25 research outputs found
Mesoscale fluid simulation with the Lattice Boltzmann method
PhDThis thesis describes investigations of several complex fluid effects., including
hydrodynamic spinodal decomposition, viscous instability. and self-assembly of a
cubic surfactant phase, by simulating them with a lattice Boltzmann computational
model.
The introduction describes what is meant by the term "complex fluid", and why
such fluids are both important and difficult to understand. A key feature of complex
fluids is that their behaviour spans length and time scales. The lattice Boltzmann
method is presented as a modelling technique which sits at a "mesoscale" level
intermediate between coarse-grained and fine-grained detail, and which is therefore
ideal for modelling certain classes of complex fluids.
The following chapters describe simulations which have been performed using
this technique, in two and three dimensions. Chapter 2 presents an investigation
into the separation of a mixture of two fluids. This process is found to involve several
physical mechanisms at different stages. The simulated behaviour is found to be in
good agreement with existing theory, and a curious effect, due to multiple competing
mechanisms, is observed, in agreement with experiments and other simulations.
Chapter 3 describes an improvement to lattice Boltzmann models of Hele-Shaw
flow, along with simulations which quantitatively demonstrate improvements in both
accuracy and numerical stability. The Saffman-Taylor hydrodynamic instability is
demonstrated using this model.
Chapter 4 contains the details and results of the TeraGyroid experiment, which
involved extremely large-scale simulations to investigate the dynamical behaviour
of a self-assembling structure. The first finite- size-effect- free dynamical simulations
of such a system are presented. It is found that several different mechanisms are
responsible for the assembly; the existence of chiral domains is demonstrated, along
with an examination of domain growth during self-assembly.
Appendix A describes some aspects of the implementation of the lattice Boltzmann
codes used in this thesis; appendix B describes some of the Grid computing
techniques which were necessary for the simulations of chapter 4.
Chapter 5 summarises the work, and makes suggestions for further research and
improvement.Huntsman Corporation Queen Mary University Schlumberger Cambridge Researc
Stochastic computational modelling of complex drug delivery systems
As modern drug formulations become more advanced, pharmaceutical companies face the need for adequate tools to permit them to model complex requirements and to reduce
unnecessary adsorption rates while increasing the dosage administered. The aim of the research presented here is the development and application of a general stochastic framework with agent-based elements for building drug dissolution models, with a particular focus on
controlled release systems. The utilisation of three dimensional Cellular Automata and Monte Carlo methods, to describe structural compositions and the main physico-chemical mechanisms, is shown to have several key advantages: (i) the bottom up approach simplifies
the definition of complex interactions between underlying phenomena such as diffusion,polymer degradation and hydration, and the dissolution media; (ii) permits straightforward extensibility for drug formulation variations in terms of supporting various geometries
and exploring effects of polymer composition and layering; (iii) facilitates visualisation, affording insight on system structural evolution over time by capturing successive stages of dissolution. The framework has been used to build models simulating several distinct
release scenarios from coated spheres covering single coated erosion and swelling dominated spheres as well as the influence of multiple heterogeneous coatings. High-performance computational optimisation enables precision simulations of the very thin coatings used and allows fast realisation of model state changes. Furthermore, theoretical analysis of the comparative impact of synchronous and asynchronous Cellular Automata and the suitability of their application to pharmaceutical systems is performed. Likely parameter distributions from noisy in vitro data are reconstructed using Inverse Monte Carlo methods and outcomes are reported
Pattern Recognition
A wealth of advanced pattern recognition algorithms are emerging from the interdiscipline between technologies of effective visual features and the human-brain cognition process. Effective visual features are made possible through the rapid developments in appropriate sensor equipments, novel filter designs, and viable information processing architectures. While the understanding of human-brain cognition process broadens the way in which the computer can perform pattern recognition tasks. The present book is intended to collect representative researches around the globe focusing on low-level vision, filter design, features and image descriptors, data mining and analysis, and biologically inspired algorithms. The 27 chapters coved in this book disclose recent advances and new ideas in promoting the techniques, technology and applications of pattern recognition
Large eddy simulation of primary liquid-sheet breakup
This research project aims at providing the aeronautical industry with a modelling
capability to simulate the fuel injection in gas turbine combustion chambers.
The path to this objective started with the review of state-of-the-art numerical
techniques to model the primary breakup of liquid fuel into droplets. Based on this
and keeping in mind the requirements of the industry, our modelling strategy led to
the generation of a mass-conservative method for efficient atomisation modelling on
unstructured meshes. This goal has been reached with the creation of high-order
numerical schemes for unstructured grids, the development of an efficient numerical
method that transports the liquid-vapour interface accurately while conserving
mass and the implementation of an algorithm that outputs the droplet boundary
conditions to separate combustion codes.
Both high-order linear and WENO schemes have been created for general polyhedral
meshes. The notorious complexity of high-order schemes on 3D mixed-element
meshes has been handled by the creation of a series of algorithms. These include
the tetrahedralisation of the mesh, which allows generality of the approach while
remaining efficient and affordable, together with a novel approach to stencil generation and a faster interpolation of the solution. The performance of the scheme has been demonstrated on typical two-dimensional and three-dimensional test cases for both linear and non-linear hyperbolic partial differential equations.
The conservative level set method has been extended to unstructured meshes and
its performance has been improved in terms of robustness and accuracy. This was achieved by solving the equations for the transport of the liquid volume fraction
with our novel WENO scheme for polyhedral meshes and by adding a flux-limiter
algorithm. The resulting method, named robust conservative level set, conserves
mass to machine accuracy and its ability to capture the physics of the atomisation
is demonstrated in this thesis.
To be readily applicable to the simulation of atomisation, the novel interfacecapturing technique has been embedded in a framework — within the open source CFD code OpenFOAM — that solves the velocity and pressure fields, outputs
droplet characteristics and runs in parallel. In particular, the production of droplet boundary conditions involves a set of routines handling the selection of drops in the level set field, the calculation of relevant droplet characteristics and their storage into data files. An n-halo parallelisation method has been implemented in OpenFOAM to perform the computations at the expected order of accuracy.
Finally, the modelling capability has been demonstrated on the simulation of
primary liquid-sheet breakup with relevance to fuel injection in aero-engine combustors.
The computation has demonstrated the ability of the code to capture the
physics accurately and further illustrates the potential of the numerical approach