3,623 research outputs found
Hybrid Lattice Boltzmann/Finite Difference simulations of viscoelastic multicomponent flows in confined geometries
We propose numerical simulations of viscoelastic fluids based on a hybrid
algorithm combining Lattice-Boltzmann models (LBM) and Finite Differences (FD)
schemes, the former used to model the macroscopic hydrodynamic equations, and
the latter used to model the polymer dynamics. The kinetics of the polymers is
introduced using constitutive equations for viscoelastic fluids with finitely
extensible non-linear elastic dumbbells with Peterlin's closure (FENE-P). The
numerical model is first benchmarked by characterizing the rheological
behaviour of dilute homogeneous solutions in various configurations, including
steady shear, elongational flows, transient shear and oscillatory flows. As an
upgrade of complexity, we study the model in presence of non-ideal
multicomponent interfaces, where immiscibility is introduced in the LBM
description using the "Shan-Chen" model. The problem of a confined viscoelastic
(Newtonian) droplet in a Newtonian (viscoelastic) matrix under simple shear is
investigated and numerical results are compared with the predictions of various
theoretical models. The proposed numerical simulations explore problems where
the capabilities of LBM were never quantified before.Comment: 32 Pages, 11 Figure
Recent advances in the simulation of particle-laden flows
A substantial number of algorithms exists for the simulation of moving
particles suspended in fluids. However, finding the best method to address a
particular physical problem is often highly non-trivial and depends on the
properties of the particles and the involved fluid(s) together. In this report
we provide a short overview on a number of existing simulation methods and
provide two state of the art examples in more detail. In both cases, the
particles are described using a Discrete Element Method (DEM). The DEM solver
is usually coupled to a fluid-solver, which can be classified as grid-based or
mesh-free (one example for each is given). Fluid solvers feature different
resolutions relative to the particle size and separation. First, a
multicomponent lattice Boltzmann algorithm (mesh-based and with rather fine
resolution) is presented to study the behavior of particle stabilized fluid
interfaces and second, a Smoothed Particle Hydrodynamics implementation
(mesh-free, meso-scale resolution, similar to the particle size) is introduced
to highlight a new player in the field, which is expected to be particularly
suited for flows including free surfaces.Comment: 16 pages, 4 figure
Phase separation processes in polymer solutions in relation to membrane formation
This review covers new experimental and theoretical physical research related to the formation of polymeric membranes by phase separation of a polymer solution, and to the morphology of these membranes. Two main phase separation processes for polymeric membrane formation are discussed: thermally induced phase separation and immersion precipitation. Special attention is paid to phase transitions like liquid-liquid demixing, crystallization, gelation, and vitrification, and their relation to membrane morphology. In addition, the mass transfer processes involved in immersion precipitation, and their influence on membrane morphology are discussed
Electrokinetic Lattice Boltzmann solver coupled to Molecular Dynamics: application to polymer translocation
We develop a theoretical and computational approach to deal with systems that
involve a disparate range of spatio-temporal scales, such as those comprised of
colloidal particles or polymers moving in a fluidic molecular environment. Our
approach is based on a multiscale modeling that combines the slow dynamics of
the large particles with the fast dynamics of the solvent into a unique
framework. The former is numerically solved via Molecular Dynamics and the
latter via a multi-component Lattice Boltzmann. The two techniques are coupled
together to allow for a seamless exchange of information between the
descriptions. Being based on a kinetic multi-component description of the fluid
species, the scheme is flexible in modeling charge flow within complex
geometries and ranging from large to vanishing salt concentration. The details
of the scheme are presented and the method is applied to the problem of
translocation of a charged polymer through a nanopores. In the end, we discuss
the advantages and complexities of the approach
Three-dimensional lattice-Boltzmann simulations of critical spinodal decomposition in binary immiscible fluids
We use a modified Shan-Chen, noiseless lattice-BGK model for binary
immiscible, incompressible, athermal fluids in three dimensions to simulate the
coarsening of domains following a deep quench below the spinodal point from a
symmetric and homogeneous mixture into a two-phase configuration. We find the
average domain size growing with time as , where increases
in the range , consistent with a crossover between
diffusive and hydrodynamic viscous, , behaviour. We find
good collapse onto a single scaling function, yet the domain growth exponents
differ from others' works' for similar values of the unique characteristic
length and time that can be constructed out of the fluid's parameters. This
rebuts claims of universality for the dynamical scaling hypothesis. At early
times, we also find a crossover from to in the scaled structure
function, which disappears when the dynamical scaling reasonably improves at
later times. This excludes noise as the cause for a behaviour, as
proposed by others. We also observe exponential temporal growth of the
structure function during the initial stages of the dynamics and for
wavenumbers less than a threshold value.Comment: 45 pages, 18 figures. Accepted for publication in Physical Review
Kinetics and thermodynamics of thermally reversible polymers:Based on the furan-maleimide DA reaction
The diene-dienophile pair furan-maleimide is a popular choice in the design of thermally reversible or self-healing polymers based on the Diels-Alder (DA) reaction. This thesis contributes fundamental insights that can be used to tailor polymer properties for specific applications and examines how to cross-link reactants in the solvent efficiently. Novel methods are introduced to analyze the kinetics and mechanisms of reversible reactions by combining Differential Scanning Calorimetry (DSC) measurements and a series of models for cross-linked furanic polyketones with bis-maleimides. Furthermore, the limitations of atomistic simulations of such systems are examined systematically to propose ways in which the DA reaction can be captured accurately, allowing for the tailoring of reversible polymer properties. Finally, a new method is presented that can be used to calculate phase diagrams of organic and polymeric liquid mixtures via the UNIQUAC model implemented in the CALPHAD method, which is crucial to study the solubility of reactants in the solvent
Deformation and break-up of viscoelastic droplets in confined shear flow
The deformation and break-up of Newtonian/viscoelastic droplets are studied
in confined shear flow. Our numerical approach is based on a combination of
Lattice-Boltzmann models (LBM) and finite difference schemes, the former used
to model two immiscible fluids with variable viscous ratio, and the latter used
to model the polymer dynamics. The kinetics of the polymers is introduced using
constitutive equations for viscoelastic fluids with finitely extensible
non-linear elastic dumbbells with Peterlin's closure (FENE-P). We quantify the
droplet response by changing the polymer relaxation time , the maximum
extensibility of the polymers, and the degree of confinement, i.e. the
ratio of the droplet diameter to gap spacing. In unconfined shear flow, the
effects of droplet viscoelasticity on the critical Capillary number
\mbox{Ca}_{\mbox{\tiny{cr}}} for break-up are moderate in all cases studied.
However, in confined conditions a different behaviour is observed: the critical
Capillary number of a viscoelastic droplet increases or decreases, depending on
the maximum elongation of the polymers, the latter affecting the extensional
viscosity of the polymeric solution. Force balance is monitored in the
numerical simulations to validate the physical picture.Comment: 34 Pages, 13 Figures. This Work applies the Numerical Methodology
described in arXiv:1406.2686 to the Problem of Droplet Break-up in confined
microchannel
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