1,721,157 research outputs found
Novel Gas Turbine Challenges to Support the Clean Energy Transition
No full textThe ongoing energy transformation, which is fueled by environmentally cautious policies, demands a full synergy with existing back-up gas turbines (GTs). Renewable energy sources (RESs), such as wind and solar, are intermittent by nature and present large variations across the span of the day, seasons, and geographies. The gas turbine is seen as an essential part of the energy transition because of its superior operational flexibility over other non-renewable counterparts, such as hydro and nuclear. Besides the technical aspects, the latter are less popular due to controversies associated with safety, ecological, and social aspects. GTs can produce when required and with acceptable reaction times and load ranges. This allows a balance between the energy supply and demand in the grid, mitigating the variations in RESs. The increased cycling due to operational flexibility has adverse effects on GT components and the unit efficiency. The latter dictates how well GTs make use of the burned fuel and influence the emissions per energy unit. This paper investigates these aspects. First, it presents the effects of increased penetration of renewable energy sources (RESs) into the grid. Second, it defines the new operation requirements including more dynamic load regimes, the provision for high occurrences of starts and stops, continuous and variant load cycling operations, extended partial loading or stand-by, and other conditions not foreseen under the classic baseload or cyclic operations. Finally, it proposes the overhauling of the present GT inspection and lifing criteria to meet the new role of GTs
New lifing criterion for land-based gas turbines in flexible operation mode
No full textUnder the ongoing global energy transition, gas turbines are increasingly experiencing new modes of operation. In the recent years, primarily in Europe and similarly in various parts of the world, renewable energies are gaining momentum to support more environmentally friendly energy policies. Renewable Energy Sources (RES), such as wind and solar are intermittent by nature and a rise in their contribution is associated with grid instabilities. As a result, reliable energy sources such as fossil fuel-based plants are required to fill flexible back-up or reserve power, capable to rapidly response in case of RES downtime. This introduces new operating conditions, characterized by very high start/stop cycles (almost daily) and load cycling operations, beyond those foreseen under the classic base-load or cyclic operations.The present criteria used for establishing the inspection intervals and components' lives, are put in place based on the assumptions that the gas turbine will operate at base load for the most part, with some exposure to cyclic operations. This paper identifies the most critical gaps in the present criteria, particularly due to increased thermal instability or sustained transient under the flexible operation requirements. (C) 2022 The Authors. Published by Elsevier Ltd
The development of a Novel Hybrid Gas Turbine digital twin to predict performance deterioration
No full textOn the possibility of using an industrial steam turbine as an air expander in a Compressed Air Energy Storage plant
No full textSmall/medium size CAES systems (1–10 MW) could be efficiently and successfully employed for off-grid and self-consumption applications and for the delivery of ancillary services on the lower grid levels. A critical issue affecting the feasibility of such systems is related to the availability of efficient and affordable air expanders. Taking into consideration that typical CAES applications are characterized by inlet pressure levels in the range of 40–60 bar, an attractive opportunity to reduce development efforts and investment costs is to resort to the consolidated steam turbine engineering practice. In the present paper, the possibility of using existing building blocks developed to assemble industrial steam turbines to arrange air expanders for CAES applications is explored. A general model for off-design calculation capable of simulating, for a given turbine geometry, steam and air operations as well, has been developed and applied to a case study. On the basis of available information about an existing industrial steam turbine, a possible arrangement for an air expander has been set up and investigated. Results have evidenced a performance loss in terms of both power output and efficiency with respect to steam operations. Nevertheless, the air expander behavior in a wide range of operation can be considered satisfactory. Therefore, the use of industrial steam turbines technology might be considered interesting for the applications under consideration
Authentication and Authorization in Web Services
No full textIn this paper, we give the design of a security model that encapsulates the basic modules needed for securing the access to a web service, which are authentication and authorization. Our model relies on WS-Security standards and another application layer technology, namely the ”Lightweight Directory Access Protocol”. We also implement and test the model, and provide several test case scenarios. Moreover, an evaluation in terms of performance is done in order to reduce the concerns about security bottleneck and overheads. Finally, we highlight some of our model’s advantages and drawbacks
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
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