1,720,953 research outputs found
Robust scheduling control of aeroelasticity.
Get PDFAeroelasticity is a broad term describing the often complex interactions between structural mechanics and aerodynamics. Aeroelastic phenomena such as divergence and flutter are potentially destructive, and thus must be avoided. Passive methods to avoid undesirable aeroelastic phenomena often involve the addition of mass and/or limiting the achievable performance
of the aircraft. However, active control methods allow both for the suppression of undesirable aeroelastic phenomena, and for utilisation of desirable aeroelastic phenomena using actuators, thus increasing performance without the associated weight penalty of passive systems. The work presented in this thesis involves the design, implementation and experimental validation of novel active controllers to suppress undesirable aeroelastic phenomena over a range of airspeeds. The controllers are constructed using a Linear Parameter Varying (LPV) framework, where the plant and controllers can be represented as linear systems which are functions of a parameter, in this case airspeed. The LPV controllers are constructed using Linear Matrix Inequalities (LMIs), which are convex optimisation problems that can be used to represent many linear control objectives. Using LMIs, these LPV controllers can be constructed
such that they self-schedule with airspeed and provide upper performance bounds during the design process. The aeroelastic phenomena being suppressed by these controllers are Limit-Cycle Oscillations (LCOs), which are a form of flutter with the aeroelastic instability bounded by a structural nonlinearity in the aeroelastic system. In this work, the aeroelastic system used is the Nonlinear Aeroelastic Test Apparatus (NATA), an experimental aeroelastic test platform located at Texas A&M University. Three and four degree-of-freedom dynamic models were derived for the NATA, which include second-order servo motor dynamics. These servo motor dynamics are often neglected in literature but are sufficiently slow that their dynamics are significant to the controlled response of the NATA. The dynamic model also incorporates quasi-steady aerodynamics, which are accurate for low Strouhal numbers calculated from the oscillation frequency of the wing. Is it shown how the dynamics of the NATA can be represented in LPV form, with a quadratic dependence on airspeed and linear dependence on torsional stiffness. Using a variety of techniques the parameters of the NATA are identified, and shown through nonlinear simulation to provide excellent agreement with experimental results. It is also argued that structural nonlinearity, in the way of a nonlinear torsional spring connecting the wing section to the base, generally improves stability due to its largely quadratic stiffness function, and hence in many instances it is safe to
linearise this nonlinearity when designing a controller. Using a H₂ generalised control problem representation of a Linear Quadratic Regulator (LQR) state-feedback controller, LPV synthesis LMIs are constructed using a standard transformation which render the LMIs affine in the transformed controller and Lyapunov matrices. These matrices have the same quadratic dependence on airspeed as the NATA model. To reduce conservatism the parameter space of airspeed versus airspeed squared is gridded into triangular convex hulls over the true parameter curve, and the LMIs are numerically optimised to give an upper bound on the H₂ norm across the design airspeed. The resulting state-feedback controller is constructed from the transformed controller and Lyapunov matrices, and can be solved symbolically as a function of airspeed, however it forms a high-order rational function of airspeed, hence it is quicker to solve for the controller gains numerically on-line. The controller is analysed for the classical measures of robustness, namely gain and phase margins, and maximum sensitivity. While not providing the guarantees of these measures that a conventional LQR controller provides, the controller is shown to be sufficiently robust across the airspeed design range. Experimental results for this controller were performed, and the results show excellent LCO suppression and disturbance rejection, the results from which are published in Prime et al. (2010). Following the above work based on a scalar performance index, the upper bound on the H₂ norm is allowed to vary with airspeed using the same quadratic dependence on airspeed as the NATA model, and the transformed controller and Lyapunov matrices. A simple method
of solving the LMIs is shown such that the LPV H₂ upper bound is as close to optimal as possible, and using this method a new controller is synthesised. This new controller is compared against the LPV LQR controller with the scalar performance index, and is shown to be closer to optimal across the airspeed design range. Nonlinear simulations of the controlled NATA using this new controller are then presented. Based on Prime et al. (2008), a Linear Fractional Transformation (LFT) is applied to the NATA model to render the dynamics dependent upon the feedback of the linear value of airspeed. This allows the LMIs to be constructed at only two points, the extreme values of the linear design airspeed, rather than gridding over the parameter space as was performed above. An output-feedback controller that itself depends upon the feedback of a function that is linearly dependent upon airspeed is constructed using an induced L₂ loop-shaping framework. The induced L₂ performance objective is based upon a Glover-McFarlane H∞ loop-shaping process where the NATA singular values are shaped using pre- and post-filters, and minimising the induced L₂ norm from both the input and output to both the input and output. An LFT controller is synthesised, and simulations are performed showing the suppression of LCOs.Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 201
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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