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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Fracture Geometry Modeling and Its Effects on Production Estimation in Shale

Luong, Linh 04 February 2016 (has links)
<p> With time naturally producing reservoirs are depleting and complex zones are explored. With new advancements in Shale gas exploration technology, the better understanding of the production from any reservoir is gained. This study is done to observe the impact of fracture geometry on production in a Shale formation using commercially available reservoir simulation software. From this, it helps to consider the reliability of simulation software. </p><p> Different scenarios of different fracture geometry were modeled for the Eagle Ford reservoir formation. Fracture geometry refers to the number of fractures in each fracture stage. The total fracture volume would be kept constant during the simulation. Production data with respect to time was analyzed and compared to real time field data. </p><p> Simulation results revealed that some of the simulation data could give a close result to actual well production and give reliable results. However, the number of fractures in each stage significantly impacts the oil flow rate as well as the cumulative oil production. The more fracture adding to each stage, the less oil production is expected. In the study, the difference in cumulative production between the least fractures in each stage, 1 fracture, and the most fractures in each stage, 6 fractures, is 400 percent. The models of 1 fracture and 2 fractures in each stage could give the closest result to the actual production; by studying more of these 2 models could give a better estimation for the field.</p>
2

Exploration of System-of-Systems Engineering (SOSE) fundamentals

Mudlapur Shivakumar, Ambika 06 May 2016 (has links)
<p> Systems-of-Systems (SoS) is a set or arrangement of component systems that results when independent and useful systems are interoperated into a larger system that delivers unique capabilities. This system comprises many component systems and when combined together as one they tend to produce far more advanced results than they did individually. Although Systems Engineering has long established its base and has acquired multiple feathers to its cap, System-of-Systems Engineering (SOSE) is still at an infant stage and yet constantly gaining value and attention. As the current theories and methodologies are very diversified and un-organized, this thesis is an attempt to provide a basic classification in the form of a literature review, developed based on extensive research of these varied opinions. Proposed approaches are suggested for future research to pursue the understanding of SOSE fundamentals </p>
3

Analysis of furrow irrigation uniformity as affected by furrow spacing.

Silva, Euzebio Medrado da. January 1990 (has links)
This research examines the effects of furrow spacing on irrigation uniformity and efficiency. Laboratory and field experiments were conducted to obtain information on soil physical characteristics, furrow infiltration and water advance data in order to validate the theoretical results. A furrow infiltration model based on Richards' equation and a finite element technique is developed and used to predict infiltrated depths in the transverse and longitudinal directions relative to the furrow centerline and furrow inlet, respectively. The model predicted measured furrow infiltration in the field from the third irrigation but failed to do so for the first and second irrigations. Simulations of furrow irrigation in a hypothetical soil with various furrow spacings showed that cumulative infiltration is not affected by furrow spacing until the lateral wetting front reaches the imaginary vertical boundary located midway between two furrows. An analysis of uniformity and efficiency from predicted water distribution profiles from field irrigated furrows are conclusive in that the use of longitudinal water distribution profile alone is not enough to assess the performance of furrow irrigation. The transverse distribution of infiltrated depths which is a function of furrow spacing must be included in the analysis.
4

Early evolution of coal nitrogen in opposed flow combustion configurations.

Ghani, Muhammad Usman. January 1990 (has links)
A laminar opposed flow, pulverized coal combustion configuration was used to explore the early evolution of light gaseous nitrogenous and hydrocarbon species into the bulk gas phase. Two coals of different ranks were considered. Effects of pyrolysis environment, particle size and heating rates were investigated. Concentration profiles of HCN, NH₃, NO, CH₄, C₂H₂, C₂H₄ and C₂H₆ were measured, under both oxidizing and reducing environments, for three particle sizes, and at high heating rates provided by the hot flue gases of a CO/O₂/Ar flame. Net rates of formation into the bulk gas phase were calculated from the experimental data after correcting for diffusion and convection effects, and were then related to particle time-temperature histories. Experimental data show that HCN precedes NH₃ and NO for both coals. It is the first light gaseous product of coal nitrogen evolution entering into the bulk gas phase. For low rank coals, either only a small amount of tar nitrogen is released or its subsequent oxidation to light gaseous products is slow. For high rank coals secondary reactions of tars are rapid and lead to substantial levels of nitrogenous species. Nature of nitrogenous species evolving into the bulk gas phase was found to be independent of particle size. Lower heating rates favor increased yields of ammonia. Evolution of hydrocarbon species from high rank coals occurs via low molecular weight species, whereas low rank coals yield high molecular weight species. Evolution of hydrocarbon species was found to be independent of particle size and heating rates. Evolution of hydrogen occurs during late stages of devolatilization indicating that it is a product of secondary pyrolysis reactions. A simple kinetic model is proposed to relate rates of formation of nitrogenous species to coal devolatilization kinetics. The latter are similar for three experiments, with fine particles, involving two coals and can be described by a single rate constant given by 63.8 exp (-5220/RT). Bituminous coal (fines), under oxidizing conditions, shows substantially higher rates, possibly due to energy feedback mechanisms in the vicinity of the particles. Literature values, which originated from solid phase measurements, underpredict the quantities of total XN entering the post flame zone by substantial amounts. Our value, which was derived from gas phase species measurements, yields a better prediction of total nitrogenous species entering the post flame zone, and can be incorporated in engineering models aiming at optimizing of pollutant emissions.
5

Effects of Qualitative Factor and Weight Assignment In Multi-criteria Inventory Ranking Method

K. C., Manish 18 February 2016 (has links)
<p> This research explores two main problems encountered in multi-criterion inventory classification and ranking. The first problem is the integration of quantitative criteria with qualitative criteria. Most of the research in the field of multi-criterion inventory classification and ranking neglects qualitative criteria, as they are difficult to apply as compared with quantitative criteria. Even for the research that considers qualitative criteria for classification and ranking, the sensitivity of the qualitative criterion has not been explored. The second problem is the weight assignment to the criteria, both qualitative and quantitative, when integrated for classification and ranking of inventory items. Weight assigned to the criteria should represent relative importance of one criterion to another. Input of inventory managers are needed in assigning the weights. </p><p> An integrated inventory ranking and classification method is developed using the Analytic Hierarchy Process (AHP) and The Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method to rank and classify inventory items using quantitative and qualitative criteria. Classification and ranking of inventory items are industry-specific and differ from one industry to another. Classification and ranking can differ significantly between industries of the same type. Even the same type of industry can have a different philosophy and objective of inventory management, which influences the relative importance of the criteria and affects the classification and ranking. Classification and ranking are sensitive to the settings of the qualitative factor. Industries that gave higher priority to qualitative factors are affected more by change in the qualitative criterion's settings, as classification and ranking changes the most for them. Ranking is very sensitive and complex, as small change in any parameter is enough to change the rank without affecting the classification.</p>
6

Investigating Biosynthetic Steps of an Angucycline Antifungal

Gladstone, S. Gabrielle 01 January 2016 (has links)
From the bacterium Streptomyces sp. SCC-2136 (ATCC 55186), two angucycline natural products are produced, designated Sch 47554 and Sch 47555. These compounds are produced through a type II polyketide biosynthetic pathway. The early biosynthetic steps to these molecules were confirmed. These include the minimal polyketide synthase (PKS), the C-9 ketoreductase, the first-ring aromatase, the subsequent ring cyclase, and two oxy-genases. Also confirmed were the biosynthetic genes responsible for production of the first amicetose moiety, as well as the glycosyltransferase that creates a C-glycosidic bond between the angucyclic scaffold and the amicetose moiety. In confirming these pathways, two new natural products were produced: GG31, an amitosylated rabelomycin, and GG53, rabelomycin hydroxylated at C-12b. Future work will be to understand the late biosynthetic steps and generate new angucyclines through combinatorial biosynthesis.
7

Numerical investigation of laminar-turbulent transition in a flat-plate wake.

Dratler, David Ira. January 1990 (has links)
Laminar-turbulent transition of high-deficit flat plate wakes is investigated by direct numerical simulations using the complete Naver-Stokes equations. The simulations are based on a spatial model so that both the base flow and the disturbance flow can develop in the downstream direction. The Navier-Stokes equations are used in a vorticity-velocity form and are solved using a combination of finite-difference and spectral approximations. Fourier series are used in the spanwise direction. Second-order finite-differences are used to approximate the spatial derivatives in the streamwise and transverse directions. For the temporal discretization, a combination of ADI, Crank-Nicolson, and Adams-Bashforth methods is employed. The discretized velocity equations are solved using fast Helmholtz solvers. Code validation is accomplished by comparison of the numerical results to both linear stability theory and to experiments. Calculations of two- and/or three-dimensional sinuous mode disturbances in the wake of a flat plate are undertaken. For calculations of two-dimensional disturbances, the wake is forced at an amplitude level so that nonlinear disturbance development may be observed. In addition, the forcing amplitude is varied in order to determine its effect on the disturbance behavior. To investigate the onset of three-dimensionality, the wake is forced with a small-amplitude three-dimensional disturbance and a larger amplitude two-dimensional disturbance. The two-dimensional forcing amplitude is varied in order to determine its influence on the three-dimensional flow field. Two-dimensional disturbances are observed to grow exponentially at small amplitude levels. At higher amplitude levels, nonlinear effects become important and the disturbances saturate. The saturation of the fundamental disturbance appears to be related to the stability characteristics of the mean flow. Larger forcing amplitudes result in the earlier onset of nonlinear effects and saturation. At large amplitude levels, a Karman vortex street pattern develops. When the wake is forced with both two- and three-dimensional disturbances, strong interactions between these disturbances is observed. The saturation of the two-dimensional disturbance causes the three-dimensional disturbance to saturate. However, this is followed by a resumption of strong three-dimensional growth that may be due to a secondary instability mechanism. Larger two-dimensional forcing amplitudes accelerate the saturation of the two-dimensional and three-dimensional disturbances as well as accelerate the resumption of strong three-dimensional growth. These interactions also result in complicated distributions of vorticity and in a significant increase in the wake width.
8

A transient heat probe sensor for measuring transpiration in the stem of woody plants.

Gomide, Reinaldo Lucio. January 1990 (has links)
A compact portable electronic system has been developed for measurement of sap flow through the xylem in the stem of woody plants. This system utilizes a single heated thermistor probe which is alternately and automatically switched between a constant (heating phase) and a variable (cooling phase) temperature mode of operation. Experiments reported here have been carried out in two distinct porous medium, packed bands and the stem of several apple trees. The system performance was tested to detect the variations in flow rate. In both mediums, results indicated that the single heated thermistor is able to work as flowmeter since its transient thermal response was affected by the local fluid flow. The natural logarithm of the fractional response of the thermistor probe indicated that the system can not be analysed as a first order model. Non-linear regression analysis showed that the relationship between the probe sensor temperature response and the time elapsed from the beginning of cooling phase is adequately fitted by an additive exponential model. A dimensionless heat transfer analysis, applied to the thermistor probe, is outlined. Problems encountered in the transient heat transfer analysis are reported.
9

A dynamic thermal model of a self-sustaining closed environment life support system.

Luttmann-Valencia, Francisco. January 1990 (has links)
A dynamic, thermal model of a Selfsustaining Closed Environment Life Support System (SCELSS), a closed system designed to extend the range of human habitat to extreme climatic zones on Earth and Near Space, is developed and used to simulate the thermal behaviour of a SCELSS located on the surface of the Earth. The resulting heat loads on the air conditioning unit for a given control strategy and two different SCELSS configurations are studied. The SCELSS is represented by thermal models of the biome, the physical structure encompassing the cover, air and vegetation, the ground, and an optional body of water, and by the model of an air handling unit, encompassing a fan, coils and a control to track prescribed biome air temperature and relative humidity set points. A modular approach is used in developing the model to allow for future expansion to include biological aspects in the representation of the SCELSS. The structure of the models in conformed to the formalism of the computer simulation program TRNSYS. A test for isothermality is used to verify the mathematical and thermodynamic behaviour of the model. Simulations with the model show that a large fraction of the solar input is converted into moisture transferred to the biome air, which has to be dehumidified in the air conditioning unit coils to maintain livable conditions inside, making substantial reheat of the air necessary. The inclusion of a pond in the SCELSS configuration proves to modify the normal path of heat through the biome substantially, reducing peak and total air conditioning loads.
10

Analysis and optimal design of a resonant switching converter for space applications.

Quintero, Francisco Javier. January 1990 (has links)
The design of converters for space applications is subject to a number of unusual constraints, such as low volume and weight, high efficiency operation, minimum components stress, low noise interference and resistance to ionizing radiation. The diode clamped series resonant converter (DCSRC) can be designed to satisfy some of the design constraints. A new approach in the analysis of the DCSRC, and a systematic way of designing for high efficiency and minimum component stress is presented. The direct relationship between the phase plane and the resonant wave shapes allows us to synthesize the closed-form solution and generate the output plane, which relates the normalized output current to the normalized output voltage for any load and any ratio of switching to resonant frequencies. The converter operation is optimized by superimposing the functions that describe the transistor stress and resonant tank component stress on the output plane. Experimental results are in good agreement with both the mathematical model and simulation. The effects of ionizing radiation on the converter performance under simulated space radiation conditions is also investigated.

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