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Liquid droplet breakup and dynamics is a phenomena of immense practical importance in a wide variety of applications in science and engineering. Albeit, researchers have been studying this problem for over six decades, the fundamental physics governing droplet deformation and fragmentation is still unknown, not to mention the formulation and development of generalized correlations to predict droplet dynamics. The presence of disparate length and time scales, along with the complex unsteady physics, makes this a formidable problem, theoretically, experimentally and computationally. One of the important applications of interest and the motivation for the current research is a liquid fueled propulsion device, such as diesel, gas turbine or rocket engine. Droplet vaporization and ensuing combustion is accelerated if the droplet size is smaller, which makes any process leading to a reduction in drop size of prime importance in the combustion system design. This thesis is an attempt to address several unanswered questions currently confronting the spray community. Unanswered questions include identification and prediction of breakup modes at varying operating conditions, quantitative description of fundamental processes underlying droplet breakup and generalized correlations for child droplet size distributions and drag coefficient associated with the deformation and fragmentation of Newtonian and non-Newtonian fluids. The present work is aimed at answering the above questions by investigating the detailed flowfield and structure dynamics of liquid droplet breakup process and extracting essential physics governing this complex multiphase phenomena. High-fidelity direct numerical simulations are conducted using a volume-of-fluid (VOF) interface capturing methodology. To isolate the hydrodynamic mechanisms dictating droplet breakup phenomena, evaporation and compressibility are neglected, and numerical studies are performed for incompressible fluids at isothermal conditions. For Newtonian fluids, four different mechanisms are identified- oscillatory, bag, multimode and shear breakup modes. Various events during the deformation and fragmentation process are quantitatively identified and correlations are developed to predict the breakup mechanisms and droplet size distributions for a broad range of operating conditions. It was found that for We > 300 and Oh < 0.1 for rho_l/rho_g = 8.29, the child droplet size distributions can be modeled by a log-normal distribution. A correlation to predict the sauter mean diameter, d32, is also developed, given by d32 / D = 8We^-0.72 / Cd. Temporal evolution of momentum balance and droplet structure are also used to calculate the drag coefficient at each time step from first principles. Results show that the drag coefficient first increases to a maximum as the droplet frontal area increases and then decreases at the initiation of breakup. The drag coefficient reaches a steady value at the end of droplet lifetime, corresponding to the momentum retained by the droplet. A correlation to predict the time-mean drag coefficient given by, Cd / Cd,0 = 2We-^0.175, is developed, which indicates that the time averaged drag coefficient decreases with Weber number. The motivation to study non-Newtonian liquid droplet breakup stems from the various advantages gelled propellants offer as compared to traditional liquid or solid propellants in combustion systems, particularly in rocket engines. It was found that the breakup behavior of pseudoplastic, non-Newtonian liquids is drastically different as compared to Newtonian droplets. Several flow features commonly exhibited by non-Newtonian fluids are observed during the breakup process. The breakup initiates with the formation of beads-in-a-string due to the non-Newtonian nature of the fluid under consideration. This is followed by rapid rotation of the droplet with the appearance of helical instability and liquid budges, which forms the sites for primary and satellite droplet shedding. Child droplet size distribution are also examined and it is found that a Gaussian curve universally characterizes the droplets produced during non-Newtonian droplet breakup process. To put all things in perspective, the objectives of the thesis were two folds: (1) elucidate breakup physics for Newtonian and non-Newtonian liquid droplet deformation and breakup, and (2) develop correlations which can be used in an Eulerian-Lagrangian framework to study large-scale engineering problems. It is hoped that this research contributed to droplet breakup and dynamics literature by providing a more thorough and quantitative understanding of the breakup phenomena of liquid droplets and furnished models which can be used in future research endeavors.

This thesis investigates the orbital debris evolution in the geosynchronous disposal orbit regime and within geosynchronous orbits effected by the geopotential wells. A propagator is developed for the accurate simulation of GEO specific orbits and the required perturbations are determined and described. Collisions are then simulated in the selected regimes using a low velocity breakup model derived from the NASA EVOLVE breakup model. The simulations described in this thesis consider a set of perturbations including the geopotential, solar and lunar gravity, and solar radiation pressure forces. This thesis is based on a prior paper and additionally seeks to address an issue in simulating East-West trapped objects. The results show that this propagator successfully simulates the presence of all wells and the East-West entrapment, and the required perturbations are outlined. Five collision test cases were simulated, one for each type of entrapment and an additional for the disposal orbit.

Severe accident studies have become important for understanding the environmental impact of nuclear power following the Three Mile Island (TMI) accident. Severe accident phenomena are interdisciplinary since they can include the interaction of molten corium with reactor structures and water, and the transport and release of fission products that carry vapors and aerosols. During an accident, molten corium may fall in the form of a jet into a water pool. The fragmentation of the corium jet is a critical process concerning Fuel-Coolant Interactions (FCI). A steam explosion could occur depending on jet fragmentation and dispersion in the water. A 2-D in-house CFD MATLAB script has been developed by employing the Volume of Fluid Method (VOF) to simulate jet fragmentation in a water pool. This research is the first study to use the Multidimensional Universal Limiter for Explicit Solution (MULES) algorithm to capture the interface behavior in the jet breakup process. The effect of the compression constant, the mesh sensitivity, and the face correction loop on the MULES are investigated in this thesis. Moreover, the effects of the jet inlet velocity and jet diameter on the jet breakup length are numerically studied using the newly developed code. The simulation results compared well with the experimental results and another numerical study found in the literature. / Master of Science / After the TMI accident, many countries have started experimental and numerical studies to investigate and predict the accident's possible outcomes. During a severe accident, the molten corium may drop into a water pool in the form of a jet. The jet contacts the water, fragments into droplets and disperses in the pool, which could then cause a steam explosion. A possible molten corium-water interaction is simulated using a 2-D in-house CFD code written in MATLAB in this study. Interface tracking is one of the most critical processes in multi-phase flow simulation, and the MULES algorithm is used to capture the interface in this study. It is the first study to use the MULES algorithm to investigate jet breakup behavior. The simulation results compared well with experimental data and other numerical studies.

Os principais mecanismos da reação supracitada foram examinados: breakup, transferência, fusão completa e incompleta e excitação inelástica. / The mains mechanisms of the mencioned reaction were study, namely: breakup, fusion (complete and incomplete), transfer and inelastic excitation.

Os principais mecanismos da reação supracitada foram examinados: breakup, transferência, fusão completa e incompleta e excitação inelástica. / The mains mechanisms of the mencioned reaction were study, namely: breakup, fusion (complete and incomplete), transfer and inelastic excitation.

Ending a relationship is a common and often difficult experience for adolescents and young adults who are dating (Furman & Wehner, 1997). Yet, little is known about how romantic relationships deteriorate prior to breakup (Carver, Joyner, & Udry, 2003; Duck, 1981). The main goal of this study is to develop a definition of relationship deterioration that delineates the process of deterioration, by specifying a beginning and end point of deterioration and identifying characteristics that distinguish deterioration from breakup. Data for this study comes from the University of Texas Tracing Relationships and Commitment study (UT-TRAC), which contains 464 participants (232 heterosexual couples) who graphed changes in commitment over a 9-month period providing reasons describing each change. Deterioration, as defined as declines in commitment, was described by both partners in a romantic dyad in 90 couples whereas 75 individuals described deterioration and their romantic partner did not. A coding manual was created and pilot-tested to measure frequency and intensity of the four characteristics of deterioration in participant’s descriptions of changes in commitment. The current investigation used multi-level modeling separately for couples experiencing deterioration (to control for the dyadic nature of the data) and individuals whose partner did not report declines in commitment. Survival analyses using logistic regressions (Singer & Willett, 2003) were applied to measure how the characteristics of deterioration could predict breakup. Results of the analyses revealed that participants who experienced a breakup were more likely to report relationship deterioration, particularly for couples where both individuals described deterioration. Hierarchical linear models revealed that more frequent amounts of the deterioration characteristics was associated with deterioration as compared to pre-deterioration. However, intensity of the characteristics was not significant in differentiating between deterioration and pre-deterioration. In comparing deterioration with breakup, frequency of the deterioration characteristics predicted breakup only in descriptions of alternative partners, whereas intensity of the all four deterioration characteristics predicted breakup ranging from 37% (more intense scores of relational uncertainty) to 74% (more intense scores of alternative partners for an individual’s partner). Implications of this study will be in terms of commitment theory in order to further understand relationship processes. / text

This study focuses on the design and development of a new spray applicator design utilizing effects of imposed pressure oscillations in conjunction with cavitation collapse energy to create distribution of fine droplets. An oscillating horn placed inside the nozzle performing high frequency oscillations is envisioned to provide the necessary pressure perturbations on the exiting liquid jet, while the nozzle geometry design in configured to amplify cavitation process. Initially, a two-zone approach modeling the nozzle interior and exterior in a separate fashion and later, a coupled strategy is proposed. Parametric studies describing the effect of horn stroke length, frequency, its position inside the nozzle in combination with different nozzle designs and liquid flow rates are explored to identify their contribution in obtaining desired cavitation characteristics. In this regard, incorporation of a backward facing step profile within the nozzle shows strong capability of generating the required cavitation and flow field distribution at the nozzle exit. The velocity modulations occuring at the nozzle exit due to oscillating horn structure result in a wide gamut of liquid structures specific to the imposed oscillation frequency and modulation amplitude. The disintegration characteristics of these modulated liquid jets are studied using a Volume-of-Fluid (VOF) interface capturing approach based on finite volume methodology employing an interface compression scheme. VOF methods are validated against experimental results and then subsequently used to study scaling parameters governing the modulated liquid jets. To perform coupled interior-exterior nozzle computations with cavitation, two new cavitation models are presented: First, a model based on Homogeneous Equilibrium assumptions for tracking cavitation events in a compressible framework is presented. Owing to its inability to simulate incompressible cavitating flows, a new cavitation event tracking model based on a Cavitation-Induced-Momentum-Defect (CIMD) correction approach is formulated utilizing a scalar transport model for vapor volume fraction with relevant transport, diffusion and source terms. Validations of both the models against experimental observations are detailed. Coupled internal-external liquid flow computations from the proposed atomizer design using a VOF-CIMD strategy shows strong potential for rapid drop formation in the presence of cavitation effects. A prototype model of a new spray applicator design is presented.

Applying Relational Goal Pursuit Theory (RGT), the present study examined the motivations for obsessive relational intrusion (ORI). Participants (n = 509) were randomly assigned to conditions that 1) primed relational or retaliatory goals, then 2) exposed to a negative romantic relationship vignette (relationship disappointment vs. explicit rejection vs. “nice” rejection), and 3) then were either induced to ruminate about the vignette events or were not. Participants reported how likely they would be to think about pursuit (e.g., frequent calls) and aggressive (e.g., threats) ORI. Contrary to expectations, rejection elicited less ORI than the relationship disappointment condition. However, it was found that 1) the ORI scale broke into a threeactor, instead of twoactor, model of pursuit, aggressive, and surveillance behavior, and 2) that motivations for each type varied. Relational goals predicted pursuit. Retaliation predicted aggression. Motives for surveillance behaviors were linked to both desires for revenge and reconciliation.