Letteratura scientifica selezionata sul tema "Accelerated Flames"
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Articoli di riviste sul tema "Accelerated Flames"
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Lou, Bo, Yonghai Qiu e Jianhong Xu. "Characteristics of diffusion flames with accelerated motion". Thermal Science 20, n. 6 (2016): 2113–24. http://dx.doi.org/10.2298/tsci150413180l.
Testo completoAbstract (sommario):
The aim of this work is to present an experiment to study the characteristics of a laminar diffusion flame under acceleration. A Bunsen burner (nozzle diameter 8 mm), using liquefied petroleum gas as its fuel, was ignited under acceleration. The temperature field and the diffusion flame angle of inclination were visualised with the assistance of the visual display technology incorporated in MATLAB?. Results show that the 2-d temperature field under different accelerations matched the variation in average temperatures: they both experience three variations at different time and velocity stages. The greater acceleration has a faster change in average temperature with time, due to the accumulation of combustion heat: the smaller acceleration has a higher average temperature at the same speed. No matter what acceleration was used, in time, the flame angle of inclination increased, but the growth rate decreased until an angle of 90?: this could be explained by analysis of the force distribution within the flame. It is also found that, initially, the growth rate of angle with velocity under the greater acceleration was always smaller than that at lower accelerations; it was also different in flames with uniform velocity fire conditions.
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Zhu, Yuejin, Lei Yu, Gang Dong, Jianfeng Pan e Zhenhua Pan. "Flow Topology of Three-Dimensional Spherical Flame in Shock Accelerated Flows". Advances in Materials Science and Engineering 2016 (2016): 1–12. http://dx.doi.org/10.1155/2016/3158091.
Testo completoAbstract (sommario):
The flow topologies of compressible large-scale distorted flames are studied by means of the analysis of the invariants of the velocity gradient tensor (VGT). The results indicate that compressibility plays a minor role in the distorted flame zone. And the joint probability density function (p.d.f.) of the Q-R diagram appears as a teardrop shape, which is a universal feature of turbulence. Therefore, the distorted flame exhibits the characteristic of large-scale turbulence combustion, especially behind the reflected shock wave, while the p.d.f. of the QS⁎-QW diagram implies that the dissipation is enhanced in the compression and expansion regions, where it is higher than that when P=0. Furthermore, we identify that the flame evolution is dominated by rotation by means of a quantitative statistical study, and the SFS topology is the predominant flow pattern. Not surprisingly, negative dilatation could suppress the unstable topologies, whereas positive dilatation could suppress the stable topologies.
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Dunn-Rankin, D., e M. A. McCann. "Overpressures from nondetonating, baffle-accelerated turbulent flames in tubes". Combustion and Flame 120, n. 4 (marzo 2000): 504–14. http://dx.doi.org/10.1016/s0010-2180(99)00109-1.
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Boettcher, Philipp A., Shyam K. Menon, Brian L. Ventura, Guillaume Blanquart e Joseph E. Shepherd. "Cyclic flame propagation in premixed combustion". Journal of Fluid Mechanics 735 (23 ottobre 2013): 176–202. http://dx.doi.org/10.1017/jfm.2013.495.
Testo completoAbstract (sommario):
AbstractIn experiments of hot surface ignition and subsequent flame propagation, a puffing flame instability is observed in mixtures that are stagnant and premixed prior to ignition. By varying the size of the hot surface, power input, and combustion vessel volume, it was determined that the instability is a function of the interaction of the flame, with the fluid flow induced by the combustion products rather than the initial plume established by the hot surface. Pressure ranges from 25 to 100 kPa and mixtures of n-hexane/air with equivalence ratios between $\phi = 0. 58$ and 3.0 at room temperature were investigated. Equivalence ratios between $\phi = 2. 15$ and 2.5 exhibited multiple flame and equivalence ratios above $\phi = 2. 5$ resulted in puffing flames at atmospheric pressure. The phenomenon is accurately reproduced in numerical simulations and a detailed flow field analysis revealed competition between the inflow velocity at the base of the flame and the flame propagation speed. The increasing inflow velocity, which exceeds the flame propagation speed, is ultimately responsible for creating a puff. The puff is then accelerated upward, allowing for the creation of the subsequent instabilities. The frequency of the puff is proportional to the gravitational acceleration and inversely proportional to the flame speed. A scaling relationship describes the dependence of the frequency on gravitational acceleration, hot surface diameter, and flame speed. This relation shows good agreement for rich n-hexane/air and lean hydrogen/air flames, as well as lean hexane/hydrogen/air mixtures.
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Kiverin, Alexey, Alexey Tyurnin e Ivan Yakovenko. "On the Critical Condition for Flame Acceleration in Hydrogen-Based Mixtures". Materials 16, n. 7 (31 marzo 2023): 2813. http://dx.doi.org/10.3390/ma16072813.
Testo completoAbstract (sommario):
The paper presents a novel numerical approach to the quantitative estimation of the concentration limits for flame acceleration in hydrogen-based mixtures. A series of calculations are carried out for hydrogen–air and hydrogen–oxygen flames in channels. The analysis of the obtained numerical results provided the value of 11 ± 0.25 % hydrogen content in the mixture as a lean concentration limit of flame acceleration that agrees well with the available experimental data. Moreover, the basic physical mechanism responsible for the transition from the steady mode of flame propagation to the accelerated one is distinguished. The mechanism is related to flame stretching in the region of interaction with the boundary layer and the competition between the joint increase in burning rate and heat losses. The novel technique for the estimation of concentration limits of flame acceleration presented here can be applied to assess combustion conditions inside combustors of energy and propulsion systems fed with hydrogen. The results are also useful in estimating explosion and fire risks in hydrogen storage, transport, and utilization facilities as parts of hydrogen energy and propulsion systems.
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Xu, Cong, Junguang Lin, Zhihua Wang, Kaidi Wan, Shien Sun e Zhijun Zhou. "Three-Dimensional Direct Numerical Simulation of Near-Field Ozone-Enhanced Lean Premixed Syngas Turbulent Jet Flame". Energies 15, n. 11 (26 maggio 2022): 3945. http://dx.doi.org/10.3390/en15113945.
Testo completoAbstract (sommario):
Due to its enhancement in the flame speed, ozone added in lean premixed syngas turbulent jet flame was investigated by the three-dimensional direct numerical simulation method in the near field of the flame. In the present study, numerical simulations were conducted in the lean premixed syngas turbulent jet flame configuration to explore the effects of ozone addition on freely-propagating turbulent flames. It was seen that turbulence began to significantly affect the flame surface to produce wrinkles in lean premixed gas flame with ozone added after 4D; ozone started to affect the composition field and temperature field after 8D; it accelerated the generation of intermediate products, OH and O radicals; and it will promote the production of CO2 in the near field range. Ozone will increase the flame surface area of the lean premixed syngas flame during the ignition period and can promote the ignition process and make the combustion occur earlier. The flame surface of the case with ozone added is more easily stretched by turbulence, and ozone can improve the stability of combustion. Ozone does not affect the effective radius of the flame curvature but will broaden the distribution of the curvature term because of the enhancement effect on the displacement speed of the flame surface.
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Di Sarli, V., A. Di Benedetto, G. Russo, S. Jarvis, E. J. Long e G. K. Hargrave. "Large Eddy Simulation and PIV Measurements of Unsteady Premixed Flames Accelerated by Obstacles". Flow, Turbulence and Combustion 83, n. 2 (11 febbraio 2009): 227–50. http://dx.doi.org/10.1007/s10494-008-9198-3.
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Zhang, Xiaoliang, Shibing Kuang, Yanli Zhao, Jun Zhang e Shengfeng Luo. "Experimental Investigation and Theoretical Analysis of Flame Spread Dynamics over Discrete Thermally Thin Fuels with Various Inclination Angles and Gap Sizes". Fire 7, n. 6 (23 maggio 2024): 177. http://dx.doi.org/10.3390/fire7060177.
Testo completoAbstract (sommario):
Flame spread over discrete fuels is a typical phenomenon in fire scenes. Experimental and theoretical research on flame spread over discrete thermally thin fuels separated by air gaps with different inclination angles was conducted in the present study. Experiments with six inclination angles ranging from 0° to 85° and various fuel coverage rates from 0.421 to 1 were designed. The flame spread behavior, the characteristic flame size, and the flame spread rate were analyzed. The results show that the flow pattern, stability, and flame size exhibit different characteristics with different inclination angles and gap sizes. As the inclination angle increases, particularly with smaller gaps, turbulent and oscillating flames are observed, while larger gap sizes promote flame stability. The mechanism of flame propagation across the gap depends on the interplay between the flame jump effect and heat transfer, which evolves with gap size. Average flame height, average flame width, and flame spread rate initially increase and then decline with the increase in fuel coverage, peaking at fuel coverage rates between 0.93 and 0.571 for different inclination angles. A theoretical model is proposed to predict the flame spread rate and the variation in the flame spread rate with inclination angle and fuel coverage. Furthermore, the map determined by inclination angle and fuel coverage is partitioned into distinct regions, comprising the accelerated flame spread region, the flame spread weakening region, and the failed flame spread region. These findings provide valuable insights into flame spread dynamics over discrete thermally thin fuels under diverse conditions.
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Schneider, F. R. N., O. H. Ramírez-Agudelo, F. Tramper, J. M. Bestenlehner, N. Castro, H. Sana, C. J. Evans et al. "The VLT-FLAMES Tarantula Survey". Astronomy & Astrophysics 618 (ottobre 2018): A73. http://dx.doi.org/10.1051/0004-6361/201833433.
Testo completoAbstract (sommario):
The 30 Doradus (30 Dor) nebula in the Large Magellanic Cloud (LMC) is the brightest HII region in the Local Group and a prototype starburst similar to those found in high redshift galaxies. It is thus a stepping stone to understand the complex formation processes of stars in starburst regions across the Universe. Here, we have studied the formation history of massive stars in 30 Dor using masses and ages derived for 452 mainly OB stars from the spectroscopic VLT-FLAMES Tarantula Survey (VFTS). We find that stars of all ages and masses are scattered throughout 30 Dor. This is remarkable because it implies that massive stars either moved large distances or formed independently over the whole field of view in relative isolation. We find that both channels contribute to the 30 Dor massive star population. Massive star formation rapidly accelerated about 8 Myr ago, first forming stars in the field before giving birth to the stellar populations in NGC 2060 and NGC 2070. The R136 star cluster in NGC 2070 formed last and, since then, about 1 Myr ago, star formation seems to be diminished with some continuing in the surroundings of R136. Massive stars within a projected distance of 8 pc of R136 are not coeval but show an age range of up to 6 Myr. Our mass distributions are well populated up to 200 M⊙. The inferred IMF is shallower than a Salpeter-like IMF and appears to be the same across 30 Dor. By comparing our sample of stars to stellar models in the Hertzsprung–Russell diagram, we find evidence for missing physics in the models above log L/L⊙ = 6 that is likely connected to enhanced wind mass loss for stars approaching the Eddington limit. Our work highlights the key information about the formation, evolution and final fates of massive stars encapsulated in the stellar content of 30 Dor, and sets a new benchmark for theories of massive star formation in giant molecular clouds.
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Hamed, AM, AE Hussin, MM Kamal e AR Elbaz. "Combustion of a hydrogen jet normal to multiple pairs of opposing methane–air mixtures". Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 231, n. 2 (6 gennaio 2017): 145–58. http://dx.doi.org/10.1177/0957650916685944.
Testo completoAbstract (sommario):
The combustion performance of a cylindrical burner accommodating up to six multiple pairs of opposing methane–air mixtures with a cross-flow of hydrogen was addressed. The cross-flow initially duplicated the stagnation impact and enriched the vortical structures. Aided by the resulting flow strain, the transport of heat and active species from the hydrogen oxidation zone to the methane reaction zones accelerated the combustion across the opposing premixed flames and reduced the peak temperature across the outer diffusion flame. Increasing the cross-flow/opposing jets’ velocity ratio to 0.89 merged the two stagnation centers and maximized the shearing stress. By the slight increase in the velocity ratio to 1.07, the H and OH pools provided for methane combustion became closer to the ports such that a hydrogen/methane mass percent of 10.3% extended the stoichiometric blowout velocity from 28.3 to 35.7 m/s. Since the turbulent kinetic energy thus increased to 8.4 m2/s2, the firing intensity reached values as high as 48.2 MW/m3. Not only was there a reduction in the residence time for NOx formation, but also the blowout velocity relative gain overrode the relative increase in the NOx formation rates such that the NOx emission index decreased to 17 g/MWhr. By the excessive increase in velocity ratio, the vortical structures shrank such that the NOx exponential increase became dominant above 21 ppm. With fuel-lean mixtures, the hydrogen was partially combusted by the excess air from the opposing flames but the blowout velocity decreased to 13.1 m/s at Φ = 0.50. The hydrogen flame NOx emissions decreased by providing the excess air at larger jets’ diameter/separation ratios, thus reducing the residence times for thermal NOx formation and simultaneously interrupting the prompt NOx formation. At the lean operational limit, tripling the number of opposing jets decreased the hydrogen flame length by 54% such that the NOx emissions decreased by 38.4%.
Tesi sul tema "Accelerated Flames"
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Vastier, Laura. "Étude de la propagation de flamme dans une atmosphère gazeuse représentative de la phase tardive d'un accident grave dans un REP". Electronic Thesis or Diss., Orléans, 2024. http://www.theses.fr/2024ORLE1020.
Testo completoAbstract (sommario):
La France possède aujourd'hui 58 réacteurs nucléaires qui permettent de fournir trois quarts de l'énergie nécessaire au bon fonctionnement de la vie quotidienne de ses 67 millions d'habitants. Cependant, cette source d'énergie n'est pas exempte d'incidents ou d'accidents, dont la gravité est classée dans ce que l'on appelle l'échelle INES (International Nuclear Event Scale).Dans le contexte de l'étude des accidents graves des réacteurs refroidis à l'eau, le risque hydrogène est défini comme la possibilité d'une perte de l'intégrité du confinement du réacteur ou de ses systèmes de sûreté à la suite d'une combustion de l'hydrogène. L'hydrogène est issu principalement de l'oxydation du zirconium des gaines et des structures des éléments combustibles lors de la phase de dégradation du cœur et de l'oxydation des métaux présents dans le bain de corium (cœur fondu) ou dans le radier lors de l'interaction du corium et du béton (phase tardive de l'accident grave). Cette interaction génère aussi un autre gaz combustible : le monoxyde du carbone. L'hydrogène et le monoxyde de carbone ainsi produits sont transférés puis transportés dans l'enceinte par les boucles de convection induites essentiellement par la condensation de la vapeur émise via la brèche primaire ou lors de l'interaction corium/béton. Suivant le brassage de l'atmosphère de l'enceinte, la répartition d'hydrogène et du monoxyde de carbone dans l'enceinte de confinement se fait de manière plus ou moins homogène. En cas de forte hétérogénéité, ces gaz combustibles peuvent atteindre des concentrations locales importantes qui dépassent le seuil d'inflammabilité du mélange gazeux. Ce travail s'intéresse à la caractérisation expérimentale des conditions d'inflammation des mélanges gazeux représentatifs de l'atmosphère de l'enceinte de confinement lors de la phase tardive d'un accident grave. À cet égard, les effets du manque d'oxygène, de la pression et de la température sont instruits. Pour ce faire, deux dispositifs expérimentaux ont été utilisés : une bombe sphérique permettant de déterminer l'influence de plusieurs paramètres initiaux sur les limites d'inflammabilité des mélanges H2/CO/Air, et une enceinte d'accélération de flamme dans le but de voir le comportement de ces flammes en présence d'obstacles dans un tube fermé représentant l'intérieur d'un REP (Réacteur à Eau Pressurisée)France currently has 58 nuclear reactors, which provide approximately three quarters of the energy needed to run the daily lives of its 67 million inhabitants. Nevertheless, this source of energy is not immune to incidents and accidents, the severity of which is classified on the International Nuclear Event Scale (INES). In the context of the study of severe accidents in water-cooled reactors, the term "hydrogen risk" is defined as the possibility of a loss of containment integrity in the reactor or its safety systems as a result of hydrogen combustion. Hydrogen is produced primarily by the oxidation of zirconium in fuel element cladding and structures during the core degradation phase, and by the oxidation of metals in the corium bath (molten core) or in the raft during the interaction of corium and concrete (late phase of a severe accident). This interaction also generates another combustible gas : carbon monoxide. The hydrogen and carbon monoxide produced in this manner are conveyed and subsequently transported into the containment via convection loops, which are primarily caused by the condensation of steam emitted via the primary breach or during the corium/concrete interaction. The distribution of hydrogen and carbon monoxide within the containment is either more or less homogeneous, depending on the mixing of the containment atmosphere. In the event of strong heterogeneity, the combustible gases can reach significant local concentrations that exceed the flammability threshold of the gas mixture.This study is concerned with the experimental characterisation of the ignition conditions of gas mixtures representative of the atmosphere in the containment during the late phase of a severe accident. The impact of oxygen deficiency, pressure and temperature are examined. In order to achieve this objective, two experimental devices were employed : a spherical bomb was utilized to ascertain the impact of a number of initial parameters on the flammability limits of H2/CO/Air mixtures, while a flame acceleration tube was employed to observe the behavior of these flames in the presence of obstacles within a closed tube, which represented the interior of a PWR (Pressurized Water Reactor)
Libri sul tema "Accelerated Flames"
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Chuck, C. Combusting flow simulations of detonation and shock-induced combustion waves for ram accelerator configurations with viscous effect. Washington, D. C: American Institute of Aeronautics and Astronautics, 1991.
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Henning, Harald Martin Jakob. The influence of the heliospheric current sheet and angular separation on flare accelerated solar wind. Stanford, Calif: Center for Space Science and Astrophysics, Stanford University, 1985.
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J, Murphy R., e United States. National Aeronautics and Space Administration., a cura di. ⁷Li and ⁷Be deexcitation lines: Probes for accelerated particle transport models in solar flares. [Washington, DC: National Aeronautics and Space Administration, 1991.
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United States. National Aeronautics and Space Administration., a cura di. Determination of solar flare accelerated ion angular distributions from SMM gamma-ray and neutron measurements and Determination of the ³He/H ratio in the solar photosphere from SMM gamma-ray measurements: Final technical report, NASA grant NAG 5-945 (07/01/87 to 08/31/89). [Washington, DC: National Aeronautics and Space Administration, 1990.
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Office, General Accounting. Department of Energy: Accelerated closure of Rocky Flats : status and obstacles : report to the Chairman, Committee on Armed Services, U.S. Senate. [Washington, D.C.]: The Office, 1999.
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Mody, Ashoka. Epilogue. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780199351381.003.0012.
Testo completoAbstract (sommario):
This concluding chapter argues that the EuroTragedy was that critics—outsiders and insiders—warned of the euro's economic flaws and the likely political damage it could do. Wrapped in an obsessive groupthink, European leaders portrayed the single currency as a “pro-European” enterprise. However, the euro delivered none of the economic benefits promised. Some analysts had predicted that the euro would cause the share of trade between Eurozone countries to increase; instead, even before the global crisis had started in 2007, the share of within-Eurozone trade had started declining and that tendency accelerated after the crisis began. When the inevitable financial crisis came—first as a global crisis and then as a rolling Eurozone crisis—the euro caused the most damage in the weakest Eurozone countries, widening existing income disparities. The chapter then points to specific measures to improve the functioning of the Eurozone.
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Determination of solar flare accelerated ion angular distributions from SMM gamma-ray and neutron measurements and Determination of the ³He/H ratio in the solar photosphere from SMM gamma-ray measurements: Final technical report, NASA grant NAG 5-945 (07/01/87 to 08/31/89). [Washington, DC: National Aeronautics and Space Administration, 1990.
Cerca il testo completoCapitoli di libri sul tema "Accelerated Flames"
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Uchida, Shu. "Georgia as a Case Study of EU Influence, and How Russia Accelerated EU-Russian relations". In Managing Security Threats along the EU’s Eastern Flanks, 131–51. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-26937-1_6.
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Reames, Donald V. "Distinguishing the Sources". In Solar Energetic Particles, 49–69. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-66402-2_3.
Testo completoAbstract (sommario):
AbstractOur discussion of history has covered many of the observations that have led to the ideas of acceleration by shock waves or by magnetic reconnection in gradual and impulsive solar energetic particle (SEP) events, respectively. We now present other compelling observations, including onset timing, SEP-shock correlations, injection time profiles, high-energy spectral knees, e/p ratios, and intensity dropouts caused by a compact source, that have helped clarify these acceleration mechanisms and sources. However, some of the newest evidence now comes from source-plasma temperatures. In this and the next two chapters, we will find that impulsive events come from solar active regions at ≈ 3 MK, controlling ionization states Q, hence A/Q, and, in most gradual events, shocks accelerate ambient coronal material from ≤1.6 MK. When SEPs are trapped on closed loops they supply the energy for flares. In addition to helping to define their own origin, SEPs also probe the structure of the interplanetary magnetic field.
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Fullstone, Gavin. "Rapid Particle-Based Simulations of Cellular Signalling with the FLAME-Accelerated Signalling Tool (FaST) and GPUs". In Methods in Molecular Biology, 191–212. New York, NY: Springer US, 2023. http://dx.doi.org/10.1007/978-1-0716-3008-2_9.
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Jackson, Rowan, Steven Hartman, Benjamin Trump, Carole Crumley, Thomas McGovern, Igor Linkov e AEJ Ogilvie. "Disjunctures of Practice and the Problems of Collapse". In Perspectives on Public Policy in Societal-Environmental Crises, 75–108. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-94137-6_7.
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AbstractThis chapter asks what insights long-term historical information from before the Great Acceleration and Anthropocene might offer to policy and practice in the twenty-first century. Conventional sustainability research usually focuses on shallower time horizons that could miss insightful environmental and social processes evolving over centuries to millennia. Although we push for increased engagement with historical researchers, parallels between pre-modern and contemporary environmental and societal challenges need to be treated with caution. So-called cases of societal collapse—often associated with environmental calamities—provide limited or at best flawed parallels with challenges faced today. The pitfalls of reductionism and determinism that often attend collapse discourse account for social agency and complexity in incomplete and unconvincing ways. Instead, we argue that historical evidence should serve as context to environmental problems faced today, as antecedents of the accelerated environmental change of later modernity rather than as direct analogies. Historical antecedents can be understood, to an extent, as previous experiments against which to test and improve theory or to structure possibilistic scenarios that help anticipate unexpected social and environmental challenges. In concluding, we suggest that researcher in historical sciences and the humanities require resources, space and incentives to explore sticky questions of uncertainty, risk, and vulnerability to environmental change together with global change researchers, policymakers, and environmental practitioners.
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Bellantoni, Christina. "The End of the Institutionalist". In Disruption?, 221–42. Oxford University PressNew York, 2024. http://dx.doi.org/10.1093/oso/9780197767832.003.0013.
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Abstract Donald Trump’s presidency accelerated what had been slowly happening in the Senate. People from both parties who had been willing to work together had increasingly less incentive to do so, even institutionalists who had always revered traditions and decorum over combative politics. At the same time, the Washington ecosystem and especially the news media did nothing but fan the flames. Using a mix of first-person narrative and reporting, this chapter explores the concept of moderation in the Senate, which among Republicans simply came to translate as “not Trump.” The Senate continued on after Trump—and has even accomplished big, bipartisan things under President Biden. But it’s broken. Shattered, even. Trump’s time in office gave no one the incentive to pick up the pieces. In the end, the chapter concludes that the Trump-era Senate prompted the end of the institutionalist.
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Ostrer, Harry. "Accelerated Rates of Mutation". In Non-Mendelian Genetics in Humans, 145–68. Oxford University PressNew York, NY, 1998. http://dx.doi.org/10.1093/oso/9780195068771.003.0009.
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Abstract The rate of mutation may be accelerated so that new alleles form in a high proportion of daughter cells. An increased rate of mutation may be a feature of a gene’s structure, which causes its replication to be unfaithful. These structures are commonly referred to as premutations. Alternatively, the machinery for replicating DNA or for repairing replication errors may be flawed as the result of a cell’s genetic constitution or its exposure to mutagenic agents. When these processes alter a mutant gene in the germ line, some offspring are nonpenetrant, whereas others are more severely affected than their parents. If the alteration of a gene occurs preferentially in either an egg or a sperm cell, then there may be a parent-of-origin effect. When these defects occur in gametes or in embryonic somatic cells, they may cause developmental abnormalities. When the mutations occur in somatic cells, they may be lethal to the cell, or they may confer a growth advantage and may even cause the cell to be malignant.
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Furman, C. Sue. "The Silent Epidemic". In Turning Point, 95–110. Oxford University PressNew York, NY, 1995. http://dx.doi.org/10.1093/oso/9780195087734.003.0006.
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Abstract It is difficult to ignore menopause symptoms like hot flashes and vaginal dryness, but osteoporosis, one of the more serious consequences of menopause, often proceeds unnoticed for years. Unfonunately, what you don’t feel can bun you. Osteoporosis accelerates the gradual rate of bone loss that is normal as one ages. This silent disease eats away at bones, leaving them porous, brittle, and very fragile. The bone that is left is normal, but sometimes there is not enough of it to maintain the integrity of the skeleton and suppon the body’s weight.
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Mishra, Ritu, Saumya Singh e Suruchi Pandey. "The Impact of Technological Advances on Cultural Conflicts within Organizations". In Business, Management and Economics. IntechOpen, 2023. http://dx.doi.org/10.5772/intechopen.113095.
Testo completoAbstract (sommario):
Although some beliefs and norms may not change, as few hold the opinion “culture reflects the heritage of society” rapid pace of digitization and pressures of global competitiveness have accelerated the organizational changing processes and employees behavior patterns. When people from various cultures get together, it might lead to misunderstandings and hostilities. Recent decades have seen significant shifts in cultural norms and values as a direct result of technological advancements. These shifts are happening faster than ever before, and they are causing tension between different cultures which is negatively impacting their Performance. This chapter will examine how technological advancements have influenced culture, and the impact of organizational culture on employee performance and behavior. And contain broad introspective musings on Cultural Shifts and historical contemporary roles of digital technologies; defining traits that encode in our minds and support positive behavior. Rest sections focus on flawed human characteristics with the concept of culture and how it is defined to examine the ways in which technology can lead to cultural change in Employees and the potential for conflict that might come from these changes. The last section will discuss the societal consequences of technologically-induced cultural shifts and techniques to cope with them.
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Kaminski, Josilene de Souza da Conceição, Aline dos Santos Moreira de Carvalho e Paloma Martins Mendonça. "Similarities of clinical practice guidelines in the management of lower pain: Literature review". In Collection of Internacional Topics in Health Sciences V.2. Seven Editora, 2024. http://dx.doi.org/10.56238/sevened2024.016-025.
Testo completoAbstract (sommario):
Introduction: Clinical practice guidelines aim to assist reasoning and clinical decision-making, improve the effectiveness and efficiency of health care and standardize conduct, including care for patients with low back pain. Considering that evidence-based practice is necessary and that healthcare decisions integrate scientific evidence, knowledge and early adherence by healthcare professionals to clinical practice guidelines can accelerate recovery and reduce costs associated with low back pain. There is no informational material that is easy to read and interpret that encompasses the similarities of important national and international guidelines in the management of low back pain. Objective: To unify the similarities in the practice guidelines of low back pain clinics, involving diagnosis and request for imaging exams, to later prepare informative material for health professionals on this topic. Methods: This is a literature review, with a bibliographic survey carried out in electronic databases: National Library of Medicine (Medicine–PubMed), Medical Literature Analysis and Retrieval System (Medline), Latin American and Caribbean Literature in Health Sciences (Lilacs), Scientific Electronic Library Online (SciELO) and Google Scholar. Results: Ten guidelines were part of this study. Recommendations for taking anamnesis and physical examination were found in all guidelines. Diagnostic screening aims to identify patients with specific conditions as the cause of low back pain, in addition to the possibility of the presence of red and yellow flags. All guidelines discussed recommend that imaging should be avoided unless there is clinical suspicion of red flag pathology, or severe or progressive neurological deficit, such as radiculopathy, neurogenic claudication, or if imaging is likely to guide additional management. Conclusion: Clinical practice guidelines for low back pain present well-established similarities in the management of low back pain. Most have common information regarding anamnesis, physical and neurological examinations and request for imaging exams. All guidelines in this study agree that imaging exams should be avoided. The preparation of the informative material will be presented in a future article, which will assist health professionals in better managing low back pain.
Atti di convegni sul tema "Accelerated Flames"
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Yoko, Matthew, e Matthew P. Juniper. "Inferring Flame Transfer Functions of Turbulent Conical Flames From Pressure Measurements". In ASME Turbo Expo 2024: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2024. http://dx.doi.org/10.1115/gt2024-122798.
Testo completoAbstract (sommario):
Abstract We use approximate Bayesian inference, accelerated by adjoint methods, to construct a quantitatively accurate model of the thermoacoustic behaviour of a turbulent conical flame in a duct. We first perform a series of automated experiments to generate a data set. The data consists of time series pressure measurements from which we extract (i) the eigenvalue, whose real part is the growth rate and imaginary part is the angular frequency, and (ii) the pressure eigenmode measured at several axial locations. We assimilate the data into a thermoacoustic network model to infer the unknown model parameters. We begin this process by rigorously characterizing the acoustics of the cold rig. We then introduce a series of different flames and infer their flame transfer functions with quantified uncertainty bounds. The flame transfer function is obtained with the flames in situ, so it accounts for any confinement or heat loss effects. The inference process uses only pressure measurements, so the technique is suitable for complex combustors where optical access is not available, provided the eigenvalue or eigenmode of oscillations can be measured. We validate the method by comparing the inferred fluctuating heat release rate against direct measurements. We find that the inferred quantities compare well with the direct measurements, but the uncertainty bounds can be large if the experimental error is large.
2
Biagioli, Fernando, Ewald Freitag e Khawar J. Syed. "Analytical Modelling of Flame-Dynamics Within Auto-Ignition Hydrogen and Methane Flames in Mach Stabilized Combustion". In ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-102235.
Testo completoAbstract (sommario):
Abstract The sequential combustion concept is characterized by two combustor stages. In the first stage a fraction of the fuel is premixed into the air flow before burning in a standard lean premixed flame. In the second stage, which is the focus of the present contribution, the remaining part of the fuel is injected into the hot products arriving from the first stage and combustion takes place in an autoignition-dominated flame. We analyse here a situation where auto-ignition in the second stage takes place in a flow subject to a positive static temperature gradient. This concept allows very short combustor residence times ans is well suited for incorporation into an integrated combustor-nozzle guide vane. In order to set up the static temperature gradient, the mixture of reactants flows through a converging-diverging channel, first accelerated to a relatively high Mach number, ca. M = 0.6, and then decelerated in the diffusing section where the flame is located. A fully analytical model describing the thermo-acoustics behaviour of the converging-diverging combustor is developed. The critical part of this exercise is given by modelling the frequency response of the heat release rate concentrated at the position of the auto-igniting flame. It is shown here how this is closely related to the response of the displacement of the flame for which a novel analytical model, free from empirical assumptions, is provided. The model is finally applied to compare hydrogen and methane flames in terms of their thermo-acoustic behaviour.
3
Nassini, Pier Carlo, Daniele Pampaloni, Antonio Andreini e Roberto Meloni. "Large Eddy Simulation of Lean Blow-Off in a Premixed Swirl Stabilized Flame". In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-90856.
Testo completoAbstract (sommario):
Abstract Modern gas turbines usually adopt very lean premixed flames to meet the current strict law restrictions on nitric oxides emissions. In such devices, strong combustion instabilities and blow-off susceptibility often prevent from achieving a stable flame in leaner conditions. Numerical models to predict the lean blow-off in turbulent flames are essential to prevent such instabilities, but the simulation of blow-off still represents a challenge, requiring the appropriate modelling for the turbulence-chemistry interactions and the highly transient behaviour of the flame near the extinction limit. The present work explores the capabilities of the widely-used Flamelet Generated Manifold model in predicting the lean blow-off of a turbulent swirl-stabilized premixed flame within LES framework. An atmospheric premixed methane-air flame, experimentally studied at the University of Cambridge, is firstly analyzed in three operating conditions approaching blow-off to validate the numerical setup. An extended Turbulent Flame Closure (TFC) model, implemented within the FGM framework in Fluent to introduce the effect of stretch and heat loss on the flame, reproduces the evolution of the key flame characteristics. Then, the chosen setup is used to study the blow-off inception and the dynamics in two conditions with different flow rate. An accelerated numerical procedure with progressive step reductions of equivalence ratio is used to trigger the blow-off. The extinction equivalence ratio is predicted quite accurately, showing that the Extended TFC is suitable for the study of the blow-off, without an increase in computational cost. The validity of the model could be extended, allowing the study of lean blow-off in realistic conditions and complex flames of gas turbine combustors.
4
Pugh, Daniel, Andrew Crayford, Philip Bowen, Tim O’Doherty e Richard Marsh. "Variation in Laminar Burning Velocity and Markstein Length With Water Addition for Industrially Produced Syngases". In ASME Turbo Expo 2014: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-25455.
Testo completoAbstract (sommario):
An outwardly propagating spherical flame has been used to characterise the influence of water addition on the combustion of variable steelworks gas compositions. Attention was given to the ratio of hydrogen and carbon monoxide within blast furnace gas, and the catalysing influence of water addition on the preponderant reaction kinetics. A nonlinear extrapolative technique was used to obtain values of laminar burning velocity and Markstein length for atmospheric combustion with air and change in equivalence ratio. Four disparate blast furnace gas mixtures were tested with increasing volumetric proportions of hydrogen in the range of one to seven percent, displacing other constituent fractions. A non-monotonic influence was observed, with propagation accelerated for compositions comprising smaller amounts of hydrogen, and the cooling impact of water addition shown to slow faster burning flames. Water addition was also shown to increase the effects of flame stretch on observed propagation rates, and the contrasting influences resulting from vapour fraction are discussed with respect to practical combustion instability, in addition to alternative synthesised fuels. Numerically modelled results were generated using the PREMIX coded CHEMKIN-PRO, and the performance of specified chemical reaction mechanisms evaluated in relation to the obtained experimental data.
5
Eder, Alexander J., Bayu Dharmaputra, Marcel Désor, Camilo F. Silva, Alex M. Garcia, Bruno Schuermans, Nicolas Noiray e Wolfgang Polifke. "Generation of Entropy Waves by Fully Premixed Flames in a Non-Adiabatic Combustor With Hydrogen Enrichment". In ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-102833.
Testo completoAbstract (sommario):
Abstract Thermoacoustic combustion instability is a major concern in gas turbine combustors with hydrogen-enriched fuels. Unsteady combustion not only generates acoustic waves, but it may also result in fluctuations of burnt gas temperature, referred to as entropy waves. They are convected by the mean flow through the combustor and can cause indirect combustion noise when they are accelerated at the exit. In this work, we demonstrate that entropy waves occur in a fully premixed burner due to unsteady heat transfer at the combustion chamber wall. This mechanism of entropy generation is often neglected in the literature. This work shows an additional mechanism in CH4-H2-air flames, through which entropy may be created even in the fully premixed case. This is due to differential diffusion which generates local fluctuations in equivalence and carbon-to-hydrogen ratios. An adiabatic flame temperature is defined based on these two quantities to examine the influence of differential diffusion on the generation of entropy fluctuations. The generation of entropy waves is investigated by applying system identification (SI) to time series data obtained from a broadband forced large eddy simulation (LES) coupled with a heat conduction solver. The entropy transfer function (ETF) and flame transfer function (FTF) identified are then compared to experimental data obtained with tunable diode laser absorption spectroscopy with wavelength modulation spectroscopy (TDLAS-WMS) for measuring temperature fluctuations, and the multi-microphone method (MMM), respectively. After validating the computational setup, the entropy frequency response is identified at various positions within the combustion chamber, and the effects of generation and convective dispersion of entropy waves are qualitatively investigated. We show that a fully premixed turbulent system may exhibit significant entropy waves caused by wall heat losses and differential diffusion of hydrogen.
6
Syed, K. J., A. C. Benim, E. Pasqualotto e R. C. Payne. "A Novel Approach to the Stabilization of Auto-Igniting Flames Within a Gas Turbine Sequential Combustor, Through the Control of Static Temperature Variation Along the Premixing and Flame Zones". In ASME Turbo Expo 2020: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/gt2020-14225.
Testo completoAbstract (sommario):
Abstract The present work proposes a novel concept for a sequential burner and combustor that can be located downstream of a first stage combustor or downstream of a turbine stage in the case of a reheat gas turbine. The novel aspect is the method of flame anchoring, which, instead of relying on dump expansion as in the present state-of-the-art, relies on setting up a static temperature gradient through the premixing and flame zones. The advantage of this is that anchoring of the auto-igniting flame is not dependent on fluid mechanic phenomena, and reaction can proceed at rates governed by the chemical kinetics. Under these circumstances, CO can reach its equilibrium in ≪ 1ms, which allows for compactness and the potential of single digit NOx emissions at hot gas temperatures in excess of 2100K. Pressure loss is a critical aspect, as the concept requires flows to be accelerated to high velocities (M∼0.7). However, it is shown that pressure losses can be limited to 4–5%. The concept is evaluated through analytical and 1D approaches, while the feasibility of achieving a design that meets the desired turbulence characteristics at an acceptable pressure loss is demonstrated by way of 3D CFD.
7
Shunn, L., F. Ham, H. A. Elasrag, J. Hoke e S. Alexander Schumaker. "GPU-Accelerated High-Fidelity Rotating Detonation Engine Simulations Using an Extended Flamelet Progress Variable Approach". In ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-101483.
Testo completoAbstract (sommario):
Abstract A fast approach is introduced to aid the evaluation and design of rotating detonation engines (RDEs) using large eddy simulation (LES). The new approach implements an extended flamelet progress variable model in the GPU-accelerated charLES CFD solver from Cascade Technologies. In the extended flamelet approach, tabulated reaction rates from unstretched laminar premixed flames are parameterized and scaled to describe the high-pressure detonation conditions in RDEs. The reaction rate scaling parameters are trained using Zeldovich-von Neumann-Döring (ZND) detonation solutions over a wide range of operating conditions. Sensitivity analysis is performed to assess the impact of the regression algorithm and best-fit scaling parameters on the reconstructed reaction rates. The method is applied to LES of the AFRL 6-inch rotating detonation engine with non-premixed injection of hydrogen in air. The GPU-resident charLES solver demonstrates speedup of almost two orders of magnitude compared to conventional CPU-based solvers and achieves turnaround of high-fidelity RDE simulations in less than one day on modest GPU resources — a critical threshold to enable the use of LES within a design cycle. The combination of reduced-order flamelet modeling and efficient GPU acceleration makes the overall approach a viable candidate for design exploration and optimization of practical RDEs.
8
Feldick, Andrew M., e Gopalendu Pal. "A New Accelerated Approach for Spectral Radiation Calculation Using K Distribution and Discrete Ordinate Methods With Application in Industrial Combustion Systems". In ASME 2019 Heat Transfer Summer Conference collocated with the ASME 2019 13th International Conference on Energy Sustainability. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ht2019-3636.
Testo completoAbstract (sommario):
Abstract The introduction of higher fidelity spectral models into a Discrete Ordinates Method (DOM) RTE solver introduces the challenge of solving the N(N+2) coupled equations in intensity over many spectral points. The inability to store intensity fields leads to a nonlinear increase in computational cost as compared to basic gray models, as the solution in an evolving field must be recalculated at each radiation time step. In this paper an approximate initialization approach is used to a reconstructed values of the intensities. This approach is particularly well suited to spectrally reordered methods, as the boundary conditions and scattering coefficients are gray. This approach leads to more tractable computational time, and is demonstrated using on two industrial scale flames.
9
Biagioli, Fernando, Holger Luebcke, Ammar Lamraoui, Khawar J. Syed e André Theuer. "Stabilization of Auto-Igniting Flames Within a Gas Turbine Sequential Combustor, Through the Control of Static Temperature Variation - Detailed Numerical Investigation". In ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2022. http://dx.doi.org/10.1115/gt2022-82592.
Testo completoAbstract (sommario):
Abstract Axially-staged combustion systems offer both enhanced operability and fuel flexibility for gas turbines, allowing stable operation and low emissions across a wide range of engine loads. The sequential combustion concept, where the first combustion stage is supported by a standard lean premixed flame, and the second stage relies on an autoignition-dominated flame forms the focus of the present contribution. Within the present state of the art, the still-oxygen-rich exhaust gases from the first stage are mixed with second-stage fuel within a sequential burner. The flow then exits into a combustor at a sudden expansion where the autoignition-initiated flame stabilizes. The purpose of the sudden expansion is to anchor the flame, as otherwise, minor perturbations in, for example, the inlet temperature, results in large excursions in the flame location. Within the presently investigated concept, rather than relying on a sudden expansion, the flame is anchored by establishing a positive static temperature gradient within the burner. The advantage of such a concept is that it potentially allows for very small combustor residence times and can be easily incorporated into an integrated combustor-nozzle guide vane. The concept does however present significant challenges, which are investigated within then present contribution. A critical challenge is that, in order to set up the static temperature gradient, the flow has to be accelerated to a relatively high Mach number, ca. 0.7, and then decelerated in a diffusing section where the flame is located. Achieving fuel/air premixing and combustion, while achieving acceptable pressure drops is not trivial at the high velocities. Additionally, the dynamic stability of the concept is not clear and needs to be investigated. Within the present work, compressible CFD is used to investigate the pressure drop characteristics within the system. It is demonstrated that for the system a total pressure drop of < 6% can be achieved. To realize this, the premixing section includes multi-point fuel injection coupled with mixing devices. The arrangement is designed to both limit excessive pressure losses by focusing losses within regions of the flow where they contribute effectively to fuel/air mixing as well as locating the flame where Rayleigh losses are acceptable. The dynamic behaviour of the system is studied by way of 2D fully premixed CFD. Investigation of the flame response to harmonic perturbations in inlet temperature shows that the flame transfer function (FTF) is characterized by amplitude growing, in line with the concept of auto-ignition at low Mach number, linearly with frequency. The rate of growth with frequency of the FTF amplitude is rather high reaching up to sixty times the imposed relative fluctuation of inlet temperature at a frequency of 600Hz. This rapid growth is in line with the behaviour of autoignition at low Mach number. A substantial difference with the low Mach number concept is given by upstream travelling acoustic waves generated by the flame that, going through high Mach number locations, can affect, in respect of the conservation of entropy transported by convection, the upstream temperature distribution and therefore auto-ignition itself.
10
Bao, Yang, e Jiming Song. "Kriging Accelerated MAPoD Analysis of Surface Flaws with Eddy Current Simulation Yang Bao1 and Jiming Song2". In ASNT Research Symposium 2023. The American Society for Nondestructive Testing Inc., 2023. http://dx.doi.org/10.32548/rs.2023.041.
Testo completoAbstract (sommario):
In this paper, the Kriging metamodel is applied to accelerate the model assisted probability of detection (MAPoD) analysis for surface flaws in eddy current nondestructive testing (ECNDT). The kernel degeneration (KD) algorithm accelerated boundary element method (BEM) EC simulation solver is selected as the physical model to generate the responses of the surface flaws in the conducting plate considering the propagations of uncertain parameters. The predicted PoD metrices by Kriging metamodel are compared well with the ones from pure physical model. Numerical results show that to reach the required accuracy, as compared with the pure BEM based physical model, Kriging metamodel can accelerate the MAPoD analysis for ECNDT problems.
Rapporti di organizzazioni sul tema "Accelerated Flames"
1
Share, Gerald H., e Ronald J. Murphy. Gamma Radiation From Flare-Accelerated Particles Impacting the Sun. Fort Belvoir, VA: Defense Technical Information Center, gennaio 2006. http://dx.doi.org/10.21236/ada594340.
Testo completo
2
Chen, Weixing. PR378-173601-Z01 Effect of Pressure Fluctuations on the Growth Rate of Near-Neutral pH SCC. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), luglio 2021. http://dx.doi.org/10.55274/r0012112.
Testo completoAbstract (sommario):
This report summarizes the work completed in PRCI SCC-2-12A project: The Effect of Pressure Fluctuations on the Growth Rate of Near-Neutral pH SCC, which is Phase 3 of the work on the same subject of investigation. The following insights from the current phase of the PRCI SCC-2-12A project are thought to be the most important: - Near neutral pH crack initiation is pressure-fluctuation dependent. Severe pressure fluctuations accelerate the fracture and spallation of mill scale on the pipeline steel surfaces, making it harder to initiate SCC cracks from the bottom of pits that are developed at flawed mill scale sites. On the other hand, the presence of a primer layer before application of the protective coating preserves the mill scale on the pipe steel surface and promotes crack initiation. - The early-stage crack growth primarily features crack length extension on the pipe surface but limited crack growth in the depth direction. Three different mechanisms of crack length extension have been identified, including that determined by the geometry of coating disbondment, a chaotic process of crack coalescence, and the ability of existing cracks to induce further crack initiation and growth. This latter process is pressure-fluctuation sensitive. - A complete set of equations governing crack growth in Stage 2 has been established based on experimental specimens with surface cracks under mechanical loading conditions realistic to pressure fluctuations during the operation of oil and gas pipelines. - The contribution to crack growth by direct dissolution of the steel at the crack tip has been determined, which has been found to be crack depth-dependent and pressure-fluctuation-sensitive. Gas pipelines operated under high mean pressure show higher rates of dissolution. - The severity of crack growth and the accuracy of the predictive model can be significantly affected by crack tip morphology, either sharp or blunt, and this would yield different threshold values for Stage 2 crack growth and therefore different lengths of remaining life. - Full scale testing was performed and has validated the crack growth models contained herein. - The PipeOnline software has been revised to incorporate the new experimental results obtained from the current PRCI SCC 2-12A project. This PipeOnline software was previously developed from the two earlier phases of the PRCI project.