1,720,999 research outputs found
Simulazione mediante modelli fem di saldature TIG e laser di piastre in lega Inconel 625
Full text linkL’obiettivo del presente studio è realizzare modelli numerici che siano di supporto per l’analisi dei fenomeni termici e strutturali relativi alla progettazione e alla realizzazione delle saldature: tale attività si suddivide a sua volta nello studio del numero e della velocità delle passate, delle potenze termiche messe in gioco, della corretta rappresentazione del comportamento del materiale, della scelta e posizionamento dei vincoli, della valutazione delle distorsioni e tensioni finali della giunzione ecc. Questa attività di studio si è avvalsa del codice agli elementi finiti ANSYS Release 11 rivelatosi idoneo a rappresentare la saldatura TIG e laser. I risultati delle elaborazioni numeriche sono stati confrontati con i dati sperimentali registrati nei laboratori ENEA. Tali prove sperimentali di saldatura testa a testa tra due piastre in INCONEL 625 sono quelle previste nell’ambito della progettazione del tokamak IGNITOR, una macchina per lo studio della fusione nucleare. In via preliminare sono state effettuate alcune considerazioni di carattere generale relative agli aspetti fisici del fenomeno, alla sua classificazione ed alla normativa corrispondente.The aim of the current study is to carry out numerical models that can support the analysis of thermal and structural phenomenon related to the design and realization of welding: this activity is divided in turn in the study of the number and the speed of passes, the thermal powers involved, the correct representation of the material behaviour, the choice of the restraints’ placement, the evaluation of the final strains and stresses in the joint and so on. This study activity has made use of Ansys Release 11 finite element code that has been revealed suitable to represent TIG and laser welding. The results of numerical calculations have been compared with the experimental data recorded in the ENEA laboratories. These butt-welding experimental tests between two plates of INCONEL 625 are the ones planned in the field of the design of IGNITOR tokamak, a machine for the nuclear fusion study. In a preliminary way some general considerations have been developed relative to the physical aspects of the phenomenon, its classification and the corresponding rules
Further improvements in the structural analysis of DEMO Divertor Cassette body and design assessment according to RCC-MRx
No full textThis paper presents the enhancements related to the structural analyses of DEMO Divertor in the framework of the EUROfusion Power Plant Physics & Technology (PPPT) program. This activity started two years ago and its preliminary results were published in previous papers. It has been divided in some areas defined by the similarity of the matters they contain: the structural analysis, of utmost importance, has been preceded by a preliminary phase, like the geometry definition or the thermal and the electric-magnetic analysis for loads evaluation; then the structural analysis has been finally confirmed with further evaluations related to excessive deformation or plastic instability. This paper discusses the improvements adopted either in the preliminary analysis or in the main structural analysis. Specifically it highlights the introduction of the thermal and electro-magnetic loads application in terms of a detailed spatial distribution that is now available. More the supports have been introduced in the model and their structural behavior has been investigated considering their interaction with the cassette. The structural assessment, according to the Design and Construction Rules for Mechanical Components of Nuclear Installation (RCC-MRx), has been performed either for the cassette or for the attachments: for the former it is positive while for the latter case serious limitations have been found. © 201
Study of dynamic amplification factor of DEMO blanket caused by a gap at the supporting key
No full textAmong the design activities of the in vessel components for DEMO promoted by European Fusion Development Agreement (EFDA) organization, this work deals with the gap required at the supporting keys of the blanket. Due to its higher operating temperatures compared to the vacuum vessel (VV) ones, this gap will increase during operation. The electro magnetic (EM) loads due to fast disruptions occur on a short time and might accelerate the blanket significantly before it touches the supporting keys, causing an impact of the blanket itself onto the keys. Depending on their stiffness, the EM loads with their short time scale could excite the structure's natural frequencies, causing dynamic amplification. Both phenomena (impact and dynamic amplification) can cause stresses in the structure significantly higher than the static ones. This work develops a finite element model of DEMO blanket to study its non-linear transient dynamic behavior under impact loadings. A VV sector, the ribs between the inner and outer VV, the backward manifolds and the supporting keys of the blanket have been modeled. The analyses have been performed with Abaqus [1] and Ansys [2] FEM codes focused on the displacements of the keys in their housing on the blanket. The dynamic amplification factor has been evaluated as the ratio of dynamic to static displacements in meaningful points of the structure for a growing gap till 5 mm. © 2015 Elsevier B.V. All rights reserved
EU-DEMO Breeding Blanket temperature evaluation before remote maintenance operation
No full textIn DEMO (the European proposal of demonstration fusion reactor) the Breeding Blanket (BB) segments shall be periodically replaced, at end of life or after failure. Any replacement of a BB segment shall be performed by Remote Handling Equipment (RHE) through the vertical upper port: any active action is executed by RHE that clamps a BB segment in the upper portion using a BB transporter. A driving requirement of DEMO commercial technology for RHE is the maximum operating temperature at the BB-RHE interface during BB replacement: the objective of this study is properly to assess this limit, being now the allowable value at 100 °C. This study deals with the Helium Cooled Pebble Bed (HCPB) concept. The initial configuration, with all sector segments (three in the outboard region and two in the inboard one) in their nominal position, has been considered; then the Finite Element model predicts if a natural convection cooling air flux inside vacuum vessel is adequate or if it is necessary a forced convection cooling system. The decay heat produced by the main blanket components (the BB modules caps and lateral walls, the backwalls, the supporting structures, the backplate manifolds, and so on) have been evaluated beforehand: the values applied as body loads in the thermal analyses have been selected within the set related to one month after shut-down. With the assumed geometrical and physical boundary conditions set for the natural and forced convection, the analyses indicate that a forced convection should be necessary to ensure compliance with the present RHE requirements. The obtained results, the analysis assumption and future analysis plan have been briefly discussed
Further finite element structural analysis of FAST Load Assembly
No full textThe FAST (Fusion Advanced Study Torus) machine is a compact high magnetic field tokamak, that will allow to study in an integrated way the main operational issues relating to plasma-wall interaction, plasma operation and burning plasma physics in conditions relevant for ITER and DEMO. The present work deals with the structural analysis of the machine Load Assembly for a proposed new plasma scenario (10 MA - 8.5 T), aimed to increase the operational limits of the machine. A previous paper has dealt with an integrated set of finite element models (regarding a former reference scenario: 6.5 MA - 7.5 T) of the load assembly, including the Toroidal and Poloidal Field Coils and the supporting structure. This set of models has regarded the evaluation of magnetic field values, the evaluation of the electromagnetic forces and the temperatures in all the current-carrying conductors: these analysis have been a preparatory step for the evaluation of the stresses of the main structural components. The previous models have been analyzed further on and improved in some details, including the computation of the out-of-plane electromagnetic forces coming from the interaction between the poloidal magnetic field and the current flowing in the toroidal magnets. After this updating, the structural analysis has been executed, where all forces and temperatures, coming from the formerly mentioned most demanding scenario (10 MA - 8.5 T) and acting on the tokamak's main components, have been considered. The two sets of analysis regarding the reference scenario and the extreme one have been executed and a useful comparison has been carried on. The analyses were carried out by using the FEM code Ansys rel. 13. © 2013 Euratom-ENEA Association sulla Fusione
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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