The use of a slim, high-pressure drilling riser for surface blowout preventer operations in the deepwater Gulf of Mexico was assessed as an alternative to conventional drilling procedures from floating units. Comparison of the low- and high-pressure system was accomplished through a detailed qualitative (assigned frequency) and quantitative (reported incidents) risk analysis using generic fault tree models to statistically determine the reliability of the system based on metocean conditions from the Gulf of Mexico. It is hoped that this investigation will serve as a starting point for drilling companies and regulatory agencies to understand the risk of implementing a high-pressure riser for surface blowout preventer applications in the Gulf of Mexico, because specific failure events and conditions of the area were considered. Despite the generic description of the drilling riser and pressure control system, the models are flexible enough to be modified and adapted to a specific rig configuration and location. Results from the qualitative comparison suggest an acceptable risk and high reliability for high-pressure riser systems and surface preventers. The quantitative portion of the study is influenced by the data quality of the high-pressure system, however it provides a range of possible reliability values with an acceptable overall risk.

The use of a slim, high-pressure drilling riser for surface blowout preventer operations in the deepwater Gulf of Mexico was assessed as an alternative to conventional drilling procedures from floating units. Comparison of the low- and high-pressure system was accomplished through a detailed qualitative (assigned frequency) and quantitative (reported incidents) risk analysis using generic fault tree models to statistically determine the reliability of the system based on metocean conditions from the Gulf of Mexico. It is hoped that this investigation will serve as a starting point for drilling companies and regulatory agencies to understand the risk of implementing a high-pressure riser for surface blowout preventer applications in the Gulf of Mexico, because specific failure events and conditions of the area were considered. Despite the generic description of the drilling riser and pressure control system, the models are flexible enough to be modified and adapted to a specific rig configuration and location. Results from the qualitative comparison suggest an acceptable risk and high reliability for high-pressure riser systems and surface preventers. The quantitative portion of the study is influenced by the data quality of the high-pressure system, however it provides a range of possible reliability values with an acceptable overall risk.

DEA ?? 63, Floating Vessel Blowout Control is a blowout containment study which was completed in 1990, and it did not include discussions about operations in the water depths we currently operate in. As offshore drilling is continuously moving into deeper and deeper waters, a need to further investigate well control and blowout containment in ultradeep water has arisen. This project describes the development and assessment of an electronic cross-reference tool for well control and blowout containment, with added focus on ultradeep water operations. The approach of this manual is fully electronic, thus being able to serve the needs of the engineer/driller with greater ease in both pre-planning and in a stressful onthe- job setting. The cross-reference is a manual for the state of the art in well control and blowout containment methodology. It provides easy-to-use topical organization by categories and subcategories, and aims at providing clear links between symptoms, causes, and solutions. Clear explanations to complicated issues are provided, and confirmation of applicable blowout intervention procedures, be it conventional or unconventional, are discussed. Human error and equipment failure are the causes of blowouts, and they are bound to happen in an ultradeep water environment. Well control events are harder to detect andhandle in ultradeep water, and quick reaction time is essential. After detection and shutin, the Driller??s method is the preferred circulation method in ultradeep water, due to its responsiveness and simplicity. In case kick handling is unsuccessful, contingency plans should be in place to handle a potential blowout. If a blowout does occur, and the blowing well does not self-kill through bridging, a dynamic kill through relief well intervention is likely to be necessary, as underwater intervention is difficult in ultradeep water. With new ultradeep water drilling technologies providing potential for increased performance, alternative well control methods might be necessary. Along with these new technologies follow new unfamiliar procedures, and proper education and training is essential.

Modern gas turbine combustors implement lean premixed (LPM) combustion system to reduce the formation of NOx pollutants. LPM technology has advanced to have the ability to produce extremely low level of NOx emissions. The current focus of research on LPM is focused on reducing the NOx emission to much smaller scales, which is mandated because of the stricter regulations and environmental concerns. However, LPM combustors are susceptible to lean blowout (LBO), and other corresponding instabilities as the combustor is operated lean. Therefore, it is essential to understand the LBO limits and dynamics of flow in lean operating conditions. One of the other primary parameters for the improved combustion chamber designs is an accurate characterization of the heat loads on the liner walls in the wide range of operating conditions. Currently, there are very limited studies on the flame side heat transfer in reacting conditions. Current gas turbine combustion technology primarily focuses on burning natural gas as the gas fuel option for industrial systems. However, interest in utilizing additional options due to environmental regulations as well as concerns about energy security have motivated interest in using fuel gases that have blends of Methane, Propane, H2, CO, CO2, and N2. For example, fuel blends of 35%/60% to 55%/35% of CH4/CO2 are typically seen in Landfill gases. Syngas fuels are typically composed primarily of H2, CO, and N2. Gases from anaerobic digestion of sewage, used commonly in wastewater treatment plants, usually have 65–75% CH4 with the balance being N2. The objective of this study is to understand the LBO limits and the effects of the instabilities that arise (called near blowout oscillations) as the combustor is operated lean. Near blowout oscillations arise as the equivalence ratio is reduced. These oscillations are characterized by continuous blowout and re-ignition events happening at low frequencies. The low-frequency oscillations have very high-pressure amplitude and can potentially damage the liner wall. The impact of the near blowout oscillations on the flow field and heat transfer on the liner walls are studied. To accomplish this, the experiments were conducted at Advanced Propulsion and Power laboratory located at Virginia Tech. A lean premixed, swirl stabilized fuel nozzle designed with central pilot hub was used for the study. Additionally, this work also studies the lean blowout limits with fuel blends of CH4-C3H8, CH4-CO2, and CH4-N2 and also their effect on the stability limits as the pilot fuel percentage was changed. Flow field during near blowout oscillations was studied using planar particle image velocimetry (PIV) and flame shapes and locations during these oscillations was studied by using high-speed imaging of the flame. A statistical tool called proper orthogonal decomposition (POD) was utilized to post-process the PIV data and high-speed imaging data. Heat transfer on the liner walls was studied using a transient IR thermography methodology. The heat transfer on the liner wall during the near blowout instabilities was resolved. LBO limits and near blowout oscillations were characterized by studying the pressure measurements in the primary combustor region. Fluctuating heat loads on the liner walls with the same frequency as that of near blowout instabilities was observed. The magnitude of fluctuation was found to be very high. Phase sorted POD reconstructed flame images demonstrated the location of the flame during near blowout oscillations. Thus, blowout and re-ignition events are resolved from the high-speed flame images. POD reconstructed flow field from the PIV data demonstrated the statistically significant flow structures during near blowout oscillations. A hypothesis for the mechanism of near blowout oscillations was explained based on the measurements and observations made. Lean Blowout limits (LBO) changed when the percentage of pilot and air flow rates was changed. As the pilot percentage increased, LBO limits improved. Results on the study of fuel mixtures demonstrate that the addition of propane, nitrogen and carbon dioxide has minimal effect on when the flame becomes unstable in lean operating conditions. However, on the other hand, the addition of diluent gas showed a potential blowout at higher operating conditions. It was also observed that Wobbe index might not be a good representation for fuels to study the fuel interchangeability in lean operating conditions. / Ph. D.

A compreensão dos mecanismos de estabilidade de chamas é de extrema importância tanto para o projeto/dimensionamento de queimadores utilizados em fornos e fornalhas industriais, câmaras de combustão de turbinas a gás e flares; como para a substituição de combustíveis em queimadores existentes. Há um intervalo de condições (como velocidade de descarga do jato e concentração de combustível na mistura gasosa) na qual a combustão estável pode ser mantida, sendo limitada por dois fenômenos denominados como liftoff (descolamento da base da chama do bocal e posterior estabilização desta a certa distância do bocal) e blowout (desprendimento e extinção da chama). Por razões de segurança, operações próximas às condições em que o blowout pode ocorrer devem ser evitadas. Muitas teorias têm sido publicadas para descrever as características de liftoff e blowout de chamas de difusão turbulenta. Este trabalho apresenta algumas destas teorias, bem como as hipóteses assumidas e os processos físicos considerados responsáveis por estes fenômenos (liftoff e blowout). Correlações para a previsão da velocidade de blowout e resultados experimentais disponíveis na literatura também são apresentados. Uma nova correlação para a velocidade de blowout é proposta, a qual se baseia nos movimentos de grande escala observados em jatos turbulentos e no adimensional número de Damköhler (relação entre o tempo de cinética química e o tempo de mistura dos reagentes e destes com os produtos da reação). Comparações entre as previsões da correlação proposta com resultados experimentais e com previsões de outras correlações disponíveis na literatura foram realizadas, para diferentes combustíveis e diâmetros de bocais. A correlação proposta apresentou boa concordância com os resultados experimentais. A partir das análises desenvolvidas neste trabalho, verificou-se que a velocidade de blowout de chamas de difusão turbulenta é função das propriedades do combustível, das características do bocal, das condições do ambiente e do adimensional número de Damköhler. / The study of flame stability is very important to the design of burners used in industrial ovens and furnaces, combustion chambers of gas turbines and flares; and fuel substitution in burners. There is a range of conditions (for example gas velocity at the nozzle exit and jet fuel concentration in the gas mixture) at which stable combustion can be maintained, being limited by two phenomena called liftoff and blowout. Lift-off is the detachment of the flame from the fuel nozzle, and blowout its detachment and extinction. Operating conditions close to stability limits should be avoided for security reasons. Many theories have been published to describe the blowout and lifted characteristics of turbulent jet diffusion flames. This document presents some theories, as well as the assumptions and physical processes considered responsible for these phenomena (liftoff and blowout). Correlations for predicting the blowout velocity and experimental results available in the literature are also shown. A new correlation is proposed, which is based on large-scale motions observed in turbulent jets and the dimensionless Damköhler number (ratio of the characteristic chemical reaction time and the time associated with the mixing of reentrained hot products into fresh reactants). Comparisons between the predictions of the proposed correlation with experimental results and predictions of other correlations available in the literature were performed for different fuels and nozzle diameters. The proposed correlation showed good agreement with the experimental results. The analyses developed in this work allow us to conclude that the blowout velocity of the turbulent diffusion flame depends on the fuel properties, characteristics of the nozzle, the environmental conditions and the Damköhler number.

A compreensão dos mecanismos de estabilidade de chamas é de extrema importância tanto para o projeto/dimensionamento de queimadores utilizados em fornos e fornalhas industriais, câmaras de combustão de turbinas a gás e flares; como para a substituição de combustíveis em queimadores existentes. Há um intervalo de condições (como velocidade de descarga do jato e concentração de combustível na mistura gasosa) na qual a combustão estável pode ser mantida, sendo limitada por dois fenômenos denominados como liftoff (descolamento da base da chama do bocal e posterior estabilização desta a certa distância do bocal) e blowout (desprendimento e extinção da chama). Por razões de segurança, operações próximas às condições em que o blowout pode ocorrer devem ser evitadas. Muitas teorias têm sido publicadas para descrever as características de liftoff e blowout de chamas de difusão turbulenta. Este trabalho apresenta algumas destas teorias, bem como as hipóteses assumidas e os processos físicos considerados responsáveis por estes fenômenos (liftoff e blowout). Correlações para a previsão da velocidade de blowout e resultados experimentais disponíveis na literatura também são apresentados. Uma nova correlação para a velocidade de blowout é proposta, a qual se baseia nos movimentos de grande escala observados em jatos turbulentos e no adimensional número de Damköhler (relação entre o tempo de cinética química e o tempo de mistura dos reagentes e destes com os produtos da reação). Comparações entre as previsões da correlação proposta com resultados experimentais e com previsões de outras correlações disponíveis na literatura foram realizadas, para diferentes combustíveis e diâmetros de bocais. A correlação proposta apresentou boa concordância com os resultados experimentais. A partir das análises desenvolvidas neste trabalho, verificou-se que a velocidade de blowout de chamas de difusão turbulenta é função das propriedades do combustível, das características do bocal, das condições do ambiente e do adimensional número de Damköhler. / The study of flame stability is very important to the design of burners used in industrial ovens and furnaces, combustion chambers of gas turbines and flares; and fuel substitution in burners. There is a range of conditions (for example gas velocity at the nozzle exit and jet fuel concentration in the gas mixture) at which stable combustion can be maintained, being limited by two phenomena called liftoff and blowout. Lift-off is the detachment of the flame from the fuel nozzle, and blowout its detachment and extinction. Operating conditions close to stability limits should be avoided for security reasons. Many theories have been published to describe the blowout and lifted characteristics of turbulent jet diffusion flames. This document presents some theories, as well as the assumptions and physical processes considered responsible for these phenomena (liftoff and blowout). Correlations for predicting the blowout velocity and experimental results available in the literature are also shown. A new correlation is proposed, which is based on large-scale motions observed in turbulent jets and the dimensionless Damköhler number (ratio of the characteristic chemical reaction time and the time associated with the mixing of reentrained hot products into fresh reactants). Comparisons between the predictions of the proposed correlation with experimental results and predictions of other correlations available in the literature were performed for different fuels and nozzle diameters. The proposed correlation showed good agreement with the experimental results. The analyses developed in this work allow us to conclude that the blowout velocity of the turbulent diffusion flame depends on the fuel properties, characteristics of the nozzle, the environmental conditions and the Damköhler number.

This thesis presents results from spatial-temporal and volumetric change analysis of blowouts on the Cape Cod National Seashore (CCNS) landscape in Massachusetts, USA. The purpose of this study is to use methods of analysing areal and volumetric changes in coastal dunes, specifically blowouts, and to detect patterns of change in order to contribute to the knowledge and literature on blowout evolution. In Chapter 2.0, the quantitative analysis of blowout change patterns in CCNS was examined at a landscape scale using Spatial-Temporal Analysis of Moving Polygons (STAMP). STAMP runs as an ArcGIS plugin and uses neighbouring year polygon layers of our digitized blowouts from sequential air photo and LiDAR data (1985, 1994, 2000, 2005, 2009, 2011, and 2012 for 30 erosional features, and 1998, 2000, 2007, and 2010 for 10 depositional features). The results from STAMP and the additional computations provided the following information on the evolution of blowouts: (1) both geometric and movement events occur on CCNS; (2) generation of blowouts in CCNS is greatest in 1985 and is potentially related to vegetation planting campaigns by the Park; (3) features are expanding towards dominant winds from the North West and the South West; (5) the erosional and depositional features are becoming more circular as they develop, (6) the evolution of CCNS blowouts follows a similar pattern to Gares and Nordstrom’s (1995) model with two additional stages: merging or dividing, and re-activation. In Chapter 3.0, the quantitative analysis of volumetric and areal change of 10 blowouts in CCNS at a landscape scale is examined using airborne LiDAR and air photos. The DEMs of neighbouring years (1998, 2000, 2007, and 2010) were differenced using Geomorphic Change Detection (GCD) software. Areal change was detected by differencing the area of polygons that were manually digitized in ArcGIS. The changes in wind data and vegetation cover were also examined. The results from the GCD and areal change analysis provide the following information on blowout evolution: (1) blowouts generate/initiate; (2) multiple blowouts can merge into an often larger blowout; (3) and blowouts can experience volumetric change with minimal aerial change and vice versa. From the analyzes of hourly Provincetown wind data (1998-2010), it was evident that blowouts developed within all three time intervals. The percentages of comparable winds (above 9.6 m s-1) were highest in 1998, 1999, 2007 and 2010. It is speculated that tropical storms and nor'easters are important drivers in the development of CCNS blowouts. In addition, supervised classifications were run on sequential air photos (1985 to 2009) to analyze vegetation cover. The results indicated an increase in vegetation cover and decrease of active sands over time. Two potential explanations that link increased vegetation to blowout development are: (1) sparse vegetation creates a more conducive environment for the initiation of blowouts by providing stability for the lateral walls, and (2) high wind events (e.g. hurricanes and nor'easters) could cause vegetation removal, allowing for areas of exposed sand for blowout initiation and development. / Graduate / 0799 / 0368 / kimia.abhar@gmail.com

This thesis presents results from spatial-temporal and volumetric change analysis of blowouts on the Cape Cod National Seashore (CCNS) landscape in Massachusetts, USA. The purpose of this study is to use methods of analysing areal and volumetric changes in coastal dunes, specifically blowouts, and to detect patterns of change in order to contribute to the knowledge and literature on blowout evolution. In Chapter 2.0, the quantitative analysis of blowout change patterns in CCNS was examined at a landscape scale using Spatial-Temporal Analysis of Moving Polygons (STAMP). STAMP runs as an ArcGIS plugin and uses neighbouring year polygon layers of our digitized blowouts from sequential air photo and LiDAR data (1985, 1994, 2000, 2005, 2009, 2011, and 2012 for 30 erosional features, and 1998, 2000, 2007, and 2010 for 10 depositional features). The results from STAMP and the additional computations provided the following information on the evolution of blowouts: (1) both geometric and movement events occur on CCNS; (2) generation of blowouts in CCNS is greatest in 1985 and is potentially related to vegetation planting campaigns by the Park; (3) features are expanding towards dominant winds from the North West and the South West; (5) the erosional and depositional features are becoming more circular as they develop, (6) the evolution of CCNS blowouts follows a similar pattern to Gares and Nordstrom’s (1995) model with two additional stages: merging or dividing, and re-activation. In Chapter 3.0, the quantitative analysis of volumetric and areal change of 10 blowouts in CCNS at a landscape scale is examined using airborne LiDAR and air photos. The DEMs of neighbouring years (1998, 2000, 2007, and 2010) were differenced using Geomorphic Change Detection (GCD) software. Areal change was detected by differencing the area of polygons that were manually digitized in ArcGIS. The changes in wind data and vegetation cover were also examined. The results from the GCD and areal change analysis provide the following information on blowout evolution: (1) blowouts generate/initiate; (2) multiple blowouts can merge into an often larger blowout; (3) and blowouts can experience volumetric change with minimal aerial change and vice versa. From the analyzes of hourly Provincetown wind data (1998-2010), it was evident that blowouts developed within all three time intervals. The percentages of comparable winds (above 9.6 m s-1) were highest in 1998, 1999, 2007 and 2010. It is speculated that tropical storms and nor'easters are important drivers in the development of CCNS blowouts. In addition, supervised classifications were run on sequential air photos (1985 to 2009) to analyze vegetation cover. The results indicated an increase in vegetation cover and decrease of active sands over time. Two potential explanations that link increased vegetation to blowout development are: (1) sparse vegetation creates a more conducive environment for the initiation of blowouts by providing stability for the lateral walls, and (2) high wind events (e.g. hurricanes and nor'easters) could cause vegetation removal, allowing for areas of exposed sand for blowout initiation and development. / Graduate / 0799 / 0368 / kimia.abhar@gmail.com

Lean combustion is increasingly employed in both ground-based gas turbines and aircraft engines for minimizing NOx emissions. Operating under lean conditions increases the risk of Lean Blowout (LBO). Thus LBO proximity sensors, combined with appropriate blowout prevention systems, have the potential to improve the performance of engines. In previous studies, atmospheric pressure, swirl flames near LBO have been observed to exhibit partial extinction and re-ignition events called LBO precursors. Detecting these precursor events in optical and acoustic signals with simple non-intrusive sensors provided a measure of LBO proximity. This thesis examines robust LBO margin sensing approaches, by exploring LBO precursors in the presence of combustion dynamics and for combustor operating conditions that are more representative of practical combustors, i.e., elevated pressure and preheat temperature operation. To this end, two combustors were used: a gas-fueled, atmospheric pressure combustor that exhibits pronounced combustion dynamics under a wide range of lean conditions, and a low NOx emission liquid-fueled lean direct injection (LDI) combustor, operating at elevated pressure and preheat temperature. In the gas-fueled combustor, flame extinction and re-ignition LBO precursor events were observed in the presence of strong combustion dynamics, and were similar to those observed in dynamically stable conditions. However, the signature of the events in the raw optical signals have different characteristics under various operating conditions. Low-pass filtering and a single threshold-based event detection algorithm provided robust precursor sensing, regardless of the type or level of dynamic instability. The same algorithm provides robust event detection in the LDI combustor, which also exhibits low level dynamic oscillations. Compared to the gas-fueled combustor, the LDI events have weaker signatures, much shorter durations, but considerably higher occurrence rates. The disparity in precursor durations is due to a flame mode switch that occurs during precursors in the gas-fueled combustor, which is absent in the LDI combustor. Acoustic sensing was also investigated in both the combustors. Low-pass filtering is required to reveal a precursor signature under dynamically unstable conditions in the gas-fueled combustor. On the other hand in the LDI combustor, neither the raw signals nor the low-pass filtered signals reveal precursor events. The failure of acoustic sensing is attributed in part to the lower heat release variations, and the similarity in time scales for the precursors and dynamic oscillations in the LDI combustor. In addition, the impact of acoustic reflections from combustor boundaries and transducer placement was addressed by modeling reflections in a one-dimensional combustor geometry with an impedance jump caused by the flame. Implementing LBO margin sensors in gas turbine engines can potentially improve time response during deceleration transients by allowing lower operating margins. Occurrence of precursor events under transient operating conditions was examined with a statistical approach. For example, the rate at which the fuel-air ratio can be safely reduced might be limited by the requirement that at least one precursor occurs before blowout. The statistics governing the probability of a precursor event occurring during some time interval was shown to be reasonably modeled by Poisson statistics. A method has been developed to select a lower operating margin when LBO proximity sensors are employed, such that the lowered margin case provides a similar reliability in preventing LBO as the standard approach utilizing a more restrictive operating margin. Illustrative improvements in transient response and reliabilities in preventing LBO are presented for a model turbofan engine. In addition, an event-based, active LBO control approach for deceleration transients is also demonstrated in the engine simulation.

This thesis describes an investigation on the blowout phenomenon in gas turbine combustors. The combustor primarily used for this study was a swirl- and dump-stabilized, atmospheric pressure device, which did not exhibit dynamic combustion instabilities. The first part of the thesis work concentrated on finding a sensing methodology to be able to predict the onset of approach of combustor blowout using optical methods. Temporary extinction-reignition events that occurred prior to blowout were found to be precursor events to blowout. A threshold based method was developed to identify these events in the time-resolved sensor output. The number and the average length of each event were found to increase as the LBO limit (fuel-air ratio) is approached. This behavior is used to predict the proximity to lean blowout. In the second part of this study, the blowout sensor was incorporated into a control system that monitored the approach of blowout and then actuated an alternate mechanism to stabilize the combustor near blowout. Enhanced stabilization was achieved by redirecting a part of the main fuel to a central preinjection pilot injection. The sensing methodology, without modification, was effective for the combustor with pilot stabilization. An event based control algorithm for controlling the combustor from blowing out was also developed in this study. The control system was proven to stabilize the combustor even when the combustor loading was rapidly changed. The final part of this study focused on understanding the physical mechanisms behind the precursor events. High speed movies of flame chemiluminescence and laser sheet scattering from oil droplets seeded into the reactants were analyzed to explain the physical processes that cause the extinction and the reignition of the combustor during a precursor event. A physical model for coupling of the fluid dynamics of vortex breakdown and combustion during precursor and blowout events is proposed. This model of blowout phenomenon, along with the sensing and control strategies developed in this study could enable the gas turbine combustor designers to design combustors with wider operability regimes. This could have significant payoffs in terms of reduction in NOx emissions from the combustor.