1,720,963 research outputs found
An experimental assessment of nonlinear effects of vertical motions of Naples systematic series planing hulls in regular waves
No full textA comprehensive experimental assessment of vertical motions and accelerations of two Naples warped hard chine hulls systematic series (NSS) hulls in regular waves is presented. The seakeeping performance in regular waves are investigated, in particular nonlinear motion responses in terms of transfer functions and higher harmonic response as a function of wave frequency, steepness, hull slenderness and speed. In order to highlight the effects of wave properties on motion responses, transfer functions of both motion harmonics and phases are presented via iso-frequency and iso-steepness plots. Slenderness ratio is found to have a notable effect on motion transfer functions only at higher speeds. The presence of a higher harmonics in motion and acceleration response is also observed and the proposed analysis shows that increasing wave steepness and speed lead to increased higher harmonics responses of both vertical motions and accelerations. The effect of slenderness ratio on the second harmonic response of heave and pitch is only noticeable at higher speed. Phase difference between wave and motions shows that higher second harmonic content is generally associated with a higher phase lead. The main novelty of the present work is represented by the extensive analysis of NSS planing hulls in regular waves. In particular the aspects concerning higher harmonics and their trends with respect to speed, wave and hull geometrical characteristics
An experimental assessment of nonlinear effects of vertical motions of Naples systematic series planing hulls in regular waves
No full textA comprehensive experimental assessment of vertical motions and accelerations of two Naples warped hard chine hulls systematic series (NSS) hulls in regular waves is presented. The seakeeping performance in regular waves are investigated, in particular nonlinear motion responses in terms of transfer functions and higher harmonic response as a function of wave frequency, steepness, hull slenderness and speed. In order to highlight the effects of wave properties on motion responses, transfer functions of both motion harmonics and phases are presented via iso-frequency and iso-steepness plots. Slenderness ratio is found to have a notable effect on motion transfer functions only at higher speeds. The presence of a higher harmonics in motion and acceleration response is also observed and the proposed analysis shows that increasing wave steepness and speed lead to increased higher harmonics responses of both vertical motions and accelerations. The effect of slenderness ratio on the second harmonic response of heave and pitch is only noticeable at higher speed. Phase difference between wave and motions shows that higher second harmonic content is generally associated with a higher phase lead. The main novelty of the present work is represented by the extensive analysis of NSS planing hulls in regular waves. In particular the aspects concerning higher harmonics and their trends with respect to speed, wave and hull geometrical characteristics
Numerical VIV analysis of a single elastically-mounted cylinder: Comparison between 2D and 3D URANS simulations
Full text linkIn this paper the numerical simulations of the flow around an elastically-mounted circular cylinder with one degree of freedom (1-DOF) with small damping parameter and small mass ratio are presented. The simulations are performed for subcritical Reynolds numbers (2.0⋅103<1.3<104), using the URANS (Unsteady Reynolds Averaged Navier Stokes) approach in combination with the SST (Shear Stress Transport) turbulence model. The simulations are carried out on 3D as well as 2D meshes. From the overall results it seems that the bi-dimensional approach could be effectively applied in the lower branch, while major discrepancies are present in the upper branch. The detailed analysis of the wake flow characteristics shows that the three dimensionality of the flow is stronger in the transition zones between the different branches. The extensive comparison between the computational simulations and the experimental results presented in this paper could be considered the “start point” in order to select the proper grid model depending on the requested accuracy
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
Roll characteristics of the Naples Systematic Series
Full text linkIn the present paper, the results from an experimental campaign aimed at the characterization of the roll characteristics of the warped hard chine models of the Naples Systematic Series (NSS) are presented. The Levenberg–Marquardt non-linear parameter identification technique has been employed to determine the damping and restoring coefficients from roll decay tests. Three differential models have been analysed to evaluate the one that provides the best fit of the experimental data. It is found a that quadratic damping model is sufficiently accurate to describe damping non-linearity, whereas a cubic restoring term is recommended to properly model the roll dynamics. Roll decay tests have been further analysed considering the linear decrement of the roll angle. The equivalent damping coefficient has been calculated for all the considered methods. Response Amplitude Operators (RAO) in regular beam waves at zero speed are presented as well as roll-heave phase response. RAOs have shown a relatively similar response of the vessels in terms of roll and heave motions. Finally, an analysis of the behaviour of the hard chine hull forms in irregular beam waves is presented, with particular emphasis on roll and heave amplitude and phase responses
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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