93 research outputs found
The relationship between viscoelasticity and elasticity
Soft materials that are subjected to large deformations
exhibit an extremely rich phenomenology, with
properties lying in between those of simple fluids and
those of elastic solids. In the continuum description of
these systems, one typically follows either the route
of solid mechanics (Lagrangian description) or the
route of fluid mechanics (Eulerian description). The
purpose of this review is to highlight the relationship
between the theories of viscoelasticity and of elasticity,
and to leverage this connection in contemporary soft
matter problems. We review the principles governing
models for viscoelastic liquids, for example solutions
of flexible polymers. Such materials are characterized
by a relaxation time λ, over which stresses relax. We
recall the kinematics and elastic response of large
deformations, and show which polymer models do
(and which do not) correspond to a nonlinear elastic
solid in the limit λ → ∞. With this insight, we split
the work done by elastic stresses into reversible and
dissipative parts, and establish the general form of
the conservation law for the total energy. The elastic
correspondence can offer an insightful tool for a broad
class of problems; as an illustration, we show how the
presence or absence of an elastic limit determines the
fate of an elastic thread during capillary instability
Nonparallel local spatial stability analysis of pipe entrance swirling flows
A spatial local viscous stability analysis of a swirling flow developing in a cylindrical pipe has been
carried out numerically. Even at moderately low swirl strengths, we have found the existence of
centrifugal modes in addition to the shear ones found in previous stability analysis of nonswirling
flows developing in pipes. It is found that these centrifugal instabilities develop at Reynolds
numbers that are much lower than those required for the growing of the shear instability. Moreover,
the extent of the region where centrifugal instabilities appear is much larger than that where the
shear layer instability grows. We have found from the analysis that the most unstable mode was the
counter-rotating one (n = -1). The critical Reynolds number for which linear analysis predicts the
growth of the convective instabilities is for the centrifugal modes one hundred times smaller than for
the shear layer ones
Factores que influyen en los consumidores para no exigir su comprobante de pago de sus transacciones en el mercado de Piura
Este estudio tuvo como objetivo, describir los factores que influyen en los consumidores para
no exigir comprobante de pago en sus transacciones comerciales, en el distrito de Piura.
Para contrastar la hipótesis, se realizó una encuesta a 384 consumidores del mercado
Modelo de Piura. Una vez aplicado el cuestionario, se analizaron los datos, lo cual permitió
confirmar la hipótesis planteada; asimismo, las causas que conllevan a que los
consumidores no exijan comprobante de pago de sus transacciones en el distrito de Piura,
entre las cuales tenemos: 1) La falta de cultura tributaria, 2) El bajo nivel de comportamiento
tributario, 3) Los inadecuados sistemas de comunicación e información que no permiten una
buena orientación a los contribuyentes del mercado del distrito de Piura, lo que origina que
cada día la evasión tributaria sea mayor
Self-similarity in the breakup of very dilute viscoelastic solutions
This is an Open Access article,
distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/
licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium,
provided the original work is properly cited.When pushed out of a syringe, polymer solutions form droplets attached by long and slender cylindrical filaments whose diameter decreases exponentially with time before eventually breaking. In the last stages of this process, a striking feature is the self-similarity of the interface shape near the end of the filament. This means that shapes at different times, if properly rescaled, collapse onto a single universal shape. A theoretical description based on the Oldroyd-B model was recently shown to disagree with existing experimental results. By revisiting these measurements and analysing the interface profiles of very diluted polyethylene oxide solutions at high temporal and spatial resolution, we show that they are very well described by the model. © 2020 Cambridge University Press
Influence of the Surface Viscosity on the Breakup of a Surfactant-Laden Drop
We examine both theoretically and experimentally the breakup of a pendant drop loaded with an
insoluble surfactant. The experiments show that a significant amount of surfactant is trapped in the resulting
satellite droplet. This result contradicts previous theoretical predictions, where the effects of surface tension
variation were limited to solutocapillarity and Marangoni stresses.We solve numerically the hydrodynamic
equations, including not only those effects but also those of surface shear and dilatational viscosities. We
show that surface viscosities play a critical role to explain the accumulation of surfactant in the satellite
droplet.Ministerio de Economía y Competitividad DPI2013-46485-C3-1-R, TRA2013- 45808-RJunta de Extremadura GR1004
Vortex breakdown in a water-spout flow
The numerical study of the steady axisymmetric air-water flow in a vertical sealed cylinder, driven by the rotating top disk, describes topological transformations as the rotation intensifies. The air meridional flow (AMF) and swirl induce meridional motions of opposite directions in water. For slow (fast) rotation, the effect of AMF (swirl) dominates. For very fast rotation, large-scale regions of clockwise meridional circulation in air and water are separated by a thin layer of anticlockwise circulation adjacent to the interface in water. This pattern develops for other fluids as well. Physical reasoning behind the flow evolution is provided
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