1,151 research outputs found
Labyrinthic granular landscapes
We have numerically studied a model of granular landscape eroded by wind. We
show the appearance of labyrinthic patterns when the wind orientation turns by
. The occurence of such structures are discussed. Morever, we
introduce the density of ``defects'' as the dynamic parameter governing
the landscape evolution. A power law behavior of is found as a function
of time. In the case of wind variations, the exponent (drastically) shifts from
2 to 1. The presence of two asymptotic values of implies the
irreversibility of the labyrinthic formation process.Comment: 3 pages, 3 figure, RevTe
Resonant and antiresonant bouncing droplets
When placed onto a vibrating liquid bath, a droplet may adopt a permanent
bouncing behavior, depending on both the forcing frequency and the forcing
amplitude. The relationship between the droplet deformations and the bouncing
mechanism is studied experimentally and theoretically through an asymmetric and
dissipative bouncing spring model. Antiresonance effects are evidenced.
Experiments and theoretical predictions show that both resonance at specific
frequencies and antiresonance at Rayleigh frequencies play crucial roles in the
bouncing mechanism. In particular, we show that they can be exploited for
droplet size selection.Comment: 4 pages, 4 figures and 1 vide
Ripple and kink dynamics
We propose a relevant modification of the Nishimori-Ouchi model [{\em Phys.
Rev. Lett.} {\bf 71}, 197 (1993)] for granular landscape erosion. We explicitly
introduce a new parameter: the angle of repose , and a new process:
avalanches. We show that the parameter leads to an asymmetry of the
ripples, as observed in natural patterns. The temporal evolution of the maximum
ripple height is limited and not linear, according to recent
observations. The ripple symmetry and the kink dynamics are studied and
discussed.Comment: 7 pages, 10 figure, RevTe
Diffusive foam wetting process in microgravity
We report the experimental study of aqueous foam wetting in microgravity. The
liquid fraction along the bubble edges is measured and is found to be a
relevant dynamical parameter during the capillary process. The penetration of
the liquid in the foam, the foam inflation, and the rigidity loss are shown all
to obey strict diffusion processes.Comment: 4 pages, 6 figures, submitted to Phys. Rev. Let
Rolling/Slipping Motion of Euler's Disk
We present an experimental study of the motion of a circular disk spun onto a
table. With the help of a high speed video system, the temporal evolutions of
(i) the inclination angle , (ii) the angular velocity and
(iii) the precession rate are studied. The influence of the mass of
the disk and the friction between the disk and the supporting surface are
considered. %The motions of disks with different masses and over different
surfaces are studied. The inclination angle and the angular velocity
are observed to decrease according to a power law. We also show that the
precession rate diverges as the disk stops. Exponents are measured
very near the collapse as well as on long range times. Collapsing times have
been also measured. The results are compared with previous theoretical and
experimental works. The major source of energy dissipation is found to be the
slipping of the disk on the plane.Comment: Submitted for publication (2003) - 6page
A fountain of droplets
A vessel is plunged upside down into a pool of 50 cSt silicone oil. An air
bell is then created. This bell is vertically shaken at 60 Hz that leads to the
oscillation of the air/oil interface. The edges of the immersed vessel generate
surface waves that propagate towards the center of the bell. When the amplitude
of the oscillation increases, wave amplitude increases. We study the influence
of the angle between successive sides on the wave patterns. Two kinds of vessel
have been studied: a triangular and a square prism. The shape of the air/oil
meniscus depends on the angle between the sides of the considered prism. As the
amplitude of the oscillation is increased, the triple line, which is the
contact line between the solid and the air/oil interface, moves up and down.
Above a given acceleration that depends on the immersion depth and on the shape
vessel, wave goes under the corner edge of the bell. During the oscillation,
the wave generates at the edges presents a singularity that leads eventually to
a jet and a drop ejection. A drop is ejected at each oscillation. More
complicated ejection can be produced with further increase of the amplitude.
This is a sample arXiv article illustrating the use of fluid dynamics videos.Comment: 3 pages, 2 figures, 2 movies (high-res and low-res
Patterns in hydraulic ripples with binary granular mixtures
An experimental study of a binary granular mixture submitted to a transient
shear flow in a cylindrical container is reported. The formation of ripples
with a spiral shape is observed. The appearance of phase segregation in those
spiral patterns is shown. The relative grain size bewteen sand species is found
to be a relevant parameter leading to phase segregation. However, the relative
repose angle is an irrelevant parameter. The formation of sedimentary
structures is also presented. They result from a ripple climbing process. The
``sub-critical'' or ``super-critical'' character of the lamination patterns is
shown to depend on the rotation speed of the container.Comment: 9 pages, 9 figures, LateX (using elsart package), submitted to Phys.
- …