52 research outputs found
Wrinkling of microcapsules in shear flow
Elastic capsules can exhibit short wavelength wrinkling in external shear
flow. We analyse this instability of the capsule shape and use the length scale
separation between the capsule radius and the wrinkling wavelength to derive
analytical results both for the threshold value of the shear rate and for the
critical wave-length of the wrinkling. These results can be used to deduce
elastic parameters from experiments.Comment: 4 pages, 2 figures, submitted to PR
Efficient and accurate simulations of deformable particles immersed in a fluid using a combined immersed boundary lattice Boltzmann finite element method
The deformation of an initially spherical capsule, freely suspended in simple
shear flow, can be computed analytically in the limit of small deformations [D.
Barthes-Biesel, J. M. Rallison, The Time-Dependent Deformation of a Capsule
Freely Suspended in a Linear Shear Flow, J. Fluid Mech. 113 (1981) 251-267].
Those analytic approximations are used to study the influence of the mesh
tessellation method, the spatial resolution, and the discrete delta function of
the immersed boundary method on the numerical results obtained by a coupled
immersed boundary lattice Boltzmann finite element method. For the description
of the capsule membrane, a finite element method and the Skalak constitutive
model [R. Skalak et al., Strain Energy Function of Red Blood Cell Membranes,
Biophys. J. 13 (1973) 245-264] have been employed. Our primary goal is the
investigation of the presented model for small resolutions to provide a sound
basis for efficient but accurate simulations of multiple deformable particles
immersed in a fluid. We come to the conclusion that details of the membrane
mesh, as tessellation method and resolution, play only a minor role. The
hydrodynamic resolution, i.e., the width of the discrete delta function, can
significantly influence the accuracy of the simulations. The discretization of
the delta function introduces an artificial length scale, which effectively
changes the radius and the deformability of the capsule. We discuss
possibilities of reducing the computing time of simulations of deformable
objects immersed in a fluid while maintaining high accuracy.Comment: 23 pages, 14 figures, 3 table
Motion of a spherical capsule in branched tube flow with finite inertia
We computationally study the transient motion of an initially spherical capsule flowing through a right-angled tube bifurcation, composed of tubes having the same diameter. The capsule motion and deformation is simulated using a three-dimensional immersed-boundary lattice Boltzmann method. The capsule is modelled as a liquid droplet enclosed by a hyperelastic membrane following the Skalak’s law (Skalak et al., Biophys. J., vol. 13(3), 1973, pp. 245–264). The fluids inside and outside the capsule are assumed to have identical viscosity and density. We mainly focus on path selection of the capsule at the bifurcation as a function of the parameters of the problem: the flow split ratio, the background flow Reynolds number Re , the capsule-to-tube size ratio a/R and the capillary number Ca , which compares the viscous fluid force acting on the capsule to the membrane elastic force. For fixed physical properties of the capsule and of the tube flow, the ratio Ca/Re is constant. Two size ratios are considered: a/R=0.2 and 0.4. At low Re , the capsule favours the branch which receives most flow. Inertia significantly affects the background flow in the branched tube. As a consequence, at equal flow split, a capsule tends to flow straight into the main branch as Re is increased. Under significant inertial effects, the capsule can flow into the downstream main tube even when it receives much less flow than the side branch. Increasing Ca promotes cross-stream migration of the capsule towards the side branch. The results are summarized in a phase diagram, showing the critical flow split ratio for which the capsule flows into the side branch as a function of size ratio, Re and Ca/Re . We also provide a simplified model of the path selection of a slightly deformed capsule and explore its limits of validity. We finally discuss the experimental feasibility of the flow system and its applicability to capsule sorting
Методическая работа в дошкольной образовательной организации как условие развития профессионально-педагогической культуры педагогов
Тема работы актуальна. В ВКР представлена методическая работа с педагогами ДОУ, по формирования профессионально-педагогической культуры. Работа имеет практическую значимост
Stationary shapes of deformable particles moving at low Reynolds numbers
Lecture Notes of the Summer School ``Microswimmers -- From Single Particle
Motion to Collective Behaviour'', organised by the DFG Priority Programme SPP
1726 (Forschungszentrum J{\"{u}}lich, 2015).Comment: Pages C7.1-16 of G. Gompper et al. (ed.), Microswimmers - From Single
Particle Motion to Collective Behaviour, Lecture Notes of the DFG SPP 1726
Summer School 2015, Forschungszentrum J\"ulich GmbH, Schriften des
Forschungszentrums J\"ulich, Reihe Key Technologies, Vol 110, ISBN
978-3-95806-083-
Numerical simulations of complex fluid-fluid interface dynamics
Interfaces between two fluids are ubiquitous and of special importance for
industrial applications, e.g., stabilisation of emulsions. The dynamics of
fluid-fluid interfaces is difficult to study because these interfaces are
usually deformable and their shapes are not known a priori. Since experiments
do not provide access to all observables of interest, computer simulations pose
attractive alternatives to gain insight into the physics of interfaces. In the
present article, we restrict ourselves to systems with dimensions comparable to
the lateral interface extensions. We provide a critical discussion of three
numerical schemes coupled to the lattice Boltzmann method as a solver for the
hydrodynamics of the problem: (a) the immersed boundary method for the
simulation of vesicles and capsules, the Shan-Chen pseudopotential approach for
multi-component fluids in combination with (b) an additional
advection-diffusion component for surfactant modelling and (c) a molecular
dynamics algorithm for the simulation of nanoparticles acting as emulsifiers.Comment: 24 pages, 12 figure
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