1,407 research outputs found
Mesoscale modelling of polyelectrolyte electrophoresis
The electrophoretic behaviour of flexible polyelectrolyte chains ranging from
single monomers up to long fragments of hundred repeat units is studied by a
mesoscopic simulation approach. Abstracting from the atomistic details of the
polyelectrolyte and the fluid, a coarse-grained molecular dynamics model
connected to a mesoscopic fluid described by the Lattice Boltzmann approach is
used to investigate free-solution electrophoresis. Our study demonstrates the
importance of hydrodynamic interactions for the electrophoretic motion of
polyelectrolytes and quantifies the influence of surrounding ions. The
length-dependence of the electrophoretic mobility can be understood by
evaluating the scaling behavior of the effective charge and the effective
friction. The perfect agreement of our results with experimental measurements
shows that all chemical details and fluid structure can be safely neglected,
and a suitable coarse-grained approach can yield an accurate description of the
physics of the problem, provided that electrostatic and hydrodynamic
interactions between all entities in the system, i.e., the polyelectrolyte,
dissociated counterions, additional salt and the solvent, are properly
accounted for. Our model is able to bridge the single molecule regime of a few
nm up to macromolecules with contour lengths of more than 100 nm, a length
scale that is currently not accessible to atomistic simulations.Comment: 23 pages, 9 figures, to be presented at Faraday Discussion 14
Mesoscale modelling of polymer aggregate digestion
We use mesoscale simulations to gain insight into the digestion of
biopolymers by studying the break-up dynamics of polymer aggregates (boluses)
bound by physical cross-links. We investigate aggregate evolution, establishing
that the linking bead fraction and the interaction energy are the main
parameters controlling stability with respect to diffusion. We show
a simplified model that chemical breakdown of the constituent
molecules causes aggregates that would otherwise be stable to disperse. We
further investigate breakdown of biopolymer aggregates in the presence of fluid
flow. Shear flow in the absence of chemical breakdown induces three different
regimes depending on the flow Weissenberg number (). i) At ,
shear flow has a negligible effect on the aggregates. ii) At , the
aggregates behave approximately as solid bodies and move and rotate with the
flow. iii) At , the energy input due to shear overcomes the
attractive cross-linking interactions and the boluses are broken up. Finally,
we study bolus evolution under the combined action of shear flow and chemical
breakdown, demonstrating a synergistic effect between the two at high reaction
rates
Holistic mesoscale modelling of concrete – recent developments
Modelling of concrete at the mesoscale is needed in many applications, but developing a realistic mesoscale model for the analysis of concrete behaviour under general loading conditions is challenging. This paper presents an overview of the development of mesoscale modelling of concrete within a finite element framework for both quasi-static and high strain rate applications. A 2D mesoscale model incorporating random aggregates and equivalent interfacial transition zones enables examination into the effects of random aggregate structure and the sub-scale non-homogeneity within the mortar matrix on the macroscopic behaviour of concrete. In applications where multi-axial stresses and confinement effects are significant, such as under high-strain rate loading where the inertial confinement plays an important role, a realistic representation of the multi-axial stress condition becomes necessary, and this requires 3D mesoscale model. Two types of 3D mesoscale concrete model have been developed, namely a pseudo-3D mesoscale model and a full 3D mesoscale model. For the explicit representation of the fracture process, a cohesivecontact approach has been implemented, at present in a 2D mesoscale framework. Illustrative examples are given to demonstrate the performance of the mesoscale models and the results are discussed
Steering in computational science: mesoscale modelling and simulation
This paper outlines the benefits of computational steering for high
performance computing applications. Lattice-Boltzmann mesoscale fluid
simulations of binary and ternary amphiphilic fluids in two and three
dimensions are used to illustrate the substantial improvements which
computational steering offers in terms of resource efficiency and time to
discover new physics. We discuss details of our current steering
implementations and describe their future outlook with the advent of
computational grids.Comment: 40 pages, 11 figures. Accepted for publication in Contemporary
Physic
Computer simulation of liquid crystals
A review is presented of molecular and mesoscopic computer simulations of liquid crystalline systems. Molecular simulation approaches applied to such systems are described and the key findings for bulk phase behaviour are reported. Following this, recently developed lattice Boltzmann (LB) approaches to the mesoscale modelling of nemato-dynamics are reviewed. The article concludes with a discussion of possible areas for future development in this field.</p
Mesoscale modelling of steel processing
Numerical methods are utilised to reproduce the evolution of a system observed in natural phenomena. Within the area of materials science there is an increase of interest in modelling techniques that can accurately predict the microstructure of a material subject to various processing conditions. Recently, there is a requirement of techniques that have the ability to be applied to systems involving microstructural change in the presence of fluid flow. This presents a challenge since the forces governing these processes involve those predominately influenced by thermodynamics as well as those influenced by hydrodynamics. The phase-field method, a popular technique used in this area, has been shown to have the ability to cope with phase transformation dynamics such as solidification and solid-state phase transformations. However, its predictive capabilities mainly apply to a flow free environment where flow effects are minimal compared to other effects. Other techniques such as smoothed particle hydrodynamics exist that are more than capable of describing the mechanisms of flow demonstrating superiority in many complex flow problems. The thermodynamic quantities related to the evolution of a system to which this method is applied must then be consistent in order to be translated between models. This thesis develops the tools necessary to deal with phase growth and microstructural change within the presence of flow. This is done by developing phase-field models that can efficiently deal with displacive transformations in steels as well as diffusive, and SPH models with the ability to be coupled with thermodynamics. The phase-field models are developed to be applied to structure growth observed at relatively low temperatures within steels, namely martensite and bainite growth. The SPH method is analysed in order to assess and provide solutions for consistency when considered for coupling with models mainly dependent on thermodynamics.Open Acces
Recommended from our members
LBM, a useful tool for mesoscale modelling of single phase and multiphase flow – the variety of applications and approaches at Nottingham
This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Giving an overview of Nottingham group’s recent progress on numerical modelling and
approaches in developing and applying the lattice Boltzmann method (LBM), the paper tries to demonstrate that the LBM is a useful tool for mesoscale modelling of single phase and multiphase flow. The variety of applications of the LBM modelling is reported, which include single phase fluid flow and heat transfer around or across rotational cylinder of curved boundary, two-phase flow in mixing layer, electroosmotically driven flow in thin liquid layer, bubbles/drops flow and coalescence in conventional channels and in
microchannels with confined boundary, liquid droplets in gas with relative large density ratio; viscous fingering phenomena of immiscible fluids displacement, and flow in porous media
- …