The vitreous cavity, the largest chamber of the eye, is delimited anteriorly by the lens and posteriorly by the retina and is filled by the vitreous humour. Under normal conditions the vitreous humour has the consistency of a gel, however, typically, with advancing age a disintegration of the gel structure occurs, leading to a vitreous liquefaction. Moreover, after a surgical procedure called vitrectomy the vitreous body may be completely removed and replaced by tamponade fluids. Besides allowing the establishment of an unhindered path of light from the lens to the retina, the vitreous also has important mechanical functions. In particular, it has the role of supporting the retina in contact to the outer layers of the eye, and of acting as a diffusion barrier for molecule transport between the anterior and the posterior segments of the eye. Studying the dynamics of the vitreous induced by eye rotations (saccadic movements) is important in connection of both the above aspects. On the one hand indications exist that the shear stress exerted by the vitreous on the retina may be connected with the occurrence of retinal detachment. On the other hand, if the vitreous motion is intense enough (a situation occurring either when the vitreous is liqueed or when it has been replaced with a uid after vitrectomy), advective transport may be by far more important than diffusion and may have complex characteristics. Advection has indeed been shown to play an important role in the transport phenomena within the vitreous cavity, but, so far, only advection due to the slow overall fluid ux from the anterior to the posterior segments of the eye has been accounted for, while fluid motion due to eye rotations, even if it is generally believed to play an important role, has been invariably disregarded. Some recent contributions have pointed out the importance of accounting for the real vitreous cavity shape in studying uid motion induced by eye rotations. Modelling the vitreous cavity as a deformed sphere, showed that the flow field displays very complex three- dimensional characteristics to which effective fluid mixing is likely to be associated. The purpose of the thesis is to model numerically the motion of the liqueed vitreous within the vitreous cavity induced by different eye movements. Create the model in the Comsol interface, compare the results with theoretical, experimental measurements and do some ow visualizations. Finally show the dependence of the streaming intensity from the amplitude of rotations and the Womersley number .

There is a renewed interest to use material as wood to construct large multi-storey buildings in Sweden, but lightweight material tends to increase the indoor temperature fluctuations during days with large changes in outdoor temperature. The problem can be resolved by integrating phase change material (PCM) in the construction. This increases thermal inertia which mitigates the fluctuations.           The scope of the study is to develop a simulation model in COMSOL Multiphysics, to validate the model experimentally and to determine the optimal position and thickness of a PCM layer in a multi-layer wall. The model, representing a building with the shape of a box, consists of two versions. The first version, called the test box, is modeled with 5 sides of pure gypsum and 1 side of PCM-gypsum composite. The second version without PCM, called the reference box, is modeled with 6 sides of pure gypsum. Since the study is focused on reducing the cooling load, the PCM gypsum composite material should function effectively during summer conditions in northern Sweden. The experimental part includes two real-life boxes, the experimental test box and reference box, built of the same type of material that is chosen for the simulation model boxes. A climate chamber is utilized for the temperature control of the two boxes while performing measurements to validate the simulation model. The simulation model showed deviations from the experimental measurements. The temperatures inside the climate chamber, at all five points of measurement, were lower than the equivalent points in the simulation. It was possible to compensate by adjusting the overall ambient temperature down with 0.6 °C in the simulation, resulting in smaller errors. The PCM positioning resulted in recommendations to place the PCM closest to the interior space. The testing of different PCM thicknesses showed the best heat storage for the thickest PCM layers, but the PCM storage efficiency should have been considered as well.

Syftet i denna studien var att ta fram en metod för att simulera spricktillväxt i enbiologisk vävnad med hjälp av FEM programmet COMSOL. Målet är att ta undersökaom COMSOL är lämpligt för sådana simuleringar samt att parametrarna som togsfram med metoden ska kunna användas för ytterligare simulationer av sammamaterial. Med COMSOL simulerades en biologisk vävnad som dras isär, där olika parametrarundersöktes. Utgångspunkten var en experimentell studie som gjorts på grisvävnad.Stora deformationer hindrade användningen av linjära beräkningar, och iställetkrävdes icke-linjära metoder. Tre olika hyperelastiska modeller jämfördes för deninitiala töjningen av materialet, och för spricktillväxten användes kohesiva zoner medtvå olika former på TSL, T raction separation law. För de hyperelastiska egenskapernasimulerades Neo-Hookean, Mooney-Rivlin och Yeoh modellerna. För spricktillväxtenanvändes en Bilinjär och en expontential TSL, båda är energibaserade. Resultaten visade att metoden är lovande men inte fullständig för att simulerabiologiska vävnader. Neo-Hookeans och Mooney-Rivlins hyperelastiska modellerräckte ej för att simulera uttöjningen, medan Yeohs modell med parametervärdenC10 = 0.21 M P a, C20 = 0.08 M P a och C30 = 0.1 M P a såg lovande ut. För TSLstod det klart att en exponentiell form passade det givna datan bäst. För simuleringenav spricktillväxten är det tre värden som ska överensstämma med det givna datan.Max lasten, förskjutningen vid begynnelse av spricktillväxt och förskjutningen vidtotalkollaps. Med de första två värden rätt var det inte möjligt, med denna modellen,att få rätt värde vid total kollaps.

Sweden is a country with a relatively high number of private wells, where about 1.2 million inhabitants in permanent housing and an equal amount in summer housing relies on private wells as their drinking water supply. At the same time the market for drinking water treatment products is unregulated regarding quality and requirements are needed. A testing facility with the aim of providing quality certifications as well as sustainability- and efficiency- tests of small scale drinking water treatment techniques is under development and located in a decommissioned groundwater treatment plant in Svanberga, outside Norrtälje, Stockholm County, Sweden. The groundwater treatment plant has three operational bedrock wells connected to it and the groundwater system is rather unknown with only a few previous studies done in the region. Better understanding of the hydrogeological system would aid in further work of evaluating the risks of contaminant spread in the region. Trough fracture outcrop mapping, geophysical Very Low Frequency measurements and groundwater modelling using COMSOL Multiphysics this master thesis have identified several possible flow paths within the bedrock connected to the GWTP. The results indicates there are one or two approximately east-west striking fracture zones that could play a major role in transportation of contaminants related to road traffic and agriculture to the wells, while several north to south striking fracture zones most likely supplies the groundwater basin with water from the thicker soil layers in the northern part of the region. Recommendations of future studies includes conducting a detailed pumping test of the operational wells in Svanberga old GWTP as well as verification of the presumed most important identified fracture zones to the south east and north in the studied area by additional geophysical investigations or  tracer tests. / Testbädd dricksvatten är ett pågående projekt och testanläggning där tester och utveckling av filter och småskaliga tekniker för rening av dricksvatten samt kvalitetscertifiering för effektivitets och hållbarhetstester kommer utföras. Testanläggningen består av ett nedlagt grundvattenverk med tre tillhörande bergborrade brunnar i Svanberga utanför Norrtälje. Grundvattensystemet och flödesvägar för grundvattnet i området är relativt okända och bättre förståelse av hydrogeologin skulle kunna bidra till framtida arbete med att identifiera och bedöma risker för föroreningstransporter i området samt till grundvattenverkets brunnar. Detta examensarbete har genom beprövade metoder i form av sprick-kartering, geofysiska undersökningar (VLF) och grundvattenmodellering med COMSOL Multiphysics identifierat flera möjliga flödesvägar i berggrunden kopplade till grundvattenverket. Resultatet från studien visar att ett antal sprickzoner i öst-västlig riktning utgör en större risk för föroreningstransport av ämnen från trafik och jordbruk samt att en större del av det vatten som tillförs grundvattensystemet troligen har sitt ursprung från tjockare morän-lager i de norra delarna av området. Provpumpningar och verifiering av de identifierade sprick-zonerna genom spårämnestester och geofysiska undersökningar bör utföras för att stärka resultaten från detta arbete och möjligen utöka kunskapen om hydrogeologin i området kring Svanberga gamla grundvattenverk.

A continuous flow, passive separation device was designed using an equivalent circuit to create variable flow rates for hydrodynamic focusing to drain channels and collection outlets. By varying the diameter of the sample inlet connection into the reservoir, the particle position was influenced significantly, which enabled desired separations. Additionally it was noted that the relative, horizontal position of the inlet also had a significant influence on particle position within the device. A dimensionless number, the Characteristic Sample Inlet, was developed to relate geometric properties of the inlet reservoir to downstream particle distribution. It was found that a 2:1 ratio between inlet reservoir and sample inlet diameter, and placed at the top of the reservoir yielded the best separation results. Fluid velocity profiles in the reservoir were explored using Comsol Multyphysics. The experimentally observed particle trajectories and COMSOL predictions were in good agreement. Based on Comsol models a dimensionless parameter to relate the unique velocity profiles within the inlet reservoir to downstream separation of particles was also developed. A mixture of 10, 5.5, and 3.0 µm particles were separated to three distinct collection outlets at 73.4%, 64.7%, and 52.8% respectively. Therefore this project shows that passive separations of particles can be achieved simply by alerting the ratio of inlet hole relative to inlet reservoir diameter, and by placing the inlet hole at the top of the reservoir.

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The jet printing of solder paste from a uid dynamics perspective involves viscosity change due to varying shear rate and eventual break o of the ejected solder paste droplet from the uid in the printer head. The ability to model the jetting process in a simulation package is important as it can be used as a tool for future development of the jetting device. The jetting process is modelled as a two phase (air - solder paste) ow with interface tracking performed using phase eld method and temporal stepping based on a second-order Backward Di erence Formula with relaxed tolerences. This thesis investigates the droplet morphology, volume and speed predictions for three di erent piston actuation modes and solder paste viscosity denitions given by the Carreau- Yasuda model. A Darcy condition with the porosity parameter is calibrated equal to unity such that the droplet speed is within the realistic range of 20 m/s - 30 m/s. The simulations are compared against previous simulation results from IBOFlow, performed within a collaboration between Mycronic AB and Fraunhofer-Chalmers Centre. As the Carreau models cannot capture the dependence of the uid viscosity of ow history, an indirect structure based viscosity model is used to compare the thixotopic behaviour. The expressions for the parameters of the structure based viscosity model are derived based on an analytical model which assumes that shear rate is constant. Experimental data for constant shear rate is curve tted on a Carreau model and an initial estimate of the parameters are obtained. The parameters are then adjusted to match experimental thixotopic behaviour. This method can be used to obtain parameter values for structure based viscosity models for uids with no previous data. Once the solder paste is ejected through the nozzle and the piston retracts, the uid undergoes stretching. Studying lament stretching during jetting is dicult as it can be driven by both droplet and piston motion. The data from an extensional rheometer is analyzed to study the lament stretching phenomenon for solder pastes. An analytical model for the critical aspect ratio is derived for a Newtonian uid lament undergoing a pure extension and modelled as a cylinder whose radius is decreases with time. The exponential decrease of the lament radius predicted by the analytical model is found to reproduce the experimental observations very well. The lament radius calculated based on the lament height from the experiments and analytical model shows that the model captures the stretching process, but the formation of beads usually seen in suspensions is not accounted for.

With a nation-wide aim toward reducing operational energy costs in buildings, it is important to understand the dynamics of controlled heating, cooling, and air circulation of an individual room, the "One-Room Model Problem." By understanding how one most efficiently regulates a room's climate, one can use this knowledge to help develop overall best-practice power reduction strategies. A key toward effectively analyzing the "One-Room Model Problem" is to understand the capabilities and limitations of existing commercial tools designed for similar problems. In this thesis we develop methodology to link commercial Computational Fluid Dynamics (CFD) software COMSOL with standard computational mathematics software MATLAB, and design controllers that apply inlet airflow and heating or cooling to a room and investigate their effects. First, an appropriate continuum model, the Boussinesq System, is described within the framework of this problem. Next, abstract and weak formulations of the problem are described and tied to a Finite Element Method (FEM) approximation as implemented in the interface between COMSOL and MATLAB. A methodology is developed to design Linear Quadratic Regulator (LQR) controllers and associated functional gains in MATLAB which can be implemented in COMSOL. These "closed-loop" methods are then tested numerically in COMSOL and compared against "open-loop" and average state closed-loop controllers. / Ph. D.