1,846 research outputs found
Experiments in free shear flows: Status and needs for the future
Experiments in free turbulent flows are recommended with the primary concern placed on classical flows in order to augment understanding and for model building. Five classes of experiments dealing with classical free turbulent flows are outlined and proposed as being of particular significance for the near future. These classes include the following: (1) Experiments clarifying the effect of density variation owing to use of different gases, with and without the additional effect of density variation due to high Mach number or other effects; (2) experiments clarifying the role and importance of various parameters which determine the behavior of the near field as well as the condictions under which any of these parameters can be neglected; (3) experiments determining the cumulative effect of initial conditions in terms of distance to fully established flow; (4) experiments for cases where two layers of distinctly different initial turbulence structure flow side by side at the same mean speed; and (5) experiment using contemporary experimental techniques to study structure in free turbulent shear flows in order to compliment and support contemporary work on boundary layers
Air entrainment through free-surface cusps
In many industrial processes, such as pouring a liquid or coating a rotating
cylinder, air bubbles are entrapped inside the liquid. We propose a novel
mechanism for this phenomenon, based on the instability of cusp singularities
that generically form on free surfaces. The air being drawn into the narrow
space inside the cusp destroys its stationary shape when the walls of the cusp
come too close. Instead, a sheet emanates from the cusp's tip, through which
air is entrained. Our analytical theory of this instability is confirmed by
experimental observation and quantitative comparison with numerical simulations
of the flow equations
Simulation of a Dripping Faucet
We present a simulation of a dripping faucet system. A new algorithm based on
Lagrangian description is introduced. The shape of drop falling from a faucet
obtained by the present algorithm agrees quite well with experimental
observations. Long-term behavior of the simulation can reproduce period-one,
period-two, intermittent and chaotic oscillations widely observed in
experiments. Possible routes to chaos are discussed.Comment: 20 pages, 15 figures, J. Phys. Soc. Jpn. (in press
Shuttle S-band communications technical concepts
Using the S-band communications system, shuttle orbiter can communicate directly with the Earth via the Ground Spaceflight Tracking and Data Network (GSTDN) or via the Tracking and Data Relay Satellite System (TDRSS). The S-band frequencies provide the primary links for direct Earth and TDRSS communications during all launch and entry/landing phases of shuttle missions. On orbit, S-band links are used when TDRSS Ku-band is not available, when conditions require orbiter attitudes unfavorable to Ku-band communications, or when the payload bay doors are closed. the S-band communications functional requirements, the orbiter hardware configuration, and the NASA S-band communications network are described. The requirements and implementation concepts which resulted in techniques for shuttle S-band hardware development discussed include: (1) digital voice delta modulation; (2) convolutional coding/Viterbi decoding; (3) critical modulation index for phase modulation using a Costas loop (phase-shift keying) receiver; (4) optimum digital data modulation parameters for continuous-wave frequency modulation; (5) intermodulation effects of subcarrier ranging and time-division multiplexing data channels; (6) radiofrequency coverage; and (7) despreading techniques under poor signal-to-noise conditions. Channel performance is reviewed
Theory of the collapsing axisymmetric cavity
We investigate the collapse of an axisymmetric cavity or bubble inside a
fluid of small viscosity, like water. Any effects of the gas inside the cavity
as well as of the fluid viscosity are neglected. Using a slender-body
description, we show that the minimum radius of the cavity scales like , where is the time from collapse. The exponent
very slowly approaches a universal value according to . Thus, as observed in a number of recent experiments, the
scaling can easily be interpreted as evidence of a single non-trivial scaling
exponent. Our predictions are confirmed by numerical simulations
The Two Fluid Drop Snap-off Problem: Experiments and Theory
We address the dynamics of a drop with viscosity breaking up
inside another fluid of viscosity . For , a scaling theory
predicts the time evolution of the drop shape near the point of snap-off which
is in excellent agreement with experiment and previous simulations of Lister
and Stone. We also investigate the dependence of the shape and
breaking rate.Comment: 4 pages, 3 figure
Damped finite-time-singularity driven by noise
We consider the combined influence of linear damping and noise on a dynamical
finite-time-singularity model for a single degree of freedom. We find that the
noise effectively resolves the finite-time-singularity and replaces it by a
first-passage-time or absorbing state distribution with a peak at the
singularity and a long time tail. The damping introduces a characteristic
cross-over time. In the early time regime the probability distribution and
first-passage-time distribution show a power law behavior with scaling exponent
depending on the ratio of the non linear coupling strength to the noise
strength. In the late time regime the behavior is controlled by the damping.
The study might be of relevance in the context of hydrodynamics on a nanometer
scale, in material physics, and in biophysics.Comment: 9 pages, 4 eps-figures, revtex4 fil
Tests of Dynamical Scaling in 3-D Spinodal Decomposition
We simulate late-stage coarsening of a 3-D symmetric binary fluid. With
reduced units l,t (with scales set by viscosity, density and surface tension)
our data extends two decades in t beyond earlier work. Across at least four
decades, our own and others' individual datasets (< 1 decade each) show viscous
hydrodynamic scaling (l ~ a + b t), but b is not constant between runs as this
scaling demands. This betrays either the unexpected intrusion of a
discretization (or molecular) lengthscale, or an exceptionally slow crossover
between viscous and inertial regimes.Comment: Submitted to Phys. Rev.
HySIA: Tool for Simulating and Monitoring Hybrid Automata Based on Interval Analysis
We present HySIA: a reliable runtime verification tool for nonlinear hybrid
automata (HA) and signal temporal logic (STL) properties. HySIA simulates an HA
with interval analysis techniques so that a trajectory is enclosed sharply
within a set of intervals. Then, HySIA computes whether the simulated
trajectory satisfies a given STL property; the computation is performed again
with interval analysis to achieve reliability. Simulation and verification
using HySIA are demonstrated through several example HA and STL formulas.Comment: Appeared in RV'17; the final publication is available at Springe
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