1,720,960 research outputs found
Z-Drive Escort Tug manoeuvrability model and simulation, Part II: A full-scale validation
No full textA deep insight into the manoeuvring characterisation of a wider class of Azimuthal Stern Drive Escort tugs (ASD) is undertaken with the scope of defining a real-time parametric manoeuvring simulation code for the free-sailing and towing operations. In the part I of the work a physics-based 4-DOF prediction parametric tool for the dynamic behaviour of the ASD tug has been developed, and a validation with model-scale Escorttowing
tests has been presented. In the present paper a second validation methodology, based on full-scale measurements, is discussed. This verification envisages simulator’s capability of describing the free-sailing performance of a different but compatible hull, having dimensions, propulsion, skeg characteristics significantly different with respect to the ‘‘parent design’’ used to develop the tool. The experimental campaign involves
the measurements purposely performed during sea trials onto two sister-ship ASD new-buildings (RM3213).
Turning circle, zig-zag manoeuvres, and Dieudonne’ spiral tests are deeply analysed and the results used for validation purpose. The simulation results showed a satisfactory agreement with the full scale manoeuvres, positively demonstrating the ability of the parametric mathematical formulations to forecast customised tug manoeuvrability for tug design purposes
Assessment of the manoeuvrability characteristics of a twin shaft naval vessel using an open-source cfd code
No full textThe purpose of this study is to assess the quality of the manoeuvre prediction of a twin-shaft naval vessel by means of a time-domain simulator based on Computational Fluid Dynamics (CFD) hydrodynamic coefficients. The simulator uses a modular approach in which the hull, rudders, appendices and propellers are based on different mathematical models. The hydrodynamic coefficients of the hull in the bare and appended configurations are computed using virtual captive tests performed with an open-source CFD code: OpenFoam. This paper demonstrates that the application of the CFD hydrodynamic coefficients led to a good estimate of the macroscopic characteristics of the main IMO manoeuvres with respect to the experimental measures. The adopted test case is the DTMB 5415M frigate both with and without appendages. This test case has been investigated in several research studies and international benchmark workshops, such as SIMMAN 2008, SIMMAN 2014 and many CFD workgroups
Escort Tug Hydrodynamic Forces Estimation in a Design Framework: From Model Test to Manoeuvrability Simulation
No full textThe manoeuvring capabilities of an escort tug are essential key-features with a view to an all-around design approach devoted to an optimum oriented framework. From the hull geometry settlement and propulsive solution definition, the ability to predict thoroughly the operative life in terms of handling, effectiveness, and safety becomes fundamental, even more with the perspective of developing smart control logics supporting the masters. With such an aim, the availability of a reliable manoeuvrability model is of fundamental importance. In this context, it is important to define an optimum set of captive manoeuvrability tests, whether experimental or numerical, in order to correctly identify the vessel escort performances in simulation; this, always keeping in mind the necessity to limit the effort in view of an application at an early-design stage. Starting from a wide experimental matrix, purposely designed and realized, the present investigation focuses on the quality and robustness of the different regression manoeuvrability models by letting vary the subsets of tests, in order to individuate, finally, which is the most suitable hull model to be adopted and which is the minimum set to be performed
Follow-the-Leader Control Strategy for Azimuth Propulsion System on Surface Vessels
No full textThis paper presents an effective autonomous follow-the-leader strategy for Azimuthal Stern Drive vessels. The control logic has been investigated from a theoretical point of view. A line-of-sight algorithm is exploited to ensure yaw-check ability, while a speed-check feature is implemented to track the velocity of the target along the path. For this purpose, a linearised manoeuvrability model for azimuthal drive surface vessels is presented. A model-based control synthesis is proposed to ensure the stability of the closed-loop system and robust PID controllers are designed by using Linear Matrix Inequalities technique. The control strategy has been successively validated in two steps, initially by using simulation techniques, and then experimentally using an outdoor scenario with model scale tugs. The path planning, navigation, guidance and control modules are studied, detailed, and digitally implemented on-board of the model scale tugs. The models are supplied with GNSS+INS navigation system. Low-level management and control of Azimuthals angles and shaft revolutions is implemented on-board. High-level decen-tralised path planning, guidance, and control sequence evaluation are dealt with at a remote ground station. In particular, the presented follow-the-leader strategy meets the most generic needs of platooning convoys, and, in the specific instance, of Escort convoy tugs. The operative profile of the latter concerns long-lasting and routine chases with the continuous demand of tuning heading and speed to track the target vessels, until the rare occurrence of an emergency event. In a realistic scenario, the proposed control system would be beneficial for the tug master’s lucidity and alertness, while reducing avoidable risks. At the end of the paper, the results of the experimental campaign are shown to demonstrate the effectiveness of the proposed control logic.Transport Engineering and Logistic
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
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 heel influence on ship manoeuvrability: Single and twin-screw surface vessels
No full textLow transverse metacentric height and high speed are peculiar destabilising factors in ship manoeuvrability according to the attainable large heeling angles. The phenomenon indeed occurs in the case of vessels characterised by loading conditions with low transverse stability — e.g. high centre of mass of container vessels and RoRos. Starting from Kijima’s single-screw container vessel evidence, an extension of the study to twin-screw ferry vessels is undertaken, with the scope of quantifying its effect in terms of turning and zig-zag IMO margins at an early design stage. Given the relevant impact, an enlarged captive model testing campaign executed on a sample of reference vessels was analysed to further characterise and extend the concepts to a broader class of modern single and twin-screw vessels, thus motivating the study. As a further result, this analysis allowed to underline the need of a review of the IMO intact stability code when dealing with heeling angle during a turn
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