This page contains general research areas in Rheology group. To see some slide presentations, click HERE.

Constitutive Modelling for Polymer Processing, in collaboration with CRC Polymer

Participants: Prof Roger Tanner, Prof Nhan Phan-Thien, Dr Simin Nasseri, Dr Shao Cong Dai, Dr Gerald Pereira, Dr Yurun Fan, Dr Matti Keentok, Vangu Kitoko, Duane Lee Wo

click on photos, to see larger size

Objective:

Fundamental studies involving kinematics of polymer solutions have been carried out in the Rheology Group with the ultimate aim of describing bulk properties of polymer solutions and melts, following an application of a deformation field. Specific topics of interest include Brownian dynamics of polymer chains, including excluded volume effects, their kink dynamics as well as diffusion in a viscous solvent; design of and behaviour of customised "electro-rheological" and "magnetic' fluids. The objective of this research is to improve the accuracy of the modelling the complete mechanical/ thermal/ geometrical behaviour of polymers as they cool from melt to finished product during the injection moulding process.

Background:

Polymer processing typically involves melting and solidification of the material, and development of process-induced molecular orientation and crystalline structure. Currently no model can describe this range of behaviour.The main feature of the proposed model are: quantitative accuracy in representing the rheological response, compressibility, effect of crystallisation, and liquid-solid phase change; predictive capability for frozen-in stresses, birefringence and molecular orientation; computational tractability and simplicity; and the ability to experimentally determine the parameters involved in the constitutive equation.To be industrially relevant, data for the model must be obtained, making the property measurement an integral part of the project. The model to be used as an industry standard will be incorporated into existing software packages, refined through trials by participants that are processors, and commercialised by Moldflow.

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Rheology of Bread Dough, in collaboration with CRC Dough

Participants: Prof. Roger Tanner, Prof. Nhan Phan-Thien, Dr. Matti Keentok, Dr Simin Nasseri, Dr. Surjani Utayakumaran, Marcus Newberry, Taisir Hubraq

Objective:

This project is concerned with the fundamental rheology of bread dough and the consequent constitutive modelling of bread dough. The rheology of bread dough is being defined under steady and oscillatory shear testing, extensional testing, creep and other techniques. Once the final data set has been obtained, a relaxation spectrum will be extracted from it, and a constitutive model will be fitted to the data. Preliminary results have been obtained for four commercial flours. Additional work is being undertaken to determine the rheological properties of a large set of genetically modified bread doughs.

Background:

Despite its obvious commercial relevance, we know rather little about the behaviour of doughs in precise rheological terms. Laboratory equipment such as the Mixograph, Farinograph and Extensograph provide empirical rheological information on dough behaviour but the lack of understanding of fundamental rheology of the doughs can lead to inconsistencies in dough behaviour between these instruments (complicating selection in breeding programs), inconsistencies in results between the laboratory and the bakery, and difficulties in understanding relationships between flour composition and rheological behaviour. We are tackling this in two ways, firstly by developing and utilising equipment for small-scale dough testing, and secondly by undertaking an extensive investigation of the fundamental rheological analysis of dough.

Micro-baking experiments show the effect of alteration of protein content of a flour on loaf height.

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Dynamics of Micromachinery in Viscous Environment, Using BEM

Participants: Prof. Nhan Phan-Thien, Dr. Simin Nasseri

Objective:

This research aims to investigate the dynamic of micro machinery. It focuses on the analysis of the motion of a small mechanical device in a viscous environment. In particular, key parameters relating to the geometry of the device required to achieve energy efficient motion will be derived. This project results in major advances in the understanding of the behaviour of electro-mechanical devices when these are miniaturised. This provides clear guidelines for the capabilities of actuators required to design and manufacture self-propelling micro electro mechanical devices.

Background:

In recent years, the Boundary Element Method (BEM) has become an efficient tool for solving engineering problems. The main advantage of the method is a reduction of dimensionality, as only the boundary of the domain needs to be discretised. This is in direct contrast to standard spatial methods (finite difference or finite elements) where the whole space outside the body needs to be meshed, increasing enormously the number of unknowns in the problem. Indeed, for three-dimensional Stokes flows, the Boundary Element Method is the only feasible numerical solution scheme.

Consequently, from a modelling point of view, the micromachine designed in this research by simulating a spermatozoon, consists of a head (which contains an electromechanical mechanism and power source) and a tail (which "oscillates" or "rotates" or "deforms" by the aid of the mechanism in head). As a result of the tail motion, it induces a net force and a net torque on the head. The problem is approached theoretically by considering the types of movement which can occur for the micromachine immersed in a viscous medium. Therefore, the modelling process has been done considering different shapes for a micromachine to obtain the maximum swimming velocity.

Schematic diagram of a micromachine with spiral tail

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Soft Tissue Rheology: Characterization and Modelling of Soft Biological Tissues

Participants: Dr. Lynne Bilston, Dr. Simin Nasseri, Dr Zizhen Liu, Rodney Fiford, Anthony Powell

Objective:

Understanding and characterizing the mechanical response of soft biological tissues is a fundamental problem in biomedical engineering. Adequate models are needed to allow the study of both normal tissue function and the effects of disease and injury on these tissues. A major research project in the fundamental mechanical behaviour of soft biological tissues is being undertaken. Particular tissues of interest are brain, spinal cord, skin, ligament, muscle, duramater, kidney and liver.

Experimental work is aimed at characterizing the non-linear viscoelastic mechanical behaviour of these tissues, using tensile testing, shear testing and biaxial testing. Analytical and numerical modelling is focussed on the development of constitutive equations for these soft tissues which account for their non-linear time dependent behaviour as well as their anisotropy. Whole organ level simulations of the tissue behaviour are also being conducted.

Background:

The mechanical behaviour of biological materials is determined by their structure. The factors which control mechanical response include the gross and microscopic tissue morphology, the chemical composition of the tissue, fluid flow within the tissue, directionality of tissue fibre structures, and the interfaces between various structures.

A project is underway to investigate the relationships between tissue structural features and the measured mechanical properties. These tissues in particular are being investigated: neural tissue (spinal cord and brain), bovine hoof material, bovine liver and pig kidney. In the case of neural tissue, the function of the tissue is strongly affected by mechanical loads, and understanding the mechanical response of the individual nerve cells and blood vessels within the tissues to mechanical loading will give insight into both normal function and injury thresholds.

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Molecular Dynamics Simulation of Polymeric Fluids in Thin Film Lubrication

Participants: Prof. Roger Tanner, Dr John Atkinson,  Dr. Ahmad Jabbarzadeh, Jim Prentzas

Objective:

Understanding properties of thin liquid films in confined geometry is very important in many applications such as lubrication, coating and polymer processing. At extreme conditions of high shear rates and temperature in ultra-thin films measuring the rheological properties and studying the behavior of the film is very difficult with experimental techniques. Molecular dynamics simulation are used in our studies to investigate the behavior of these thin films that exhibit deviation from continuum mechanics. This is mainly because of inhomogeneity that is a result of wall effect. These thin films show enhanced viscosity and shear thinning effects, We have studied many properties of the confined film, the effect of the wall properties on its behavior, boundary conditions, slip, rheological properties and structural effects.

Background:

Molecular dynamics simulations are used as a first principle method to study physical phenomena. This method is specially useful where there is no existing model for the problem under investigation or the existing models do not work. In principle using Newton's second law and integrating the equations of motion, positions and velocities of the atoms are calculated. Then statistical mechanics principles are used to calculate tome average macroscopic properties such as, temperature, pressure, stress tensor, viscosity, etc of the material. The beauty of molecular dynamics is that you need only few hundred or few thousand atoms to examine the properties of the matter. This means a sample only few nano-meter on each side.

In rheology group we have put emphasis on the rheological properties of confined films and complex flows through narrow channels. We use a complex and realistic model to simulate molecules such as, tetracosane, squalane, short polyethylene molecules and linear and branched molecules (example) . Some of the research work in this area are shown below:

1. Model lubricant consisted of branched molecules of 2,3,6,7,10,11,hexapropyldodecane is confined between to solid walls and undergone shear flow at shear rate of 10¹¹ 1/s. The film thickness in 7.2 nm. See AVI format (17 MB)
2. Simulation of Poiseuille flow throgh a narrow channel and over a sharp corner. Molecules are Hexadecane (C₁₆H₃₄) molecules. See AVI format (10 MB)
3. Simulation of C₁₀₀H₂₀₂ molecules near the wall asperities. See the Animated GIF format file (6.6 MB) or AVI format (10 MB)
4. A single molecule of 2,3,6,7,10,11,hexapropyldodecane is shown in Couette shear flow simulation of these branched molecules. See the Animated GIF format (105 KB) or the AVI format (1.04 MB)
5. A single molecule Squalane is shown in Couette shear flow simulation of these branched molecules. See the Animated GIF format (110 KB)or the AVI format (1.1 MB)
6. A single molecule tetracosane is shown in Couette shear flow simulation of these linear molecules. See the Animated GIF format (110 KB) or the AVI format (1.1 MB).

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3D Numerical Simulation of Viscoelastic Fluid Flow

Participants: Prof. Roger Tanner, Prof. Nhan Phan-Thien, Dr. Shicheng Xue

Objective:

The overall objective is to develop a novel (in terms of accuracy and efficiency) approach to the computation of 3D viscoelastic flows, particularly to produce a working program capable of analyzing 3D complex flows of polymer melts. In view of its time and space saving features, it is quite feasible to develop Finite Volume Methods (FVM) into the viscoelastic flow computational area by introducing proper viscoelastic models and novel numerical schemes. The significance for the field of computational rheology is twofold: 1) the ability to simulate realistic 3D melt flow processes such as extrusion, die-filling and calendering, 2) a better understanding of high-stress regions at separation points, including the setting of appropriate boundary conditions, which will lead to improved process design. Another important application is to evaluate the modelling of viscoelastic materials by comparing numerical predictions with experimental observations.

Background:

By modelling a process mathematically, and solving the system of governing equations efficiently with the aid of high-speed digital computers, the unknowns involving in the process can be numerically predicted and visualized in a modern way. It is an efficient complement and economic supplement for theoretical and experimental investigation approaches, especially for the cases where experimental approaches are not feasible.

CFD (Computational Fluid Dynamics) has been successfully employed in a wide range of scientific researches and engineering applications. However, when it is directly used for computational rheology in which more factors are involved, such as the non-linear responses of materials, long-range fluid (elastic) memory effects, some difficulties arise, such as convergence of numerical methods. Also, some of the distinct features of the process can only be observed in a three dimensional (3D) space, thus, a 3D numerical simulation has to be implemented for the predictions, thus, efficiency of the numerical method being of importance with limited computer resources for industrial applications.

Vortex enhancement in 4 to 1 contraction flow of Boger-fluid

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Suspension Rheology

Background:

In a collaborative effort with Moldflow Inc. the Rheology group is involved in fundamental research improving our understanding of polymers and suspensions with Newtonian and Non-Newtonian solvents. The characterisation of suspensions are of interest in a diverse range of applications such as for plasma and blood products for the biological sciences, and other various industrial processes involving e.g., paints, slurries and long distance piping. Another immediate application for the suspension research undertaken in this group is for the enhancement of injection moulded plastics. The work from this research will lead to better and more capable techniques and products for a wide range of commercial products and industrial applications.

Current fields of research in the rheology group include:

1) Fibre Suspension- Numerical Simulations for Newtonian and Non-Newtonian Solvents, Containing Rigid or Non-rigid Fibres

Participants: Prof. Roger Tanner, Prof. Nhan Phan-Thien, Prof Xi-Jun Fan and Clint Joung

Objective:

We are able to successfully predict the bulk rheological properties of multiple rigid fibre suspensions using theoretical research, Monte-Carlo based methods, and also through the direct simulation and tracking of multiple individual suspension particles in numerical simulation. The SyDCom computing facility consisting of 32 Dec-alpha workstations, and parallelized computing techniques (PVM) allows large computationally intensive simulations of this type to be conducted within this department. The rigid fibre suspension simulations have been extended to study the effects of particulate shape on rheological bulk properties. Existing theoretical predictions for qualitatively different behaviour have been verified using recently developed flexible fibre models and numerical simulations.

The eigenvectors of the fibre suspension orientation tensor <PP> form a orthogonal vector triplet - and may be represented with the three main axes of an ellipsoid. This figure shows the orientation evolution of the suspension in a shear flow.

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2) Electro-Rheological Suspensions and Their Applications

Participants: Prof. Nhan Phan-Thien, Prof. Roger Tanner, Dr. Howard See

Objective:

This project is a systematic investigation of some of the key unresolved issues related to the mechanisms of electro-rheological fluid behaviour. We aim to gain an understanding of the key mechanisms governing the fluid behaviour, by a series of rheological measurements using controlled samples and conditions, complemented by the development of appropriate microstructural models. These studies will contribute towards optimisation of the material properties, helping to facilitate commercialisation of ERF technology.

Background:

Recently, there has much interest in electro-rheological fluids (ERF) which are "smart materials" with rheological properties that can be dramatically altered by an externally applied electric field (of the order of kV/mm). The tunable flow properties of these particulate suspensions offer many potential applications, such as adjustable vibration damping devices and valves. There has been considerable activity in both industry and academe in USA, Japan, Korea and the European countries to understand the fundamental mechanisms behind ERF behaviour, with a view to developing optimal materials and efficient applications. However, the commercialisation of this technology is still hindered by our incomplete understanding.

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3) The computational research is aimed at handling non-linearities encountered in flows of viscoelastic fluids through development of appropriate computational techniques (boundary element, finite volume, spectral and Browninan methods), as well as creation of effective distributed systems.

part a: Application of CDLBEM on Motion of Particles in Shear Flows of Viscous Fluid, via PVM

part b: Effective Moduli of Particulate Solids, Lubrication Approximation Method

Participants: Prof. Nhan Phan-Thien, Prof. Xi-Jun Fan, Dr. Simin Nasseri, Fuzhong Qi

Objective:

The aim of this research is the numerical simulation of the motion of solid spherical particles in shear Stokes flows. Using the "Completed Double Layer Boundary Element Method (CDLBEM)" via distributed computing under "Parallel Virtual Machine (PVM)", the effective viscosity of suspension has been calculated for a finite number of spheres in a cubic array, or in a random configuration. In the simulation presented in this research, the short range interactions via "lubrication forces" are also taken into account, via the range completer in the formulation, whenever the gap between two neighbouring particles is closer than a critical gap. The rigid spherical particles with uniform radius in cubic lattices (simple, body-centred and face-centred), and in random configuration are considered.

© Rheology Group, School of AMME, The University of Sydney

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