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Instantaneous measurements of forces and moments on pv modules scaled as flat plates
No full textBibliography: p. 130-138Many pages are in colour.Inclined flat plates of aspect ratios, ARs, between 1 and 10 are the fundamental geometry for a number of wind engineering systems. Our particular interest is in photovoltaic (PV) modules and arrays mounted on flat roofs at the high angles required for optimum energy production in high latitudes. Usually PV modules are mounted of a number of similar units. However, wind loads on an isolate PV module are useful to determine the baseline performance. The wind loads on these structures can be very high and any correlation between, say, the instantaneous lift and drag can cause overturning moments that are not obvious from knowing only the mean drag and lift. This report describes a detailed examination of the three instantaneous forces and moments acting on an isolate module over a wide range of angles and at varying distances from the wind tunnel floor which represents a flat roof, in order to get a comprehensive set of mean lift, drag, and moment data for wind engineering purposes. The measurements were undertaken in the 0. 76 m x 1.3 7 m environmental wind tunnel at the University of Calgary. The nominal wind speed was 19 mis and the model sizes were chosen to keep the blockage below 3 .5 %. The flat plates with maximum AR=9 were attached to a sting to simulate an open support structure as distinct from the molded plastic pods that are becoming common for mounting modules at low angles. The forces and moments were measured by an ATI multi-axis force/torque sensor holding the sting to a solid frame. Forces and Moments acting on the sting were measured prior the tests with the flat plate to account for the effect of the sting drag on the measurements. The experimental set-up was checked by measurements of normal plates in the free stream for which the drag coefficient is well established. Results are in good agreement with the literature. The AR showed to be an important parameter affecting wind loads. Drag and lift are mainly due to pressure rather than shear stresses at all distances above the wind tunnel floor. The level of fluctuation of Co increased as o. increased and as the distance between the model and the wall decreased. In the free stream position, high values of CL for AR '.S 1 at 25° :S o. '.S 55° are related with high values of C0. The location of COP is close to the centre of the plate for all AR at 25° :So. '.S 55° in the free stream position, but in proximity to the wall, the COP is located close to the centre of the plate for AR :S 2.5 at all a. The estimation of both instantaneous COP and correlation coefficients were adversely affected by the fluctuations in the sting drag
A Hybrid Multi-Objective Evolutionary Algorithm for Wind-Turbine Blade Optimization
No full textA concurrent-hybrid non-dominated sorting genetic algorithm II (hybrid NSGA-II) has been developed and applied to the simultaneous optimization of the annual energy production, flapwise root-bending moment and mass of the National Renewable Energy Laboratory's (NREL) 5MW wind-turbine blade. To estimate the aerodynamic and structural performance, blade element momentum (BEM) and beam models were developed and validated. By hybridizing a multi-objective evolutionary algorithm (MOEA) with gradient-based local search, it is believed that the optimal set of blade designs could be achieved at lower computational cost than for a conventional MOEA. To compare the rate of convergence between the hybrid and non-hybrid NSGA-II on the NREL 5MW blade optimization, a computationally intensive case requiring 110,000 objective-function evaluations was performed using the non-hybrid NSGA-II. From this particular case, a 1.8% increase in the annual energy production and 4.7% decrease in the flapwise root-bending moment with the same mass as the NREL 5MW blade was achieved. The inclusion of local gradients in the blade optimization, however, shows no improvement in the convergence for this three-objective problem. A study on the gradient quality shows that the numerical instability of BEM and beam models hinders suitable gradient calculations
Development, Control and Recovery of Leading- and Trailing-Edge Vortices in Tandem-Airfoil Configurations
No full textParticle Image Velocimetry (PIV) has been used to uncover the two distinct aerodynamic mechanisms associated with cruise and hover conditions in tandem-airfoil configurations, i.e. dragonfly flight. The studies performed here have been carried out at transitional Reynolds numbers and reduced frequencies corresponding to dragonfly flight, which in turn are relevant to the development of Micro Air Vehicles (MAVs). The associated vortex dynamics of these strongly separated flows have been examined using vortex-tracking, pressure-integration and control-volume methods. To a lesser extent, direct force measurements and URANS-based numerical simulations have been used to support the findings. At first the formation and manipulation of leading-edge vortices (LEVs) and trailing-edge vortices (TEVs) for a single airfoil have been examined using non-sinusoidal kinematics and the theory of optimal vortex formation. Results show that the development of the LEV can be modified without the need for a span-wise flow, contrary to popular belief. In a similar fashion, the TEV can be reduced or even completely mitigated through the superposition of a quick-pitch motion near the bottom of the stroke. Subsequently, the studies of tandem configurations in cruise conditions revealed that the vortex-formation process for the forefoil is strongly influenced by the placement of a hindfoil in its wake, be it static or moving. In strong agreement with observations made on live dragonflies, airfoil configurations with specific out-of-phase kinematics of approximately ψ=60° were found to generate net thrust. The mechanism for this thrust production was identified as the formation of a leading-edge suction bubble on the hindfoil induced by the passing of the forefoil LEV. Similarly, the passing forefoil TEV was found to induce a vortex on the hindfoil, which in turn helped reduce power consumption on the upstroke. Finally, time-resolved PIV investigations into tandem hovering identified a beneficial interaction at ψ=90° in which the forefoil TEV interacted with the development of the hindfoil LEV. This aerodynamic mechanism in turn adjusted the strength and positioning of the hindfoil TEV, thus affecting thrust and power consumption. This result agrees with observations in nature and analogous force measurements for three-dimensional flapping wings, suggesting again that a span-wise flow is not necessarily a requirement for efficient vortex control but rather a result of the evolutionary restrictions in nature towards root-flapping flight
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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