3,106 research outputs found
Wave-number dependence of the transitions between traveling and standing vortex waves and their mixed states in the Taylor-Couette system
Previous numerical investigations of the stability and bifurcation properties
of different nonlinear combination structures of spiral vortices in a
counterrotating Taylor-Couette system that were done for fixed axial
wavelengths are supplemented by exploring the dependence of the vortex
phenomena waves on their wavelength. This yields information about the
experimental and numerical accessability of the various bifurcation scenarios.
Also backwards bifurcating standing waves with oscillating amplitudes of the
constituent traveling waves are found.Comment: 4 pages, 5 figure
Bifurcation of standing waves into a pair of oppositely traveling waves with oscillating amplitudes caused by a three-mode interaction
A novel flow state consisting of two oppositely travelling waves (TWs) with
oscillating amplitudes has been found in the counterrotating Taylor-Couette
system by full numerical simulations. This structure bifurcates out of axially
standing waves that are nonlinear superpositions of left and right handed
spiral vortex waves with equal time-independent amplitudes. Beyond a critical
driving the two spiral TW modes start to oscillate in counterphase due to a
Hopf bifurcation. The trigger for this bifurcation is provided by a nonlinearly
excited mode of different symmetry than the spiral TWs. A three-mode coupled
amplitude equation model is presented that captures this bifurcation scenario.
The mode-coupling between two symmetry degenerate critical modes and a
nonlinearly excited one that is contained in the model can be expected to occur
in other structure forming systems as well.Comment: 4 pages, 5 figure
Spiral vortices traveling between two rotating defects in the Taylor-Couette system
Numerical calculations of vortex flows in Taylor-Couette systems with counter
rotating cylinders are presented. The full, time dependent Navier-Stokes
equations are solved with a combination of a finite difference and a Galerkin
method. Annular gaps of radius ratio and of several heights are
simulated. They are closed by nonrotating lids that produce localized Ekman
vortices in their vicinity and that prevent axial phase propagation of spiral
vortices. Existence and spatio temporal properties of rotating defects, of
modulated Ekman vortices, and of the spiral vortex structures in the bulk are
elucidated in quantitative detail.Comment: 9 pages, 9 figure
Competition between Traveling Fluid Waves of Left and Right Spiral Vortices and Their Different Amplitude Combinations
Stability, bifurcation properties, and the spatiotemporal behavior of
different nonlinear combination structures of spiral vortices in the counter
rotating Taylor-Couette system are investigated by full numerical simulations
and by coupled amplitude equation approximations. Stable cross-spiral
structures with continuously varying content of left and right spiral modes are
found. They provide a stability transferring connection between the initially
stable, axially counter propagating wave states of pure spirals and the axially
standing waves of so-called ribbons that become stable slightly further away
from onset of vortex flow.Comment: 4 pages, 5 figure
Controlling the stability transfer between oppositely traveling waves and standing waves by inversion-symmetry-breaking perturbations
The effect of an externally applied flow on symmetry degenerated waves
propagating into opposite directions and standing waves that exchange stability
with the traveling waves via mixed states is analyzed. Wave structures that
consist of spiral vortices in the counter rotating Taylor-Couette system are
investigated by full numerical simulations and explained quantitatively by
amplitude equations containing quintic coupling terms. The latter are
appropriate to describe the influence of inversion symmetry breaking
perturbations on many oscillatory instabilities with O(2) symmetry.Comment: 4 pages, 4 figure
The Effects of Additives on the Physical Properties of Electroformed Nickel and on the Stretch of Photoelectroformed Nickel Components
The process of nickel electroforming is becoming increasingly important in
the manufacture of MST products, as it has the potential to replicate complex
geometries with extremely high fidelity. Electroforming of nickel uses
multi-component electrolyte formulations in order to maximise desirable product
properties. In addition to nickel sulphamate (the major electrolyte component),
formulation additives can also comprise nickel chloride (to increase nickel
anode dissolution), sulphamic acid (to control pH), boric acid (to act as a pH
buffer), hardening/levelling agents (to increase deposit hardness and lustre)
and wetting agents (to aid surface wetting and thus prevent gas bubbles and
void formation). This paper investigates the effects of some of these variables
on internal stress and stretch as a function of applied current density.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
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