A helicopter rotor in descent flight encounters its own wake, resulting in a doughnut-shaped ring around the rotor disk, known as the Vortex Ring State (VRS). Flight in VRS condition can be dangerous as it may cause uncommanded drop in descent rate, loss of control effectiveness, power settling, excessive thrust and torque fluctuations, and vibration. As simple momentum theory is no longer valid for a rotor in VRS, modeling of rotor inflow in VRS continues to challenge researchers, especially for flight simulation applications. In this dissertation, a simplified inflow model, called the ring vortex model, is developed for a helicopter rotor operating in descent condition. By creating a series of vortex rings near the rotor disk, the ring vortex model addresses the strong flow interaction between the rotor wake and the surrounding airflow in descent flight. In addition, the total mass flow parameter in the existing inflow models is augmented to create a steady state transition between the helicopter and the windmill branches. With the ring vortex model, rotor inflow can now be adequately predicted over a wide range of descent rates. Validations of the ring vortex model for helicopter rotors are conducted extensively in axial and inclined descent. Effects from blade taper, blade twist, and rotor thrust are also investigated with further application of the finite-state inflow model. The ring vortex model is applied to a single main-rotor helicopter. The main effort is to establish VRS boundary based on heave stability criterion. In addition, two important phenomena observed in the descent flight tests are addressed in the dynamic simulation, including uncommanded drop in descent rate and loss of collective control effectiveness. The ring vortex model is further applied to a side-by-side rotor configuration. Lateral thrust asymmetry on the side-by-side rotor configuration can be reproduced through uneven distribution of vortex rings at the two rotors. Two important issues are investigated, including the impact of vortex rings on lateral thrust deficit and on lateral AFCS limit.

This work provides a semi-analytical development of the pressure-mobility behavior of solution gas-drive reservoir systems producing below the bubble point pressure. Our primary result is the "characteristic" relation which relates normalized (or dimensionless) pressure and mobility functions. This formulation is proven with an exhaustive numerical simulation study consisting of over 900 different cases. We considered 9 different pressure-volume-temperature (PVT) sets, and 13 different relative permeability cases in the simulation study. We also utilized 7 different depletion scenarios. The secondary purpose of this work was to develop a correlation of the "characteristic parameter" as a function of rock and fluid properties evaluated at initial reservoir conditions such as: API density, GOR, formation volume factor, viscosity, reservoir pressure, reservoir temperature, oil saturation, relative permeability end points, corey exponents and oil mobility: We did successfully correlate the characteristic parameter as a function of these variables, which proves that we can uniquely represent the pressure-mobility path during depletion with specific reservoir and fluid property variables, taken as constant values for a particular case. The functional form of our correlation along with all relevant equations are shown on the body of this document.

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The purpose of this study is to assess the dewatering requirements of planned open pit nickel mining at &Ccedil / aldag Site in Western Turkey. Dewatering is required for safe and efficient working conditions and pit wall stability. With this scope, a groundwater model of the study area is developed and used to predict the dewatering rate. The methodology mainly involves data collection, site hydrogeologic characterization and development of conceptual model, followed by construction and use of a groundwater model to predict the dewatering requirements of the mine site. The groundwater flow modeling is carried out using MODFLOW software and the dewatering simulations are carried out using MODFLOW Drain package. The drain cell configuration is determined by pit boundaries and invert elevations of drains corresponded to the bench elevations that will be achieved with respect to the mining schedule. In the transient model runs, monthly time steps were used. Using the outflow from in-pit drain cells, the v monthly dewatering rates are calculated. In order to assess the impacts of the hydraulic conductivity of the laterite on the pit inflow rates, simulations were carried out for different values of hydraulic conductivity of laterites. The predicted flow rate using the calibrated model is 107.54 L/s. A tenfold reduction in the hydraulic conductivity of laterite resulted in three fourths of decrease in the flow rate (24.42 L/s). Consequently, a wide range of flow rates for different hydraulic conductivity values of laterite was calculated. In order to confirm the hydraulic conductivity of laterites in the area, and to obtain a realistic dewatering rate, further pumping tests are needed.

Fourier-based stochastic simulation of wind fields commonly used in wind turbine loads computations is unable to account for contrasting states of atmospheric stability. Flow fields in the stable boundary layer (SBL), for instance, have characteristics such as enhanced wind shear and veering wind direction profiles; the influence of such characteristics on utility-scale wind turbine loads has not been studied. To investigate these influences, we use large-eddy simulation (LES) to generate inflow wind fields and to estimate load statistics for a 5-MW wind turbine model. In the first part of this thesis, we describe a procedure employing LES to generate SBL wind fields for wind turbine load computations. In addition, we study how large-scale atmospheric conditions affect the characteristics of wind fields and turbine loads. Next, in the second part, we study the contrasting characteristics of LES-SBL and stochastic NBL flow fields and their influences on wind turbine load statistics by isolating effects of the mean wind (shear) profile and of variation in wind direction and turbulence levels over the rotor sept area. Among large-scale atmospheric conditions, the geostrophic wind speed and surface cooling rate have the greatest influence on flow field characteristics and, thus, on wind turbine loads. Higher geostrophic winds lead to increased mean and standard deviation values of the longitudinal wind speed at hub height. Increased surface cooling rates lead to steeper shear profiles and appear to also increase fatigue damage associated with out-of-plane blade root moments. In summary, our studies suggest that LES may be effectively used to model wind fields in the SBL, to study characteristics of turbine-scale wind fields, and to assess turbine loads for conditions that are not typically examined in design standards. / text

In 2011, Texas experienced the worst drought in recorded history. This has escalated concerns regarding environmental flows needed to sustain freshwater and estuarine systems as human needs are addressed during drought periods. In this thesis, I analyze fish assemblages and water quality variables in order to observe the effects of drought in the lower Neches River below the saltwater barrier located upstream from Beaumont, Texas. Fish and water quality samples were taken during drought conditions during fall 2011 and summer 2012, after a season of rain. During fall 2011, sites surveyed above the barrier had lower salinity but similarly low dissolved oxygen (DO) levels compared with sites surveyed below the barrier. Salinity levels during fall 2011 were relatively high (reaching up to 15 ppt), whereas salinity during summer 2012 never rose above 1.5 ppt. For gillnet samples obtained during fall 2011, fish species richness was higher in December following a series of rain events than during drought conditions in October and November. Although fish species richness was similar between fall 2011 and summer 2012, species composition varied greatly. For seine samples obtained during summer 2012, species richness was higher during May and July (when the barrier was open) than during June and August (when the barrier was closed). Species richness was lowest for sites in closest proximity to a paper mill effluent discharge pipe located below the barrier. Also, species richness was higher at sites above the barrier than at sites below the barrier regardless of whether or not the barrier was closed. Multivariate statistical analyses of gillnet samples revealed a large amount of compositional overlap among fish assemblages, regardless of time period and location; however, analyses of seine samples revealed that fish assemblages above the barrier were different than those from samples obtained below the barrier and that fish assemblages varied based on time period. Results indicate that, during periods of low flow, water quality deteriorates in the Lower Neches River below the saltwater barrier. During these periods of environmental degradation, fish assemblages have reduced diversity and sensitive freshwater species decline in abundance, with some absent from survey samples.

This dissertation comprises theoretical and empirical models to manage watersupply risk in irrigated agriculture. While irrigation is by itself a strategy to regulate thesupply of water for farm use, water systems that depend on surface water sources are stillsubject to the random inflows that feed their reservoirs. Depending on the size of thereservoir, the demand for irrigation, and the seasonal distribution of inflows, wateravailability may decrease to levels that severely constraint agricultural production. Thisdissertation begins with a theoretical examination of on-farm cropping decisions underwater endowment risk. However, the analysis is extended to the use of a risk-sharinginnovation to transfer the water availability risk outside an irrigation district. Specifically,the design, use, and economic feasibility of an inflow-based derivative are studied for theRio Mayo irrigation district, located in Northwestern Mexico.On the theoretical front, the analysis consists of modeling the on-farm economicsof hedging against uncertain irrigation endowments. The basic model starts by analyzingthe role of crop diversification. As expected, the firm responds to higher degrees of risk,as measured by the variance in the supply of water, by allocating less land towards thewater-intensive crops. The underlying motivation in these strategies is the need to avoidthe relatively larger reductions in productivity sustained by water-intensive cropportfolios. However, crop diversification comes at the cost of reduced profits. As analterative to crop diversification, the model is modified to study the role of an institutionthat transfers water contingent on the states of nature. The extension shows that, undercertain conditions, enrolling in such a scheme produces the same profit as undercertainty.In the empirical component of the dissertation, the economics of an inflow-basedderivative are examined. The modeling strategy consists of simulating the economicenvironment and hydrological profile of the Adolfo Ruiz Cortinez Reservoir on the RioMayo irrigation district. Specifically, a stochastic dynamic simulation model is developedthat captures the intra and inter seasonal risk aspects associated with water risk and wateruse for irrigated agriculture. The results indicate that the inflow-based derivative is aviable instrument in the terms of affordability (i.e. premiums) and yield effective incomeprotection (i.e. risk reduction).

Este trabalho tem como objetivo analisar a estrutura do desemprego dos jovens no Brasil, procurando identificar os motivos da taxa de desemprego dos jovens ser muito superior à dos adultos. Apesar de sua importância, este tema tem recebido pouca atenção na literatura sobre o mercado de trabalho brasileiro. Na primeira análise deste estudo, decompõe-se a taxa de desemprego em dois determinantes, duração média e taxa de entrada no desemprego de jovens, adultos e idosos; percebe-se que a duração do desemprego é praticamente a mesma para as três categorias, enquanto a taxa de entrada dos jovens é maior que a das outras duas, sendo, portanto, o determinante que faz com que o desemprego juvenil seja mais elevado que o de trabalhadores mais velhos; assim, com uma nova decomposição da taxa de entrada de jovens, verifica-se que cerca de 80% dessa taxa é composta de jovens que já trabalharam. Outro método será o cálculo, para jovens e adultos, das matrizes de transição entre os estados do mercado de trabalho. Para avaliar a questão do desemprego dos jovens no Brasil, recalcula-se as taxas de desemprego de cada categoria, substituindo uma de cada vez nas matrizes, as probabilidades de transição da outra categoria; os resultados mostram a alta rotatividade dos jovens no mercado de trabalho. Com esses resultados, conclui-se que a causa do alto desemprego dos jovens não está na dificuldade em conseguir o primeiro emprego. / This work has the purpose to analyze the youth unemployment structure in Brazil, trying to identify the reasons for the youth unemployment rate being so superior relative to the unemployment of adults. Despite its importance, this subject has received less attention in the Brazilian labor market literature. In the first analysis of this work, the unemployment rate will be decomposed into two determinants, mean duration and inflow rate for young, adult and old people; it is noticed that the unemployment duration is practically the same for the three categories, but the youth inflow rate is relatively higher than the other two ones, being so, the determinant that makes youth unemployment be higher than unemployment of older workers; and, with a new decomposition of youth inflow rate, it is verified that about 80% of this rate is composed of young people that have already worked. Another method will be the calculus, for young and adult people, of the transition matrices between labor market states. To evaluate where is the problem of Brazilian youth unemployment, it is recalculated these rates for each one of the categories, substituting one at a time in the matrices, the transition probabilities of the other category; results show the high turnover of the category in labor market. With these results, it is concluded that the reason of the high youth unemployment is not the difficulty of finding the first job.

In this degree thesis, the research team analyses different ways of monitoring water flow in wastewater channels finds an effective way of processing data using machine learning on collected data from a specific area and sets up a system for finding correlations between rain levels, water usages and wastewater flow to detect infiltrations and inflow water in wastewater channels. The study concludes that a sensor network is most suited for monitoring wastewater channels and that machine learning could be used to detect infiltration and inflow water using different types of data.

<p>A three-dimensional computational fluid dynamics (CFD) model has been developed to simulate the distribution of automobile emissions on and near a highway. A variety of k-ε turbulence models were adopted to simulate the turbulence flow, and a non-reaction species model was coupled to simulate the dispersion of emissions. The models were first validated by comparing velocity profiles and normalized emission concentration with wind tunnel experiments, and good agreement was observed. Next, further simulation and analysis revealed that T-shaped noise barriers could reduce more emissions concentration in downstream areas than rectangular noise barriers; however, the noise barrier shape effects on the dispersion of emissions were also influenced by inflow conditions. Thirdly, the traffic flow conditions on the highway made a difference to the dispersion of emissions. Automobile wakes not only existed behind vehicles but also induced turbulence on adjacent lanes, causing more emissions on the highway. Low traffic speed, such as congestion, would result in more emissions remaining on the highway as well. At last, vehicle body shapes modified the flow patterns by their slant angles and heights. Vehicles with slant angles on both front and rear sides had the least concentration of emissions at the center of the highway.</p>