1,720,978 research outputs found
A framework of a data-driven model for ship performance
No full textAn accurate assessment of a ship's required power is increasingly relevant for ship operations. We used a simplified framework of a data-driven model to predict ship's fuel consumption. Our approach was based on the learning capabilities of a generalized AutoML (Automated Machine Learning) process, trained with a variety of databases obtained from Computational-Fluid-Dynamics (CFD) simulations or from simplified numerical methods. These CFD simulations were conducted by solving the Reynolds Averaged Navier-Stokes (RANS) equations, using the STARCCM + commercial CFD software to calculate the ship resistance at speed under different operating conditions. Initially, we conducted a statistical analysis to select the independent variables before fitting the regression models and identifying potentially wrong assumptions. The AutoML process allowed optimizing the model's hyperparameters and designing the topology of the neural networks. For a set of unknown scenarios, comparative predictions obtained from the data-driven model and from numerical simulations showed that the data-driven model, trained with results obtained from CFD simulations, accurately and efficiently predicted ship operational parameters under realistic operating conditions, thereby dispensing with the need to perform elaborate CFD computations. Specifically, this low-cost and efficient operational data-driven technique forecasted the ship's operational fuel consumption although only a limited amount of recorded operational data was available
Data-driven model assessment: A comparative study for ship response determination
No full textSeveral machine learning approaches to determine ship responses via data-driven models have been applied. Input features and parameters used relied on time-series analyses obtained from computational-fluid-dynamics approach. As inputs into the data-driven model, the heave and pitch motions of a ship advancing in irregular, i.e., natural seaway were considered. By using different models in the framework of machine learning, required computation for the associated ship motions may be avoided, thus reducing the computational effort to forecast ship motions. Comparative predictions with numerical simulations revealed that the deep-neural-network method for training in auto-machine-learning instructions yielded the highest accuracy in heave motion, resulting in a non-normalized mean-absolute-error of 0.74, against the corresponding error of 1.07 from numerical computations, whereas the method trained with the tree-based models (the extreme gradient boosting and the Hist gradient boosting regressor) predicted less accurate motions for the tested ship. The model trained with the random forest regressor exhibited an error of 1.10. Numerical simulation based on a field method proved to be the most suitable choice for pitch motion. Despite the few samples available to train the regressors, results demonstrated that the measured data was sufficient to assess the developed data-driven model for ship response determination
On Some Subclasses of Strongly Starlike Analytic Functions
Full text linkThe aim of the present article is to investigate a family of univalent analytic functions on the unit disc defined for by \Re (\frac{zf'(z)}{f(z)}) > 0, |(\frac{zf'(z)}{f(z)})^2 - M|<M, z \in D. Some proprieties, radius of convexity and coefficient bounds are obtained for classes in this family.</p
Influence of Shallow Water on Rudder Induced Forces
No full textProceedings verfügbar unter: https://blueoasis.pt/nutts-2023/#proceeding
Numerical study on steady wave drift forces of an obliquely moving ship
No full textThis paper considers numerical computation of the steady wave drift forces acting on an obliquely moving ship. The traditional forward speed seakeeping problem was extended to consider the ship with a drift angle. A computer code was developed based on a time domain Rankine panel method. Once the velocity potential around the hull was determined, the first order wave induced motions were calculated and then the second order wave drift forces were evaluated using a near field method. Based on the developed code, the longitudinal and transverse steady wave drift force, as well as the steady yaw moment were computed for a container ship in head and beam waves. The effects of the drift angle on the steady wave drift forces were included and discussed. The numerical results were compared with the published experimental measurements, which shows fairly good agreement
Wave-Induced Motions of Moored and Coupled Multi-Body Offshore Structures
No full textIn the recent past, very large floating structures (VLFS) are used to realize a variety of large marine facilities like floating piers, bridges or logistical hubs, substituting the traditional bottom mounted structures. In most cases VLFSs consist of a number of individual modules that are assembled with connectors and hold in place by mooring systems. To ensure proper working and safety conditions, their hydrodynamic response in different sea states needs to be investigated. Previous investigations relied mainly on potential flow solvers which do not account for viscous and other nonlinear effects. However, flow properties under severe conditions are highly nonlinear. To capture the physics of such phenomena field methods are the preferred choice. The present work aims to investigate the hydrodynamic response of such a moored and coupled multi-body VLFS in waves using a flow code that computes multiphase unsteady incompressible flow simulations using the Navier Stokes equations coupled with a six-degrees-of-freedom (6 DOF) multi-body solver and mooring model. A total number of 14 simulations have been conducted for single and multiple cuboid set-ups. The set-ups are based on the model tests performed at TU Delft. The hydrodynamic responses were assessed and show a favourable comparison for most cases between the computed and measured results
ELT Course Descriptions in Tertiary Education: A Critical-interpretative Investigation
No full textThe course description is a brief, yet comprehensive, written account of a course teachers produce and give to their students at the beginning of courses. Course descriptions (CDs) are routinely produced and used in many educational institutions. However, with the exception of few passing references to them in Elliot (1997) and Swales (1990), discourse analysis has not sought to provide good understanding. This study is an attempt to fill in such a gap in knowledge by exploring the CD in the context of higher education in the United Arab Emirates, where the researcher has been working up to the completion of the present study.
Employing the technique of triangulation, the study forms a methodology that combines Foucault’s approach to discourse, action research and the critical and interpretative paradigms as a basis for analyzing data from 12 CDs, questionnaires and interviews. On the level of analysis, Foucault’s approach to discourse has been operationalized by Systemic Functional Linguistics and Bernstein’s theory of pedagogic discourse. Within the framework of the Systemic Functional Linguistics, the CD as a text is approached from three perspectives: Field, Tenor and Mode. This has revealed the overwhelming use of long clauses, the constitution of the student as’expected to study‘, not as thinking or knowing entity, the use of the Declarative Mood, ambiguity of the source and receiver, ellipsis and obligatory sections.
The purpose of investigating the CD within the framework of Bernstein’s theory of pedagogic discourse was to shed light on CD perspectives that could not be accounted for by the text analysis on its own. Thus, it described the roles, production, transmission and reproduction processes of the CD and the attitudes of teachers and students towards it. Thus, it has been concluded that the CD is dominantly regulative, that it is imposed by the Accreditation Committee under the pressure of globalization and that its use needs to be improved or stopped
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
- …
