1,720,960 research outputs found
Automation of the finishing process of steel yacht hulls based on optical scanning
No full textPurpose: The manufacturing of large yacht hulls is a complex process in the shipbuilding industry. The traditional approach is based on the pre-fabrication of large steel panels that are welded together to form 3D superstructure assemblies. One of the most relevant aspects of a yacht is its visual impact. For this reason, a finishing phase is usually carried out in order to obtain a final target surface with smooth curvature. Current methodologies mainly rely on manual processes thus requiring a great amount of time and well-experienced workers. Method: This paper introduces an innovative methodology representing the basis for the automation of the finishing phase of large yacht hulls. The proposed approach is based on the measurement of the as-built hull surface through the integration of an active stereo vision system and a complex mechanical tracking system. A procedure to define the target surface has been developed by integrating information deriving from both the design and the as-built shapes. Result: The developed methodology has been tested on a broadside region of the hull of a 59 metres yacht assembled within a shipyard. A target surface, differing as little as possible from the design surface, has been modelled in order to obtain a uniform curvature shape. A finishing phase has then been carried out by applying a layer of filler and by milling the hull’s surface. Discussion & Conclusion:
Results obtained have demonstrated the feasibility of the proposed approach, speeding up the whole process and guaranteeing fair reflection line patterns on the manufactured surface
A novel test rig for the dynamic characterization of large size tilting pad journal bearings
Full text linkThe present work concerns the realization of a test bench for the dynamic characterization of high performance tilting pad journal bearings, within a collaboration between the Department of Civil and Industrial Engineering of Pisa, GE Oil&Gas and
AM Testing. The objective is to cover journal diameters of interest of GE, from 150 to 300 mm, with peripheral speeds up to 150 m/s, static load up to 270 kN, dynamic loads up to 30 kN and frequencies up to 350 Hz, performances that make the apparatus very competitive worldwide. The adopted configuration has the test article (TA) floating at the mid-span of a rotor supported by two rolling bearings. The TA is statically loaded by a hydraulic actuator and excited dynamically by two orthogonal hydraulic actuators. Construction was recently concluded and preliminary tests are under way. In order to assess in advance the possible accuracy of the tests, a dynamic lumped parameter model of the test bench was developed to perform virtual experiments, including several possible sources of experimental errors and uncertainties. The model was implemented using reduced stiffness and mass matrices obtained from Finite Element Analysis by Component Modal Synthesis
Modifica di un modello analitico per lo studio di tenute gas a nido d'ape e confronto con dati sperimetali
No full textHoneycomb gas seals are used in turbomachines as a possible alternative to labyrinth seals when a damping effect is desired. However, the prediction of the dynamical behaviour is still an open issue. A software tool based on an isothermal bulk-flow model is currently available. In our work, the prediction capabilities of bulk-flow models, without the isothermal assumption, have been investigated. A more flexible tool has been developed to test the effects of other assumptions, and the results of the simulations have been compared with new experimental data
PROVE DI IDENTIFICAZIONE DEI COEFFICIENTI DINAMICI DI CUSCINETTI A PATTINI OSCILLANTI SU BANCO PROVA VIRTUALE
No full textA test rig for the identification of the dynamic coefficients of tilting pad journal bearings is currently under construction. The present work aims at assessing the accuracy of prospect tests. A dynamic lumped model of the test cell has been developed to include a number of possible sources of systematic errors. Virtual tests can be run on this model to evaluate the errors. The lumped model, implemented in MATLAB, is based on reduced stiffness and mass matrices obtained by finite element analysis (in ANSYS) using the Component Modal Synthesis method. The deformation of the housing ring into a roughly elliptic shape was found to be critical and suggested a stiffening design intervention
Review and upgrade of a bulk flow model for the analysis of honeycomb gas seals based on new high pressure experimental data
No full textThe design of the gas seals used in centrifugal compressors and axial turbines requires to consider not only their aptitude to reduce leakage, but also their contribution to the overall
dynamics of the machine. Honeycomb and hole pattern annular seals are often employed in compressors for the end balance piston seal or as the central balance piston seal in a back-to-back arrangement. In contrast to labyrinth seals, they show a beneficial damping effect.
In order to obtain an effective tool for predicting the leakage and the dynamic response of
honeycomb seals, a bulk flow model has been devised in the past and, implemented in numerical codes, it is presently used in the design process. This kind of codes, however, require
simplifying assumptions: in particular, one reference code available to the authors adopts the hypothesis of isothermal process. However, as the required level of confidence in seal design is increasing due to the fact turbomachinery design is more challenging, an experimental validation and possibly some refinement are needed. In this work, the bulk flow model was reviewed and the sensitivity to different hypotheses was explored. New experimental data from a high pressure test rig were compared with the results of simulations
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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