10 research outputs found
Bending-Filament Model for the Buckling and Coiling Instability of Viscous Fluid Rope
A simple model is proposed for the buckling and coiling instability of a
viscous "fluid rope" falling on a plane. By regarding a fluid rope as a
one-dimensional flow, this model accounts for only the axial and shared viscous
forces. Our model successfully reproduces several experiments with no
adjustable parameters, such as the existence of three distinct coiling regimes
reported in Phys. Rev. Lett. 93, 214502 (2004). Our model allows for the
discussion of unsteady motion. An expression for the critical fall height at
which the coiling frequency changes from a decrease to increase was
phenomenologically derived. It was found that the coil-uncoil transition shows
remarkable hysteresis only for weak gravity condition.Comment: 4 pages, 6 figure
Experimental observation of shear thickening oscillation
We report experimental observation of the shear thickening oscillation, i.e.
the spontaneous macroscopic oscillation in the shear flow of severe shear
thickening fluid. The shear thickening oscillation is caused by the interplay
between the fluid dynamics and the shear thickening, and has been predicted
theoretically by the present authors using a phenomenological fluid dynamics
model for the dilatant fluid, but never been reported experimentally. Using a
density-matched starch-water mixture, in the cylindrical shear flow of a few
centimeters flow width, we observed strong vibrations of the frequency around
20 Hz, which is consistent with our theoretical prediction.Comment: 4pages, 5 figure
Fluid dynamics of dilatant fluid
Dense mixture of granules and liquid often shows a sever shear thickening and
is called a dilatant fluid. We construct a fluid dynamics model for the
dilatant fluid by introducing a phenomenological state variable for a local
state of dispersed particles. With simple assumptions for an equation of the
state variable, we demonstrate that the model can describe basic features of
the dilatant fluid such as the stress-shear rate curve that represents
discontinuous severe shear thickening, hysteresis upon changing shear rate,
instantaneous hardening upon external impact. Analysis of the model reveals
that the shear thickening fluid shows an instability in a shear flow for some
regime and exhibits {\it the shear thickening oscillation}, i.e. the
oscillatory shear flow alternating between the thickened and the relaxed
states. Results of numerical simulations are presented for one and
two-dimensional systems.Comment: 12 pages, 17 figure
A theoretical and numerical approach to "magic angle" of stone skipping
We investigate oblique impacts of a circular disk and water surface. An
experiment [ Clanet, C., Hersen, F. and Bocquet, L., Nature 427, 29 (2004) ]
revealed that there exists a "magic angle" of 20 [deg.] between a disk face and
water surface which minimize the required speed for ricochet. We perform
3-dimensional simulation of the water impacts using the Smoothed Particle
Hydrodynamics (SPH) and analyze the results with an ordinal differential
equation (ODE) model. Our simulation is in good agreement with the experiment.
The analysis with the ODE model give us a theoretical insight for the ``magic
angle" of stone skipping.Comment: 4 pages, 4figure
Separation of long DNA chains using non-uniform electric field: a numerical study
We study migration of DNA molecules through a microchannel with a series of
electric traps controlled by an ac electric field. We describe the motion of
DNA based on Brownian dynamics simulations of a beads-spring chain. Our
simulation demonstrates that the chain captured by an electrode escapes from
the binding electric field due to thermal fluctuation. We find that the
mobility of chain would depend on the chain length; the mobility sharply
increases when the length of a chain exceeds a critical value, which is
strongly affected by the amplitude of the applied ac field. Thus we can adjust
the length regime, in which this microchannel well separates DNA molecules,
without changing the structure of the channel. We also present a theoretical
insight into the relation between the critical chain length and the field
amplitude.Comment: 12 pages, 9 figure
Collision of One-Dimensional Nonlinear Chains
We investigate one-dimensional collisions of unharmonic chains and a rigid
wall. We find that the coefficient of restitution (COR) is strongly dependent
on the velocity of colliding chains and has a minimum value at a certain
velocity. The relationship between COR and collision velocity is derived for
low-velocity collisions using perturbation methods. We found that the velocity
dependence is characterized by the exponent of the lowest unharmonic term of
interparticle potential energy