Spillways are hydraulic structures that allow dams to release and convey surplus water or flood from the reservoir to the downstream channel. The spillway is a safety structure that prevents the overtopping of the dam. Many dam failure disasters were due to the inadequate capacity of the spillway, which fully illustrates the prominence of spillway design. According to the control structure, spillways can be divided into gated and ungated type. The gated spillway provides better control of the managed water level and reduces the elevation of the top of the dam. Researchers have mostly used experimental models to investigate these two types of spillways in previous literature. In the past few years, following the rapid development of numerical simulation technology, there have been more studies on the numerical modeling of spillways. However, most of the literature was about ungated spillways and most of it considered the case of low head ratios, while the case with gates, especially the case of vertical plane gates, was less investigated. In this study, the hydraulic characteristics, such as velocity, pressure, and discharge coefficient, of the ungated and gated ogee spillways are investigated by means of physical and numerical models for the case of low and high head ratios. The study covered head ratios varying from 1.4 to 4.6 and the relative gate-openings varying from 0.5 to 2. The second main objective of this study was to evaluate the performance of the numerical model to simulate gated and ungated spillways. It mainly employed 2DV OpenFOAM to simulate three turbulence models (realizable k-ε, RNG k-ε, k-ω SST), and the results were compared and calibrated with the experimental results from the physical model tests performed by the author to verify the performance of the numerical model. This study aims to demonstrate that the numerical model can be used as a complementary tool to the physical model to measure the hydraulic performance of ogee spillways.

Recent tsunami events have inflicted devastating damage to coastal communities. Existing design standards provide a certain level of evaluation of tsunami effects such that critical infrastructure can be designed to resist tsunamis. Tsunami momentum flux, used to design structures is a function of water level height and velocity of tsunami bores. Understanding tsunamis and developing mitigation measures is essential. So far, some mitigation measures have been suggested, and to improve them, further investigations are required. The design of tsunami inundation effects mitigation canals is one of the suggested solutions which has received limited attention. The first objective of this study was to investigate the effects of a rectangular canal on the hydrodynamics of turbulent bores before and after the canal by conducting a series of physical experiments. A dam-break wave was used to simulate the tsunami-like turbulent waves passing over a smooth and horizontal surface, in the presence and/or absence of a canal. Three canal water depths were used to model shallow, moderate, and deep conditions, and three canal widths were also selected to model narrow to wide conditions while the dam break waves were generated from three different impoundment depths in a reservoir located upstream of the canal. The dam-break wave propagation over a horizontal, dry, and smooth bed revealed four regimes describing the variations of bore height with time. The time to reach the maximum bore height and the quasi steady-state regime were correlated with each impoundment depth and an empirical formulation was proposed to estimate the onset of the quasi steady-state flow. The maximum bore heights measured before and after the mitigation canal location were approximately 40 % and 50 % respectively, higher compared with those recorded in the corresponding tests without the presence of a canal. The second objective of this study was to experimentally investigate the effects of canal depth on the time history of bore height and its velocity. The experimental results were used for calibration and validation of a developed numerical model. The rapid release of an upstream impoundment water depth was employed to generate a bore analogous to a tsunami-induced inundation. The time histories of wave heights and velocity were measured upstream and downstream of the canal. The recorded time-series of the water surface levels and velocities were compared with the simulation results and good agreement was found between experimental and numerical water surface profiles using a Root Mean Square Error (RMSE) and the Relative Error. Three turbulence models:, namely the standard k-ε, the Realizable k-ε, and the RNG k-ε were tested, and it was found that all turbulence models perform well but the standard k-ε model provided satisfactory accuracy. The velocity contour plots for shallow, medium, and deep mitigation canals showed the formation and evolution of jets of different characteristics. The energy dissipation and air bubble entrainment of the tsunami bore, as it plunged into a canal, increased as the canal depth increased, and the jet flow of the maximum bore velocity decreased with increased canal depth. It was found that the eye of the vortex in the canal moved steadily in the downstream direction. Generally, the bore fully plunged almost nearly into the middle of the canal and started to divide into two small vortices. The third objective of this study dealt with a sequence of numerical experiments conducted to investigate the impact of mitigation canals on the hydrodynamics of a tsunami-like turbulent bore moving across a flat bed. The effects of mitigation canal depth and its orientation on the reduction of maximum specific momentum and energy of turbulent bores crossing over it were investigated numerically. Variations in the ratio between the downstream and upstream maximum specific momentum and mean flow energy decreased as the canal depth increased, and the time history of the mean flow energy over a canal with a rectangular endwise profile revealed that the canal depth affects the jet stream of the maximum mean flow energy. As the canal depth increased, the period of time needed to dissipate the area of the jet stream with the maximum turbulent kinetic energy, vorticity, and energy dissipation rate decreased. Both the angled and perpendicular to flow direction canals caused the maximum specific momentum and energy of the turbulent bore to decrease downstream of the canal. The specific momentum and energy achieved their highest values for a canal orientation of 45º. The greatest reductions in maximum specific momentum for turbulent bores over canals with different depths and orientations were achieved for 𝜃 = 30°.

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In regions with cold climates, a layer of ice often forms on vehicle windshields, whichobstructs the driver’s view. To address this issue, vehicles are equipped with internal defrosters. However, at Scania, the evaluation of defroster design performancecurrently relies on time-consuming and costly physical testing. A more effectiveapproach would be to employ numerical techniques to accurately forecast defrostingpatterns. This would offer valuable insights for analyzing the defroster’s performanceduring the design phase.The objective of this thesis is to develop a methodology using the open-source CFDsoftware OpenFOAM to predict the performance of a vehicle’s defrosting system.This approach presents a quicker and more convenient way to design the systemcompared to conventional testing methods. Experimental results were obtained bymonitoring the defrosting process at regular intervals. However, uncertainties existedregarding boundary and ambient conditions as the experiments were not conductedto validate the CFD results. The temperature profile and mass flow rate at the inlet were unknown. The model’s geometry was pre-processed using ANSA, and thevolume mesh for the truck cabin was generated using the SnappyHexMesh utilityin OpenFOAM. Mesh verification demonstrated good quality, and the realizable k-εturbulence model was utilized. The Grid Convergence Index (GCI) was employedto compare different mesh sizes, ultimately achieving a converged mesh. The RKEmodel was found to be computationally efficient and suitable for defrosting simulations, producing similar results to the k-ω SST turbulence model.A time step study was conducted to determine an efficient time-step. Additionally,a temperature study was performed to address the uncertainty surrounding the inlet temperature. Various design points were examined, involving different heat-uptimes and maximum temperatures. The results indicated that a heat-up time of 600seconds and a maximum temperature of 308 Kelvin yielded similar outcomes to theexperiments. To address uncertainty regarding the inlet mass flow rate, a study wasconducted by varying the mass flow rate. Comparing the results with the experimental data, a mass flow rate of 450 kg/hr provided the most comparable defrostingperformance. The study also investigated the impact of the exterior domain anddetermined that removing it would lead to inaccurate defrosting predictions due to alack of heat transfer. Furthermore, a comparison of OpenFOAM and StarCCM+ forsteady-state solutions demonstrated satisfactory results in terms of turbulent kineticenergy and wall shear stress at the windshield. Attempts to optimize defrosting performance included optimizing the shape of the defroster vents. The effect of rotatingthe vents relative to the windshield surface on defrosting was assessed, but it wasconcluded that the angle had minimal impact on performance or the methodology isnot sensitive enough to differentiate the minor differences.In conclusion, this thesis presents an efficient methodology utilizing OpenFOAM topredict defrosting performance, encompassing complete windshield defrosting timeand ice melting rate. It holds potential for future defroster design processes. Furtherstudies could focus on alternative meshing methods to reduce computational costs.

An alternative formulation of the governing equations of a dynamical system, called the multi-scale localized perturbation method, is introduced and derived for the purpose of solving complex geophysical flow problems. Simulation variables are decomposed into background and perturbation components, then assumptions are made about the evolution of these components within the context of an environmental flow in order to close the system. Once closed, the original governing equations become a set of one-way coupled governing equations called the "delta form" of the governing equations for short, with one equation describing the evolution of the background component and the other describing the evolution of the perturbation component. One-way interaction which arises due to non-linearity in the original differential equations appears in this second equation, allowing the background fields to influence the evolution of a perturbation. Several solution methods for this system of equations are then proposed. Advantages of the delta form include the ability to specify a complex, temporally- and spatially-varying background field separate from a perturbation introduced into the system, including those created by natural or man-made sources, which enhances visualization of the perturbation as it evolves in time and space. The delta form is also shown to be a tool which can be used to simplify simulation setup. Implementation of the delta form of the incompressible URANS equations with turbulence model and scalar transport within OpenFOAM is then documented, followed by verification cases. A stratified wake collapse case in a domain containing a background shear layer is then presented, showing how complex internal gravity wave-shear layer interactions are retained and easily observed in spite of the variable decomposition. The multi-scale localized perturbation method shows promise for geophysical flow problems, particularly multi-scale simulation involving the interaction of large-scale natural flows with small-scale flows generated by man-made structures. / Master of Science / Natural flows, such as those in our oceans and atmosphere, are seen everywhere and affect human life and structures to an amazing degree. Study of these complex flows requires special care be taken to ensure that mathematical equations correctly approximate them and that computers are programmed to correctly solve these equations. This is no different for researchers and engineers interested in studying how man-made flows, such as one generated by the wake of a plane, wind turbine, cruise ship, or sewage outflow pipe, interact with natural flows found around the world. These interactions may yield complex phenomena that may not otherwise be observed in the natural flows alone. The natural and artificial flows may also mix together, rendering it difficult to study just one of them. The multi-scale localized perturbation method is devised to aid in the simulation and study of the interactions between these natural and man-made flows. Well-known equations of fluid dynamics are modified so that the natural and man-made flows are separated and tracked independently, which gives researchers a clear view of the current state of a region of air or water all while retaining most, if not all, of the complex physics which may be of interest. Once the multi-scale localized perturbation method is derived, its mathematical equations are then translated into code for OpenFOAM, an open-source software toolkit designed to simulate fluid flows. This code is then tested by running simulations to provide a sanity check and verify that the new form of the equations of fluid dynamics have been programmed correctly, then another, more complicated simulation is run to showcase the benefits of the multi-scale localized perturbation method. This simulation shows some of the complex fluid phenomena that may be seen in nature, yet through the multi-scale localized perturbation method, it is easy to view where the man-made flows end and where the natural flows begin. The complex interactions between the natural flow and the artificial flow are retained in spite of separating the flow into two parts, and setting up the simulation is simplified by this separation. Potential uses of the multi-scale localized perturbation method include multi-scale simulations, where researchers simulate natural flow over a large area of land or ocean, then use this simulation data for a second, small-scale simulation which covers an area within the large-scale simulation. An example of this would be simulating wind currents across a continent to find a potential location for a wind turbine farm, then zooming in on that location and finding the optimal spacing for wind turbines at this location while using the large-scale simulation data to provide realistic wind conditions at many different heights above the ground. Overall, the multi-scale localized perturbation method has the potential to be a powerful tool for researchers whose interest is flows in the ocean and atmosphere, and how these natural flows interact with flows created by artificial means.

Durante el proceso de apertura y cierre de un inyector Diesel, las características del combustible a la salida de la tobera cambian significativamente como consecuencia del movimiento de la aguja. Este hecho tiene una enorme influencia en el desarrollo del chorro y en el proceso de mezcla entre el aire y el combustible y, por tanto, en el posterior proceso de combustión. Sin embargo, y a pesar de su importancia, todavía hoy existen multitud de cuestiones sobre el proceso de inyección que permanecen sin resolver debido, en parte, a la dificultad para llevar a cabo experimentos a levantamientos de aguja parciales. Teniendo en cuenta lo anterior, la presente tesis se ha centrado en el estudio de la influencia del levantamiento de aguja sobre el flujo interno en toberas de inyección Diesel. Este trabajo se ha llevado a cabo mediante simulaciones tridimensionales del flujo en condiciones cavitantes y no cavitantes, modelando la cavitación mediante un modelo de equilibrio homogéneo implementado en OpenFOAM. Antes de analizar en profundidad la influencia de la posición de la aguja, el código ha sido puesto a punto y validado con resultados experimentales en un orificio calibrado, una tobera monorificio y una tobera multiorificio en condiciones de levantamiento de aguja máximo. El modelo de cavitación ha mostrado una gran precisión en la predicción del gasto másico, el flujo de cantidad de movimiento, la velocidad, los coeficientes de flujo y la apariencia de la cavitación. Además, los resultados computacionales y experimentales obtenidos en la validación del código han servido para estudiar alguno de los fenómenos asociados a la cavitación, como el colapso de gasto másico o el aumento de velocidad y de turbulencia. Tras la validación del código, éste ha sido utilizado para analizar la influencia del levantamiento de aguja en una tobera microsaco real. Inicialmente, se ha llevado a cabo un estudio de más de 500 ejecuciones simulando diferentes levantamientos de aguja fijos mediante métodos RANS. En este estudio, centrado principalmente en las características del combustible a la salida de la tobera y en el desarrollo de la cavitación, se ha podido observar un cambio significativo en el aspecto de la cavitación en función de la posición de la aguja: para levantamientos grandes, el vapor se desarrolla a lo largo de la parte superior del orificio, mientras que para levantamientos pequeños, la cavitación aparece en el asiento de la aguja y en la parte inferior del orificio para contrapresiones relativamente bajas. Este hecho tiene una enorme influencia sobre los valores de gasto másico, de flujo de cantidad de movimiento y de velocidad efectiva, los cuales apenas varían para levantamientos de aguja mayores de 75 ¿m. Posteriormente, los efectos del levantamiento de aguja han sido estudiados aplicando métodos LES. El uso de Large Eddy Simulation ha proporcionado información de gran relevancia sobre el flujo interno, especialmente sobre el desarrollo de la turbulencia y su interacción con el fenómeno de la cavitación. Los resultados de este estudio han demostrado que la cavitación favorece el desarrollo de la turbulencia, provocando un cambio notable de los niveles de turbulencia y de la región más turbulenta de la tobera en función de la posición de la aguja. Además, los resultados han puesto en evidencia la existencia de una cierta interacción o interdependencia entre ambos fenómenos, puesto que la turbulencia tiene a su vez importantes efectos sobre la apariencia de la cavitación. Profundizando en el desarrollo de la turbulencia, se ha observado también un aumento significativo del número de vórtices presentes en el fluido y un descenso de su tamaño a medida que la aguja desciende. Finalmente, se ha analizado la influencia del levantamiento de aguja mediante malla móvil, reproduciendo así el movimiento real de la aguja durante todo el proceso de inyección. Este último estudio ha sido posible gracias a la modificación del código y ha sido utilizado a partir de condiciones de contorno proporcionadas por un modelo unidimensional del inyector creado en AMESim. Por una parte, se han comparado los resultados obtenidos mediante simulaciones estacionarias y transitorias, mostrando diferencias despreciables en el cálculo de las características del combustible en la salida de los orificios de la tobera. No obstante, se ha detectado un menor volumen de combustible en fase vapor en las simulaciones transitorias, especialmente para pequeños levantamientos de aguja. Por otra parte, se ha comparado la tasa de inyección experimental con la tasa obtenida en OpenFOAM y AMESim. Dicha comparación ha permitido demostrar el gran potencial de AMESim y el buen comportamiento de OpenFOAM para predecir la tasa de inyección. / Martínez López, J. (2013). Estudio computacional de la influencia del levantamiento de aguja sobre el flujo interno y el fenómeno de la cavitación en toberas de inyección diésel [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/29291