional geometries to evaluate the capability of the approximate equations of motion considered. Results from the computations indicate good agreement with higher order solutions and experimental results for a variety of wing, body and wing-body shapes for values of the hypersonic similarity parameter M delta approaching one. Case computational times of a minute were achieved for practical aircraft arrangements
Isometric immersions, energy minimization and self-similar buckling in non-Euclidean elastic sheets
The edges of torn plastic sheets and growing leaves often display
hierarchical buckling patterns. We show that this complex morphology (i)
emerges even in zero strain configurations, and (ii) is driven by a competition
between the two principal curvatures, rather than between bending and
stretching. We identify the key role of branch-point (or "monkey-saddle")
singularities in generating complex wrinkling patterns in isometric immersions,
and show how they arise naturally from minimizing the elastic energy.Comment: 6 pages, 6 figures. This article supersedes arXiv:1504.0073
On the perturbative expansion of boundary reflection factors of the supersymmetric sinh-Gordon model
The supersymmetric sinh-Gordon model on a half-line with integrable boundary
conditions is considered perturbatively to verify conjectured exact reflection
factors to one loop order. Propagators for the boson and fermion fields
restricted to a half-line contain several novel features and are developed as
prerequisites for the calculations.Comment: 19 pages, 2 figure
Mass Exchange Dynamics of Surface and Subsurface Oil in Shallow-Water Transport
We formulate a model for the mass exchange between oil at and below the sea
surface. This is a particularly important aspect of modeling oil spills.
Surface and subsurface oil have different chemical and transport
characteristics and lumping them together would compromise the accuracy of the
resulting model. Without observational or computational constraints, it is thus
not possible to quantitatively predict oil spills based upon partial field
observations of surface and/or sub-surface oil. The primary challenge in
capturing the mass exchange is that the principal mechanisms are on the
microscale. This is a serious barrier to developing practical models for oil
spills that are capable of addressing questions regarding the fate of oil at
the large spatio-temporal scales, as demanded by environmental questions. We
use upscaling to propose an environmental-scale model which incorporates the
mass exchange between surface and subsurface oil due to oil droplet dynamics,
buoyancy effects, and sea surface and subsurface mechanics. While the mass
exchange mechanism detailed here is generally applicable to oil transport
models, it addresses the modeling needs of a particular to an oil spill model
[1]. This transport model is designed to capture oil spills at very large
spatio-temporal scales. It accomplishes this goal by specializing to
shallow-water environments, in which depth averaging is a perfectly good
approximation for the flow, while at the same time retaining mass conservation
of oil over the whole oceanic domain.Comment: 18 pages, 6 figure
Random sampling of an AC source: A tool to teach probabilistic observations
An undergraduate level experiment is described to demonstrate the role of
probabilistic observations in physics. A capacitor and a DC voltmeter are used
to randomly sample an AC voltage source. The resulting probability distribution
is analyzed to extract information about the AC source. Different
characteristic probability distributions arising from various AC waveforms are
calculated and experimentally measured. The reconstruction of the AC waveform
is demonstrated from the measured probability distribution under certain
restricted circumstances. The results are also compared with a simulated data
sample. We propose this as a pedagogical tool to teach probabilistic
measurements and their manipulations.Comment: Revtex4 file, 10 pages with 8 figure
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