608 research outputs found
Liquid interfaces in viscous straining flows: Numerical studies of the selective withdrawal transition
This paper presents a numerical analysis of the transition from selective
withdrawal to viscous entrainment. In our model problem, an interface between
two immiscible layers of equal viscosity is deformed by an axisymmetric
withdrawal flow, which is driven by a point sink located some distance above
the interface in the upper layer. We find that steady-state hump solutions,
corresponding to selective withdrawal of liquid from the upper layer, cease to
exist above a threshold withdrawal flux, and that this transition corresponds
to a saddle-node bifurcation for the hump solutions. Numerical results on the
shape evolution of the steady-state interface are compared against previous
experimental measurements. We find good agreement where the data overlap.
However, the numerical results' larger dynamic range allows us to show that the
large increase in the curvature of the hump tip near transition is not
consistent with an approach towards a power-law cusp shape, an interpretation
previously suggested from inspection of the experimental measurements alone.
Instead the large increase in the curvature at the hump tip reflects a
logarithmic coupling between the overall height of the hump and the curvature
at the tip of the hump.Comment: submitted to JF
Still water: dead zones and collimated ejecta from the impact of granular jets
When a dense granular jet hits a target, it forms a large dead zone and
ejects a highly collimated conical sheet with a well-defined opening angle.
Using experiments, simulations, and continuum modeling, we find that this
opening angle is insensitive to the precise target shape and the dissipation
mechanisms in the flow. We show that this surprising insensitivity arises
because dense granular jet impact, though highly dissipative, is nonetheless
controlled by the limit of perfect fluid flow.Comment: 5 pages, 5 figures, submitted to Physical Review Letter
Dense Suspension Splat: Monolayer Spreading and Hole Formation After Impact
We use experiments and minimal numerical models to investigate the rapidly
expanding monolayer formed by the impact of a dense suspension drop against a
smooth solid surface. The expansion creates a lace-like pattern of particle
clusters separated by particle-free regions. Both the expansion and the
development of the spatial inhomogeneity are dominated by particle inertia,
therefore robust and insensitive to details of the surface wetting, capillarity
and viscous drag.Comment: 4 pages (5 with references), and a total of 4 figure
Blocking a wave: Frequency band gaps in ice shelves with periodic crevasses
We assess how the propagation of high-frequency elastic-flexural waves
through an ice shelf is modified by the presence of spatially periodic
crevasses. Analysis of the normal modes supported by the ice shelf with and
without crevasses reveals that a periodic crevasse distribution qualitatively
changes the mechanical response. The normal modes of an ice shelf free of
crevasses are evenly distributed as a function of frequency. In contrast, the
normal modes of a crevasse-ridden ice shelf are distributed unevenly. There are
"band gaps", frequency ranges over which no eigenmodes exist. A model ice shelf
that is 50 km in lateral extent and 300 m thick with crevasses spaced 500 m
apart has a band gap from 0.2 to 0.38 Hz. This is a frequency range relevant
for ocean wave/ice-shelf interactions. When the outermost edge of the crevassed
ice shelf is oscillated at a frequency within the band gap, the ice shelf
responds very differently from a crevasse-free ice shelf. The flexural motion
of the crevassed ice shelf is confined to a small region near the outermost
edge of the ice shelf and effectively "blocked" from reaching the interior.Comment: 6 pages, 4 figures, accepted to Annals of Glaciolog
- …