1,720,961 research outputs found
L1adaptive attitude augmentation of a small scale unmanned helicopter
No full textIn this paper, the L1 attitude control augmentation of an aerobatic helicopter is described. The baseline controller is divided into two loops, an attitude loop, and an angular speed loop. The attitude loop generates an angular reference speed for the angular speed loop, which finally provides the collective commands to the helicopter. Both loops are augmented through an L1 adaptive controller whose low-pass filter bandwidth is tuned considering a simplified helicopter actuation and flapping dynamics model. Simulation results are shown, and the baseline and the augmented controllers are compared
Understanding the effects of rotor dynamics on helicopter incremental non-linear controllers
No full textWith an increasing trend towards automatic flight control system applied to rotorcraft, the goal of the present paper is to understand the effects of rotor dynamics on the design of robust incremental non-linear controllers such as INDI (Incremental nonlinear Dynamic Inversion) and IBS (Incremental Backstepping Control). Nonlinear dynamic controllers are a desirable solution to helicopter flight control as it can solve its highly nonlinear dynamic behavior. However, conventional nonlinear controllers heavily rely on the availability of accurate model knowledge and this can be problematic for rotorcraft. Therefore, incremental control theory can solve the modelling errors sensitivity by relying on the information obtained from the sensors instead. The paper will demonstrate that for helicopters the incremental nonlinear controllers depend on the delays introduced in the controller by rotor dynamics. The paper will show how the residualization and synchronization methods need to be applied to an IBS controller in order to remove the effects of the flapping (disc-tilt) dynamics from the controller. This indicates that the incremental nonlinear controllers can have relatively small stability robustness margin when subjected to rotorcraft time delays and unmodelled dynamics that influence the feedback path and should be therefore carefully applied
L1 ADAPTIVE SPEED CONTROL FOR A HELICOPTER
No full textAdaptive control theory is used to improve robustness of systems against model uncertainties and disturbances. Two of the main drawbacks of adaptive controllers is the lack of criteria to measure the robustness of the controller and the speed of the adaptation loop. In L1 adaptive control theory both problems are solved by the introduction of a low pass filter in the control input. The L1 adaptive control robustness and stability are guaranteed by numerical criteria. L1 adaptive control raised a great interest in the aerospace field due to the presence of nonlinear and uncertain dynamics that affects aircraft flight performances. Such strategy by the way has not been widely used and explored for rotorcrafts. In this article the authors propose an L1 output feedback speed controller for helicopters. The control system architecture is tested by means of a simulation test campaign through the use of a nonlinear helicopter model. Both performances and robustness of the controller are evaluated, even in presence of disturbances
An Improved Stability Analysis for the L1 Adaptive Augmentation of a Baseline Controller
No full textThis paper revises the SISO output feedback L1 adaptive control architecture and the L1 adaptive augmentation of a baseline controller. An improved stability condition for the baseline L1 augmentation architecture is derived. The proposed improved way of performing the stability analysis can be less conservative, and this result may help certify the baseline augmentation for a broader range of uncertainties and disturbances
Flight dynamic modeling and stability of a small-scale side-by-side helicopter for Urban Air Mobility
Full text linkThis paper aims to explore the development of a flight dynamics model for a small-scale side -by -side helicopter and describe its trim and stability characteristics. The helicopter is considered a suitable candidate for Urban Air Mobility (UAM) solutions, because of its reliable design and low noise characteristics, but still very small knowledge is present on the mathematical modeling approaches and dynamic properties. A 14 degrees of freedom nonlinear mathematical model is developed and semi -analytical models are employed to account for the presence of the shrouds. An iterative trim routine is developed and applied with a suitable control mix that allows the use of classic helicopter controls. To control the vertical speed and roll rate, the paper assumes an equal collective pitch and lateral cyclic in the two rotors, while a uniform plus a differential longitudinal cyclic is adopted for pitch and yaw maneuvers. The paper discusses unique characteristics of the side -by -side configuration as obtained from the stability analysis: an unstable high -frequency mode, governed by the vertical velocity and pitch angle arises when the center of gravity (CG) of the vehicle is aligned or placed in front of the two main rotors. Similarly, both lateral phugoid and roll subsidence modes are sensitive to the CG location. The side -byside configuration presents also a stable spiral mode which needs to be carefully designed
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
L1 Adaptive Control for Small-Scale Unmanned Helicopters: Enhancing Speed Regulation
Full text linkThis paper focuses on the application of L1 adaptive control to the speed autopilot loop of small-scale unmanned helicopters. The L1 adaptive control technique is investigated for its potential to provide reliable speed control, particularly in handling external disturbances and model uncertainties. Although L1 adaptive control has been widely studied, its application to small-scale unmanned helicopters remains relatively unexplored. Through numerical simulations and a preliminary experimental test campaign conducted on a small rotary-wing platform, this paper contributes to validating L1 adaptive control as a promising solution for speed regulation in unmanned helicopter platforms
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