<p>This study comprises experimental investigations and theoretical/empirical analyses of three forced-convective (pumped) boiling schemes: (i) confined round single jet and jet array impingement boiling, and flow boiling through conventional-sized (ii) concentric circular annuli and (iii) rectangular channels. These schemes could be utilized in the thermal management of various applications including high-heat-flux electronic devices, power devices, electric vehicle charging cables, avionics, future space vehicles, etc.</p>

This thesis evaluates two variants of Volumeof fluid method, namely Piecewise Linear Interface Construction (PLIC) and Multidimensional Tangent of Hyperbola for Interface Capturing (MTHINC) used in two-fluid simulations for interface tracking.Simulations of a single rising bubble in different conditions are performed aimed to assess the accuracy of the methods, and to check their convergence with grid size. The results show that both methods demonstrate convergence with mesh refinement, while PLIC captures the transient part of rising process of bubble more accurately than MTHINC in 2D case. / Denna avhandling utvärderar två varianter av metoden Volume of fluid för flerfas strömningar, nämligen Piecewise Linear Interface Construction (PLIC) och Multidimensional Tangent of Hyperbola for Interface Capturing (MTHINC) som används i tvåvätskesimuleringar för gränssnittsspårning.Simuleringar av en enda stigande bubbla under olika förhållanden utförs för att bedöma metodernas noggrannhet och för att kontrollera deras konvergens med gridsstorlek. Resultaten visar att båda metoderna visar konvergens med grid förfining, medan PLIC fångar den övergående delen av stigande bubbelprocess mer exakt än MTHINC i 2D-fall.

An Eulerian-Eulerian model for dilute gas-particle turbulent flows is developed for engineering applications. The aim is to understand the effect of particles on turbulent flows. The model is implemented in a finite element code which is used to perform numerical simulations. The feedback from the particles on the turbulence and the mean flow of the gas in a vertical channel flow is studied. In particular, the influence of the particle response time and particle volume fraction on the preferential concentration of the particles near the walls, caused by the turbophoretic effect is explored. The study shows that the particle feedback decreases the accumulation of particles on the walls. It is also found that even a low particle volume fraction can have a significant impact on the turbulence and the mean flow of the gas. A model for the particle fluctuating velocity in turbulent gas-particle flow is derived using a set of stochastic differential equations. Particle-particle collisions were taken into account. The model shows that the particle fluctuating velocity increases with increasing particle-particle collisions and that increasing particle response times decrease the fluctuating velocity. / QC 20101124

<p>This research demonstrates a method of data collection to analyse and compare flows of bicycle (with historic data) and pedestrian activity using automatic counters and manual counts in Santiago, Chile. An outstanding challenges facing planning for non-motorized transportation (bicycle and pedestrian) is the lack of consistent information on usage and demand of these modes. This is probably the single greatest impediment to being able to understand the behaviour of travelers using these modes. Further, without consistent and accurate information on demand and usage, it is difficult to measure the real benefits of public investments on health, travel time, and other relevant indicators, and to compare these modes to alternatives such as public transit or private automobile. For these reasons, this research aims to measure bicycle and pedestrian activity in specific points of Santiago-Chile. This study is divided into two sections: 1. Measuring bicycle activity in behaviour s of Antonio Varas Ave. and Simon Bolivar Ave. (Case study 1) and Pocuro Ave., Antonio Varas Ave. and Andrés Bello Ave. (Case study 2); and 2. Measuring bicycle and pedestrian activity in the Metropolitan Park of Santiago. This research is designed to (a) evaluate existing bicycle and pedestrian data sources, (b) conduct comprehensive counts of bicyclists and pedestrians using automatic and manual counting methods and (c) analyze the growth rate of bicycle users. This research presents materials developed including a literature review, research objectives, data collection methodology, results from the data collection effort, analysis, conclusions and future recommendations.</p> / Master of Science (MSc)

Nanoparticle-based technologies are an emerging field with the promise to impact a wide range of application areas. However, that potential is somewhat married to a host of research questions that remain to be answered. This work explores the surface modification of magnetic nanoparticles in a controlled fashion to produce hybrid nanoparticle (metal/polymer) systems with different morphologies, understand in-situ behavior of stimuli-responsive polymers grafted to a substrate, and obtain better computational methods for particle-tracking and -deposition. Nanoparticle surface modification was performed using ATRP, obtaining homo-, block-co-, and ‘twoaced/biphasic’ polymer structures on the nanoparticle surfaces. Biphasic Janus nanoparticles (JPs) were formed using a magnetic nanoparticle core and an innovative technique combining non-covalent solid protection with sequential controlled radical polymerization to form the two surface-grafted polymer phases. Surface-confined polymerizations were conducted using pH- and thermo-responsive materials. Poly(methacrylic acid) (PMAA) and a series of (aminoalkyl) methacrylate polymers were used as pH responsive polymers. Additionally, poly(N-isopropylacrylamide) (PNIPAM) was selected as the thermo-responsive material for this study. In-situ characterization techniques, including atomic force microscopy (AFM), dynamic light scattering (DLS), and ellipsometry, were used to evaluate the thermo- and pH-responsiveness of these stimuli responsive materials. A new general-oscillator (GENOSC) model was used to determine swelling ratio, thickness, and optical constant changes in the polymer brush as pH was changed in-situ. AFM was used to study morphological changes due to changes in pH and temperature. Nanoparticle temperature responsiveness was investigated using DLS. A related effort involved the use of computational fluid dynamic (CFD) methods to track (micron-sized) particles in certain geometries, including a human lung morphology. Predicted particle transport and deposition was compared to Lagrangian computational approaches and available experimental data. The Eulerian particle phase modeling method developed resulted in the accurate prediction of both near-wall particle tracking and wall deposition. This Eulerian-Eulerian model is a new tool that has potential for particle tracking in physiological morphologies. This combination of experimental and computational research has led to new nano- and micro-particle surface modification methods and particle transport modeling.

<p> Wireless communication has been thriving in recent years. Developments in the hardware and software industries enable more and more devices to be embedded in wireless communication modules. All kinds of interesting applications based on wireless connections are emerging, demanding simple and efficient ways to inter-connect different devices. Bluetooth is an industry standard initially proposed by Ericsson, IBM, Microsoft and some other leading IT companies to meet this growing demand. Initially, it intended to provide universal low cost, low power, and low complexity wireless interface to various devices. Furthermore, it also proposed to provide the possibility of interconnecting a number of mobile devices to form a network. However, the details of network formation and operation have not yet been regulated. In this work, we will investigate Bluetooth enabled network formation issues (especially when the traffic patterns on the network are well known).</p> <p> In this thesis, we use a small indoor area network model with a wired infrastructure network installed in the wall. A number of mobiles are distributed in the area and require inter-connectivity with each other and/or the outside world through multiple gateways. Unbalanced traffic in the network may result in hotspots leading to poor network throughput. Therefore, a centralized network formation algorithm is needed for Bluetooth networks to solve this problem.</p> <p> This thesis proposes novel Network Formation based on a Traffic Distribution (NFTD) mechanism. This centralized mechanism co-ordinates the behavior of mobiles and is implemented on gateways (also called access points). It forms the network topology according to the traffic distribution so that the path length of hotspot flows can be limited in order to maximize the network capacity. Last but not least, infrastructure networks provide free high-speed links for mobiles to further increase network capacity. The proposed mechanism is a promising mechanism as supported by simulation results.</p> / Thesis / Master of Applied Science (MASc)

Yes / Understanding the dynamic free surface of geophysical flows has the potential to enable direct inference of the flow properties based on measurements of the free surface. An important step is to understand the inherent response of free surfaces in depth-limited flows. Here a model is presented to demonstrate that free surface oscillatory spatial correlation patterns result from individual surface features oscillating vertically as they advect over space and time. Comparison with laboratory observations shows that these oscillating surface features can be unambiguously explained by simple harmonic motion, whereby the oscillation frequency is controlled by the root-mean-square water surface fluctuation, and to a lesser extent the surface tension. This demonstrates that the observed “complex” wave pattern can be simply described as an ensemble of spatially and temporally distributed oscillons. Similarities between the oscillon frequency and estimated frequency of near-bed bursting events suggest that oscillon behaviour is linked with the creation of coherent flow structures.

Unsteady flowfields are integral to high-speed applications, demanding precise modelling to characterize their unsteady features accurately. The simulation of unsteady supersonic and hypersonic flows is inherently computationally expensive, requiring a highly refined mesh to capture these unsteady effects. While anisotropic metric-based adaptive mesh refinement has proven effective in achieving accuracy with much less complexity, current algorithms are primarily tailored for steady flow fields. This thesis presents a novel approach to address the challenges of anisotropic grid adaptation of unsteady flows by leveraging a data-driven technique called Dynamic Mode Decomposition (DMD). DMD has proven to be a powerful tool to model complex nonlinear flows, given its links to the Koopman operator, and also its easy mathematical implementation. This research proposes the integration of DMD into the process of anisotropic grid adaptation to dynamically adjust the mesh in response to evolving flow features. The effectiveness of the proposed approach is demonstrated through numerical experiments on representative unsteady flow configurations, such as a cylinder in a subsonic flow and a cylinder in a supersonic channel flow. Results indicate that the incorporation of DMD enables an accurate representation of unsteady flow dynamics. Overall, this thesis contributes to making advances in the adaptation of unsteady flows. The novel framework proposed makes it computationally tractable to track the evolution of the main coherent features of the flowfield without losing out on accuracy by using a data-driven method. / Master of Science / Simulating unsteady, high-speed fluid flows around objects like aircraft and rockets poses a significant computational challenge. These flows exhibit rapidly evolving, intricate pattern structures that demand highly refined computational meshes to capture accurately. However, using a statically refined mesh for the entire simulation is computationally prohibitive. This research proposes a novel data-driven approach to enable efficient anisotropic mesh adaptation for such unsteady flow simulations. It leverages a technique called Dynamic Mode Decomposition (DMD) to model the dominant coherent structures and their evolution from snapshot flow field data. DMD has shown powerful capabilities in identifying the most energetic flow features and their time dynamics from numerical or experimental data. By integrating DMD into the anisotropic mesh adaptation process, the computational mesh can be dynamically refined anisotropically just in regions containing critical time-varying flow structures. The efficacy of this DMD-driven anisotropic adaptation framework is demonstrated in representative test cases - an unsteady subsonic flow over a circular cylinder and a supersonic channel flow over a cylinder. Results indicate that it enables accurate tracking and resolution of the key unsteady flow phenomena like vortex shedding using far fewer computational cells compared to static mesh simulations. In summary, this work makes anisotropic mesh adaptation computationally tractable for unsteady flow simulations by leveraging data-driven DMD modelling of the evolving coherent structures. The developed techniques pave the way for more accurate yet efficient unsteady CFD simulations.

In this dissertation, we examine whether the disposition effect, the tendency to sell winners and hold losers, exists among U.S. equity mutual funds and how the disposition effect influences fund performance and particularly flows. We find that a significant fraction (32%) of all funds exhibit some degree of disposition behavior. These funds underperform funds that are not disposition prone by 4-6% per year. Moreover, we find that the disposition effect has a significant impact on future fund flows. Without controlling for performance, disposition-prone funds experience 2-3% less flows each quarter than other funds. The difference in flows is probably due to poor performance of such funds. However, even after controlling for performance and other factors that potentially influence flows, funds with a high disposition effect experience 0.7-2% less flows than funds without such behavior. Past research has found that funds with low tax overhang garner larger inflows. Though disposition-prone funds are likely to have a lower tax overhang because they sell their winners quickly, we find that fund flows to disposition-prone funds are smaller than flows to non-disposition oriented funds after controlling for tax overhang. These results suggest that performance and tax efficiency as well as tax overhang are all important to mutual fund investors. / Ph. D.

The accurate and efficient numerical simulation of geophysical flows is of great interest in numerical weather prediction and climate modeling as well as in numerous critical areas and industries, such as agriculture, construction, tourism, transportation, weather-related disaster management, and sustainable energy technologies. Oceanic and atmospheric flows display an enormous range of temporal and spatial scales, from seconds to decades and from centimeters to thousands of kilometers, respectively. Scale interactions, both spatial and temporal, are the dominant feature of all aspects of general circulation models in geophysical fluid dynamics. In this thesis, to decrease the cost for these geophysical flow computations, several types of multiscale methods were systematically developed and tested for a variety of physical settings including barotropic and stratified wind-driven large scale ocean circulation models, decaying and forced two-dimensional turbulence simulations, as well as several benchmark incompressible flow problems in two and three dimensions. The new models proposed here are based on two classes of modern multiscale methods: (i) interpolation based approaches in the context of the multigrid/multiresolution methodologies, and (ii) deconvolution based spatial filtering approaches in the context of large eddy simulation techniques. In the first case, we developed a coarse-grid projection method that uses simple interpolation schemes to go between the two components of the problem, in which the solution algorithms have different levels of complexity. In the second case, the use of approximate deconvolution closure modeling strategies was implemented for large eddy simulations of large-scale turbulent geophysical flows. The numerical assessment of these approaches showed that both the coarse-grid projection and approximate deconvolution methods could represent viable tools for computing more realistic turbulent geophysical flows that provide significant increases in accuracy and computational efficiency over conventional methods. / Ph. D.