1,721,152 research outputs found
Effect of struts and central tower on aerodynamics and aeroacoustics of vertical axis wind turbines using mid-fidelity and high-fidelity methods
Full text linkThis study investigates the impact of struts and a central tower on the aerodynamics and aeroacoustics of Darrieus Vertical Axis Wind Turbines (VAWTs) at chord-based Reynolds numbers of 8.12 × 104. A 2-bladed H-Darrieus VAWT is used, featuring a 1.5m diameter, a solidity of 0.1 and a blade cross-section of symmetrical NACA 0021. The turbine design is kept simple and straight-bladed which is essential for isolating and analyzing the specific effects of struts and a tower. The high-fidelity Lattice Boltzmann Method (LBM) in PowerFLOW 6-2020 and the mid-fidelity Lifting Line Free Vortex Wake (LLFVW) method in QBlade 2.0 are employed, with the mid-fidelity method providing a faster analytical tool for insights into the turbine performance. Firstly, both the LLFVW (mid-fidelity) and LBM (high-fidelity) methods effectively capture the general trends observed in VAWT power performance. However, the former predicts mean thrust values that are approximately 10% higher, and mean torque values that are approximately 19% higher, in comparison to the latter. Subsequently, the former predicts lower streamwise wake velocities relative to those predicted by the latter. These differences increase in configurations that include struts and a tower (to 30% - 31%). Secondly, the presence of struts and a tower leads to a reduction in both mean power (by 15% to 55%) and thrust (by 3% to 3.6%), with a further small decrease observed when doubling the tower diameter (power and thrust both by 0.5% to 3%). The struts predominantly affect the spanwise distribution of blade loading, while the tower impacts the azimuthal variation of blade loading. Additionally, the addition of struts and a tower reduces low-frequency noise (50-200 Hz) while increasing high-frequency noise (> 300 Hz). The observed decrease in mean blade loading results in reduced low-frequency noise, while the increase in high-frequency noise is ascribed to the increased intensity of BWI/BVI leading to higher unsteady loading fluctuations on blades.Wind Energ
Aerodynamic and aeroacoustic investigation of vertical axis wind turbines with different number of blades using mid-fidelity and high-fidelity methods
Full text linkThe aerodynamics and aeroacoustics of small-scale Darrieus vertical axis wind turbine (VAWT) are investigated at chord-based Reynolds number below 4e5. A statistical temporal and grid convergence study is conducted to analyse the thrust and torque coefficients. Four different VAWTs with different numbers of blades (1, 2, 3, and 4) are investigated using both the high-fidelity Lattice Boltzmann Method (LBM) and mid-fidelity Lifting Line Free Vortex Wake (LLFVW) method. The statistical temporal convergence is achieved much earlier for the 1-bladed rotor than for the 3-bladed rotor, using both methods. Power performance analysis reveals that VAWTs with more blades generate more power at lower Tip Speed Ratios (TSRs), while VAWTs with fewer blades generate more power at higher TSRs. The aerodynamic efficiency of each blade decreases as the number of blades increases, leading to a decreased amplitude of rotor loading variation in a single rotation. Both the mid-fidelity LLFVW and high-fidelity LBM capture these physical trends well. However, LLFVW predicts lower peak thrust and torque values in a single rotation and higher streamwise velocities in the wake, as compared to LBM. Moreover, the former predicts higher average power output than the latter, and the discrepancy increases as the number of blades increases. In terms of noise, at constant TSR, low-frequency BPF noise is found to be higher in VAWTs with fewer blades, while high-frequency noise is found to be higher in VAWTs with more blades. Overall Sound Pressure Level values revealed that overall noise increased with an increase in the number of blades except for the 4-bladed VAWT for which the noise decreased
Unsteady 1D and 2D hydraulic models with ice dam break for quaternary megaflood, Altai mountains, southern Siberia
No full textOne of the largest known floods occurred during the Late Quaternary, emanating from an ice-dammed lake in Asia. Glacial lake Kuray–Chuja was formed by a 600-m-high ice dam converging in the Chuja River valley of the Altai Mountains in southern Siberia. The dam impounded up to 594 km3 of water in the Kuray and Chuja basins.At least three floods from lake Kuray–Chuja occurred, but only the largest, or the most recent, is modelled herein. The discharge, through an ice dam breach by tunnelling or over-topping, is analysed using dam breach equations including one specifically developed for ice dam failures. From these calculations it is concluded that the ice dam need not have failed when the water was at a maximum depth (i.e. 600 m deep) but, in consideration with flood routing models, it is probable that the lake emptied by over-topping under conditions of maximum water level. Although an over-topping model is favoured, a collapse of the ice dam due to initial tunnel development in the ice body cannot be precluded.The resultant flood wave ran down the Chuja River valley to the confluence with the Katun River and beyond. One-dimensional and two-dimensional unsteady and non-uniform flow modelling of the flood wave routed down the river valleys is presented that includes modelling a channel bifurcation at the confluence and backwater effects. The depth of the flood model is constrained by the altitudes of the tops of giant bars deposited by the palaeoflood, which indicate maximum flood stage.The results of the ice dam failure calculations and the flow modelling are independent of each other and are consistent, indicating in each case a flood of the order of 10 M m3 s? 1, with best-fit solutions providing estimated peak flood discharges of 9 to 11 M m3 s? 1. A breach, 1 km wide and 250 m deep, developed in the ice dam in as little as 11.6 h whereas the flood duration required to evacuate the total lake volume was around 1 day
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
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
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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