1,721,063 research outputs found
Coupled thermal-hydraulic/electromagnetic analysis and interpretation of the test results of the ITER TFPRO2 OST1 conductor
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A novel thermo-mechanical approach to DC performance modelling of Nb3Sn superconducting cable-in-conduit conductors in ITER perspective
No full textWithin the framework of the International Thermonuclear Experimental Reactor (ITER) activities, tests of Nb3Sn-based cable-in-conduit conductors (CICC) for the ITER magnets have shown a hitherto unexplained decreasing performance (with respect to the measured single strand performance) at increasing thermo-mechanical load. This behaviour, which is rather ubiquitous as it affects both Model and Insert Coils and short straight samples as well, has been tentatively attributed, among other possible causes, to strand bending, not included in the ITER design criteria before the Model Coil tests. However, no quantitative verification of the idea has been presented so far and indeed, in order to reproduce the measured performance, ad-hoc fitting parameters in the form of a fictitious current-magnetic field (IxB) dependent average extra compression of the cable have been introduced.
In this work we present a novel thermo-mechanical model suitably developed for Nb3Sn-based CICC. We study the behaviour of the conductor by means of a hierarchical multi-scale procedure. At the first level the strand can be modelled as a beam, defined by enriched kinematics to take into account its fibrous structure. At the following level, the behaviour of a triplet of strands is influenced by friction among strands, their pointwise contacts and the helicoidal geometry. The triplet is substituted with a single beam type element that can be suitably parameterised to work with different values of parameters in order to fit different cabling stages. We propose an algorithm for an automatic generation of parameters, depending on the geometry at each step of the hierarchy. In this way the performance of each cabling stage is analysed, making a recursive substitution of discrete models involving many beams with a single, continuous beam model, which characteristics are identified from the previous level. This chain of computations can be performed in a reasonable time when the effective properties are read as an output signal from a sufficiently trained Artificial Neural Network (ANN), which approximates the functional dependence of effective material properties on parameters describing the micro-structure. This procedure leads finally to the computation of the strain distribution inside the cable volume.
The computed strain distribution is input to the critical current density jC scaling law for the single strand, together with the magnetic field distribution. The local electric field E, resulting from an empirical power law of the usual form E = EC (j/jC)n, is suitably averaged on the cable cross section and integrated along the CICC in order to obtain the voltage. Voltage-temperature and/or voltage-current characteristics for the CICC, as typically measured during DC performance tests, are then computed by the Mithrandir/M&M code for given reference scenarios. These characteristics are analyzed from the point of view of the IxB dependence and compared with measured ones, where available. Implications for the ITER design will also be discussed
Analysis of Thermal-Hydraulic Gravity/ Buoyancy Effects in the Testing of the ITER Poloidal Field Full Size Joint Sample (PF-FSJS)
No full textThe PF-FSJS is a full-size joint sample, based on the NbTi dual-channel cable-in-conduit conductor (CICC) design currently foreseen for the International Thermonuclear Experimental Reactor (ITER) Poloidal Field coil system. It was tested during the summer of 2002 in the Sultan facility of CRPP at a background peak magnetic field of typically 6 T. It includes about 3 m of two jointed conductor sections, using different strands but with identical layout. The sample was cooled by supercritical helium at nominal 4.5-5.0 K and 0.9-1.0 MPa, in forced convection from the top to the bottom of the vertical configuration. A pulsed coil was used to test AC losses in the two legs resulting, above a certain input power threshold, in bundle helium backflow from the heated region. Here we study the thermal-hydraulics of the phenomenon with the M&M code, with particular emphasis on the effects of buoyancy on the helium dynamics, as well as on the thermal-hydraulic coupling between the wrapped bundles of strands in the annular cable region and the central cooling channel. Both issues are ITER relevant, as they affect the more general question of the heat removal capability of the helium in this type of conductors
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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