The addition of hydrogen and oxygen to a hydrocarbon fuel mixture has a significant effect on its sooting tendencies at high pressures. Understanding the mechanism behind and rates of soot formation is key to proper chemical modeling of fireballs. This research aims to investigate the soot formation rates and soot induction times of several intermediary chemicals found in energetic material (EM) combustion. Three common EM combustion intermediaries, acetylene, ethylene, and propyne are studied. Hydrogen and oxygen are added to the hydrocarbon fuel to observe their effect on parameters such as induction time and total soot yield. A laser absorption spectroscopy system was utilized to measure soot formation time history during experiments. The diagnostic instrument employs a low-noise continuous wave laser at 635 nm. The laser was transmitted through the test section of a shock tube device and its intensity during an experiment was measured. The data was used to determine estimated soot yield and soot induction times. This work will extend the chemical modeling capabilities of the National Nuclear Security Administration (NNSA) with an improved understanding of soot formation in fireball conditions.

Both experimental and numerical investigations of converging shock waves have been performed. In the experiments, a shock tube was used to create and study converging shock waves of various geometrical shapes. Two methods were used to create polygonally shaped shocks. In the first method, the geometry of the outer boundary of the test section of the shock tube was varied. Four different exchangeable shapes of the outer boundary were considered: a circle, a smooth pentagon, a heptagon, and an octagon. In the second method, an initially cylindrical shock wave was perturbed by metal cylinders placed in various patterns and positions inside the test section. For three or more regularly spaced cylinders, the resulting diffracted shock fronts formed polygonal shaped patterns near the point of focus. Regular reflection was observed for the case with three cylinders and Mach refection was observed for cases with four or more cylinders. When the shock wave is close to the center of convergence, light emission is observed. An experimental investigation of the light emission was conducted and results show that the shape of the shock wave close to the center of convergence has a large influence on the amount of emitted light. It was found that a symmetrical polygonal shock front produced more light than an asymmetrical shape. The shock wave focusing was also studied numerically using the Euler equations for a gas obeying the ideal gas law with constant specific heats. Two problems were analyzed; an axisymmetric model of the shock tube used in the experiments and a cylindrical shock wave diffracted by cylinders in a two dimensional test section. The results showed good agreement with the experiments. The temperature field from the numerical simulations was investigated and shows that the triple points behind the shock front are hot spots that increase the temperature at the center as they arrive there. As a practical example of shock wave focusing, converging shocks in an electrohydraulic lithotripter were simulated. The maximum radius of a gas bubble subjected to the pressure field obtained from the lithotripter was calculated and compared for various geometrical shapes and materials of the reflector. Results showed that the shape had a large impact while the material did not influence the maximum radius of the gas bubble. / QC 20100706

Mitigation of the blast risk associated with terrorist attacks and accidental explosions threatening critical infrastructure has become a topic of great interest in the civil engineering community, both in Canada and abroad. One method of mitigating blast risk is to retrofit vulnerable structures to resist the impulsive effects of blast loading. A comprehensive re-search program has been undertaken to develop fibre reinforced polymer (FRP) retrofit methodologies for structural and non-structural elements, specifically reinforced concrete slabs and walls, subjected to blast loading. The results of this investigation are equally valid for flexure dominant reinforced concrete beams subject to blast effects. The objective of the research program was to generate a large volume of research data for the development of blast-resistant design guidelines for externally bonded FRP retrofit systems. A combined experimental and analytical investigation was performed to achieve the objectives of the program. The experimental program involved the construction and simulated blast testing of a total of thirteen reinforced concrete wall and slab specimens divided into five companion sets. These specimens were subjected to a total of sixty simulated explosions generated at the University of Ottawa Shock Tube Testing Facility. Companion sets were designed to study one- and two-way bending, as well as the performance of specimens with simply-supported and fully-fixed boundary conditions. The majority of the specimens were retrofitted with externally bonded carbon fibre reinforced polymer (CFRP) sheets to improve overall load-deformation characteristics. Specimens within each companion set were subjected to progressively increasing pressure-impulse combinations to study component behaviour from elastic response up to inelastic component failure. The blast performance of companion as-built and retrofitted specimens was quantified in terms of measured load-deformation characteristics, and observed member behaviour throughout all stages of response. The results show that externally bonded FRP retrofits are an effective retrofit technique to improve the blast resistance of reinforced concrete structures, provided that debonding of the composite from the concrete substrate is prevented. The test results also indicate that FRP retrofitted reinforced concrete structures may survive initial inbound displacements, only to failure by moment reversals during the negative displacement phase. The experimental test data was used to verify analytical techniques to model the behaviour of reinforced concrete walls and slabs subjected to blast loading. The force-deformation characteristics of one-way wall strips were established using inelastic sectional and member analyses. The force-deformation characteristics of two-way slab plates were established using commonly accepted design approximations. The response of all specimens was computed by explicit solution of the single degree of freedom dynamic equation of motion. An equivalent static force procedure was used to analyze the response of CFRP retrofitted specimens which remained elastic after testing. The predicted maximum displacements and time-to-maximum displacements were compared against experimental results. The analysis indicates that the modelling procedures accurately describe the response characteristics of both retrofitted and unretrofitted specimens observed during the experiment.

Mitigation of the blast risk associated with terrorist attacks and accidental explosions threatening critical infrastructure has become a topic of great interest in the civil engineering community, both in Canada and abroad. One method of mitigating blast risk is to retrofit vulnerable structures to resist the impulsive effects of blast loading. A comprehensive re-search program has been undertaken to develop fibre reinforced polymer (FRP) retrofit methodologies for structural and non-structural elements, specifically reinforced concrete slabs and walls, subjected to blast loading. The results of this investigation are equally valid for flexure dominant reinforced concrete beams subject to blast effects. The objective of the research program was to generate a large volume of research data for the development of blast-resistant design guidelines for externally bonded FRP retrofit systems. A combined experimental and analytical investigation was performed to achieve the objectives of the program. The experimental program involved the construction and simulated blast testing of a total of thirteen reinforced concrete wall and slab specimens divided into five companion sets. These specimens were subjected to a total of sixty simulated explosions generated at the University of Ottawa Shock Tube Testing Facility. Companion sets were designed to study one- and two-way bending, as well as the performance of specimens with simply-supported and fully-fixed boundary conditions. The majority of the specimens were retrofitted with externally bonded carbon fibre reinforced polymer (CFRP) sheets to improve overall load-deformation characteristics. Specimens within each companion set were subjected to progressively increasing pressure-impulse combinations to study component behaviour from elastic response up to inelastic component failure. The blast performance of companion as-built and retrofitted specimens was quantified in terms of measured load-deformation characteristics, and observed member behaviour throughout all stages of response. The results show that externally bonded FRP retrofits are an effective retrofit technique to improve the blast resistance of reinforced concrete structures, provided that debonding of the composite from the concrete substrate is prevented. The test results also indicate that FRP retrofitted reinforced concrete structures may survive initial inbound displacements, only to failure by moment reversals during the negative displacement phase. The experimental test data was used to verify analytical techniques to model the behaviour of reinforced concrete walls and slabs subjected to blast loading. The force-deformation characteristics of one-way wall strips were established using inelastic sectional and member analyses. The force-deformation characteristics of two-way slab plates were established using commonly accepted design approximations. The response of all specimens was computed by explicit solution of the single degree of freedom dynamic equation of motion. An equivalent static force procedure was used to analyze the response of CFRP retrofitted specimens which remained elastic after testing. The predicted maximum displacements and time-to-maximum displacements were compared against experimental results. The analysis indicates that the modelling procedures accurately describe the response characteristics of both retrofitted and unretrofitted specimens observed during the experiment.

Deformation and fracture behaviour of the slender diaphragm with cross incisions is simulated by the developed finite element model. The influence of incisions geometry on the critical pressure of diaphragms was examined by applying deformation and fracture criteria. Original experiments of diaphragms with incisions were performed. / Išnagrinėjus ir palyginus įvairius skaičiuojamuosius baigtinių elementų modelius buvo ištirta ir nustatyta įpjovos geometrijos įtaka smūginio dujų vamzdžio liaunos diafragmos su kryžmine įpjova kritiniam slėgiui pagal ribinius deformavimo ir irimo kriterijus. Atlikti originalūs eksperimentiniai diafragmų deformavimo ir irimo tyrimai.

Išnagrinėjus ir palyginus įvairius skaičiuojamuosius baigtinių elementų modelius buvo ištirta ir nustatyta įpjovos geometrijos įtaka smūginio dujų vamzdžio liaunos diafragmos su kryžmine įpjova kritiniam slėgiui pagal ribinius deformavimo ir irimo kriterijus. Atlikti originalūs eksperimentiniai diafragmų deformavimo ir irimo tyrimai. / Deformation and fracture behaviour of the slender diaphragm with cross incisions is simulated by the developed finite element model. The influence of incisions geometry on the critical pressure of diaphragms was examined by applying deformation and fracture criteria. Original experiments of diaphragms with incisions were performed.

Mitigation of the blast risk associated with terrorist attacks and accidental explosions threatening critical infrastructure has become a topic of great interest in the civil engineering community, both in Canada and abroad. One method of mitigating blast risk is to retrofit vulnerable structures to resist the impulsive effects of blast loading. A comprehensive re-search program has been undertaken to develop fibre reinforced polymer (FRP) retrofit methodologies for structural and non-structural elements, specifically reinforced concrete slabs and walls, subjected to blast loading. The results of this investigation are equally valid for flexure dominant reinforced concrete beams subject to blast effects. The objective of the research program was to generate a large volume of research data for the development of blast-resistant design guidelines for externally bonded FRP retrofit systems. A combined experimental and analytical investigation was performed to achieve the objectives of the program. The experimental program involved the construction and simulated blast testing of a total of thirteen reinforced concrete wall and slab specimens divided into five companion sets. These specimens were subjected to a total of sixty simulated explosions generated at the University of Ottawa Shock Tube Testing Facility. Companion sets were designed to study one- and two-way bending, as well as the performance of specimens with simply-supported and fully-fixed boundary conditions. The majority of the specimens were retrofitted with externally bonded carbon fibre reinforced polymer (CFRP) sheets to improve overall load-deformation characteristics. Specimens within each companion set were subjected to progressively increasing pressure-impulse combinations to study component behaviour from elastic response up to inelastic component failure. The blast performance of companion as-built and retrofitted specimens was quantified in terms of measured load-deformation characteristics, and observed member behaviour throughout all stages of response. The results show that externally bonded FRP retrofits are an effective retrofit technique to improve the blast resistance of reinforced concrete structures, provided that debonding of the composite from the concrete substrate is prevented. The test results also indicate that FRP retrofitted reinforced concrete structures may survive initial inbound displacements, only to failure by moment reversals during the negative displacement phase. The experimental test data was used to verify analytical techniques to model the behaviour of reinforced concrete walls and slabs subjected to blast loading. The force-deformation characteristics of one-way wall strips were established using inelastic sectional and member analyses. The force-deformation characteristics of two-way slab plates were established using commonly accepted design approximations. The response of all specimens was computed by explicit solution of the single degree of freedom dynamic equation of motion. An equivalent static force procedure was used to analyze the response of CFRP retrofitted specimens which remained elastic after testing. The predicted maximum displacements and time-to-maximum displacements were compared against experimental results. The analysis indicates that the modelling procedures accurately describe the response characteristics of both retrofitted and unretrofitted specimens observed during the experiment.

Applications of natural gases that contain high levels of hydrogen have become a primary interest in the gas turbine market. For reheat gas turbines, understanding of the ignition delay times of high-hydrogen natural gases is important for two reasons. First, if the ignition delay time is too short, autoignition can occur in the mixer before the primary combustor. Second, the flame in the secondary burner is stabilized by the ignition delay time of the fuel. While the ignition delay times of hydrogen and of the individual hydrocarbons in natural gases can be considered well known, there have been few previous experimental studies into the effects of different levels of hydrogen on the ignition delay times of natural gases at gas turbine conditions. In order to examine the effects of hydrogen content at gas turbine conditions, shock-tube experiments were performed on nine combinations of an L9 matrix. The L9 matrix was developed by varying four factors: natural gas higher-order hydrocarbon content of 0, 18.75, or 37.5%; hydrogen content of the total fuel mixture of 30, 60, or 80%; equivalence ratios of 0.3, 0.5, or 1; and pressures of 1, 10, or 30 atm. Temperatures ranged from 1092 K to 1722 K, and all mixtures were diluted in 90% Ar. Correlations for each combination were developed from the ignition delay times and, using these correlations, a factor sensitivity analysis was performed. It was found that hydrogen played the most significant role in ignition delay time. Pressure was almost as important as hydrogen content, especially as temperature increased. Equivalence ratio was slightly more important than hydrocarbon content of the natural gas, but both were less important than pressure or hydrogen content. Further analysis was performed using ignition delay time calculations for the full matrix of combinations (27 combinations for each natural gas) using a detailed chemical kinetics mechanism. Using these calculations, separate L9 matrices were developed for each natural gas. Correlations from the full matrix and the L9 matrix for each natural gas were found to be almost identical in each case, verifying that a thoughtfully prepared L9 matrix can indeed capture the major effects of an extended matrix.

Cette thèse étudie le transfert de chaleur par rayonnement observé dans les conditions d'écoulement raréfié, en régime hypersonique qui seraient rencontrés au cours d'une mission d'aérocapture dans l'atmosphère de Titan. Des estimations précises du rayonnement hors-équilibre dans des écoulements à grande vitesse tels que ceux autour des corps de re-entrée, sont indispensables pour la conception de systèmes de protection thermique plus efficace. Parce que la masse du système de protection thermique est une fraction importante de la masse totale du véhicule, il ya un grand intérêt dans la conception de systèmes plus légers et plus efficaces. Les expériences en vol sont coûteuses et contraignantes, c'est pourquoi l'essai en laboratoire dans des installations capables de produire des écoulements hypersoniques est nécessaire. Malheureusement, les échelles de longueur généralement impliquées dans les expériences en vol sont trop grandes pour être testées dans des installations expérimentales et donc des modèles réduits de véhicules 'aeroshells' sont généralement testés. Les tubes d'expansion de l'université de Queensland - X1, X2 et X3 - ont été largement utilisés pour la modélisation à l'échelle réduite des écoulements hypersoniques (Morgan 2001). Pour les installations d'essais au sol telle que la soufflerie X2, une mise à l'échelle binaire est utilisée pour tester des modèles à échelle réduite de véhicules de vol, ce qui constitue le paramètre le plus important à respecter afin de reproduire un vol à haute vitesse. La mise à l'échelle binaire, appelé aussi 'mise à l'échelle 'ƒÏL', exige que le produit de la densité et de la longueur caractéristique du véhicule soit conservé entre le vol et les conditions expérimentales. Toutefois, il a été montré par Capra (2007) que le transfert de chaleur par rayonnement ne suit pas cette même loi de mise à l'échelle, et la similitude n'est pas crée pour les cas en vol où le transfert de chaleur par rayonnement et par convection sont fortement couplés. Cela peut entraîner d'importantes erreurs dans les estimations des propriétés d'écoulement associée et l'estimation du transfert de chaleur due au rayonnement. L'installation X2 a été modifiée en 2006 pour permettre l'expérimentation à basse pression en mode tube à choc non-réfléchi. L'utilisation d'un tube à choc non-réfléchi a permis la mesure du transfert de chaleur par rayonnement à la densité réelle en vol et supprimé les problèmes d'échelle liés à la mesure des rayonnements sur les véhicules en modèle réduit, au moins pour une partie de l'écoulement. Des mesures ont été effectuées dans la région immédiatement située derrière le choc et le long de la ligne médiane de l'écoulement de base, où le choc reste plan. Les écoulements externes, tels que ceux entourant une capsule de re-enntrée, n'ont pas été reproduits. La limite de basse pression d'exploitation était d'environ 10 Pa, limitée par la croissance de la couche limite sur les murs. / This thesis investigates the radiative heat transfer encountered in rarefied, hypervelocity flow conditions such as would be experienced during an aerocapture mission to Titan. Accurate estimates of the nonequilibrium radiation involved in high speed operations such as reentry are essential in order to design these thermal protection systems more efficiently. Because the mass of the thermal protection system is a large fraction of the overall vehicle mass, there is great interest in designing lighter and more efficient systems. Flight experiments are expensive and restrictive, hence laboratory testing is needed in facilities that are capable of producing hypervelocity flow. Unfortunately, as the size of a typical flight vehicle is too large to reasonably test in experimental facilities, subscale models of the aeroshell vehicles are generally tested. The University of Queensland's expansion tube facilities - X1, X2 and X3 - have been widely used for subscale modelling of hypersonic flowfields (Morgan 2001). Ground testing facilities such as the X2 facility take advantage of binary scaling to test small scale models of flight vehicles, which is the most important parameter to match in order to reproduce high speed flight. Binary scaling, also called 'ƒÏL' scaling, requires that the multiplication of density and the characteristic length of the vehicle be balanced between flight and experimental conditions. However, it was shown by Capra (2007) that radiative heat transfer does not follow this same scaling factor, and true similarity with flight is not created for flows where the radiative and convective heat transfer are strongly coupled. This can result in significant errors in the estimates of the associated flow properties and the estimation of the heat transfer due to radiation. The X2 facility was modified in 2006 to allow experimentation at low pressures in nonreflected shock tube mode. Nonreflected shock tube operation allowed the taking of true-flight density measurements of the radiative heat transfer and removed the scaling problems involved in radiation measurements for model vehicles, at least for part of the flowfield. Measurements were made in the region immediately behind the shock along the centreline of the core flow, where the shock remained planar. External flow fields, such as those surrounding a reentry capsule, were not reproduced. The low density operating limit was approximately 10 Pa, limited by boundary layer growth on the walls.

Most of the research on high strain rate effects on wood since the 1950s has been on impact loading. Very limited work has been conducted on full-scale wood specimens under blast loading. In North America, the prevalence of these structures makes them susceptible to unintended blast effects. The question on how to retrofit and protect these structures against blast loads has still not been addressed adequately, and design provisions for new wood structures against blast are not comprehensive. Far-field explosion effects were simulated using the University of Ottawa shock tube. Twenty-five light-frame wood stud walls were tested dynamically. The research program aimed to determine the response of light-frame wood stud walls to blast loads that correspond to the heavy to blow-out damage levels. The results showed that, under idealized simply supported end conditions, the stud walls failed in flexure. Under heavier loads, ripping of sheathing commonly used in light-frame wood structures was observed, which caused premature failure of the assembly because the load was not fully distributed to the studs. The use of stiffer sheathing or reinforcing the sheathing provided a better load path and the wall was capable of reaching its full capacity. The effect of using realistic boundary connection details was investigated, and the results showed that typical connection detailing performed poorly under blast loads. Designed steel brackets connecting the studs to the rim-joist allowed for the studs to reach their full capacity. An analytical single degree-of-freedom model was generated using material properties obtained from static testing. The model was validated using the experimental results from the shock tube testing. Also, a catcher system consisting of welded-wire-mesh was incorporated into the wall system in order to diminish debris throw.