published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Orthopaedics and Traumatology / Master / Master of Philosophy

<p>When studying the structure formation and fragmentation of complex atomic and nuclear systems it is preferable to start with simple systems where all details can be explored. Some of the knowledge gained from studies of atomic dimers can be generalised to more complex systems. Adding a third atom to an atomic dimer gives a first chance to study how the binding between two atoms is affected by a third. Few-body physics is an intermediate area which helps us to understand some but not all phenomena in many-body physics.</p><p>Very weakly bound, spatially very extended quantum systems with a wave function reaching far beyond the classical forbidden region and with low angular momentum are characterized as halo systems. These unusual quantum systems, first discovered in nuclear physics may also exist in systems of neutral atoms.</p><p>Since the first clear theoretical prediction in 1977, of a halo system possessing an Efimov state, manifested in the excited state of the bosonic van der Waals helium trimer ⁴₂He₃, small helium and different spin-polarised halo hydrogen clusters and their corresponding isotopologues have been intensively studied the last three decades.</p><p>In the work presented here, the existence of the spin-polarized tritium trimer ground state, ³₁H₃, is demonstrated, verifying earlier predictions, and the system's properties elucidated. Detailed analysis has found no found evidence for other bound states and shape resonances in this system. The properties of the halo helium trimers, ⁴₂He₃ and ⁴₂He₂-³₂He have been investigated. Earlier predictions concerning the ground state energies and structural properties of these systems are validated using our three-dimensional finite element method. In the last part of this work we present results on the bound states and structural properties of the van der Waals bosonic atomic trimers Ne₃ and Ar₃. We believe to be the first to find evidence of a possible shape resonance just above the three-body dissociation limit of the neon trimer.</p>

General anisotropic constitutive laws and relevant dynamic equations of motion for porous media are described. The accuracy of various discretization algorithms in space and in time was surveyed. Results of these models and algorithms were compared to the exact solutions. Appropriate models and algorithms for further studies of spinal motion segments were then determined. Poroelastic axisymmetric finite element models, simulating spinal motion segments were analyzed and studied. Material properties of the intervertebral disc were derived by fitting experimental data based on porous medium theory using one-dimensional mathematical models. Structural models for the normal and degenerative processes were simulated for investigation of nutritional supply routes in the disc. Detailed structural anaalyses and failure conditions in various spinal motion segments were studied. Results of finite element analyses were consistent with the experimental observations. Nonlinear elastic material behavior of the solid skeleton was assumed and relevant formulas in creep were derived and examined. Preliminary results indicated that the nonlinear poroelastic material law used here may be useful in future analysis of the disc in finite element models of spinal motion segments.

A hp-finite element method is implemented to numerically study the modes of waveguides with two dimensional cross-section and to compute electromagnetic scattering from three dimensional objects. A method to control the chromatic dispersion properties of photonic crystal fibers using the selective hole filling technique is proposed. The method is based on a single hole-size fiber geometry, and uses an appropriate index-matching liquid to modify the effective size of the filled holes. The dependence of dispersion properties of the fiber on the design parameters such as the refractive index of the liquid, lattice constant and hole diameter are studied numerically. It is shown that very small dispersion values between 0±0.5ps/nm-km can be achieved over a bandwidth of 430-510nm in the communication wavelength region of 1300-1900nm. Three such designs are proposed with air hole diameters in the range 1.5-2.0μm. A novel multi-core fiber design strategy for obtaining a at in-phase supermode that optimizes utilization of the active medium inversion in the multiple cores is proposed. The spatially at supermode is achieved by engineering the fiber so that the total mutual coupling between neighboring active cores is equal. Different designs suitable for different fabrication processes such as stack-and-draw and drilling are proposed. An important improvement over previous methods is the design simplicity and better tolerance to perturbations. The optimal implementation of perfectly matched layer (PML) in terms of minimizing the computational overhead it introduces is studied. In one dimension it is shown that PML implementation with a single cell and a high order finite element produces minimal overhead. Estimates of optimal cell size and optimal finite element degree are given. Based on the single cell implementation of PML in three dimensions, field enhancement in metallic bowties is computed.

No description available.

Permanent magnets are today widely used in electrical machines of all sorts. With their increase in popularity, the amount of research has increased as well. In the wind power project at Uppsala University permanent magnet synchronous generators have been studied for over a decade. However, a tool for studying demagnetization has not been available. This Ph.D. thesis covers the development of a simulation model in a commercial finite element method software capable of studying demagnetization. Further, the model is also capable of simulating the connected electrical circuit of the generator. The simulation model has continuously been developed throughout the project. The simulation model showed good agreement compared to experiment, see paper IV, and has in paper III and V successfully been utilized in case studies. The main focus of these case studies has been different types of short-circuit faults in the electrical system of the generator, at normal or at an elevated temperature. Paper I includes a case study with the latest version of the model capable of handling multiple short-circuits events, which was not possible in earlier versions of the simulation model. The influence of the electrical system on the working point ripple of the permanent magnets was evaluated in paper II. In paper III and VI, an evaluation study of the possibility of creating a generator with an interchangeable rotor is presented.  A Neodymium-Iron-Boron (Nd-Fe-B) rotor was exchanged for a ferrite rotor with the electrical properties almost maintained.

Les travaux de thèse portent sur l'évaluation et la robustesse des stratégies adaptées pour la simulation de grandes structures avec non-linéarités non équitablement réparties, tels le flambage local, et des non-linéarités globales dans les structures aéronautiques. La stratégie dite de « relocalisation non-linéaire » permet l'introduction de schémas de résolution non-linéaire par sous-structure au sein des méthodes de décomposition de domaine classiques.Dans un premier temps, les performances et la robustesse de la méthode sont présentées sur des exemples de structures représentatives des cas industriels. Dans un second temps, la stratégie est complètement parallélisée et des études de « speed-up » et de « extensibilité » sont menées. Enfin, la méthode est testée sur des structures réalistes et de grandes tailles. / The thesis work focus on the evaluation and the robustness of adapted strategies for the simulation of large structures with not equitably distributed nonlinearities, like local buckling, and global nonlinearities on aeronautical structures. The nonlinear relocalization strategy allows the introduction of nonlinear solving schemes in the sub-structures of the classical domain decomposition methods.At a first step, the performances and the robustness of the method are analysed on academic examples. Then, the strategy is parallelized and studies of speed-up and extensibility are carried out. Finally, the method is tested on larger and more realistic structures.

M.Ing. / Optical fibre Bragg gratings are a periodic variation of the refractive index in the core of an optical fibre andmay be formed by exposure to intense UV laser light under specific conditions. Light at a certain wavelength, called the Bragg wavelength, is reflected back when illuminating the grating with a light source. Bragg gratings can relatively easily be employed as strain and temperature sensors, but have small sensitivity for pressure. Special transducers are required to increase the sensitivity. A pressure sensor was manufactured by coating a fibre Bragg grating with a polymer. The polymer coating converts transverse pressure into longitudinal strain through the Poisson effect inside the polymer coating. This thesis investigates the sensitivity of themanufactured Bragg grating pressure sensor, by using the method of finite element analysis. An account of the experimental setup, whereby the Bragg grating is written with a frequency tripled Nd:YAG laser, is given. The process whereby the fibre is coated with the polymer is described. The sensor is characterized through experimental results and a comparison is made between theoretical and experimental results. Uses for this sensor and ways with which the sensitivity may be increased are suggested as future work.

<p></p><p>Granular material blending plays an important role in many industries ranging from those that manufacture pharmaceuticals to those producing agrochemicals. The ability to create homogeneous powder blends can be critical to the final product quality. For example, insufficient blending of a pharmaceutical formulation may have serious consequences on product efficacy and safety. Unfortunately, tools for quantitatively predicting particulate blending processes are lacking. Most often, parameters that produce an acceptable degree of blending are determined empirically.</p> <p> </p> <p>The objective of this work was to develop a validated model for predicting the magnitude and rate of granular material mixing and segregation for binary mixtures of granular material in systems of industrial interest. The model utilizes finite element method simulations to determine the bulk-level granular velocity field, which is then combined with particle-level diffusion and segregation correlations using the advection-diffusion-segregation equation. </p> <p> </p> <p>An important factor to the success of the finite element method simulation used in the current work is the material constitutive model used to represent the granular flow behavior. In this work, the Mohr-Coulomb elastoplastic (MCEP) model was used. The MCEP model parameters were calibrated both numerically and experimentally and the procedure is described in the current work. Additionally, the particle-level diffusion and segregation correlations are important to the accurate prediction of mixing and segregation rates. The current work derived the diffusion and segregation correlations from published literature and determined a methodology for obtaining the particle diffusion and segregation parameters from experiments.</p> <p> </p> <p>The utility of this modelling approach is demonstrated by predicting mixing patterns in a rotating drum and Tote blender as well as segregation patterns in a rotating drum and during the discharge of conical hoppers. Indeed, a significant advantage of the current modeling approach compared to previously published models is that arbitrary system geometries can be modeled.</p> <p> </p> <p>The model predictions were compared with both DEM simulation and experiment results. The model is able to quantitatively predict the magnitude and rate of powder mixing and segregation in two- and three-dimensional geometries and is computationally faster than DEM simulations. Since the numerical approach does not directly model individual particles, this new modeling approach is well suited for predicting mixing and segregation in large industrial-scale systems.</p><br><p></p>