1,720,970 research outputs found
Numerical Simulations of a Horizontal Axis Wind Turbine in Icing Conditions with and Without Electro-Thermal Ice Protection System
No full textIn this work, a preliminary design of an Electro-Thermal Ice Protection System (IPS) is performed on the NREL 5 MW reference wind turbine. A 3-hour rime icing event is simulated numerically with and without the IPS. The IPS is designed considering a uniform heat flux in the stream-wise and span-wise directions. Two protected regions are considered in the span-wise direction, covering the outer half and the outer third of the blade, respectively. Moreover, different power consumptions are compared, keeping the blade clean or leading to run-back ice formations. The aerodynamic coefficients of each blade section are computed to compare the effect of the different ice shapes at various angles of attack with the reference solution, i.e., the clean blade. The resulting power curves are compared with the clean blade to quantify power and energy losses. Results show that run-back ice can cause worse performance with respect to the ice accretion occurring without IPS. During ice accretion, the energy loss resulting from this simplified IPS design is higher than the one caused by the ice accretion without IPS. However, if the time frame following ice accretion is considered, considerably higher energy savings are obtained when at least the outer third of the blade is kept clean
Numerical simulations of ice accretion on wind turbine blades: are performance losses due to ice shape or surface roughness?
Full text linkIce accretion on wind turbine blades causes both a change in the shape of its sections and an increase in surface roughness. These lead to degraded aerodynamic performances and lower power output. Here, a high-fidelity multi-step method is presented and applied to simulate a 3 h rime icing event on the National Renewable Energy Laboratory 5 MW wind turbine blade. Five sections belonging to the outer half of the blade were considered. Independent time steps were applied to each blade section to obtain detailed ice shapes. The roughness effect on airfoil performance was included in computational fluid dynamics simulations using an equivalent sand-grain approach. The aerodynamic coefficients of the iced sections were computed considering two different roughness heights and extensions along the blade surface. The power curve before and after the icing event was computed according to the Design Load Case 1.1 of the International Electrotechnical Commission. In the icing event under analysis, the decrease in power output strongly depended on wind speed and, in fact, tip speed ratio. Regarding the different roughness heights and extensions along the blade, power losses were qualitatively similar but significantly different in magnitude despite the well-developed ice shapes. It was found that extended roughness regions in the chordwise direction of the blade can become as detrimental as the ice shape itself
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
Towards an open-source framework for Fluid–Structure Interaction using SU2, MBDyn and preCICE
Full text linkFluid-Structure Interaction (FSI) problems are a primary concern for the aerospace industry. Predicting the deformation of flexible structures due to aerodynamic forces is essential in different scenarios, e.g., for determining the performance of rotorcrafts and wind turbines. In this context, we present a new high-fidelity, open-source, modular, and user-friendly FSI simulation framework by coupling the well-established fluid solver SU2 with the multi-body structural solver MBDyn. The SU2 suite solves steady and unsteady Euler and RANS equations using a finite volume method on unstructured grids. The aerodynamic loads on the surfaces are then passed to MBDyn. Through a multi-body analysis, rotations, displacements, and the structural response of rotorcraft systems are efficiently computed and exchanged back with the fluid solver. A partitioned approach is used between the two codes, each specific for a single physical domain. Both explicit and implicit coupling were considered. The coupling is obtained through the library preCICE, which treats the two specialized solvers as "black boxes"and provides data mapping between non-matching grids. Classical FSI test cases are presented and results are compared with data from literature to validate the framework
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
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