1,721,064 research outputs found
Vibration analysis of super-yachts: Validation of the Holden Method and estimation of the structural damping
Full text linkThe hull excitation generated by marine propellers constitutes one of the most significant vibration sources affecting comfort on passenger ships. Consequently, the evaluation of the propeller-generated excitation through reliable numerical tools during the preliminary stage of ship design is fundamental. The Holden Method (HM) is an empirical tool utilized to calculate the propeller-induced pressure distribution on a ship hull. The present paper validates the HM, which is applied to a twin-screw, 54-m super-yacht. Finite Element Analysis (FEA) is used to benchmark the HM numerical predictions against a set of full-scale vibration measures. The outcomes show that the magnitude of the propeller-induced dynamic excitation predicted by the HM is overestimated. Thereafter, the calibrated propeller-induced forces and the diesel engine excitation are applied to the FE model to perform a series of forced vibration analyses and estimate the global structural damping coefficient of the super-yacht. The study highlights the necessity of developing new empirical methodologies, analogous to the HM, to be applied to modern small luxury vessels
Green shipping—multifunctional marine scrubbers for emission control: Silencing effect
Full text linkScrubber systems abate the sulphur oxide emissions of engines when cheap fuel oils that are high in sulphur content are employed as combustibles. However, the ships with these voluminous devices installed on board is space demanding. This work analyses the feasibility of incorporating the acoustic abatement of the exhaust gas noise functionality into the scrubber design to provide a combined scrubber–silencer system. For this purpose, a finite element analysis is performed on a simple expansion chamber, which is assessed using both analytical and experimental data. The transmission loss is the acoustic parameter chosen in this work. The numerical model depicts a good correlation with the transmission loss measured on a model scale scrubber. Finally, scrubber geometry modifications alter the transmission loss, changing and/or enhancing its featuring. These abilities indicate the feasibility to confer to scrubber silencing effects
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
Effect of propeller phase angles on the vibration response of a twin-screw super-yacht
No full textPropeller-induced hull excitation is one of the most important causes of the vibration levels experienced in the habitable decks of ships. A reliable assessment of on-board vibrations during the early stage of ship design requires the development of practical and efficient numeric techniques. This paper studies the influence of different phase offsets between the two propeller-induced forces on the vibration responses on the deck floors of a 54 metres super-yacht. The two propeller-induced hull forces are evaluated via the Holden Method and calibrated utilizing full-scale vibration measures. Hence, the tuned forces are applied to a FE model of the vessel by progressively shifting their relative phase angles. A series of FE linear dynamic analyses are performed to estimate the vibration levels on different deck zones on the ship. The outcomes of the simulations point out remarkable divergences between the vibration levels on the deck areas, when different propeller phase angles are implemente
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
The experimental characterization of resilient mounting elements for the prediction of the structure-borne noise on board cruise ships
No full textIn this paper, authors show the implementation to a real case of the single point method for the prediction of the structure-borne noise levels released by a resilient mounted diesel engine to the ship structures. The evaluation of the structure-borne noise is based on the source velocity levels measured at the diesel engine feet during the test run, on the resilient mounting impedance obtained by specific laboratory tests, and on the mobility levels of the diesel engine seating measured when the ship is under construction and the diesel engine not yet installed. Special emphasis is given to the experimental tests aimed to the dynamic characterization of the resilient mounting elements. The paper presents the fundamentals of the method for the dynamic characterization of resilient mounting elements (RME) through the experimental measurement of their dynamic transfer stiffness (DTS) at both low and high frequencies
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