Use this list for quick links to a particular area:
The development of shear bands in granular materials
(Hughes, Tordesillas, Vicendese)
Incipient Slumping and Yield stress (Chamberlain, Landman, Sader)
Pair Interactions in confined systems
High-frequency electrokinetics (Mangelsdorf, Carnie, Poliak)
Particle interactions in electrokinetics (Carnie with J Ennis(CSIRO))
The effect of fluid damping on Atomic Force Microscopy
Modelling the cooking of cereals
Applications of electrokinetics in electrochromatography (Carnie, Shugai, Baygents)
Phase Behaviour in Colloidal Systems (Petris, Chan)
Coning Problem in Two Phase Flow (Chan, Hughes, Poliak with L Paterson (CSIRO))
A finite element analysis of soil-tyre interaction based
on the contact mechanics theory of rolling and/or sliding bodies
Surface corrugation on unsealed roads
(Tordesillas, with Hill, JM Wollongong University)
To be completed
The slump test is a cheap, easy way of measuring the shear yield stress of a particulate slurry.
Knowledge of the yield stress of mineral tailing slurries is an important part of an
integrated system for dry disposal of such tailings. A simple model for linking yield stress
and slump height is available. However this simple model makes several unphysical assumptions
and does not give a good understanding of the stress and flow during a slump test.
A better theoretical analysis of the slump test is desirable to give physical insight
into the stresses and flow and to asses the validity of the simple model.
A model for calculating the stresses and plastic flow of the slurry using slipline field
theory is progressing.
To be completed
The theory developed by Mangelsdorf and White [J. Chem. Soc. Faraday Trans. (1992), 88, 3567-3581]
to calculate the electrophoretic mobility of a spherical colloidal particle subjected to an
oscillating electric field has become the standard benchmark for comparing approximate
analytic theories of the dynamic mobility.
We are attempting to generalize the current treatment of dynamic mobility to allow for particles
made of porous material or conductive material. Preliminary work on hydrodynamics of an oscillating
porous particle has been completed. To faciitate such work, we are also re-examining the current
numerical algorithm, which fails for low salt systems.
The effect of particle interactions on electrophoretic mobility has so far been limited to the case
of thin double layers. The effect of particle interactions for finite double layer thickness
(say ka in the range 1 to 30 ) has been investigated by several methods. Reflection results
have been obtained for the case of two spherical particles with low zeta potentials and expressions
derived for the suspension mobility of a mildly polydisperse suspension in terms of the two-particle
mobilities. Expressions for the fluctuations in the suspension mobility have also been derived and
both expressions evaluated using the reflection results. In order to test the reflection results,
we extend Teubner's method [J Chem Phys, 76, 11 (1982)] to the case of two particles interacting
with thick double layers, again for low zeta potentials. The results for two-particle mobilities,
suspension mobility and mobility fluctuations are compared extensively to reflection calculations
for the same system in a recent publication (Shugai et. al.1997 see below). Similar techniques
can be used for the case of a particle in a bounded flow. Typical examples are a sphere near
a planar wall and a sphere on the axis of a cylinder with field along the cylinder axis.
Reflection results have been obtained for these cases. Numerical results have been completed
and submitted for publication. The reflection results for the sphere in a cylinder
- modified to account for a closed system - have been used to explain experimental
results for protein electrophoresis through porous membranes. Numerical results and
reflections results have also been obtained for the case of the dynamic mobility
which describes the response of a suspension to an oscillating electric field.
A new expression has been obtained for the dynamic mobility of a suspension of
particles with thick double layers using Batchelor's renormalization method.
The results of this study are being prepared for publication now. Finally,
similar numerical techniques have been used to find the axial dynamic mobility
for a spheroid with finite double layer thickness.
It is hoped to compare these to corresponding results for a disc and a rod.
To be completed
To be completed
Electrochromatography, whereby an electric field is applied opposing the elution of a solution
through a packed chromatography bed, is a new technique being used for the separation of protein
mixtures and DNA fragments. As yet the mechanism of the separation is unclear. We have started
investigating this technique, first by regarding each bead in the bead in isolation
- a spherical collector model- and in pairs - the gap between beads being a prototype pore.
We are currently extending the modelling to more realistic representations of the packed bed.
The coexistence of a gas and liquid phases, observed in experiments and Monte Carlo simulations
of dilute charged colloidal dispersions, cannot satisfactorily be explained in terms of
classical DLVO theory. In such a system of colloids and counterions,
the van der Waals interaction between colloids is negligible, and the effect
is purely electrostatic. Traditional wisdom dictates that a gas-liquid phase transition
can only occur with an attractive pair interaction.
However in DLVO theory, the pair interaction between like charged colloids is always repulsive.
The aim of this project is to seek a physical explanation of the behaviour of such systems.
A qualitative analytic explanation has been produced using an extension
of the Debye-Hückel theory, without the assumption of a pairwise attractive
electrostatic interaction. A more advanced computational theory is being developed,
involving the calculation of appropriate pair distribution functions using the
renormalized mean spherical approximation (RMSA) and Poisson-Boltzmann (PB) theory.
Relevant thermodynamic quantities such as the internal energy, free energy and
pressure can then be determined and compared with two-component Monte Carlo simulations.
The aim of this project is to elucidate the sensitivity and effectiveness of physical parameters
that can be used to control the position of the oil/water interface during the withdrawal of oil
from underground reservoirs. The problem, known as the dual completion problem is an attempt to
increase the oil production rate by simultaneously withdrawing water that lies below the oil reserve.
This arrangement has the possibility of preventing the breakthrough of the oil/water interface at
the oil production point by controlling the position of the oil/water interface.
The determination of the dimensions of the soil-tyre contact area, and the stresses and
deformations of the tyre and soil within this area, remains the key challenge in soil-vehicle
interaction mechanics. Computer models of vehicle traction and mobility rely on accurate
information about these contact properties for input, and the lack of such information imposes
severe practical limitations on these models. In this work, we use Contact Mechanics theory
to develop a three dimensional model of soil-tyre interaction which can accurately predict
these contact properties at any given instant of the process. Preliminary results with experimental
validation have been obtained for plane strain soil-tyre interaction systems
( Proceedings, The Royal Society of London. Series A 455:261-283, 1999;
Quarterly Journal of Mechanics and Applied Mathematics 52;99-110, 1999).
This project is funded by the United States Army Research Office for future use in
the evaluation of mobility and performance of newly-fielded prototype and "virtual" prototype
Surface corrugation on unsealed roads is a familiar phenomenon, giving rise to vehicle damage
and adversely affecting passenger safety and comfort. The resolution of the problem by grading
is costly (over 1 billion dollars per year in Australia), time consuming, and, moreover,
is effective only in the short term. The aim of this project is to utilise the continuum
theory of granular materials to formulate a proper mathematical model for the formation
of surface corrugation on unsealed roads, and to investigate the effect of other factors,
such as the constitution of underlying strata, road curvature and other variables involving road usage.