8,237 research outputs found
NASA Wallops Flight Facility Air-Sea Interaction Research Facility
This publication serves as an introduction to the Air-Sea Interaction Research Facility at NASA/GSFC/Wallops Flight Facility. The purpose of this publication is to provide background information on the research facility itself, including capabilities, available instrumentation, the types of experiments already done, ongoing experiments, and future plans
On alpha stable distribution of wind driven water surface wave slope
We propose a new formulation of the probability distribution function of wind
driven water surface slope with an -stable distribution probability.
The mathematical formulation of the probability distribution function is given
under an integral formulation. Application to represent the probability of time
slope data from laboratory experiments is carried out with satisfactory
results. We compare also the -stable model of the water surface slopes
with the Gram-Charlier development and the non-Gaussian model of Liu et
al\cite{Liu}. Discussions and conclusions are conducted on the basis of the
data fit results and the model analysis comparison.Comment: final version of the manuscript: 25 page
Quasinormal ringing of acoustic black holes in Laval nozzles: Numerical simulations
Quasinormal ringing of acoustic black holes in Laval nozzles is discussed.
The equation for sounds in a transonic flow is written into a
Schr\"{o}dinger-type equation with a potential barrier, and the quasinormal
frequencies are calculated semianalytically. From the results of numerical
simulations, it is shown that the quasinormal modes are actually excited when
the transonic flow is formed or slightly perturbed, as well as in the real
black hole case. In an actual experiment, however, the purely-outgoing boundary
condition will not be satisfied at late times due to the wave reflection at the
end of the apparatus, and a late-time ringing will be expressed as a
superposition of "boxed" quasinormal modes. It is shown that the late-time
ringing damps more slowly than the ordinary quasinormal ringing, while its
central frequency is not greatly different from that of the ordinary one. Using
this fact, an efficient way for experimentally detecting the quasinormal
ringing of an acoustic black hole is discussed.Comment: 9 pages, 8 figures, accepted for publication in Physical Review
Study of effects of space power satellites on life support functions of the earth's magnetosphere
The effects of the Satellite Solar Power System (SSPS) on the life support functions of the earth's magnetosphere were investigated. Topics considered include: (1) thruster effluent effects on the magnetosphere; (2) biological consequences of SSPS reflected light; (3) impact on earth bound astronomy; (4) catastrophic failure and debris; (5) satellite induced processes; and (6) microwave power transmission. Several impacts are identified and recommendations for further studies are provided
Directional Soliton and Breather Beams
Solitons and breathers are nonlinear modes that exist in a wide range of
physical systems. They are fundamental solutions of a number of nonlinear wave
evolution equations, including the uni-directional nonlinear Schr\"odinger
equation (NLSE). We report the observation of slanted solitons and breathers
propagating at an angle with respect to the direction of propagation of the
wave field. As the coherence is diagonal, the scale in the crest direction
becomes finite, consequently, a beam dynamics forms. Spatio-temporal
measurements of the water surface elevation are obtained by
stereo-reconstructing the positions of the floating markers placed on a regular
lattice and recorded with two synchronized high-speed cameras. Experimental
results, based on the predictions obtained from the (2D+1) hyperbolic NLSE
equation, are in excellent agreement with the theory. Our study proves the
existence of such unique and coherent wave packets and has serious implications
for practical applications in optical sciences and physical oceanography.
Moreover, unstable wave fields in this geometry may explain the formation of
directional large amplitude rogue waves with a finite crest length within a
wide range of nonlinear dispersive media, such as Bose-Einstein condensates,
plasma, hydrodynamics and optics
Scattering theory of walking droplets in the presence of obstacles
We aim to describe a droplet bouncing on a vibrating bath using a simple and
highly versatile model inspired from quantum mechanics. Close to the Faraday
instability, a long-lived surface wave is created at each bounce, which serves
as a pilot wave for the droplet. This leads to so called walking droplets or
walkers. Since the seminal experiment by {\it Couder et al} [Phys. Rev. Lett.
{\bf 97}, 154101 (2006)] there have been many attempts to accurately reproduce
the experimental results. We propose to describe the trajectories of a walker
using a Green function approach. The Green function is related to the Helmholtz
equation with Neumann boundary conditions on the obstacle(s) and outgoing
boundary conditions at infinity. For a single-slit geometry our model is
exactly solvable and reproduces some general features observed experimentally.
It stands for a promising candidate to account for the presence of arbitrary
boundaries in the walker's dynamics.Comment: 17 pages, 5 figure
Recurrence in the high-order nonlinear Schr\"odinger equation: a low dimensional analysis
We study a three-wave truncation of the high-order nonlinear Schr\"odinger
equation for deepwater waves (HONLS, also named Dysthe equation). We validate
our approach by comparing it to numerical simulation, distinguish the impact of
the different fourth-order terms and classify the solutions according to their
topology. This allows us to properly define the temporary spectral upshift
occurring in the nonlinear stage of Benjamin-Feir instability and provides a
tool for studying further generalizations of this model
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