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C M Care

Publications and source records attributed to C M Care.

12 recordsLinked to original sources
PubMed2006

Control of the nematic-isotropic phase transition by an electric field.

We use a relatively simple continuum model to investigate the effects of dielectric inhomogeneity within confined liquid-crystal cells. Specifically, we consider, in planar, cylindrical, and spherical geometries, the stability of a nematic-isotropic interface subject to an applied voltage when the nematic liquid crystal has a positive dielectric anisotropy. Depending on the magnitude of this voltage, the temperature, and the geometry of the cell, the nematic region may shrink until the material is completely isotropic within the cell, grow until the nematic phase fills the cell, or, in certain geometries, coexist with the isotropic phase. For planar geometry, no coexistence is found, but we are able to give analytical expressions for the critical voltage for an electric-field-induced phase transition as well as the critical wetting layer thickness for arbitrary applied voltage. In cells with cylindrical and spherical geometries, however, locally stable nematic-isotropic coexistence is predicted, the thickness of the nematic region being controllable by alteration of the applied voltage.

Journal Article↗
PubMed2006

Shear viscosity of bulk suspensions at low Reynolds number with the three-dimensional lattice Boltzmann method.

We report three-dimensional parallel Lagrangian particle simulations using the lattice Boltzmann method, conducted at a low Reynolds number. Using modified Lees-Edwards boundary conditions and directly calculated viscous dissipation, we show that it is possible to recover excellent agreement with the Einstein viscosity formula in the low concentration limit and to predict viscosity corrections for larger concentrations.

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PubMed2006

Improved simulation of drop dynamics in a shear flow at low Reynolds and capillary number.

The simulation of multicomponent fluids at low Reynolds number and low capillary number is of interest in a variety of applications such as the modeling of venule scale blood flow and microfluidics; however, such simulations are computationally demanding. An improved multicomponent lattice Boltzmann scheme, designed to represent interfaces in the continuum approximation, is presented and shown (i) significantly to reduce common algorithmic artifacts and (ii) to recover full Galilean invariance. The method is used to model drop dynamics in shear flow in two dimensions where it recovers correct results over a range of Reynolds and capillary number greater than that which may be addressed with previous methods.

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PubMed2005

A multi-component lattice Boltzmann scheme: towards the mesoscale simulation of blood flow.

While blood at the macroscopic scale is frequently treated as a continuum by techniques such as computational fluid dynamics, its mesoscale behaviour is not so well investigated or understood. At this scale, the deformability of each cell within the plasma is important and cannot be ignored. However there is currently a lack of efficient computational techniques able to simulate a large number of deformable particles such as blood cells. This paper addresses this problem and demonstrates the applicability of the authors' recent multi-component lattice Boltzmann method for the simulation of a large number of mutually immiscible liquid species [Dupin MM, Halliday I, Care CM. Multi-component lattice boltzmann equation for mesoscale blood flow. J Phys A: Math Gen 2003;36:8517-34]. In here, biological cells are treated as immiscible, deformable, and relatively viscous drops (compared to the surrounding fluid). The validation of the model is based on the work of Goldsmith on the flow of solid particles, deformable particles and red blood cells [Goldsmith HL, Marlow JC. Flow behavior of erythrocytes. II. Particle motions in concentrated suspensions of ghost cells. J Colloid Interf Sci 1979;71:383-407]. We demonstrate, in particular, that the model recovers Goldsmith's observations on the flow properties of red blood cells and also the experimental observations of Frank on the flow of solid beads [Frank M, Anderson D, Weeks ER, Morris JF. Particle migration in pressure-driven flow of a brownian suspension. J Fluid Mech 2003;493:363-78]. The current article is the first validation of our new lattice Boltzmann model for a large number of deformable particles in this context and demonstrates that the method provides a new, and effective, approach for the modeling of mesoscale blood flow.

Biological Transport↗
PubMed2004

A many-component lattice Boltzmann equation simulation for transport of deformable particles.

We review the analysis of single and N-component lattice Boltzmann methods for fluid flow simulation. Results are presented for the emergent pressure field of a single phase incompressible liquid flowing over a backward-facing step, at moderate Reynolds Number, which is compared with the experimental data of Denham & Patrick (1974 Trans. IChE 52, 361-367). We then access the potential of the N-component method for transport of high volume fraction suspensions of deformable particles in pressure-driven flow. The latter are modelled as incompressible, closely packed liquid drops. We demonstrate the technique by investigating the particles' transverse migration in a uniform shear ('lift'), and profile blunting and chaining.

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PubMed2004

A lattice Boltzmann model of flow blunting.

We review our recent multi-component lattice Boltzmann equation method for the simulation of a large number of mutually immiscible liquid species and then apply it to the simulation of dense volume fraction suspensions of deformable particles in internal geometry. In particular, we illustrate the scope of our method by applying it to the simulation of pipe flows containing a high volume fraction of monodisperse suspended, deformable particles. The particles are modelled as immiscible, relatively viscous liquid drops. We modify the 'solidity' of the particles by modifying their viscosity and surface tension and demonstrate the effect of the solidity upon the blunting of the velocity profile.

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PubMed2004

Shape of an isotropic droplet in a nematic liquid crystal: the role of surfactant.

We investigate theoretically, and numerically, the shape of a droplet of an isotropic fluid immersed in a nematic liquid crystal in the presence of an interfacial layer of surfactant; the droplet size is assumed to be small compared to the extrapolation length of the nematic and homeotropic alignment is favored by the anchoring energy at the nematic-isotropic interface. In a certain range of droplet sizes, the droplets are found to be lens shaped with the rotation axis aligned along the imposed director field and the aspect ratio dependent upon the ratio of anchoring strength and surface tension coefficients. For anchoring strengths large compared to the surface tension, the curvature of the edge of lens is controlled by the bending rigidity of surfactant.

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PubMed2003

Generalized lattice Boltzmann algorithm for the flow of a nematic liquid crystal with variable order parameter.

A lattice Boltzmann (LB) scheme is described, which recovers the equations developed by Qian-Sheng for the hydrodynamics of a nematic liquid crystal with a tensor order parameter. The standard mesoscopic LB scalar density is generalized to a tensor quantity and the macroscopic momentum, density, and tensor order parameter are recovered from appropriate moments of this mesoscopic density. A single lattice Boltzmann equation is used with a direction dependent Bhatnagar, Gross, and Krook (BGK) collision term, with additional forcing terms to recover the antisymmetric terms in the stress tensor. A Chapman-Enskog analysis is presented, which demonstrates that the Qian-Sheng scheme is recovered, provided a lattice with sixth-order isotropy is used. The method is validated against analytical results for a number of cases including flow alignment of the order tensor and the Miesowicz viscosities in the presence of an aligning magnetic field. The algorithm accurately recovers the predicted changes in the order parameter in the presence of aligning flow, and magnetic, fields. Preliminary results are given for an extension of the method to model the interface between isotropic and nematic fluids.

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PubMed2003

Lattice Boltzmann algorithm for surface tension with greatly reduced microcurrents.

We present an algorithm for inserting an interface between the immiscible phases of a multicomponent lattice Boltzmann fluid which is based solely upon the appropriate continuum physics: stress boundary conditions and continuity of velocity. Results are presented for the algorithm when applied to static, neutrally buoyant drops. It is shown that the present algorithm gives a significant reduction in the spurious velocities which are reported for previous schemes and a concomitant improvement in the isotropy of the interface.

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PubMed2001

Lattice Boltzmann equation hydrodynamics.

By inserting position and time dependent "source" or "forcing" terms into the microscopic evolution equation of a lattice Boltzmann fluid and treating the generalized scheme within the usual Chapman-Enskog methodology, we show that the emergent dynamics of the lattice fluid may be usefully transformed. Our method of adjustment is demonstrated by implementing the cylindrical polar coordinate form of the continuity and momentum equations on a rectangular lattice and generating results for pipe flow. With straightforward systematic adjustment of the simulation, our approach produces results in excellent agreement with theory.

Journal Article↗
PubMed1999

Rosenbluth chain cluster growth in the study of micelle self-assembly.

A Rosenbluth algorithm [J. Chem. Phys. 23, 356 (1955)] for enumerating clusters of chains is presented. The method is used to undertake a direct enumeration of the cluster partition function for small clusters in a three-dimensional lattice model of a binary mixture of amphiphile and solvent. In this model, the amphiphiles are represented as connected chains on a lattice, with vacant sites representing the solvent. The results from the Rosenbluth method are compared with those obtained by Metropolis Monte Carlo simulations which allow free self-assembly of clusters. The agreement between the two methods allows an unambiguous identification of the packing entropy associated with micelle self-assembly. Results are presented for unbranched chains having two head and four tail segments (H2T4) and also four head and four tail segments (H4T4). Although the cluster enumeration method described in this paper has been developed for micellar systems, it will have applications in a variety of areas including nucleation and percolation.

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