1,720,961 research outputs found
An Overview of Planing Monohulls Transverse Dynamic Stability and Possible Implications with Static Intact Stability Rules
No full textThe problem of transverse dynamic stability of high speed craft is a complex topic, presently not comprehensively addressed in literature, where material on vertical motions and relevant instabilities is more easily available.
The present work, based on a PhD project [1], reports an overview of existing literature on the topic, focussing then on the Lewandowski methodology assessing the dynamic stability of hard chine monohulls; such methodology has been applied to selected hulls belonging to Series 62, in order to assess the sensitivity of the numerical tool and the influence of various geometrical parameters. Moreover, a comparison between dynamic stability results and existing stability regulations, allowed some possible guidelines to be developed for the preliminary design phase in order to avoid transverse stability problems. The study clearly indicates the need for further studies in order to enhance the applied methodology. To this aim, extensive experimental investigations are deemed essential
Application of the Probabilistic Approach to Naval Ships for the Damage Survivability Assessment: An Investigation Case
No full textThe assessment of a damaged ship has been a matter of investigation, discussion and renovation among the naval architects and in the scientific community during the latest decades, due to the strong harmonization process carried out at the IMO (International Maritime Organization). Since 2009 the probabilistic methodology is the unified approach in the merchant industry, both for passenger and cargo ships.
In this paper the probabilistic approach is regarded as ahypothetical, interesting and a useful tool also in the warship context, especially when considering and defining the survivability characteristics of a ship in a preliminary design phase. In the present article the probabilistic approach proposed by the IMO is presented and briefly overviewed; moreover its possible transferability to the naval field is discussed in two steps: 1) the analysis in principle of the results of its application to a naval patrol vessel; 2) the analysis of its suitability to address the vulnerability characteristics of the ship in terms of survivability. In the end the guidelines for its possible transfer to naval field are described and proposed by their application to the above mentioned naval patrol vessel
Static and dynamic stability of planing boats: application cases for an harmonized rule perspective
No full textA comprehensive investigation of recreational small craft characteristics, during the design process, should include also stability assessment of boats underway at high speed. To this aim, in order to gain insight about the transverse dynamic stability of planing boats, a methodology has been considered and implemented, following the approach proposed by Lewandowsky. An application is performed to Series 62 boats and the successive derived hulls tested at Delft University. Two different deadrise values and some other parameters like loading coefficient, longitudinal position of centre of gravity LCG and length on beam ratio are considered in the analysis, with the aim to ascertain the sensitivity of the method and to investigate a wide range of cases. Calculation are performed with and without appendages. Results are presented in terms of the maximum non dimensional KG in relation with volume Froude number. Successively, the ISO12217 stability standards are applied to the investigated cases: besides the zero speed condition, some artificial static conditions are modelled by imposition of proper draft and trim, as identified at different speeds. The max KG curve derived from the basic zero speed criteria, i.e. positive GMT, is also calculated. The resultant maximum KG curves are compared with the values found out during the dynamic investigation, allowing to get an insight in a safety rule perspective
Numerical Prediction Of Hull Force For Low Velocity Manoeuvring
No full textIn the last decades problems related to ship manoeuvrability have gained more importance in the context of naval architecture. Among them, problems related to slow speed manoeuvrability, such as port manoeuvres and dynamic positioning (DP), for which less data is available with respect to the conventional manoeuvrability at cruising speed, have taken more and more importance. The classical manoeuvring models have been developed to evaluate the ship force for high forward speed and low drift angle, therefore in case of slow speed manoeuvres, where high angle of attack must be taken into account, they do not provide accurate results. Despite the lower number of studies, also in this case different models have been proposed by various authors during years. The accuracy of codes to predict the ship manoeuvring capabilities are, obviously, strongly correlated with the accuracy of the prediction of the ship hydrodynamic forces, which are computed via regression formulae based, commonly, on existing experimental data. In the case of slow speed manoeuvring, unfortunately, only few data are available, representing an issue for the prediction of ship capabilities. In the present paper at first a comparison of different empirical models to evaluate the main ship force components for slow speed manoeuvring is presented. Then a RANS approach in order to tune coefficients for low velocity models has been explored, in order to evaluate its ability to compensate the lack of experimental data and provide a suitable alternative in the design phases
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
Wind tunnel experimental investigation of the aerodynamic coefficients reduction due to sheltering surroundings on a cruise ship moored in port
No full textThe recent growth of cruise and container ships size, which is involving the shipping industry, determines the greater and greater importance of evaluating properly the wind actions on such big ships, especially during the mooring phase. Accidents and damages may occur in port areas during extreme wind events due to the breakage of mooring clamps, jeopardizing the safety of human beings and vessels as well as producing significant economic losses. Despite extreme winds are one of the main dangers for large ships within ports and standardised procedures to accurately assess wind loads are still missing. To shed light on this topic, a set of wind tunnel tests was carried out to investigate the shielding effect that the surroundings can play in reducing the wind forces acting on a 1:600 model of the large cruise ship in the Port of Monfalcone (Italy). The longitudinal and transversal forces and yaw moment were measured for three main sets of tests: (1) open sea condition; (2) ship and quay; (3) ship, quay, and other shielding ship upwind. The results showed a strong dependence of the wind load on the cruise ship according to different surrounding configurations. In particular, a reduction of the aerodynamic forces up to 60% for the wind directions orthogonal with respect to the ship was measured. On one hand, this demonstrated quantitatively that the shielding effects of complex surrounding buildings may guarantee an increase in port safety with the reduction of the overall forces acting on ships. On the other hand, it highlights the huge uncertainty which currently characterizes the assessment of wind loads in the mooring system design, pointing out that a novel approach should be adopted in which every mooring system is designed on a specific site-analysis base
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
A Practical Method for the Prediction of Planing Craft Motions in Regular and Irregular Waves
No full textLeisure boats market has constantly grown during the
recent years, entailing an increasing need of design tools. This seems particularly urgent for seakeeping and hydrodynamic performance prediction in the field of planing boats.
Numerical methodologies are almost consolidated
instruments for conventional displacement ships, while some
shortcomings are still to be faced and overcome concerning
planing craft, due to the high complexity of the hydrodynamic
problem.
The present paper describes a simplified methodology for
the prediction of pitch, heave and roll motions of a planing
boat, in regular and irregular waves. In the formulation, a 2D
approach is adopted, based on ‘momentum theory’; various
aspects of the wedge-theory are used in order to model the
sectional characteristics, with particular attention to the added mass.
A validation of the proposed methodology concerning vertical
motions is presented against data available in literature
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