A wide range of industrial processes involve multiphase granular flows. These include catalytic reactions in fluidized beds, the pneumatic conveying of raw materials and gas-particle separators. Due to the complex nature of multiphase flows and the lack of fundamental understanding of the phenomena in a multiphase system, appropriate design and optimized operation of such systems has remained a challenging field of research. Design of these processes is hampered by difficulties in upscaling pilot scale results, the difficulties involved in experimental measurements and in finding reliable numerical modelling methods. Significant work has been carried out on numerical modelling of multiphase systems but challenges remain, notably computational time, appropriate definition of boundary conditions, relative significance of effects such as lift and turbulence and the availability of reliable model validation. The work presented in this thesis encompasses experimental and numerical investigations of horizontal pneumatic conveying. In the experimental work, carefully controlled experiments were carried out in a 6.5 m long, 0.075 m diameter horizontal conveying line with the aid of the laser Doppler anemometry (LDA). Initially, LDA measurements were performed to measure the gas velocity in clear flow. Good agreement was observed between the theory and experimental measurements. For two-phase experiments, spherical and non-spherical particles with different sizes and densities were used to study the effect of particle size and solid loading ratio on the mean axial particle velocity. Three different sizes of spherical glass beads, ranging from 0.9 mm to 2 mm and cylindrical shaped particle of size 1x1.5 mm were employed. It was found that by increasing the particle size and solid loading ratios, the mean axial particle velocity decreased. Turbulence modulation of the carrier phase due to the presence of spherical particles was also investigated by measuring fluctuating gas velocity for clear gas flow and particle laden flow with different particle sizes and solid loading ratios. Results suggested that for the size ranges of particles tested, the level of gas turbulence intensity increased significantly by adding particles, and the higher the solid loading ratio, the higher the turbulence intensity. With the rapid advancement of computer resources and hardware, it is now possible to perform simulations for multiphase flows. For a fundamental understanding of the underlying phenomena in pneumatic conveying, the coupled Reynolds averaged Navier-Stokes and discrete element method (RANS-DEM) was selected. The aim of the modelling section of this study was to evaluate the abilities of coupled RANSDEM to predict the phenomena occurring in a research-sized pneumatic conveying line. Simulations for both one-way and two-way RANS-DEM coupling were performed using the commercial coupled software FLUENT-EDEM in an Eulerian- Lagrangian framework, where the gas is simulated as a continuum medium, while solid phase is treated as a discrete phase. In one-way coupling simulations, a considerable discrepancy in mean axial particle velocity was observed compared to the experimental results, meaning two-way coupling was required. It was further found that the inclusion of Magnus lift force due to particle rotation was essential to reproduce the general behaviour observed in the experiments. Turbulence modulation also was investigated numerically. Experimental and simulation results of gas and particle velocities were compared showing that the RANS-DEM method is a promising method to simulate pneumatic conveying. However, some discrepancy between simulation and experimental results was observed. Most studies in two-phase flow fields have focused on spherical particles. However the majority of particles encountered in industry involve non-spherical granules which show considerably different transportation behaviour compared with spherical particles. Further modelling of cylindrical particles was conducted using a multisphere model to represent cylindrical particles in the DEM code. Drag and lift forces and torque equations were modified in the code to take the effect of particle orientation into account. The framework developed was evaluated for two test cases, indicating a good agreement with the analytical and experimental results. The transportation of isometric (low-aspect-ratio) non-spherical particles in pneumatic conveying was also modelled. The simulation results of mean axial particle velocity agreed well with the experimental measurements with the LDA technique.

Syftet med denna uppsats är att studera uppfattningar om invandring och skapandet av vi och dem genom att problematisera kvantitativ forskning. Vi har använt oss av kvalitativ metod i form av semistrukturerade intervjuer. Forskning visar att klasstillhörighet påverkar människors attityder. Vårt urval i studien är högutbildade med minst kandidatexamen, urvalet motiveras genom att högutbildade generellt har en mer tolerant attityd till invandring. Analys av den insamlade empirin gjordes genom att hitta de bärande teman genom kodning som resulterade i de teoretiska begreppen: etnicitet, vi och dem och klass. Resultatet i studien visar att genom att fördjupa den kvantitativa undersökningen finns fler variabler att ta hänsyn till. I resultatet finns en problematisering kring kultur och religion som både visade att respondenterna ser Sverige som ett mångkulturellt samhälle men även att det finns en oförståelse för andra kulturer och religioner. Resultatet i studien visar att bilden av invandrare kan vara föränderlig samt att boendesegregation och ojämlika villkor på arbetsmarknaden, skapar en diskriminering i samhället. / <p>2016-06-07</p>

No description available.

The aim of this work is to look into the applicability of Discrete Element Modelling (DEM) coupled to Computational Fluid Dynamics (CFD) to simulate micro-scale colloidal particles immersed in fluid. Numerical methods were implemented through the commercial framework of EDEM2.3. As opposed to dissolved matter, which behaves as a continuum within the fluid medium, particulate matter is made of discrete entities that interact amongst themselves, and with the fluid and any physical boundaries. Particulate matter is ubiquitous in many purification processes that would beneficiate from having an easy way to model particle dynamics immersed in water. In an effort to understand better the dynamics of particle deposition under surface forces and hydraulic forces, a micro-scale numerical model was built adopting both a mechanistic and a statistical approach to represent the forces involved in colloidal suspension. The primary aim of the model was to simulate particle aggregation, deposition and cluster re-suspension in real world micro-systems. Case studies include colloidal flocculation in a constricted tube, and colloidal fouling around membrane filtration feed spacers. This work used a DEM-CFD coupling method that combined the DEM particle flow simulation with hydrodynamics forces from a velocity field computed through CFD. It also implemented boundary-particle and particle-particle interactions by enabling the modelling of surface and interfacial forces. Two kinds of coupling method were considered: two-way and one-way coupling. Two-way coupling is suitable for high particle concentration flow where particle loading affects the hydrodynamics. One-way coupling is suitable for dispersed particle configuration where the flow field is assumed to be undisturbed by the particles. The advantages and drawbacks of both techniques for micron-size particles were investigated. EDEM 2.3 was customised with plug-ins to implement Van der Waals forces and Brownian forces and its post-processing features offered the ability to investigate easily the microparticles behaviour under the influence of fluid forces. In this context, DEM-CFD modelling using EDEM 2.3 represents an improvement on previously published works as it enables higher visibility and reproducibility along with increasing the number of potential users of such modelling. Emphasis was given in presenting original findings and validation results that illustrate DEMCFD applicability, with respect to modelling of hydraulically mediated colloidal surface interaction; while highlighting factors that limit the ability of the technique. For instance, the effect of particle disturbance on the surrounding medium currently proves difficult to model.

Student Number : 9806611F - PhD thesis - School of Chemical and Metallurgical Engineering - Faculty of Engineering and the Built Environment / Modelling of comminution in tumbling mills is usually done using the selection and breakage function models. While this has been a success for ball milling it has not been the case with Autogenous and Semi- Autogenous mills where performance is easily affected by slight variations in operations. A numerical model, Discrete Element Method (DEM) a much more detailed model for the nonlinear behaviour of mill loads is proposed as a possible solution to this problem. The Discrete Element Method algorithm is a numerical technique for solving problems that involve a large number of interacting bodies. The dissipative forces (normal, tangential or frictional) at points of contact are modelled using a springslider- dashpot and the dynamics of the particles are modelled by applying Newton’s laws of motion. A record of information about contact events occurring during simulation is stored in the output files and can be thereafter applied for a wide range of purposes. The contact events and their corresponding energy levels derived from the simulation are applied to determine the particle failure rate in a mill. The probability of particle failure does however also depend on the inherent fracture properties of a material; hence particle fracture tests on the ore samples were conducted using the JK drop-weight impact test machine. Using this tool, data that related the probability of breakage to the energy input and the number of impact attempts were obtained and a model describing this relationship was derived. Using the energy spectra that resulted from the simulations of milling and the Breakage probability model, an attempt was made to predict the experimental results of a mill operating under a wide range of conditions. Good prediction was achieved after a careful choice of model parameters. A systematic approach of establishing the most suitable parameters is recommended for future work. These parameters would also compensate for conditions beyond the limits of the model such as particles being too small to simulate or having a complex shape. The predictions were based on two size fractions as a way of making this task more manageable. It is apparent that this work can be extended to do a full SAG and AG mill simulation.

No description available.

Syftet med den här uppsatsen är att undersöka hur väl svenska och finlandssvenska niondeklassare hanterar utvalda svenska skrivregler och det svenska skriftspråket. Vidare undersöks huruvida det finns olikheter länderna emellan, samt mellan kön. Undersökta språkdrag är fyra till antalet: förekomst av särskrivning, hantering av gemener och versaler, inslag av engelska respektive finska samt hantering av pronomina de, dem och dom. Undersökningsmaterialet består av 100 diskursiva elevtexter från Sverige och Finland, jämnt fördelade mellan länderna. Texterna kommer från nationella prov i ämnet svenska (Sverige) respektive modersmål och litteratur (Finland) genomförda våren 2010 av elever i årskurs 9. En kvantitativ forskningsmetod är tillämpad i denna studie; samtidigt är undersökningen även en kvantitativ jämförelse länderna emellan. Resultatet visar att eleverna i stort hanterar undersökta svenska skriftspråksnormer. Det råder dock tveksamheter gällande hur ord skrivs samman på ett korrekt sätt och när ord stavas med stor respektive liten begynnelsebokstav. Främmande ord och uttryck förekommer inte i någon större utsträckning i de undersökta diskursiva texterna. En viss tveksamhet råder även gällande bruket av personliga pronomen i tredje person plural då somliga elever blandar tal- och skriftspråksformer i sina texter samt överanvänder objektsformen. Vid en jämförelse av variabeln kön visar det sig att pojkarna i min studie har fler felaktigheter i sina texter än vad flickorna har. Överlag behärskar de finlandssvenska eleverna undersökta språkdrag med större säkerhet än de svenska eleverna.

Syfte: Svenska Elles personporträtt har studerats med syfte att belysa hur ett Vi och Dem förhållande konstrueras, men även för att klargöra vilka som utgör Vi och Dem i kontexten. Detta för att ta reda på vilka sociala konstruktioner som Elle medverkar till. Metod: Studien är en kritisk diskursanalys vilken är inspirerad av Norman Fairclough Critical discourse analysis. Texterna har vidare behandlats utifrån en symtomal innehållsanalys, med hjälp utav verktyg hämtade ur semiotiken. Resultat: Studiens resultat visar på att ett specifikt narrativ appliceras på samtliga av Elles personporträtt. Detta sker likt en schablon som skapar en fiktiv karaktär av intervjuobjektet vilket därmed konstrueras till ett Vi. Genom flertalet faktorer exkluderas läsaren i relation till vi:et och blir därmed ett uttalat Dem.

Users of current Digital Photogrammetric Systems (DPS) can now rapidly generate dense Digital Elevation Models (DEMs) with a minimal amount of training. This procedure is controlled through a set of strategy parameters embedded in the software. Previous research into the effect of these parameters on the resulting DEMs produc'ed mixed results, with some researchers finding that significant changes to the DEM can be made through manipulation of the parameters whilst others suggested that they have little effect. This thesis builds upon this early work to develop two systems that provide assistance for novice users. The first technique optimises the parameters with respect to DEM accuracy and takes the form of an expert system and compares the output from the DEM with a knowledge base to prescribe an improved set of parameters. The results suggest that the system works and can produce improvements in the accuracy of a DEM. It was found that in certain circumstances, changes to the parameters can have a significant effect on the resulting DEM, but this change does not occur across the entire DEM. The second aspect of the thesis details the development of a completely new approach that automatically detects low accuracy areas of the DEM and presents this information graphically. This is an important development since, as documented in the current literature, few quality control procedures are offered to users. The user can use this information to assist in the manual checking and editing of the final DEM, thus speeding up the workflow and improving the accuracy of the output. The results of tests (using the ERDAS Imagine OrthoMAX software) on a wide variety of imagery are presented and show that the technique reliably detects areas of a DEM with high errors. More significantly, the technique has also been tested on two other DPSs (Zeiss Phodis TS and VirtuoZo) and it was found that it worked well for the Zeiss system but could not be applied to the VirtuoZo software. This demonstrates that the research is not limited to the users of one software package and is of interest to the wider photogrammetric community.

A numerical model based on the discrete element (DE) method, for modelling the flow of irregularly shaped, smooth-surfaced particles in a 3-D system is presented. An existing DE program for modelling the contact between spherical particles in periodic space (without real walls or boundaries) was modified to model non-spherical particles in a system with containing walls. The new model was validated against analytical calculations of single particle movements and also experimentally against data from physical experiments using synthetic non-spherical particles at both a particle and bulk scale. It was then used to study the effect of particle shape on the flow behaviour of assemblies of particles with various aspect ratios discharging from a flat-bottomed hopper. The particles were modelled using the Multi-Sphere Method (MSM) which is based on the CSG (Constructive Solid Geometry) technique for construction of complex solids by combining primitive shapes. In this method particle geometry is approximated using overlapping spheres of arbitrary diameter which are fixed in position relative to each other. The contact mechanics and contact detection method are the same as those used for spheres, except that translation and rotation of element spheres are calculated with respect to the motion of the whole particle. Numerical simulations of packing and flow of particles from a flat-bottomed hopper with a range of aspect ratios were performed to investigate the effect of particle shape on packing and flow behaviour of a particulate assembly. It was found that the particle shape influenced both bed structure and flow characteristics such as flow pattern, shear band strength and the occurrence of bridging. The flow of the bed of spherical particles was smoother than the flow of beds of elongated particles in which flow was fluctuating and there was more resistance to shear.