1,720,958 research outputs found
High-order implementation of the kinematic Laplacian equation method by spectral elements
Full text linkA novel high-order implementation for the Navier–Stokes equations in the vorticity–velocity formulation is presented. It is based on the kinematic Laplacian equation (KLE) method introduced in a previous work as a low-order finite-element approach. Different aspects of the high-order implementation by spectral elements of this novel procedure are discussed. The well-known problem of a semi-infinite region of stationary fluid bounded by an infinite horizontal flat plate impulsively started is used in different ways to conduct comparative evaluation tests. This time dependent boundary-layer-development problem has an exact analytic solution, and may be regarded as a canonical problem for the subject of generation of vorticity boundary conditions in vorticity–velocity approaches. Results are analyzed and conclusions presented.Fil: Ponta, Fernando Luis. Michigan Technological University; Estados UnidosFil: Otero, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería; Argentin
Structural analysis of wind-turbine blades by a generalized Timoshenko beam model
Full text linkAn important aspect in wind-turbine technology nowadays is to reduce the uncertainties related to blade dynamics by the improvement of the quality of numerical simulations of the fluid-structure interaction process. A fundamental step in that direction is the implementation of structural models capable of capturing the complex features of innovative prototype blades, so that they can be tested at realistic full-scale conditions with a reasonable computational cost. To this end, we developed a code based on a modified implementation of the variational-asymptotic beam sectional (VABS) technique proposed by Hodges et al. VABS has the capacity of reducing the geometrical complexity of the blade section into a stiffness matrix for an equivalent beam, allowing accurate modeling of the 3D structure of the blade as a 1D finite-element problem. In this paper, we report some recent results we have obtained by applying our code to full-scale composite laminate wind-turbine blades, analyzing the fundamental vibrational modes and the stress load in normal operational conditions.Fil: Otero, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Simulación Computacional para Aplicaciones Tecnológicas; Argentina. Michigan Technological University; Estados UnidosFil: Ponta, Fernando Luis. Michigan Technological University; Estados Unido
On the sources of cyclic loads in horizontal-axis wind turbines: The role of blade-section misalignment
Full text linkIn this paper we investigate the sources of cyclic loads affecting the structural solicitation and power production in Horizontal Axis Wind Turbines, in particular the role of blade-section misalignment. These loads could become determinant in future designs of extra-large turbines, limiting lifespan due to fatigue of structural and mechanical components. Gravity loads would also become more significant in future up-scaled machines due to the square-cube law relation between energy capture and rotor mass. We identify the different constructive factors and physical mechanisms which constitute the sources of the cyclic loads on the rotor, and present a methodology to analyze the contribution of each one of them. We propose six hypothetical scenarios to illustrate the individual effect of each of the aforementioned sources on the aerodynamic and structural variables that characterize the operational state of the turbine. We analyze the evolution of aerodynamic variables which characterize rotor interference and its relation with the angle of attack on the blade sections. Structural variables are also analyzed, showing the contribution of both aerodynamic and gravity loads, inducing out-of-plane bending and torsional oscillations, and how these could be activated by bend-twist coupling on the blade structural response.Fil: Otero, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Simulación Computacional para Aplicaciones Tecnológicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería; Argentina. Michigan Technological University; Estados UnidosFil: Ponta, Fernando Luis. Michigan Technological University; Estados Unido
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
The adaptive-blade concept in wind-power applications
Full text linkOne of the technological challenges in wind power is the development of a next generation of feasible upscaled turbines of cheaper construction that may further reduce generation costs. But limitations in the current blade technology constitute a technological barrier that needs to be overcome. As the size of the typical turbine increases, savings in weight and complexity in the rotor design and its auxiliary mechanisms, like the pitch-control actuators, become more important. The notion of smart or intelligent advanced blades that can control themselves and reduce (or completely eliminate) the need of an active control system is a very attractive prospect for future developments in blade technology.
The idea of wind turbine rotors which automatically adapt to the meteorological and working conditions is not entirely new. It has been around for the last two or three decades, and several control systems have been proposed to achieve this goal using either a purely-passive or a combination of active-passive means. Blade adaptiveness can be achieved by means of inducing coupling among modes of deformation of the blade which are usually only slightly coupled. For instance, coupling between bending and twisting can be used to control power production, to reduce vibration and extreme loads, and to improve fatigue performance. In this case, as aerodynamic loads begin to bend the blade, flexo-torsional modes induce a twist. This changes the angle of attack on the airfoil sections, reducing the lift force acting on the blade.
In this paper, we are going to review different aspects of the adaptive-blade concept development, covering a historical overview, recent advances, and future trends.Fil: Ponta, Fernando Luis. Michigan Technological University; Estados UnidosFil: Otero, Alejandro Daniel. Michigan Technological University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rajan, Anurag. Michigan Technological University; Estados UnidosFil: Lago, Lucas Ignacio. Michigan Technological University; Estados Unido
Analysis of alternative adaptive geometrical configurations for the NREL-5MW wind turbine blade
Full text linkThe correct prediction of flexo-torsional deformation is of capital importance for the future development of advanced wind-turbine blade prototypes. Coupling between bending and twisting can be used to reduce extreme loads and improve fatigue performance. This is the principle of the adaptive blades, where the incremental loads are reduced when, as the blade bends, the flexo-torsional modes of the blade structure produce a change in twist, and so in the angle of attack, modifying the lift force acting on the blade sections. Bend-twist coupling could be achieved either by modifying the internal structure (structural adaptiveness), or by readapting the geometry of the blade (geometrical adaptiveness). These two techniques can be used independently or combined, complementing each other. We have developed a novel computational tool for the aeroelastic analysis of wind-turbine blades, which allows a full representation of the flexo-torsional modes of deformation of the blade as a complex structural part and their effects on the aerodynamic loads. In this paper, we report some recent results we have obtained applying our code to the analysis of geometrical adaptive blades, taking full advantage of the coupled deformation modes that our aeroelastic code can represent. We analyze alternative blade configurations for the NREL-5 MW wind-turbine, optimizing the design to mitigate vibration and improve fatigue performance.Fil: Lago, Lucas Ignacio. Michigan Technological University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ponta, Fernando Luis. Michigan Technological University; Estados UnidosFil: Otero, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ingeniería; Argentin
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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