1,720,961 research outputs found
Dynamic simulation of a COGAS ship propulsion plant
No full textIn a previous paper the authors presented a comparison between a COGAS plant specifically designed and the original prime mover (a two stroke diesel engine) used for the propulsion of a large container ship. The comparison showed some advantages of the COGAS solution from both technical and commercial points of view, advantages that could become more evident, in a near future, also from an economic point of view, because of the adoption of increasingly stringent emission regulations in the shipping sector.
A feasibility study of the COGAS solution requires the availability of numerical models not only for the propulsion system design and performance evaluation in steady state operation, but also for the dynamic simulation of its behavior in every off-design and transient condition. The last feature is important for the development of the propulsion control system.
The paper presents a COGAS plant dynamic simulator, putting into evidence in particular detail the model of the heat recovery steam generator, the most critical component as regards transient situations. For the mentioned container vessel the prime mover dynamic analysis is combined with the overall propulsion system simulation, allowing to obtain some significant results relative to acceleration and deceleration maneuvers of the ship
Additive Manufacturing Application to a Ship Propeller Model for Experimental Activity in the Cavitation Tunnel
No full textAdditive manufacturing (AM), or three dimensional printing, is a modern way to build objects with possibly a high degree of accuracy and favorable cost/benefit ratio. This approach is widely used by many manufacturing industries and a certain interest for this innovative production technology is also growing in the ship design and production field. To this regard, the experimental activity at the model scale is often necessary for the ship performance assessment in the design phase. In the article, preliminary results of a propeller model for the cavitation tunnel, built with additive technology, are presented, showing the strengths and weaknesses of the printed model. Moreover, as an introductive overview, different AM technologies are briefly described, with the aim to point out potential applicability to ships
Extensive Cavitation Tunnel Acoustic Characterization of Controllable Pitch Propellers
No full textExperimental tests in model-scale are the currently established (and more reliable) methods for the propeller acoustic characterization. However, they are affected by uncertainties mostly due to scale effects, which make it difficult to consistently reproduce in model-scale some of full-scale functioning conditions.
In order to cope with this issue, it is interesting to define empirical formulations to shape the most significant cavitating phenomena in terms of URN spectrum. A suitable approach for the determination of such formulations may consist in the experimental characterization of model propellers collecting a large amount of data such to accurately describe propeller functioning conditions and related noise emissions. Collected data should be then analysed to extrapolate desired formulations exploiting advanced data analysis techniques.
In the present work the acoustical characterization of two propellers, performed at the University of Genoa cavitation tunnel, is presented. The collected sample includes cavitation buckets with inception points of different phenomena, noise spectra, pressure pulses and photos picked up at various pitches and functioning points, including off design conditions
COGAS plant as possible future alternative to the diesel engine for the propulsion of large ships
No full textExperimental analysis of blade root cavitation erosion on set of model propellers
No full textThe objective of the present study is to investigate by model tests the erosion caused by blade root cavitation for a set of three marine propellers. Experiments have been carried out using soft paint technique together with cavitation observations in the UNIGE cavitation tunnel. Three standard cameras and one high speed camera have been used to observe the damage patterns and cavitation dynamics, respectively. Standard cameras are fixed on the top of test section to continuously monitor the effect of erosion damage on the blade root, the high-speed camera has been placed at different positions to investigate detailed evolution and collapse of bubbles on pressure and suction side of propeller blades. Soft paint results showing damages pattern have been analysed simultaneously with the high speed videos, and showed remarkable agreement between the occurrence of damage on the blades and the bubble collapse of cavitation. The proposed methodology allows comparing different propellers in terms of cavitation aggressiveness. The comparison of these results with full-scale data provides useful indications to propeller designers when root cavitation cannot be avoided
Computer Vision Analysis of Cavitation Erosion at Propeller Blade Root
No full textThis paper presents an experimental approach for investigating erosive cavitation phenomena occurring at the blade root of marine propellers.
The primary objective of this work is to develop a method that provides quantitative measurements of the size and dynamics of cavitating structures occurring at the blade root of marine propellers.
The selected case study is a four-bladed, controllable-pitch model propeller tested under specific loading and flow conditions.
The proposed method combines high-speed video recordings with advanced computer vision techniques to quantify the evolution of the cavitating area as a function of the blade’s angular position. The resulting data provides valuable information on the unsteady behavior of erosive cavitation.
Future developments will integrate these measurements with data on the extent and growth rate of surface damage obtained through computer vision and the soft paint technique.
By correlating the cavitation flow characteristics with the erosion patterns, the proposed approach will enable a more comprehensive understanding of the mechanisms driving cavitation damage.
The integration of traditional experimental tools with automated vision-based analysis demonstrates strong potential for achieving more detailed, localized, and quantitative assessments of erosive cavitation, paving the way for improved prediction and mitigation strategies
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Experimental Analysis of Cavitation Erosion on Blade Root of Variable Pitch Propeller
No full textThe aim of this study is to experimentally investigate the cavitation
erosion on the blade root of a model scale controllable pitch propeller. Tests are
carried out in a cavitation tunnel, using the soft paint technique to study cavitation
erosion, exploiting also two standard cameras and one high speed camera to study
the damage patterns and cavitation dynamics, respectively. Standard cameras are
placed on the top of test section in order to periodically monitor the occurrence of
damages on the layer of paint. The high-speed camera has been used instead to
analyse bubble dynamics and identify potentially erosive phenomena. Three
different cavitation bubble structures on the blade root have been identified in the
present study: streak cavitation, spherical bubble cavitation, and twisting bubble
cavitation. The paint tests results have been analysed together with high-speed
videos, showing a remarkable agreement between the occurrence of damage and
cavitation collapse phenomena. The results demonstrated two regions on the
propeller blade root with high risk of erosion: (1) suction side blade root showed
significant damage pattern due to single bubble as well as bubble assembly collapse,
and (2) pressure side blade root showed slight damage pattern due to spherical
bubble collapse
Variations on the Author
Get PDF“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
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