1,720,962 research outputs found
Contact Pressure Evolution in Classic Pin-on-Disc Tests
No full textWear of mechanical components is a problem due to the related material and energy consumption. Its reduction is important for sustainability particularly according with the Goal 12 “Responsible Consumption and Production”. In order to design components with lower wear experimental tests are usually performed. The most common configuration used is the pin-on-disc one where a spherical pin is put in contact with the plane surface of a disc. While in certain real contacts the contact pressure does not vary much, the wear of the surface specimens during running of a pin-on-disc test, commonly performed at constant normal load using a spherical pin, produces variations. The aim of this work is to investigate how significant and rapid the reduction of pressure throughout the test can be. An estimation of the pressure variation is made based on the results of two tests in different extreme conditions: wear occurring on the spherical pin only and wear on the flat surface of the disc only. The analysis shows that the pressure reduction in the first case is faster than the second one
Pivot Rolling Motion Effect in Rocker Back Tilting Pad Journal Bearings: First Comparison Between Experiment and Simulation
No full textThe theoretical contact point of the pivot in Rocker Back (RB) tilting pad journal bearings (TPJB) is normally considered fixed in common software programs for the study of the bearing rotordynamic behavior. In a previous paper the authors proposed an equivalent pivot rotational stiffness to be implemented in commercial software to simulate the effect of the variation of the circumferential coordinate of the theoretical contact point due to the pad rolling motion in RB TPJB. This work is devoted to a preliminary comparison of the predicted performance and the experimental one for a 280 mm diameter RB TPJB in different operating conditions in order to validate the proposed approach. The inclusion of a pivot rotational stiffness among the data for simulation affects especially the cross-coupled dynamic coefficients. The latter, predicted as negligible without the new implementation, were closer, in order of magnitude, to the experimental results
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
The Applicability of the Hertzian Formulas to Point Contacts of Spheres and Spherical Caps
Full text linkHertzian formulas are commonly used for the evaluation of deformation and pressure distribution of non-conformal and slightly conformal mechanical pairs to estimate component stiffness and durability. For the sake of simplicity, their use is extended even to those cases in which Hertz’s hypotheses do not hold. This paper summarizes Hertz’s theory and compares the results obtained with theoretical and finite element analysis of the point contact of non-conformal and conformal pairs made of spheres, caps, and spherical seats. This study was motivated by the non-Hertzian behavior of a tilting pad bearing ball-and-socket pivot conforming contact observed by the authors in previous experiments. In particular, the displacement and force relation were investigated by varying the geometrical parameters, the materials, the boundary conditions, and the friction coefficient. In the case of non-conformal contact, the parameter variations had negligible effect in agreement with Hertz’s theory while for conformal contact, the cap and seat height and width and the relative clearance were the most influential parameters on the non-Hertzian behavior. These novel results indicate that in conformal pairs, such as for tilting pad bearing ball-and-socket pivots, whenever Hertz’s hypotheses are not satisfied and the assessment of contact stiffness is crucial, Hertzian formulas should not be applied as done in common practice, instead more accurate numerical or experimental evaluation should be made
Turbulence Effects in Tilting Pad Journal Bearings: A Review
Full text linkThis paper reviews the current knowledge on turbulence effects in tilting pad journal bearings. Turbulence is becoming increasingly important in the design of hydrodynamic bearings due to the trend to increase power density in turbomachines and consequently the operating speeds of the hydrodynamic bearings. Turbulence has a series of effects on the bearing performance which may be beneficial or detrimental, depending on the operating conditions. The main turbulence models are recalled and a historical overview on the evolution of numerical simulations of turbulent flow in tilting pad journal bearings is presented. The two broad simulation strategies used are the generalized Reynolds equation and computational fluid dynamics. The main experimental works are then reviewed, and a unified comparison of these works is provided. Novel results on the critical Reynolds number in a tilting pad journal bearing are reported. Much emphasis is given on the experimental evidence for laminar-to-turbulent transition. The evidence used in the literature is reviewed and its reliability is discussed. Lastly, some future research directions are suggested
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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