1,720,959 research outputs found
Development of a floating Vertical Axis Wind Turbine for the Mediterranean Sea
Full text linkDifferently from Horizontal Axis Wind Turbines (HAWTs), which are the reference technologies in the wind market for their reliability and maturity, Vertical Axis Wind Turbine (VAWT) applications are related to small-scale contexts, such as providing electricity in isolated areas or urban settings. Consequently, the capacity of VAWTs results significantly lower than the order of megawatts and does not exceed a few tens of kilowatts. A promising field of application for VAWTs is the floating offshore: among the main advantages there are an increased static stability, by placing the rotor-nacelle assembly (RNA) at the base of the VAWT and reduced operational and maintenance (O&M) costs. Moreover, the different wake dynamics allows to reduce the aerodynamic losses, allowing closer turbine installations. However, to be competitive with floating HAWTs, it is necessary to have numerical models for the analysis and simulation of multi-megawatt VAWTs. This paper aims to introduce a time domain model of a floating vertical axis wind turbine, developed within the Matlab-Simscape environment. The model comprises an aerodynamics module, based on Double Multiple Stream Tube theory while hydrodynamics is modelled using WEC-Sim. A case study, involving a Darrieus H-rotor VAWT tested in the Mediterranean Sea and supported by a semisub foundation, the OC4-DeepCwind, is introduced. The results obtained are compared with those from QBlade, a software developed by TU Berlin, demonstrating a good agreement between the two codes
Fatigue assessment of a new concept for a floating barge with pendulum for offshore wind turbines in MOST
Full text linkAmong floating foundations for offshore wind turbines, the barge is considered one of the most cost-effective platforms, owing to its ease of manufacturing, transport, and installation. However, the barge platform is susceptible to wave-induced stress due to its extensive waterplane area, potentially leading to fatigue in critical structural components such as the platform, tower, nacelle components and moorings. This paper delves into the prospect of mitigating fatigue damage in the barge concept by introducing a pendulum ballast, which can be installed at the offshore site using polyester ropes. The primary focus of this research is the assessment of the 'barge-pendulum' concept, aimed at reducing load cycles that could lead to fatigue failure, with a specific emphasis on the tower base as a representative indicator of device damage. The analysis is conducted using MOST, a time-domain simulation code developed in Matlab-Simscape environment. The findings show that the barge-pendulum concept has a poorer performance in terms of fatigue life, due to the increased sensitivity to wave forces
Sistema di ormeggio adattivo per corpo galleggiante
No full textUno scopo generale della presente invenzione è realizzare sistemi di ormeggio per corpi galleggianti che consentano al corpo galleggiante di permanere sul pelo libero del bacino idrico. Un altro scopodella presente invenzione è quello di realizzare sistemi di ormeggio per corpi galleggianti che consentano al corpo galleggiante di orientarsi correttamente rispetto alla posizione del sole. Questi ed altri scopi e vantaggi, che saranno compresi meglio in seguito, sono raggiunti secondo la presente invenzione avente le caratteristiche enunciate nella rivendicazione indipendente. Forme di realizzazione preferenziali dell’invenzione sono definite nelle rivendicazioni dipendenti.
In sintesi, secondo un primo aspetto dell’invenzione, la presente invenzione si riferisce a un sistema di ormeggio per corpo galleggiante configurato per essere disposto in un bacino idrico che comprende almeno tre mezzi di collegamento e orientamento, ciascuno avente una prima estremità predisposta per essere collegata al corpo galleggiante e una seconda estremità predisposta per essere collegata in una posizione fissa al bacino idrico. Inoltre, il sistema comprende mezzi di avvolgimento e svolgimento per l’avvolgimento e lo svolgimento degli almeno tre mezzi di collegamento e orientamento per cui gli almeno tre mezzi di collegamento e orientamento sono ciascuno avvolgibile e svolgibile, definendo ciascuno una lunghezza operativa tra le rispettive prima e seconda estremità. Primi mezzi sensori sono predisposti per misurare escursioni batimetriche del bacino idrico e un sistema di controllo è predisposto per comandare i mezzi di avvolgimento e svolgimento e regolare la lunghezza operativa di ciascuno degli almeno tre mezzi di collegamento e orientamento in base alle escursioni batimetriche misurate dai primi mezzi sensori, consentendo pertanto al corpo galleggiante di permanere sul pelo libero del bacino idrico. Secondo un secondo aspetto, l’invenzione comprende un corpo galleggiante comprendente un sistema di ormeggio
Estimating the Cost of Wave Energy Converters at an Early Design Stage: A Bottom-Up Approach
Full text linkThe role of ocean energy is expected to grow rapidly in the coming years, and techno-economic analysis will play a crucial role. Nowadays, despite strong assumptions, the vast majority of studies model costs using a top-down approach (the TdA) that leads to an unrepresentative economic model. WEC developers usually go through the the TdA approach because more detailed cost data are not available at an earlier design stage. At a very advanced design stage, some studies have also proposed techno-economic optimisation based on the bottom-up approach (BuA). This entails that the detailed cost metrics presented in the literature are very specific to the WEC type (hence not applicable to other cases) or unrepresentative. This lack of easily accessible detailed cost functions in the current state of the art leads to ineffective optimisations at an earlier stage of WEC development. In this paper, a BuA for WECs is proposed that can be used for techno-economic optimisation at the early design stage. To achieve this goal, cost functions of most common components in the WEC field are retrieved from the literature, exposed, and critically compared. The large number of components considered allows the results of this work to be applied to a vast pool of WECs. The novelty of the presented cost functions is their parameterization with respect to the technological specifications, which already enables their adoption in the design optimisation phase. With the goal of quantifying the results and critically discuss the differences between the TdA and the BuA, the developed methodology and cost functions are applied to a case study and specifically adopted for the calculation of the capital cost of PeWEC (pendulum wave energy converter). In addition, a hybrid approach (HyA) is presented and discussed as an intermediate approach between the TdA and the BdA. Results are compared in terms of capital expenditure (CapEx) and pie cost distribution: the impact of adopting different cost metrics is discussed, highlighting the role that reliable cost functions can have on early stage technology development. This paper proposes more than 50 cost functions for WEC components. Referring to the case study, it is shown that while the total cost differs only slightly (11%), the pie distribution changes by up to 22%. Mooring system and power take-off are the cost items where the TdA and the HyA differ more from the BuA cost estimate
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
Dynamic Motion Evaluation of a Novel Hybrid Wind and Wave Integrated Platform
No full textHybrid wind and wave platforms are among the most promising tech-nologies to foster access to untapped renewable energy in deep seas. This tech-nology aims to leverage synergies between wave and wind conversion systems by sharing costs, such as mooring and electrical connection, and combining their power production. The platform is usually a floating offshore wind turbine (FOWT) integrated with one or more wave energy converter (WEC) devices. WECs, compared to FOWT, are less mature technologies as there is a general lack of design convergence nor a standard layout. This paper investigates the ca-pabilities of a new hybrid concept developed at Politecnico di Torino, which in-tegrates a FOWT with three point absorber WECs, such WECs are integrated into the floating structure and are fundamental to obtaining the desired hydrostatic and dynamic stability. The in-house hydrostatic stability tool and the time domain model MOST are used to analyse the hybrid system motions performances with two modes: WEC activated or blocked; in this way, this paper purports to criti-cally discuss differences and advantages of the hybrid WEC-activated solution with respect to rigid floating substructures. The WEC-activated scenario outper-forms the blocked configuration, with a 12% reduction of the nacelle accelera
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
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