1,720,961 research outputs found
LNG Risk Mitigation: a Comparison Between Active and Passive Barriers
Full text linkIn the last years, there has been a rapid increase in the proposals for regasification terminals to import Liquefied Natural Gas (LNG) mainly due to the global uncertainties of the energy market. Therefore, there has been a fast increase in the interest in the risk assessment of LNG regasification terminals. LNG is not poisonous; instead, its rapid evaporation together with the vapour phase flammability presents a non-negligible risk. The concentration range in which the gas-air mixture at ambient conditions is flammable is about 4.4%v/v (Lower Flammability Limit - LFL) to 15% v/v (Upper Flammability Limit - UFL). One of the major accidental scenarios, involved in an LNG regasification terminal, is the breakage of a pipeline carrying natural gas in the liquid phase. This would result in the release of large amounts of LNG leading to a fast-evaporating pool and, consequently, to a large flammable cloud and possibly to fires and explosions. Therefore, mitigation measures must be provided to reduce the risk up to an acceptable value; among the various mitigation measures, a protective barrier able to limit the hazardous distance related to a given accidental scenario (and therefore to protect sensible population living close to the regasification terminal) can be used. In their simplest configuration, passive mitigation barriers are high walls acting as obstacles on the cloud path, therefore enhancing the flammable cloud-air mixing. Unfortunately, to be effective passive barriers often must be quite high, possibly preventing their practical implementation. As an alternative, active barriers can be used where the flammable cloud-air mixing is enhanced not only thanks to the wake effect of the wall but also to the direct entrainment into the flammable cloud. This entrainment can be induced (for instance) either by high-velocity jets or by fans. Therefore, the main aim of this paper is to provide a comparison among the pros and contras of using passive vs. active barriers to reduce the hazardous distance related to an accidental scenario in an LNG regasification terminal. In particular, the various barrier configurations were investigated through Computational Fluid Dynamic (CFD) simulations using the Ansys Fluent 2023R2 suite of programs
Cuboid obstacle influence on high-pressure jet dispersion: A CFD study
Full text linkIn the context of the process industry safety, one of the main accidental scenarios is the release of high-pressure gaseous material. Since natural gas is highly flammable, the likelihood of ignition increases as the jet develops, with a maximum area of effect related to its lower flammability limit (LFL). This work aims at simulating and evaluating the interaction between high-pressure natural gas jets and cuboid obstacles, which were selected due to their prevalence in the process industry as storage units or buildings present in industrial parks. The maximum extent of the cloud at the LFL of natural gas is often influenced by the jet-obstacle interactions, necessitating complex numerical methods like computational fluid dynamics (CFD) for accurate estimation. Therefore, this study provides pivotal insights that challenge traditional modelling approaches, like integral ones, offering cost-effective alternatives where needed without compromising on safety. The findings indicate that using a CFD approach is not always necessary, as it largely depends on the storage pressure, diameter size, and the release height of the jet. At storage pressures of 65–130 bar with an orifice diameter of 2.54 cm, and a release height above 2.75 m, simpler methods like integral models are applicable without any substantial reliability loss. This is especially true when the cuboid obstacle is farther away from the release source. At lower release heights, especially if coupled with a larger orifice diameter, the CFD approach should be utilised as jet-cuboid interactions become highly relevant to the development of the jet
Interaction of Steam Curtains with High-Pressure Jets
Full text linkIn the industrial context, the risk of accidental release to the environment is an event which can occur in different chemical plant areas and cause serious consequences. In the presence of a hazard, risk management involves reducing the probability or the magnitude of the damage without extinguishing the hazard itself. Forms of mitigation can be primary or secondary, according to the target chosen to work on: primary refers to a reduction of the vulnerabilities of the element interested in a possible breakage (for example, hardening the coating of the device), whereas secondary mitigation refers to reduce the effects (consequences around the broken one). Considering the design of the equipment in a state-of-the-art manner, secondary mitigation methods focus on three possible strategies: procedural systems, passive-type systems, and active-type systems. Passive-type systems are devices designed to confine the leakage to a target area, defend a sensitive area using physical barriers or protect the equipment (such as fireproof coatings in the presence of fuels). Active mitigation systems, on the other hand, exploit the introduction of turbulence in the dispersing cloud, e.g., by adding a fluid to it, and could be successful with gas releases. Among the active mitigation barriers, one of the devices considered is the vapour curtain, but nowadays the understanding of the variables involved in their effectiveness, especially how to manipulate them to achieve the best result, is still not entirely clear. This work aims to show the efficiency of steam curtains in diluting a high-pressure methane jet by conducting computational fluid dynamics simulations with ANSYS 19.1® software. In doing so, several evaluations were made on the impact that certain operational parameters may have on the efficiency of the system, such as the pressure of the vapour, the position of the vapour curtain along the axis of the release and the amount of the release (obtained varying the diameter of the release)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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