69 research outputs found
Silo collapse under granular discharge
We investigate, at a laboratory scale, the collapse of cylindrical shells of
radius and thickness induced by a granular discharge. We measure the
critical filling height for which the structure fails upon discharge. We
observe that the silos sustain filling heights significantly above an
estimation obtained by coupling standard shell-buckling and granular stress
distribution theories. Two effects contribute to stabilize the structure: (i)
below the critical filling height, a dynamical stabilization due to granular
wall friction prevents the localized shell-buckling modes to grow irreversibly;
(ii) above the critical filling height, collapse occurs before the downward
sliding motion of the whole granular column sets in, such that only a partial
friction mobilization is at play. However, we notice also that the critical
filling height is reduced as the grain size, , increases. The importance of
grain size contribution is controlled by the ratio . We
rationalize these antagonist effects with a novel fluid/structure theory both
accounting for the actual status of granular friction at the wall and the
inherent shell imperfections mediated by the grains. This theory yields new
scaling predictions which are compared with the experimental results.Comment: Original work, 13 pages and 11 figure
BPS Configurations in Smectics
It is typical in smectic liquid crystals to describe elastic deformations
with a linear theory when the elastic strain is small. We extend the recent,
exact solution of Brener and Marchenko to more general one-dimensional
deformations, including multiple edge dislocations by relying on the
Bogomol'nyi, Prasad and Sommerfield (BPS) decomposition. We introduce an
approximation for the deformation profile far from a spherical inclusion and
find an enhanced attractive interaction at long distances due to the nonlinear
elasticity.Comment: 4 pages, RevTeX, 2 figures, corrected typo
Phase Separation of Rigid-Rod Suspensions in Shear Flow
We analyze the behavior of a suspension of rigid rod-like particles in shear
flow using a modified version of the Doi model, and construct diagrams for
phase coexistence under conditions of constant imposed stress and constant
imposed strain rate, among paranematic, flow-aligning nematic, and log-rolling
nematic states. We calculate the effective constitutive relations that would be
measured through the regime of phase separation into shear bands. We calculate
phase coexistence by examining the stability of interfacial steady states and
find a wide range of possible ``phase'' behaviors.Comment: 23 pages 19 figures, revised version to be published in Physical
Review
Rheology of Lamellar Liquid Crystals in Two and Three Dimensions: A Simulation Study
We present large scale computer simulations of the nonlinear bulk rheology of
lamellar phases (smectic liquid crystals) at moderate to large values of the
shear rate (Peclet numbers 10-100), in both two and three dimensions. In two
dimensions we find that modest shear rates align the system and stabilise an
almost regular lamellar phase, but high shear rates induce the nucleation and
proliferation of defects, which in steady state is balanced by the annihilation
of defects of opposite sign. The critical shear rate at onset of this second
regime is controlled by thermodynamic and kinetic parameters; we offer a
scaling analysis that relates the critical shear rate to a critical "capillary
number" involving those variables. Within the defect proliferation regime, the
defects may be partially annealed by slowly decreasing the applied shear rate;
this causes marked memory effects, and history-dependent rheology. Simulations
in three dimensions show instead shear-induced ordering even at the highest
shear rates studied here. This suggests that the critical shear rate shifts
markedly upward on increasing dimensionality. This may in part reflect the
reduced constraints on defect motion, allowing them to find and annihilate each
other more easily. Residual edge defects in the 3D aligned state mostly point
along the flow velocity, an orientation impossible in two dimensions.Comment: 18 pages, 12 figure
Encoding conformance checking artefacts in SAT
Conformance checking strongly relies on the computation of artefacts, which enable reasoning on the relation between observed and modeled behavior. This paper shows how important conformance artefacts like alignments, anti-alignments or even multi-alignments, defined over the edit distance, can be computed by encoding the problem as a SAT instance. From a general perspective, the work advocates for a unified family of techniques that can compute conformance artefacts in the same way. The prototype implementation of the techniques presented in this paper show capabilities for dealing with some of the current benchmarks, and potential for the near future when optimizations similar to the ones in the literature are incorporated.Peer ReviewedPostprint (author's final draft
Encoding conformance checking artefacts in SAT
Conformance checking strongly relies on the computation of artefacts, which enable reasoning on the relation between observed and modeled behavior. This paper shows how important conformance artefacts like alignments, anti-alignments or even multi-alignments, defined over the edit distance, can be computed by encoding the problem as a SAT instance. From a general perspective, the work advocates for a unified family of techniques that can compute conformance artefacts in the same way. The prototype implementation of the techniques presented in this paper show capabilities for dealing with some of the current benchmarks, and potential for the near future when optimizations similar to the ones in the literature are incorporated.Peer ReviewedPostprint (author's final draft
Recent experimental probes of shear banding
Recent experimental techniques used to investigate shear banding are
reviewed. After recalling the rheological signature of shear-banded flows, we
summarize the various tools for measuring locally the microstructure and the
velocity field under shear. Local velocity measurements using dynamic light
scattering and ultrasound are emphasized. A few results are extracted from
current works to illustrate open questions and directions for future research.Comment: Review paper, 23 pages, 11 figures, 204 reference
Boundary effects on the maximal angle of stability of a granular packing
PACS. 81.05.Rm Porous materials; granular materials - 83.70.Fn Granular solids,
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