Commodity projection studies anticipate an exponential increase in copper demand and decreasein mill grade of deposits currently exploited globally. Most of this demand is driven by theindispensable use of copper in electrification and currently, the growing demand in the contextof the green transition. To meet this challenge while supplying society with copper, producerssuch as Boliden AB have plans for exploration and expansion projects to increase their reservesand in turn increase production through efficient measures. As grinding is a bottleneck to mineralprocessing and the most energy intensive, more efficient comminution systems are beingconsidered for environmental sustainability. These are required to have lower energyconsumption while achieving the required liberation or better for subsequent processing byflotation. Consequently, the literature review shows there is a research query on whether more can beexpected from comminution to optimise for downstream processing. With most publishedresearch being on particles with a P80 less than 100 μm, there exists a gap in investigating theeffect of grinding on flotation for coarser size fractions which this degree project focuses on.Importantly, it includes evaluating chalcopyrite liberation and flotation performance when usinga Novel Comminution Device. Three grinding mills were considered, a vertical roller mill (VRM),a Novel Comminution Device (NCD), with a rod mill as the reference mill. The scope of this studywas an analysis of the mill products’ particle size distribution, chalcopyrite liberation andinvestigation of the flotation performance of the products from the three mills. This was done ona Cu-Au-Ag ore from the Boliden Aitik mine in northern Sweden. Particle size distribution (PSD) analysis revealed that at comparable P80 values, the VRMproduced particles had broader PSD curves than the rod mill, while the NCD provided a steeperproduct size distribution than its reference rod mill products. The chalcopyrite liberation analysisusing QEMSCAN automated mineralogy showed that for samples split into three size fractions, -45 μm, +45/-90 μm and +90 μm, the VRM and rod mill products had their highest proportion offree to liberated particles within the intermediate size fraction while for the NCD sample this waswithin the fine fraction. Overall, the NCD product had the highest free to liberated particles acrossall fractions. From shape analysis based on scanning electron microscopy (SEM) images, it wasobserved that the NCD produced particles with the higher elongation than the VRM and rod mill. The flotation performance was assessed with respect to the mass pull, kinetics, grade andrecovery in the concentrate and separation efficiency. The rougher batch flotation tests indicatedthat flotation of the VRM ground samples had higher mass pull, Cu recovery, faster kinetics andlower Cu grade than the samples from the reference rod mill. This was also a similar outcome forthe NCD with the exception of higher mass pull at an increased collector dosage in the rod millcase. For all the mills, the general trend showed that an increase in P80 was associated withreduced mass pull. Overall, at similar flotation conditions, despite having one of the coarsest P80s,the NCD product showed the fastest Cu recovery kinetics, highest total recovery and selectivityindex. The rod mill reference test samples gave the highest grade but the lowest recovery. The findings illustrate that there is a significant difference in PSD broadness between productsfrom different mills at comparable P80. The differences in flotation performance between thethree mill products were mainly attributed to differences in liberation, potential differences insurface activation between wet and dry grinding methods and to some extent, steepness of thePSD curve. Based on the high recovery yet low grade of the NCD ground product, this is best suitedfor the rougher flotation stage. Future studies should therefore include cleaner stage flotation andoptimisation tests for the NCD with respect to reagent dosages and hydrodynamic conditions.

The soil-structure interface is fundamental to the performance of many geotechnical engineering systems; including penetration test devices, deep foundations, and retaining structures. In geotechnical engineering structures, the counterface may range from a polymer in the case of a geosynthetically reinforced earth retaining structure to steel for cone penetration testing or pile foundations. Interface strength is affected by many factors, among which surface roughness is the most dominant. To date common practice has been to characterize counterface surface roughness by a roughness parameter based on only its spatial properties and soil roughness separately by various incompatible means resulting in two roughness values unrelated to each other. The vast number of analyzing methods and developed parameters reveal the general confusion regarding this concept. Rather than analyzing the particulate and continuum media separately, it is compulsory to coalesce the analysis and quantify the relative nature of interface behavior. This can be accomplished by examining the particulate and continuum media through the same powerful tools. The motive of this study is to develop a unified approach to determining the index properties of particles and surfaces in a particle-surface interface. This is accomplished by examining several particle shape and surface roughness parameters in terms of their ability to uniquely describe and distinguish particulate medium and continuum roughness, respectively. In this study, surfaces are analyzed as derived particles by wrapping surface profiles and particles are evaluated as derived surfaces via unrolling particle outlines. In addition, particle shape parameters are modified to allow surface roughness analysis and surface roughness parameters are modified to characterize particle shape. A unified approach for particulate shape and continuum roughness would ultimately lead to a better understanding of micro-scale interaction mechanism and better quantification of macro-scale mobilized resistance for soil and engineering surface interaction.

This thesis analyses the impact of granular aggregates with structures using experiments and numerical simulations. Original contributions include an insight into multiple factors affecting the loading and damage to the structures, along with study of numerical parameters important for realistic prediction of the interaction between the granular media and structures. It extends the current understanding related to such interactions, with an underlying motivation to guide strategies in order to reduce the structural damage. The response of structures impacted by granular media (sand or soil) is of significant research interest for many applications. One of the applications is for landmine explosions which causes ejection of soil from ground and damage to structures impacted by this ejected soil. Experimentation is done in a laboratory setting where the cylindrical sand slugs are generated at high speed using an impulse provided by a piston. This induces a velocity gradient along the slug, because of which the slug expands during the flight before impacting the target. Deformable as well as rigid flat targets are considered in two orientations relative to the incoming slug: perpendicular (i.e. normal orientation) and inclined at an angle of 45°. The targets are supported by force transducers to capture the loading from the slug. Simulations are performed using a combination of discrete particle and finite element schemes, which enables the analysis of the fully coupled interaction between the flowing granular media and the structure. A contact model involving multiple parameters is used for inter-particle and particle-target contact. Firstly, a numerical analysis is performed to characterise the temporal evolution of slugs and their impact on monolithic beams constrained at the ends. Out of all the parameters used for inter-particle contact definition in discrete particle method, only the contact stiffness is found to effect the velocity gradient in the slug before it impacts the target. Other factor influencing the gradient is the acceleration provided by the piston. A strong dependence of beam deflection on the stand-off distance is observed due to the velocity gradient in the slugs. As the second step, the effect of target surface properties on the transmitted momentum is analysed. Experiments are done by applying coatings of different hardness and roughness on the target surface impacted by sand slugs. For normally oriented targets, the transmitted momentum is observed to be insensitive to the change in surface coating. In contrast, for inclined targets, a significant influence of coatings is observed. Additionally, the momentum transmitted to the inclined targets is always less than that for normal targets. Numerical analysis of this surface effect reveals that assuming the slug particles to be spherical shape in simulations does not capture the particle/target interactions accurately and under-predicts the frictional loading on the target. Following this, a detailed numerical study is done to understand the effect of the shape of particles in the slug. Simple shaped non-spherical particles are constructed by combining spherical sub-particles. With increasing angularity of particles in the slug, the frictional loading on the target is shown to increase. This results in an increase of momentum transmitted to inclined targets. For normally oriented targets however, the particle shape does not affect the overall transmitted momentum, which is a behaviour similar to that observed when studying the effect of target surface properties. In addition, effect of fracture of particles in the slug is analysed by using beam connections between sub-particles that break during the impact with the target. If the fracture results in increasing particle angularity, the transmitted momentum increases, whereas the situation reverses if fracture results on more spherical shaped particles. Lastly, a strategy to reduce the loading on the targets is analysed by using sacrificial coating on the target surface. In experiments, this coating is placed on the rigid target surface using a lubricant at their interface. When impacted by the slug, this coating slides on the target surface, resulting in a reduction of frictional loading on the target. If the friction at the coating/target interface vanishes, the transmitted momentum approaches the theoretical minimum value. Simulations are used to first validate the experimental observations and then to extend the concept of sliding coatings using deformable targets. Both the transmitted momentum and deflections depended on the thickness of the target and coating. When a coating is used, the deflections increase due to reduction in target thickness. It is found that the best strategy to reduce the damage to the target is to use least possible thickness of the coating and minimise the friction at the interface between the coating and the target. The presented work examines many of the factors that affect the loading on the target impacted by granular slugs, in addition to characterising the expansion of slugs before the target impact. The analysed factors include those already known such as target stand-off distance, inclination and unveils others such as target surface properties and granular properties. The numerical analysis discloses important parameters and shows the effect of particle shape, highlighting the shortcomings of widely used spherical particle assumption in the numerical studies. A strategy using a sacrificial coating to reduce damage to the target is also analysed.

The change in morphology of a char particle affects both its trajectory and carbon consumption rate, hence the performance and efficiency of an entrained-flow gasifier. Among key processes taking place in the gasifier, the char conversion process is a limiting step for the overall carbon conversion. For that reason, the Ph.D. thesis presents the evolution of morphology of char particles during the carbon conversion process using particle-resolved transient CFD calculations. Analyses of numerical data obtained from the transient CFD calculations were carried out. As a result, new sub models related to the drag coefficient and the fundamental parameters of char conversion model were emerged. The new sub models were applied for modeling a pressured entrained-flow gasifier at laboratory scale. The numerical results of the gasifier show a good agreement with experimental data and an improvement of the sub models applied.

Granular materials are characterized by its discrete nature which makes their behaviour very complex to understand when subjected to various loading situations. Comparing other materials, the understanding of granular materials is poor. This is because experimental analysis provides the macroscopic responses of the considered assembly whereas the discrete nature of the particles point to the fact of understanding the micro scale details and correlating it with the overall behaviour. Among the various modeling tools viz. analytical, physical or numerical, Discrete Element Method (DEM) a numerical technique, originally developed by Cundall (1971, 1974) and modified by Cundall and Strack (1979a, 1979b) is widely used for granular materials. Later a thorough description of DEM was given by Cundall (1988) and Hart et al (1988). Moreover Cundall & Hart (1992) reported discrete element code as one which allows finite displacements and rotations of discrete bodies along with recognition of new contacts as the calculation progresses which is followed in particle flow code and is used for this study. Generally the discrete particles are modeled as discs or spheres in 2-D and 3-D simulations respectively. The discs or spheres were considered as it is very easy to characterize the grain interactions and the contact detection. Even though the significance of particle shape has been reported in literature, a comprehensive 3-D study of the effect of particle shape on the various aspects of soil behaviour is lacking and is not reported. Particle shape is generally defined in terms of elongation, roundness and texture. Elongation is an indication of the particle aspect ratio whereas roundness measures the sharpness or angularity of particle’s edges and corners. Texture is related to the roughness of the surface. Particle gradation also plays a role in the mechanical behaviour. The influence of each of these factors on the mechanical behaviour of the assembly is important. Hence the major factors like elongation, texture etc which are used to define the particle shape are incorporated in this study. Evaluating the particle shape is another hurdle. In this study, the particle shape is analyzed using a 3D laser scanner which helps to identify the major and minor axis lengths of the particle. Additionally, the effective use of 3D DEM on large scale real life applications incorporating the particle shape effect is also not dealt with very extensively. Hence in this research, a comprehensive study on the calibration of DEM using glass beads, effect of particle shape on drained and undrained monotonic behaviour, liquefaction, post liquefaction and dynamic properties and the application of DEM to a grain polishing machine and an underground tunnel assembly is presented. In the present study, a set of drained triaxial tests were done on glass bead assembly using a laboratory triaxial set up. The glass beads used for the test were spherical and ellipsoidal in shape. The shape of glass beads was characterized through a sophisticated method of 3D laser scanning. In this scanning, the shape of the image of the glass bead is captured through an array of digitized points. These images obtained as unstructured 3D triangular meshes on processing will render the long and short axes of the particle which can be used for proper modeling of the particle shape. After obtaining the long and short axes for the particles, the same is used for the numerical modeling of the glass beads. The numerical simulation results have shown that the assembly modeled with clumped particles gives results qualitatively and quantitatively similar to the observed experimental macro responses. Hence this is used to demonstrate the power of DEM to realistically model the granular behaviour by incorporating the particle shape effect. In addition, undrained simulation of granular material has been numerically predicted from drained triaxial tests which are similar to the approach proposed by Norris et al (1997). An excellent correlation between undrained results predicted from drained triaxial test and undrained test (performed under constant volume conditions) has been observed. This further underlines the fact that the constant volume simulations are equivalent to undrained tests. Having validated the DEM results to the values obtained from the experiments on glass beads, a series of monotonic drained and undrained triaxial tests were performed on cylindrical assemblies of height to diameter ratio 2:1. Four different sets of assemblies were prepared which consists of particles of different aspect ratio to study the influence of particle shape. The behaviour of these assemblies under drained shearing indicates that the strength of the clumped assemblies is higher than that of the spherical assembly at all confining pressures. This has been explained from the magnitude of the anisotropic vi coefficients associated with the fabric and normal contact force tensors. It is also noted that eventhough both assemblies reach the peak strength at the same axial strain, the strain softening associated with the clumped assembly is very rapid which is due to the fact that clumps try to push each other apart as it offers more resistance to rotation resulting in dilation. Another significant observation is that a general increase in aspect ratio will not keep on increasing the strength. As the aspect ratio increases, the particles have a tendency to orient along their larger dimensions. This helps them to attain the lowest potential energy leading to a stable equilibrium and resulting in inherent fabric anisotropy. But when the particles try to align along the larger dimension, the formation of strong contact forces along the direction of loading is hindered. In addition, the lower strength associated with the higher aspect ratio particle assembly can also be attributed to the formation of unexpected void spaces when these longer particles bridge gaps over the underlying grains. The critical state studies indicate that the clumped assembly is having a higher residual strength compared to that of the spherical assembly. In the case of clumped assemblies also, irrespective of the initial loose or dense state of the assembly and the confining pressure applied, the samples reached the same critical state which underlines that the critical state is unique for a granular material. Moreover, the critical state line is non-linear for both the spherical and clumped assemblies. The studies conducted on the liquefaction behaviour indicates that at lower confining pressures the assemblies with particles consisting of lower aspect ratios loses its strength at less number of cycles which can be attributed to the interlocking of non-spherical particles resulting in higher number of contacts per particle. Moreover, during the initial cycles of loading, it is seen that the strong contacts are predominantly in the vertical direction or more precisely along the direction of maximum axial strain. But the plots extracted at higher cycles indicated that the strong contacts along the vertical direction have diminished considerably. This reduction in contact force magnitude and force chain indicates a drop in the number of contacts and is clearly visible in the gradual decrease of average coordination number. Another significant observation is that as the confining stresses increases, the rate of pore pressure generation of the assembly vii consisting of only spherical particles is less compared to the other two samples. Furthermore, at higher confining pressures, when the load direction reverses, the fabric of the clumped assemblies fails to change to a new orientation immediately. But to retain equilibrium the force anisotropy will quickly adjust itself. This mismatch results in losing the contacts and resulting in lower strength and less resistance to liquefaction at higher stresses for assemblies consisting of clumped particles. The post liquefaction study of the numerically liquefied samples shows that the assembly consisting of clumped shaped particles gained strength at a much faster rate compared to the assembly consisting of only spheres. This may be attributed to the ability of the clumps to rearrange themselves on a faster rate compared to that of the spherical particles. The rate of development of average coordination number is very significant as it explains the ability of the assembly to build up the deviatoric stress from a complete collapsed structure. As the contacts develop, the average coordination number as well as the deviatoric stress starts increasing with both the values higher for the assembly consisting of clumped particles. The evaluation of the dynamic properties viz. shear modulus and damping ratio showed a trend similar to the experimental observations on real granular materials. It is observed that the normalized shear modulus reduces with an increase in shear strain and the rate of reduction is very high at low strains for all the samples. It can be seen that as the confining pressure increases, the normalized shear modulus value also increases and the rate of increment is higher for the assemblies consisting of non-spherical particles. Furthermore, for all the samples the threshold shear strain is about 0.001 up to which the behaviour is elastic. Beyond the threshold shear strain, the variation of the normalized shear modulus ratio is non-linear. At small shear strains, the energy dissipation is low resulting in smaller values of damping. As the strains increase, the non-linearity in the constitutive behaviour results in higher material damping leading to high damping value. The simulations of the food polishing machine helps to understand the pattern of hitting of clumped grains on the wall with due importance to the velocity of hit, angle of hit, force of hit, and the number of grains hitting the wall. The modeling and subsequent extraction of the data helped to identify that the wear and tear of the machine was not uniform and was clustered to specific regions due to the non-uniform distribution of the considered parameters. This helped to design a more sophisticated system such that the parts which are subjected to more deterioration are provided with additional support. To bring out the effect of the particle shape, simulations are performed using spherical particles and the results show that the pattern of variation is same, but the magnitudes are different owing to the less surface area associated with the spherical particles. The 3-D simulations of an underground tunnel assembly in a weak weathered rock helped to understand the variation in the stability of the system with and without lining. It was observed that the introduction of lining resulted in a more stable configuration and the circumferential stresses were found to be distributed uniformly around the tunnel. FEM simulations also show a similar trend of stress and strain variations but were unable to capture the ground loosening around the tunnel and the formation of the ground arch whereas DEM could realistically capture all these phenomena. It was observed that as the shape changes from sphere to non-spherical particles, circumferential stresses around the tunnels increased. In addition, as the distance from the tunnel face increases, the strains are reduced. The maximum vertical strain near the crown of the tunnel is observed for the assembly consisting of spherical particles. In short, this research is focused on a comprehensive understanding of the particle shape effect on the mechanical behaviour of granular mass. Numerical simulations incorporating the shape effect has been done on drained and undrained monotonic shear tests, critical state, liquefaction, post liquefaction and dynamic properties. Besides, the granular dynamics simulation of the movement of long food grains in a food polishing machine and the behaviour of an underground tunnel in a granular assembly is also reported.