There has been, and will continue to be, tremendous growth in the use and distribution of liquefied natural gas (LNG). As LNG poses the hazard of flammable vapor cloud formation from a release, which may result in a massive fire, increased public concerns have been expressed regarding the safety of this fuel. In addition, regulatory authorities in the U.S. as well as all over the world expect the implementation of consequence mitigation measures for LNG spills. For the effective and safer use any safety measure to prevent and mitigate an accidental release of LNG, it is critical to understand thoroughly the action mechanisms. Water spray curtains are generally used by petro-chemical industries to prevent and mitigate heavier-than-air toxic or flammable vapors. It is also used to cool and protect equipment from heat radiation of fuel fires. Currently, water spray curtains are recognized as one of the economic and promising techniques to enhance the dispersion of the LNG vapor cloud formed from a spill. Usually, water curtains are considered to absorb, dilute, disperse and warm a heavier-than-air vapor cloud. Dispersion of cryogenic LNG vapor behaves differently from other dense gases because of low molecular weight and extremely low temperature. So the interaction between water curtain and LNG vapor is different than other heavier vapor clouds. Only two major experimental investigations with water curtains in dispersing LNG vapor clouds were undertaken during the 1970s and 1980s. Studies showed that water spray curtains enhanced LNG vapor dispersion from small spills. However, the dominant phenomena to apply the water curtain most effectively in controlling LNG vapor were not clearly demonstrated. The main objective of this research is to investigate the effectiveness of water spray curtains in controlling the LNG vapor clouds from outdoor experiments. A research methodology has been developed to study the dispersion phenomena of LNG vapor by the action of different water curtains experimentally. This dissertation details the research and experiment development. Small scale outdoor LNG spill experiments have been performed at the Brayton Fire Training Field at Texas A&M University. Field test results regarding important phenomena are presented and discussed. Results have determined that the water curtains are able to reduce the concentration of the LNG vapor cloud, push the vapor cloud upward and transfer heat to the cloud. These are being identified due to the water curtain mechanisms of entrainment of air, dilution of vapor with entrained air, transfer of momentum and heat to the gas cloud. Some of the dominant actions required to control and disperse LNG vapor cloud are also identified from the experimental tests. The gaps are presented as the future work and recommendation on how to improve the experiments in the future. This will benefit LNG industries to enhance its safety system and to make LNG facilities safer.

Dilution and ore recovery/loss have an important role in calculation of mineral reserves. Each percent increase in dilution and decrease in recovery negatively affects economic value of the reserve. These parameters are mainly controlled by the quality of the mine design and stoping practice. This study provides an approach developed for dilution and recovery/ore loss calculations. The contribution of mine design software (MineSight) and the recent survey technique called Cavity Monitoring System (CMS) were presented in this study. The purpose was to compare the new approach with the old system where the calculations had been done according to some assumptions and to optimize mineral reserve estimation process. Results indicate that the new approach used in reserve estimation process gives ~1.6% closer tonnages to the actual numbers and the grades are both ~1.6% closer to the actual values numbers when compared with the old system.

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In wireless location system, geometric relationship between the base station (BS) and the mobile station (MS) may affect the accuracy of MS location estimate. The effect is called Geometric Dilution of Precision (GDOP). Given the information of geometric configuration of BS and MS locations, the GDOP value can be calculated accordingly. In fact, the GDOP value is considered as ratio factor between the location error and measurement noise. A higher GDOP value indicates larger location error in the location estimator. Therefore the GDOP can be utilized as an index for observing the location precision of the MS under different geometric layout. The accuracy of location estimation can be improved by changing the BS device element locations. In the thesis, a time different of arrival (TDOA) wireless location system with mobile base station (MBS) is considered. Changing the geometric layout between the BS and the MS by relocating the MBS, the GDOP effect can be reduced and the accuracy of location estimation also can therefore be improved. Since the simulated annealing (SA) is capable of escaping the local minimum and finding the global minimum in an objective function, the SA algorithm is used in finding the best solution in a defined function based on the GDOP distribution. The best solution is then the destination of an MBS in the process of MS location estimation. When relocating an MBS from its initial location to the best location, it is likely that the MBS enters regions with high GDOP effects. To avoid the problem, the steepest descent (SD) algorithm is utilized for path planning. First, we establish the objective function which consists of the GDOP information and the angle of movement. A nearby location that has the minimum value of objective function is selected as the next move. The process continues until the MBS reaches the destination. A variety of cases are investigated by computer simulations. Simulation results show that the proposed approach can effectively find the best locations for MBSs to relocate. Based on the relocation and path planning, the GDOP effects can be reasonably reduced, and therefore the higher location accuracy is achieved.

In der Reaktorsicherheitsforschung sind auftriebsgetriebene Strömungen von Relevanz für Störfall-szenarien mit Verdünnung der Borkonzentration und für thermische Schockbelastungen des Reak-tordruckbehälters. In der numerischen Simulation der Strömungen werden neben der Berücksichtigung der Auftriebskräfte Quell- und Korrekturterme in die Bilanzgleichungen für die turbulente Energie und die turbulente Dissipation eingeführt. Es wurden erweiterte Modelle entwickelt, in die zusätzliche Gleichungen für die Turbulenzgrößen turbulenter Massenstrom und Dichtevarianz eingehen. Die Modelle wurden in den CFD-Code ANSYS-CFX implementiert. Die Validierung der Modelle erfolgte an einem speziellen Versuchsaufbau (VeMix-Versuchsanlage), mit Einspeisung von Fluid höherer Dichte in eine Vorlage. Als Kriterien für die Validierung wurde der Umschlag zwischen impulsdominiertem Strömungsregime mit vertikalem Jet oder ein vertikales Absinken bei Dominanz von Dichteeffekten herangezogen sowie lokale Konzentrationsmessungen mit Hilfe eines speziell entwickelten Leitfähigkeits-Gittersensors. Eine Verbesserung der Simulation dichtedominierter Vermischungsprozesse mit den erweiterten Turbulenzmodellen konnte allerdings nicht nachgewiesen werden, da die Unterschiede zwischen den Rechnungen mit verschiedenen Turbulenzmodellen zu gering sind. Andererseits konnte jedoch die Simulation der Stratifikation von Fluiden unterschiedlicher Dichte im kalten Strang einer Reaktoranlage deutlich verbessert werden. Anhand der Nachrechnung von Ver-suchen am geometrisch ähnlichen Reaktor-Strömungsmodell ROCOM wurde gezeigt, dass diese Stratifikation von bedeutendem Einfluss auf die Vermischung und somit letztendlich auch auf die Temperatur- bzw. Borkonzentrationsverteilung innerhalb des Reaktordruckbehälters ist. Sie lässt sich nur korrekt simulieren, wenn ausreichend große Abschnitte des kalten Stranges mit modelliert werden. Somit konnte doch eine bessere Vorhersagegenauigkeit der Simulation der Vermischung erreicht werden. In reactor safety research, buoyancy driven flows are of relevance for boron dilution accidents or pressurised thermal shock scenarios. Concerning the numerical simulation of these flows, besides of the consideration of buoyancy forces, source and correction terms are introduced into the balance equations for the turbulent energy and its dissipation rate. Within the project, extended turbulence models have been developed by introducing additional balance equations for the turbulent quantities turbulent mass flow and density variance. The models have been implemented into the computati-onal fluid dynamics code ANSYS-CFX. The validation of the models was performed against tests at a special experimental set-up, the VeMix facility, were fluid of higher density was injected into a vertical test section filled with lighter fluid. As validation criteria the switching-over between a momentum controlled mixing pattern with a horizontal jet and buoyancy driven mixing with vertical sinking down of the heavier fluid was used. Additionally, measurement data gained from an especially developed conductivity wire mesh sensor were used. However, an improvement of the modelling of buoyancy driven mixing by use of the extended models could not be shown, because the differences between calculations with the different models were not relevant. On the other hand, the modelling of the stratification of fluids with different density in the cold leg of a reactor primary circuit could be significantly improved. It has been shown on calculations of experi-ments at the ROCOM mixing test facility, a scaled model of a real reactor plant, that this stratification is relevant as a boundary condition for the mixing process inside the reactor pressure vessel. It can be correctly simulated only if sufficient large parts of the cold legs are included in the modelling. On this way, an improvement of the accuracy of the prediction of mixing processes was achieved.

Two of the main safety and health issues recognized during deep cut coal mining are methane and dust hazards. Advances in continuous miner technology have improved safety and productivity. However, these advances have created some environmental problems, notably more dust and methane being generated at the face during coal extraction. Results of studies performed in the last three decades concerning the face ventilation for deep cut mining showed very complicated airflow behavior. The specifics of flow patterns developed by the face ventilation systems presents significant challenge for analytical description even for equipment-free entry. Fortunately, there are methods, such as numerical simulations that could be used to provide an engineering solution to the problem. Computational Fluid Dynamics (CFD) codes have been successfully applied during the last decade using the power of Supercomputers. Although significant progress has been made, a benchmark industry oriented CFD code dedicated to face ventilation is still not available. The goal of this project is to provide the mining industry a software for CFD analysis and design of face ventilation systems. A commercial CFD system SC/Tetra Thermofluid Analysis System with Unstructured Mesh Generator, copyright © Cradle Co, was selected for a development platform. A number of CFD models were developed for the needs of this study including methane release, dust generation, 3D models of commonly used continuous mining machines, scrubbers and water spray systems. The developed models and the used CFD code were successfully validated in the part for methane dilution, using available data from small scale and full scale experiments. The developed models for simulation of dust control systems need to be validated in the future. The developed code automates all necessary steps needed for simulation of face ventilation systems, starting with the construction of a 3D model, generation of the computational mesh, solving and monitoring the calculations, to post-processing and graphical representation of the obtained results. This code shall allow mining engineers to design better and safer face ventilation systems while providing the Mine Safety and Health Administration (MSHA) a tool to check and approve the industry’ proposed ventilation plans.

Improving and predicting the accuracy of positioning estimates derived from the global positioning system (GPS) continues to be a problem of great interest. Dependable and accurate positioning is especially important for navigation applications such as the landing of commercial aircraft. This subject gives rise to many interesting and challenging mathematical problems. This dissertation investigates two such problems. The first problem involves the study of the relationship between positioning accuracy and satellite geometry configurations relative to a user's position. In this work, accuracy is measured by so-called dilution of precision (DOP) terms. The DOP terms arise from the linear regression model used to estimate user position from GPS observables, and are directly related to user position errors. An analysis of the statistical properties explaining the behavior of the DOP terms is presented. The most accurate satellite geometries and worst configurations are given for some cases. The second problem involves finding methods for detecting and repairing cycle-slips in range delay data between a satellite and a receiver. The distance between a satellite and a receiver can be estimated by measuring the difference in the carrier frequency phase shift experienced between the satellite and receiver oscillators. Cycle-slips are discontinuities in the integer number of complete cycles in these data, and are caused by interruptions or degradations in the signal such as low signal to noise ratio, software failures, or physical obstruction of the signals. These slips propagate to errors in user positioning. Cycle-slip detection and repair are crucial to maintaining accurate positioning. Linear regression models and sequential hypothesis testing are used to model, detect, and repair cycle-slips. The effectiveness of these methods is studied using data obtained from ground-station receivers.

Thesis (M.S. )--Duquesne University, 2007. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references (p. 59-61) and index.

Thesis (Ph. D.)--Ohio State University, 2005. / Available online via OhioLINK's ETD Center; full text release delayed at author's request until 2006 Nov 29