1,720,964 research outputs found
Wind Tunnel Tests of an Aeroelastic Model with Multiple Control Surface Freeplay Nonlinearities
No full textNumerical and Experimental Investigations on Freeplay-Based LCO Phenomena on a T-Tail Model
No full textLimit cycle oscillations (LCO) are of great interest for aeronautic engineers. They may strongly affect performance and life of aeroservoelastic systems. For quite some time, studies have focused on increasing the understanding of the physics behind the freeplay-induced LCOs, striving to find general rules, particularly, if possible, for certification purposes. However, few studies reproduced experimentally the gap sizes required by regulatory agencies, and no experimental studies tackled dynamically time-varying nonlinearities. In the present work, a new experimental capability is presented. The final goal is to capture by tests the behavior of realistic systems, with fully flexible control surfaces, efficient variation of freeplay magnitude, and the time-varying evolution of freeplay. The new experimental model created also makes it possible to change the nominal stiffness at the hinge and the control surface inertia, effectively allowing the study of the sensitivity to parametric uncertainty. Several experimental campaigns will be carried out using this new experimental test article and capabilities, providing valuable data that can also be used by other researchers or practitioners to verify their numerical methods. In the context of this first manuscript, some numerical methods have also been introduced and explored. Initial experimental results have been generated. The results are of great interest, as they show a peculiar limit cycle behavior that cannot fully be modeled using a describing function approach. This exemplifies the necessity to always complement frequency domain LCO simulations with time marching simulations. Further, it was experimentally shown that even when current certification freeplay limits are met LCO can develop. However, with careful design the effect of LCO on the main structure of an aeroservoelastic system can be minimized, as it will also be shown
Final Validation and Performance Assessment of a Full-Scale Morphing Droop Nose Demonstrator
Full text linkExperimental Studies on Dynamic Freeplay Nonlinearity
No full textIn the present manuscript, some novel results obtained in the context of an ongoing research at POLIMI are presented. The work focuses on the effect of multiple freeplay nonlinearities on the aeroelastic behaviour of a full-configuration aeroelastic wind tunnel aircraft model. The demonstrator is equipped with an active flutter suppression system, allowing the study of the interactions between the LCO created by the nonlinearities and the control system. In the first phase of the project, the horizontal tail plane was redesigned and used to extensively study a single nonlinearity, both with static and dynamic gap. It was found that LCO could be observed regardless of the gap size, including regulatory agencies’ limits. Also, the mechanism triggering LCO was studied, which is strongly related to the turbulence level. The effect of different rates of change of the gap size are discussed. Presentation of results for the horizontal tail are followed by results for the new version of the vertical tail plane. Preliminary numerical results are presented, showing a similar behaviour of the rudder LCO relative to the elevator LCO of the horizontal planes. In the next stage of the project, planned for the end of 2022, the entire aircraft model will be tested with all the nonlinearities active simultaneously
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
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