The study presented in this thesis investigates the passive exchange of enclosed water with seawater in an offshore wind turbine foundation. This thesis was undertaken in collaboration with Vattenfall R&D, Älvkarleby, Sweden. The water exchange is studied by utilizing Computational Fluid Dynamics (CFD) simulations. A standard monopile foundation, which is installed in Horns Rev 3 wind farm, is considered for the study. The considered geometry consists of two replenishment holes.  The study aims to develop a methodology to utilize CFD simulations to quantify the exchange rate of water. CFD enables studying the effects of different wave parameters and sea states on the economic exchange rate. However, the secondary aim to develop the methodology for the CFD simulations is also to utilize the available computational resources efficiently.  The CFD methodology incorporates the learning from experiments and utilizes a semi-circular domain to enclose the control volume. The results from a mesh sensitivity study establish that a coarser mesh in the domain and a finer mesh within the monopile, coupled with Implicit LES is appropriate to study the overall effect of wave motion on the exchange rate. Also, the additional term scalar transport, incorporated to study the change in concentration within the monopile, provided an appropriate and computationally efficient tool to visualize the variation in water concentration.

Transportation sector is the backbone of today’s society and its being revolutionized by the development of electric cars. The subject of electrification of the fleet involves many challenges starting from building the require infrastructure all the way to securing raw material for batteries. Charging times and energy density are also two major challenges especially in heavy transportation. With current technologies it is impractical to use electric trucks as the advantages of direct injection engines are unmatched. A typical diesel car or truck has a very long range reaching around 1000 km using single fuel tank. The high energy density of fossil fuels is a corner stone of the heavy transportation sector. It is hard to imagine electric trucks without a breakthrough in battery technology that has very high energy density. High pressure combustion has great potential in extracting more power from liquid fuel. This is mainly attributed to the instant vaporization because of the vanishing surface tension once the fuel goes through a supercritical process, thus energy to vaporize the fuel is saved. Another advantage is in the better mixing that the highly dense and the highly diffused fluid possesses in that region. On the other hand, many of the modelling aspects requires to be investigated. For example, which equation of state predicts the correct density and what are the effect of the pressure and temperature dependant fluid properties on the spray development. To isolate the effect of the high pressure combustion from other possible modelling effects and to facilitate the investigation, simulations using both OpenFOAM and CONVERGE were conducted. First the morphologies of Spray C was numerically characterized under high-temperature and high-pressure conditions. The Volume of fluid method captured the cavitation properly upon using 7.8 μm mesh. The mass flow rate and the transient of the injection process were accurately captured. Implementation of appropriate high pressure models using OpenFOAM to account for real fluid effects showed that three-parameter Redlich-Kwong Peng-Robinson equation of state were superior than two-parameters realfluid equation of state. The correctness of fuel density and viscosity is dependant of the equation of state with ideal gas equation of state being inferior to the realfluid equation of state. The combustion characteristics of Spray A were investigated using coupled Eulerian-Lagrangian approach. This approach demonstrated the ability of the modeling framework in predicting wide variety of parametric effects.

The amount of energy enclosed in ocean waves has been classified as one of the most promising renewable energy sources. Nowadays, different wave energy conversion (WEC) systems are being investigated, but only a few concepts have been operated in a sea environment. One of the largest challenges is to guarantee the offshore survivability of the devices in extreme wave conditions. However, there are large uncertainties related to the prediction of extreme wave loads on WECs.  Highfidelity computational fluid dynamics (CFD) simulations can resolve nonlinear hydrodynamic effects associated with wave-structure interaction (WSI). This thesis explores the point-absorbing WEC developed by Uppsala University in extreme wave conditions. The dynamic response and the forces on key components (mooring line, buoy, generator's end-stop spring) of the device are studied and compared. The high nonlinear phenomena accompany the steep and high waves, i.e., breaking behavior, slamming loads can be well-captured by the highfidelity CFD simulations. A commonly used methodology for extreme waves selection, recommended by technical specifications and guidelines, is the environmental contour approach. The 100-year contour in Hamboldt Bay site in California and the 50-year contour in the Dowsing site, outside the UK, are utilized to extract the extreme waves examined in the present thesis. Popular methodologies and data from different sources (observational and hindcast data) are examined for the environmental contour generation providing useful insights. Moreover, two popular approaches for the numerical representation of the extreme sea states, either as focused wave or as equivalent regular wave, were examined and compared. A midfidelity model of the WEC is successfully verified, as the utilization of lower fidelity tools in the design stage would reduce the computational cost. Last but not least, in CFD simulations the computational grid is sensitive in large motions, something often occurs during extreme-WSI. The solution of this issue for the open source CFD software OpenFOAM is provided here.

This thesis examines water mixing and exchange in a drinking water reservoir operated by themunicipal association Norrvatten. Recent water samples from the reservoir’s outgoing waterhave shown an increase in culturable bacteria during late summer and fall. This thesis utilizesComputational Fluid Dynamics (CFD) modeling and analysis in OpenFOAM to simulatereservoir inflow and outflow, analyzing mixing processes and their relationship to operationalstrategies. The objective is to understand the correlation between the residence time of waterand microbial growth and propose operational improvements to increase the exchange of waterin order to achieve improved water quality. A trace element was implemented in the CFDmodel to simulate the residence time of water. Initial simulations were based on the reservoir’shistorical operational data, utilizing temperature and water level measurements providedby Norrvatten. After the initial simulations, four alternative simulations were performed,comparing different operational strategies by modifying inflow parameters. Inflow parametersthat were changed were the volumetric inflow rate, water level variation, and the temperatureof the inflowing water. The post­processing in ParaView focused on the thermal stratificationand residence time distribution near the outlet during each mixing process. The study revealeda complex relationship between flow conditions and microbial growth, making it challengingto identify a clear pattern. However, based on the simulations with the alternative operationalstrategies it was concluded that the set of operational strategies called ”Strategy 1” generated themost optimal flow conditions. This strategy involves a three times larger volumetric inflow rate(an increase from 0.05 to 0.15 m^3/s) and a water level that is kept at the same values comparedto the original simulation. Strategy 1 resulted in a 3.6 % higher water exchange compared to theoriginal simulation. In comparison to the other simulated strategies, Strategy 1 generates thehighest water exchange, with a 63.6 % increase compared to the worst­-case scenario involvingcolder inflow. The conclusion that could be drawn is that the most favorable operationalstrategies involve higher volumetric inflow rates, lower water levels, and an incoming watertemperature that is higher than the initial reservoir temperature.

El modelado CFD se ha convertido en una herramienta aceptada y ampliamente utilizada en el ámbito del diseño de motores de combustión interna alternativos. Los modelos de combustión avanzados ayudan a comprender los fenómenos complejos químicos y físicos del proceso de combustión y aportan información detallada que no se puede obtener con experimentos. Indudablemente, el modelado del proceso de combustión turbulenta parcialmente premezclada característico de los chorros Diesel es particularmente difícil y por lo tanto es un tema de gran interés para la comunidad científica. Los retos más importantes del modelado de este tipo de llamas son la predicción del proceso del auto-encendido, caracterizado por el tiempo de retraso, y la estructura de la llama cuasi-estacionaria con su característica longitud de lift-off. Estos dos parámetros globales de los chorros Diesel son importantes por varios aspectos. Primero, es relativamente sencillo medir estos dos parámetros y por lo tanto utilizarlos para la validación de modelos y segundo, son factores determinantes en el proceso de la combustión en un motor. El auto-encendido marca el inicio de la tasa de liberación de calor y la longitud de lift-off desempeña un papel fundamental en la formación de hollín. El mecanismo de estabilización de la llama en la zona del lift-off todavía no es bien conocido aunque existen diferentes teorías en la literatura, por lo que su modelado es en la actualidad un reto no resuelto. De acuerdo con el contexto descrito previamente, en este trabajo se pretende implementar un modelo de combustión integrado en un solver RANS utilizando la plataforma CFD OpenFOAM de código abierto. El modelo propuesto está basado en el concepto de flamelets usando una química detallada combinado con funciones de probabilidad determinadas a priori (presumed-PDF) para considerar el efecto de interacción entre la química y las características del flujo turbulento, que implica hipótesis importantes. En primer lugar, con el concepto flamelet se asume que una llama Diesel turbulenta quema localmente como un conjunto de llamas laminares de difusión de flujos opuestos. En segundo lugar se asume que las fluctuaciones de las propiedades introducidas por el flujo turbulento, que son las responsables de los fenómenos de interacción entre la química y la turbulencia durante la combustión, siguen un comportamiento estadístico en el tiempo de acuerdo a una distribución de probabilidad conocida a priori. Los fenómenos complejos del auto-encendido de hidrocarburos exigen el uso de mecanismo químicos detallados para recuperar satisfactoriamente los tiempos de retraso del auto-encendido en un rango amplio de condiciones termoquímicas. Una estrategia de interés para mantener los costes computacionales dentro de límites aceptables consiste en pre-tabular los resultados del cálculo de la química en tablas. Los parámetros independientes de estas tablas son la fracción de mezcla, la variable de progreso y la tasa de disipación escalar. Además, la hipótesis de que la distribuciones de probabilidad de las fluctuaciones generadas por la turbulencia sobre las propiedades del flujo son conocidas permite generar una tabla con la información química del problema apta para su aplicación en cálculo CFD en un entorno RANS. Esta aproximación basada en la pre-tabulación de los resultados químicos presenta dos ventajas fundamentales, siendo la primera de ellas la posibilidad de considerar modelos avanzados de interacción química-turbulencia y la segunda el relevante ahorro de tiempo de cálculo. Sin embargo, estas tablas representan un gran espacio de datos cuya gestión eficiente no es trivial. El desarrollo de un almacenamiento adecuado para un acceso de datos rápido y directo así como un esquema de interpolación multidimensional también forma parte del presente trabajo. / Winklinger, JF. (2014). Implementation of a combustion model based on the flamelet concept and its application to turbulent reactive sprays [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48488

Fossil fuel is an important energy source, but is unavoidabiy running out. Since the cellulosic material is the most abundant source of organic matter, the ethanol, which is produced from cellulosic waste materials, is gaining more and more attention. These materials are cheap, renewable and their availability makes them superior compared to other raw materials. The cellulose must be hydrolyzed to glucose before it can be fermented to ethanol. The enzymatic hydrolysis of cellulose using cellulase enzymes is the most widely used method. The production cost of cellulase enzymes is the major cost in ethanol manufacture. To optimize the cost of ethanol production, enzyme stability needs to be improved through maintaining the activity of the enzymes and by optimizing the production of the cellulase. The aim of researchers, engineers and industrials is to get more biomass for the same cost. The filamentous fungus Trichoderma reesei has a long history in the production of the cellulase enzymes. This production can be influenced strongly by varying the growth media and culture conditions (pH, temperature, DO, agitation,... ). At present, it is my opinion that no modelling study has included both the hydrodynamic and kinetic aspects to investigate the effect of shear and mass transfer on the morphology of microorganisms that influence the rheology of the broth and production of cellulase. This thesis presents the development of a mathematical model for cellulase production and the growth of biomass in an airlift bioreactor. The kinetic model is coupled with the methodology of two-phase flow using mathematical models based on the bubble break-up and coalescence to predict mass transfer rate, which is one of the critical factor in the fermentation. A comparison between the results obtained by the developed model and the experimental data is given and discussed. The design proposed for the airlift geometry by Ahamed and Vermette enables us to get a high mass transfer and production rate. The results are very promising with respect to the potential of such a model for industrial use as a prediction tool, and even for design.

A numerical model was developed to evaluate the performance of detailed solid oxide fuel cell (SOFC) anode microstructures obtained from experimental reconstruction techniques or generated from synthetic computational techniques. The model is also capable of identifying the linear triple phase boundary (TPB) reaction sites and evaluating the effective transport within the detailed structures, allowing a comparison between the structural properties and performance to be conducted. To simulate the cell performance, a novel numerical coupling technique was developed in OpenFOAM and validated. The computational grid type and mesh properties were also evaluated to establish appropriate mesh resolutions to employ when studying the performance. The performance of a baseline synthetic electrode structure was evaluated using the model and under the applied conditions it was observed that the ionic potential had the largest influence over the performance. The model was used in conjunction with a computational synthetic electrode manufacturing algorithm to conduct a numerical powder to power parametric study investigating the effects of the manufacturing properties on the performance. An improvement in the overall performance was observed in structures which maximized the number of reaction sites and had well established transport networks in the ion phase. From the manufacturing parameters studied a performance increase was observed in structures with low porosity and ionic solid volume fractions near the percolation threshold, and when the anodes were manufactured from small monosized particles or binary mixtures comprising of smaller oxygen ion conductive particles. Insight into the anode thickness was also provided and it was observed that the current distribution within the anode was a function of the applied overpotential and an increase in the overpotential resulted in the majority of the current production to increase and shift closer to the electrode-electrolyte interface. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2013-10-01 09:41:47.617

This master thesis was provided by Scania AB. The objective of this thesis was to modify an application in the free Computational Fluid Dynamics software OpenFOAM to be able to handle spray and wall film modeling of a Urea Water Solution together with Conjugate Heat Transfer. The basic purpose is to widen the knowledge of the vaporization process of a Urea Water Solution in the exhaust gas after treatment system for a diesel engine by using OpenFOAM. First, urea has been modeled as a very viscous liquid at low temperature to mimic the solidication process of urea. Second, the development of the new application has been done. At last, test simulations of a simple test case are performed with the new application. The results are then compared with simplied hand calculations to verify a correct behavior of certain exposed source terms. The new application is working properly for the test case but to ensure the reliability, the results need to be compared with another Computational Fluid Dynamics software or more preferable, real experiments. For more advanced geometries, the continued development presented last in this thesis is highly recommended to follow.

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Lorsqu'une suspension concentrée est en écoulement, il est fréquent d'observer que la concentration en particules ne reste pas homogène mais que les particules migrent vers des régions préférentielles de l'écoulement. Globalement, il existe deux types de modèles pour décrire cette interaction entre l'écoulement et la structure qui apparaît dans la suspension. Les premiers sont assez phénoménologiques et reposent sur l'étude des collisions qui surviennent entre les particules en écoulement. Ils donnent lieu à une description de la migration en terme de diffusion des particules. Le second modèle, appelé "Suspension Balance Model" (SBM), fait appel à l'action des contraintes normales d'origine particulaire engendrées par l'écoulement. Ce modèle semble très pertinent mais son utilisation souffre du manque de données sur les contraintes normales dans les suspensions. Ce manuscrit rapporte une étude expérimentale et numérique de la rhéologie et de la migration induite par un écoulement dans des suspensions non-browniennes concentres. La partie expérimentale consiste à mesurer, en géométrie torsionnelle plan-plan, la viscosité, les deux différences de contraintes normales et le tenseur des contraintes particulaires. Les contraintes particulaires déterminées expérimentalement sont alors injectées dans le "Suspension Balance Model" qui relie le flux de particules à la divergence du tenseur des contraintes particulaires, dans le cas d'un écoulement de cisaillement simple. Les équations couplées de la conservation de la masse, des particules et du moment d'inertie sont implémentées dans OpenFOAM et résolues par la méthode des volumes finis. Les résultats numériques sont comparés à des résultats numériques et expérimentaux de la littérature. Enfin, le SBM est généralisé pour être utilisé dans tout type d'écoulement à 2 dimensions ; les cas du cisaillement d'un nuage de particules et de l'effet de la gravité dans un écoulement de Couette horizontal sont traités.