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January 1989 - present
Publications
Publications (410)
The primary functions of the stomach, including mixing, digestion, and emptying, are affected by the spatial distribution of content properties, and how this distribution changes in response to gravity and wall contraction forces. One aspect that is not well studied is the buoyancy effects that result from content with heterogenous density. A buoya...
A particle scale model based on a full two-way coupling of the Discrete Element Method (DEM) and Smoothed Particle Hydrodynamics (SPHs) methods is applied to SAG mills. Motion and collisions of resolved coarser particles within an SAG mill are performed by the DEM component. Fine particles in the feed combine with the water to form a slurry, which...
Dysphagia is a medical term used to describe difficulty in swallowing food, liquids, or saliva. It can have serious consequences, such as malnutrition, dehydration, and an increased risk of aspiration pneumonia and death. Texture-modified foods (TMFs) and thickened fluids are often utilized as a therapeutic intervention in management of dysphagia,...
Abstract: The rate of gastric (or stomach) emptying following a meal has important implications for health, including satiety and blood glucose regulation, which relate to obesity and diabetes, and the development of new drug delivery systems. This process is driven by the pressure gradient between the stomach and the duodenum, which is generated b...
This study examines how granular mixtures of differently shaped particles segregate in a Freeman (FT4) rheometer. The mixtures contained two sets of particles with varying shapes and relative sizes. While our main focus was on the effect of particle shape on segregation, we recognized that even slight differences in size could lead to segregation....
Peristaltic flow is important in many biological processes, including digestion, and forms an important component of any in silico model of the stomach. There is a clear need to verify the simulations of such flows. An analytical solution was identified that can be used for model verification, which gives an equation for the net volumetric flow ove...
Segregation of granular mixtures in the Freeman FT4 rheometer, a specific example of the more general process of segregation induced via a rapidly rotating object, is studied. The granular mixture comprises two sets of particles that can differ in intrinsic (particle-scale) properties, such as their size, shape, density, or friction. The Discrete E...
The classical paradigm of the ‘big magma tank’ chambers in which the melt differentiates, is replenished, and occasionally feeds the overlying volcanos has recently been challenged on various grounds. An alternative school of thought is that such large, long-lived and largely molten magma chambers are transient to non-existent in Earth’s history. O...
Distal limb injuries are common in racing horses and track surface properties have been associated with injury risk. To better understand how track surfaces may contribute to equine limb injury, we developed the first 3D computational model of the equine hoof interacting with a racetrack and simulated interactions with model representations of 1) a...
Elastoplastic frictional collisions are encountered in a wide range of applications. For modelling these, inclusion of both the elastoplastic material response and history-dependent collisional forces is essential. The Collisional-SPH method, originally developed for elastic collisions, incorporates frictional collision forces into SPH and accounts...
Landslides may be triggered by a variety of external factors and can lead to dramatic human and economic consequences. Systematically investigating all possible parameters that could potentially influence the extent of a landslide is costly and generally not practical. In this paper, a methodology to numerically assess the impact of potential lands...
A new multi-stage three-dimensional transient computational model to simulate powder bed fusion (L-PBF) additive manufacturing (AM) processes is presented. The model uses the discrete element method (DEM) for powder flow simulation, an extended smoothed particle hydrodynamics (SPH) for melt pool dynamics and a semi-empirical microstructure evolutio...
Screw conveyors are widely used in several industries to transport various granular materials needed to manufacture products or components in a product chain. Degradation of the material and variable packing in the screw pitches are some of the significant operational concerns. This paper explores the effect that particle shape has on the material’...
An emerging and increasingly pervasive school of thought is that large, long-lived and largely molten magma chambers are transient to non-existent in Earth’s history 1–13 . These ideas attempt to supplant the classical paradigm of the ‘big magma tank’ chambers in which the melt differentiates, is replenished, and occasionally feeds the overlying vo...
The pressure distribution between the rolls in a HPGR (High Pressure Grinding Rolls) is usually expected to vary significantly in the axial direction due to the end effects at the end of the rolls. This is based on the idea that particles near the ends of the rolls are less well confined which makes them more mobile with reduced ability to be trapp...
Substantial challenges must be addressed to simulate food processing operations including realistic prediction of liquid and solid mixing, fragmentation of solids and liquids, multiphase behaviour, and interactions with complex machinery geometries. A particle-based modelling approach is presented which comprises Smoothed Particle Hydrodynamics (SP...
The accuracy of SPH in predicting rebound kinematics in granular flow applications involving non-spherical granules is investigated. For this, the rebound behavior of an ellipsoidal granule impacting an elastic substrate is analyzed for different impact angles and for different initial orientations of the granule. The friction modeling capabilities...
Accurate modeling of rebound kinematics in particle-substrate collisions is essential in a wide range of applications like milling and mixing. To accurately model these real-world collisions the forces arising due to elastoplastic deformation and friction need to be modelled accurately. In this study the use of frictional boundary conditions in mod...
Metal additive manufacturing based on powder bed fusion processes is increasingly important. However, highly transient physical phenomena that occur in these processes at different length scales are difficult to observe. Challenging and costly experiments are usually needed to obtain data for process understanding and improvement. Computational mod...
This paper presents a set of related methods for performing a computational geometry analysis of a cone crusher shape that provides geometric information for use in understanding cone crusher flows and breakage and their variation with key crusher geometric parameters. Algorithms that are able to calculate geometric measures such as the variation o...
Industrial-scale discrete element simulations typically generate Gigabytes of data per time step, which implies that even opening a single file may require 5 - 15 minutes on conventional magnetic storage devices. Data science’s inherent multi-disciplinary nature makes the extraction of useful information challenging, often leading to undiscovered d...
A coupled DEM + SPH model can be used to predict the motion and breakage of resolved coarser particles within a SAG mill. The fine product from coarse particle fracture can then be included in the slurry phase modelled using SPH. This allows, in principle, the prediction of the breakage and transport of coarser material and the transport of the fin...
A series of challenging fluid flow applications are used to demonstrate the powerful capabilities of the SPH method. The applications are classified according to whether they are industrial, geophysical or biophysical in nature. The versatility and flexibility of SPH allows it to be used to predict wide ranges of flow types with diverse coupled sec...
Particle scale modelling of comminution processes can provide significant insight into the flow of particles, their breakage, the effect of slurry, wear and energy utilisation within these machines. The ability to use such models to assist in faster and lower cost design of new comminution devices and in the improvement of existing ones will be cri...
This second part paper explores rock breakage mechanisms, the life cycle of rocks in mills and the strong influence of end walls on charge motion within mills. We present recent advances in particle-based modelling of mills for comminution focused around wear and the effect of slurry and slurry phase grinding. Three mill scenarios are considered:
1...
A series of 8 laboratory experiments was used to investigate the dynamics of a few almost neutrally-buoyant finite-size particles in the entire volume of a rectangular tank open to air and filled with water. Stirring was achieved by a cylinder executing a two-dimensional periodic Lissajoux figure. The rate and direction of stirring by the cylinder...
The use of asymmetrical strokes is common in freestyle swimming because of breathing and strength laterality. In this study, the asymmetrical freestyle swimming performance of a male elite level swimmer who breathed every second arm stroke (unilaterally) was investigated. A laser body scan and multi-angle video footage of the athlete were used to g...
Granular material (GM) is the second most manipulated substance in the world and is present in most industries either as raw materials or finished products. Often the temperature of the granular material needs to be manipulated for example in the case of heating iron ore to induce a phase change or to be kept within a certain temperature range in t...
In modelling and simulation a user performs complex sequences of tasks that are intrinsically linked in the form of networks. Tasks include simpler steps such as copying and transforming files to using mesh generation or visualisation software to create inputs or to analyse outputs. Typically, these sequences involve manual steps which are time exp...
The Stirred Media Detritor (SMD) is one of the milling devices used in concentrators for fine and ultra-fine grinding applications. The SMD has a vertically orientated octagonal shell which supports a vertical shaft that has protruding impeller arms to agitate the charge. There is very little understanding of the motion and physical structure of th...
Kayak racing performance is known to be dependent on technique, strength and equipment, but the relationship between these factors and performance is not well understood. Complete experimental measures of stroke technique and the interactions between the water and the paddle and the boat are not practical in a racing environment. Instead, simulatio...
Particle shape affects the resistance to shear of a granular material and its flow characteristics. Rocks in a Semi-Autogenous Grinding (SAG) mill range in shape from quite rounded to quite angular depending on how long they have been in the mill and whether they have undergone body breakage recently due to collisions within the mill. However, almo...
The impact of the shape representation used for rock particles in a DEM model of a SAG mill on charge dynamics and energy utilisation is investigated. A 1.8-m diameter pilot scale SAG mill which includes realistic end walls and a discharge grate is used. This size of mill is used for scale-up and design processes for industrial SAG mills so underst...
In this paper we detail the development of a combined DEM-SPH model for spray impingement into a pool of water or onto a flat surface on which a pool of water can build up. The spray is represented by discrete particles which can collide with solid objects, each other and also merge with liquid surfaces. The liquid pool dynamics are solved for usin...
Applying DEM to prediction of tumbling mill performance is challenging because several different modes of breakage are active in the process. Here we use measured data from a well characterised ore in a well instrumented, 1.2 m diameter pilot scale mill to validate direct DEM prediction of particle size reduction. The key comminution mechanisms inv...
Coupled DEM+SPH models are able to predict the motion of the coarse particulates and the slurry phase in a SAG mill. An extension of this model is proposed in which breakage of coarser particles (which are resolved in the DEM sub-model) in accordance with the incremental damage theory is included. This allows direct prediction of the resident size...
The transport and mixing properties of a co-rotating twin screw extruder with both screw elements and kneading blocks are explored using the smoothed particle hydrodynamics method. The use of a Lagrangian method enables simulation of extruders partially or fully filled with fluid and is not limited by problems associated with extreme mesh deformati...
Discrete Element Method (DEM) modelling of the motion of balls and rocks in grinding mills allows the flow structure and material transport to be understood. It also provides information on the energy dissipated in every collision of resolved particles (which here are 25–200 mm). These energy dissipation events control the nature and intensity of t...
The stomach is a critical organ for food digestion but it is not well understood how it operates, either when healthy or when dysfunction occurs. Stomach function depends on the timing and amplitude of wall contractions, the fill level and the type of gastric content. Using a coupled biomechanical-Smoothed Particle Hydrodynamics (B-SPH) model, we i...
The Smoothed Particle Hydrodynamics (SPH) method is used to determine the flow through a model screw extruder at low Reynolds number with an emphasis on resolving the flow in narrow gaps, which are known to produce high shear rates and generate large temperatures. Firstly we demonstrate the validity of the SPH methodology by comparison on simple fl...
Screens are often used to separate large volumes of granular materials according to size. Discrete Element Method (DEM) modelling using non-spherical particle representations has previously provided increased understanding of the operation of such industrial screens operating both wet and dry. If a granular material has any combination of moderate...
Rotary kilns are used in several minerals processing operations, as well as related industries such as cement manufacture. Since they involve complex multiphase heat and mass transfer processes, optimization would ideally be guided by numerical modelling. A new generic hierarchical approach is proposed in this paper, sequentially combining 2D Discr...
A set of 22 three-dimensional DEM simulations are used to understand and quantify the relationship between key charge locations and three important operating parameters – fill level, lifter height and mill speed for a generic SAG mill. The charge shape and location are characterised by the shoulder, head, bulk and impact toe positions and are asses...
This paper reports on the development and evaluation of an SPH (Smoothed Particle Hydrodynamics) model for high pressure water flow through and from a nozzle and prediction of its break up into a spray of high speed water droplets. This appears to be the first application of the SPH technique to fully model a high pressure nozzle. The model predict...
Coupled DEM/SPH flow models of rock/slurry flow are developed in order to investigate the effect of feed rate on the operation of the feed box which is used to pre-mix the solid feed with water before it is presented as slurry to the screen. For the feed box, rocks were fed into the feed box from a conveyor and travelled through a series of interme...
Understanding the relationships between front crawl swimming technique and the corresponding fluid dynamics is important to athletes seeking improved performance and an edge over their rivals. Computational fluid dynamics (CFD) swimming modelling provides a controlled and unobtrusive capability that provides many previously immeasurable quantities...
Discharge of finer rock, pebbles, ball scats and slurry from mills and its flow through trommels and into other processing operations all affect the performance of overflow ball mills. Modelling of the coarser rock components and the grinding media is best done using the Discrete Element Method (DEM) while modelling of the slurry component is best...
The simple problem of the normal impact of a sphere with a target wall is used to evaluate various elastic-plastic normal contact force models reported in the literature. Both non-adhesive and adhesive contact force models are considered, including both models based on contact mechanics theory and other simpler models frequently used in Discrete El...
Using DEM particle simulations we consider segregation of a binary granular particle mixture in a slowly rotating cylindrical tumbler where the particles differ only in their shape—spherical versus more cubical particles. We find that the more cubical particles segregate to the inner core of the particle bed while the spherical particles segregate...
Discrete Element Method (DEM) simulation with non-round particles and including breakage has been used to understand the breakage behaviour and operating performance of an industrial scale cone crusher using a representative ore. The breakage model uses a replacement strategy and impact energy specific progeny size data from a Drop Weight Test (DWT...
Food transport through different sections of the gastrointestinal tract for the purposes of digestion and waste removal is an essential physiological function for life. Mechanical and chemical breakdown of food takes place throughout the gastrointestinal tract. Periodic muscular contraction and relaxation of the intestinal walls agitate, mix and pr...
Smoothed Particle Hydrodynamics (SPH) is a numerical method that does not use a mesh or grid when solving a set of partial differential equations. This makes it particularly useful in application to solid mechanics problems where the sample undergoes large deformation. Whereas mesh-based methods have difficulty when the sample becomes severely dist...
This paper presents recent work on modelling of industrial particle and multiphase flows using combinations of DEM for resolved particle flow and either grid based CFD or meshless SPH for gas-particle and free surface fluid-particle flows respectively. Current examples of such modelling for dry industrial granular flows (DEM only applications) focu...
Faults are very important geological structures in the context of oil and gas exploration. A thorough characterisation of their mechanical properties is therefore essential for predictive modelling of their activation processes. Generally these properties are derived from a combination of laboratory experiments and numerical simulations but fault s...
Grinding mill performance is typically controlled by making operating adjustments and taking external measurements to infer what is happening inside the mill. So optimising existing machines or designing new ones is difficult and expensive. DEM now offers a broad range of capabilities to look inside these mills to gain improved understanding of cha...
Scale-up is a process of developing a larger version of a processing machine based on the performance of a smaller machine. For mills, scale-up is made difficult by the different rates at which different physical processes occurring within the machine change with the increasing size. Discrete Element Method (DEM) modelling can now be performed at a...
The wear of the mantle and concave of a cone crusher cause significant liner erosion that leads to changes in the shape of the crushing zones which in turn lead to changes in the crushing performance which leads to further changes in the wear of the liners. It is not sufficient to understand the performance of the new liners for a crusher, but rath...
The impact of a rogue wave on floating, moored offshore structures is a highly non-linear problem that has application to the design, operation and safety of offshore platforms. During such an impact, the platform׳s mooring system must maintain a safe platform attitude and withstand the forces from impact and the resulting platform motion. Here we...
In this paper, a novel mesh-free approach is applied for modelling thermo-mechanical responses in a three-dimensional arc welding configuration using the Smoothed Particle Hydrodynamics (SPH) method. A fully coupled three-dimensional elastoplastic and heat transfer analysis is used to analyse the flow pattern of the filler material and the resultin...
The rationale and methods for modeling oral digestion of food are reviewed. Such modeling can facilitate better understanding of the first stage of digestion and can directly contribute to the development of new and improved foodstuffs that promote better health outcomes and which are more suited to aging populations. The challenges for such modeli...
A computational model for use with DEM (Discrete Element Method) is proposed for the five mechanisms applying to particle comminution in AG, SAG and coarse feed ball mills. Chipping and rounding are mechanisms that lead to preferential mass loss from corners and edges of particles and which produce shape change for the particles as well as size red...
Abstract Food digestion involves the flow of material and its transformation from entry into the mouth, during passage along the gastrointestinal tract, to its eventual exit from the body. The range of food materials and their complex structures and the range of processes that are used by the human body to liberate nutrients for absorption are vari...
The stomach is a critical organ for food digestion but it is not well understood how the stomach operates, either when it is healthy or when dysfunction occurs. Stomach function depends on the timing and amplitude of stomach contractions, the fill level of contents and the type of gastric contents. Using a coupled biomechanical-Smoothed Particle Hy...
Food transport through different sections of the gastrointestinal tract for the purposes of digestion and waste removal is an essential physiological function for life. Mechanical and chemical breakdown of food takes place throughout the intestines. Periodic muscular contraction and relaxation of the intestinal walls agitate, mix and propel the mul...
The handling of particulate materials in industry often involves equipment subject to highly abrasive conditions. Progressive damage to this equipment over time can significantly alter the nature of the interaction between the particulates and the equipment surfaces. This can lead to changes in material transport resulting in reduced or unpredictab...
A multiscale model for including interstitial powder or fine particles in DEM simulations of grinding mills is proposed. This consists of a traditional DEM model at the macroscale which includes only grinding media and potential coarser fractions of feed and product. Microscale models are embedded within this macroscale model. These can be sufficie...
A predictive model that allows mill fill level and the lifter height to be determined from measurements of the head, bulk and impact toe positions for a generic SAG mill has been developed using data from a series of three dimension DEM simulations. A Design of Experiment (DOE) approach is used to define a series simulation conditions with the two...
A novel multiscale model is proposed for the evolution of faults in rocks, which predicts their internal properties and permeability as strain increases. The macroscale model, based on smoothed particle hydrodynamics (SPH), predicts system scale deformation by a pressure-dependent elastoplastic representation of the rock and shear zone. Being a con...
The connections between swimming technique and the fluid dynamical interactions they generate are important for assisting performance improvement. Computational fluid dynamics (CFD) modelling provides a controlled and unobtrusive way for understanding the fundamentals of swimming. A coupled biomechanical-Smoothed Particle Hydrodynamics (SPH) fluid...
Discrete element method modelling is used to study the effect of particle shape on the flow dynamics and mixing in a high shear mixer. The blade generates strong flow over its top surface while compacting and pushing forward particles that are directly in front of the blade. A complex three dimensional flow is established with vertical and radial f...
A novel approach for modelling thermo-mechanical responses in an arc welding process is developed using the mesh-free smoothed particle hydrodynamics (SPH) method. It is illustrated by simulating a simple arc welding configuration. A multi-physics framework is used for solving the fully coupled elastoplastic and thermal analysis. Both the plastic d...
We present a discrete particle based method capable of realistically representing the entire boiling process including nucleation, bubble formation, growth, bursting, vapour and steam formation at the fluid free surface. The underlying fluid simulation is based on the mesh-free Smoothed Particle Hydrodynamics method. Vapour bubbles are created at n...
Discharge of pebbles, finer rock, ball scats and slurry from mills and its flow through trommels, and into other processing operations has strong impacts on overflow ball mill performance. Modelling of the coarser rock components is best done using the Discrete Element Method (DEM) while modelling of the slurry component is best done using a compat...
In particulate systems with short-range interactions, such as granular matter
or simple fluids, local structure plays a pivotal role in determining the
macroscopic physical properties. Here, we analyse local structure metrics
derived from the Voronoi diagram of configurations of oblate ellipsoids, for
various aspect ratios $\alpha$ and global volum...
Accurate numerical simulation can provide crucial information useful for a greater understanding of destructive granular mass movements such as rock avalanches, landslides, and pyroclastic flows. It enables more informed and relatively low cost investigation of significant risk factors, mitigation strategy effectiveness, and sensitivity to initial...
Propulsion of intestinal contents involves coordinated contractions and relaxations of the muscle controlled by polarised enteric neural reflex pathways. Due to the inaccessibility of the small and large bowel, obtaining detailed manometric measurements in the gut or visualizing the movement of digesta is difficult in vivo. Computational modelling...
Computational modelling is often used to reduce trial extrusions through accurate defect prediction. Traditionally, metal extrusion is modelled using mesh based finite element methods. However, large plastic deformations can lead to heavy re-meshing and numerical diffusion. Here we use the mesh-less smoothed particle hydrodynamics method since it a...
DEM simulation using a breakage model is applied to study a broad range of existing impact based crushers to better understand machine level operation and to demonstrate that such modelling is now possible. Predictions for a range of types of hammer mills, vertical and horizontal shaft impactors are presented. The breakage method used is based on f...
Discrete Element Method (DEM) simulation using a breakage model is applied to study a broad range of existing compression based crushers to better understand machine level operation and to demonstrate that such modelling is now possible. Predictions for five types of crushers: jaw crusher, cone crusher, gyratory crusher, impact crusher and double r...
Predictions of particle flow and compression breakage of non-round rock passing through an industrial scale cone crusher are presented. The DEM (Discrete Element Method) particle breakage model is generalised to allow non-round particles to be broken into non-round progeny. Particles are broken in this DEM model when the elastic energy of a contact...
The Isamill is a horizontal stirred media mill used for fine and ultrafine grinding. Discrete Element Method (DEM) simulation has been used in this paper to study the behaviour of the media and the collisional environment in a full industrial scale Isamill. The DEM modelling has been able to provide a general understanding of the force balances tha...
The Isamill is a horizontal stirred media mill used for fine and ultrafine grinding of slurry transported rock particles. The charge motion is analysed using two different approaches, (1) a fluid only model, and (2) a 1-way coupled DEM + SPH model. The flow pattern when the classifier is closed is regular with a pair of oppositely oriented vortices...
A coupled DEM (discrete element method) and SPH (smoothed particle hydrodynamics) method is used to predict the motion of the solid particles interacting with slurry flow. DEM simulates the motion of the coarser particulates while SPH simulates the slurry (water and finer particulates). This three dimensional method is demonstrated for multiphase m...
Wear prediction is important in the development and optimisation of liner design, and for helping to manage reline strategies. DEM is able to predict wear and profile evolution of liners over the life cycle for specific sets of conditions. However, real operation conditions often vary – usually in ways that are not known in advance, which limits th...
Patient-specific geometric factors together with traditional risk factors may aid the early identification of patients at high risk of developing carotid artery disease requiring surgical intervention. Recent studies have linked aspects of carotid geometry to the pathogenesis of internal carotid artery (ICA) stenosis. Abnormal wall shear stress (WS...
The accuracy and stability of the classical formulation of the smoothed particle hydrodynamics (SPH) method for modelling compression of elastic solids is studied to assess its suitability for predicting solid deformation. SPH has natural advantages for simulating problems involving compression of deformable solids arising from its ability to handl...
