1,720,992 research outputs found
A Non Conventional UAV In Ground Effect: Synthesis of a Robust Flight Control System,
No full textABSTRACT
This paper discusses the synthesis of an Extended Kalman Filter (EKF) to perform both wind velocities and state
estimation for a non conventional UAV flying in ground effect. Since, in IGE flight, motions into the symmetry
plane are of primary concern, the study focuses on the longitudinal aircraft dynamics. The proposed estimator
requires measurement of few flight variables, easily obtainable by means of conventional sensors; besides, it
does not use Inertial Measurement Unit (IMU). To simulate a low cost sensing equipment, the model outputs are
corrupted by white noise of relatively high standard deviation. Furthermore, to cope with the low rate of the
GPS with respect to the other sensors, the EKF algorithm is modified to allow for a dual rate measurement
model. State propagation is obtained by means of an accurate, highly non-linear mathematical model of the
UAV dynamics which allows to cope with both the non conventional configuration and ground effect. Combined
estimation of the UAV state and wind velocity is obtained by augmenting the system state vector with the wind
velocity components. Numerical simulations show the effectiveness of the proposed method in widely different
maneuvering conditions mixing IGE and OGE flight stages and in presence of largely dissimilar wind
disturbance characteristics. The performance advantages with respect to a classical, computationally simpler
estimation scheme are also highlighted. Closed loop simulations have shown the suitability of the obtained state
estimates for control purposes
I WIG’s: MEZZI INNOVATIVI PER IL TRASPORTO CIVILE Un’ipotesi di impiego per i collegamenti a medio raggio nel Mediterraneo
No full textDiurnal and nocturnal ranging behaviour of Stone-curlews Burhinus oedicnemus nesting in river habitat RID B-9642-2008
No full textStudying a species under a range of conditions is essential for fully understanding its ecology and for predicting its response to human impacts on the environment. We investigated the spatial behaviour and the habitat characteristics of foraging areas of Eurasian Stone-curlews breeding in an important but poorly investigated habitat, gravel riverbed, throughout the full 24-h cycle. The data collected for 17 radiotagged birds nesting in the Taro River Regional Park (Parma, Italy) showed a clear split between diurnal and nocturnal spatial behaviour. Almost all diurnal fixes and about two-thirds of nocturnal ones were located in the gravel riverbed, which not only provided suitable breeding territories but probably part of the food resources needed for reproduction. Nocturnal excursions from breeding sites to feeding areas (mostly farmland), sometimes of a few kilometres, indicated that these resources do not cover all of the birds' needs. Night spotlight counts of foraging birds in the agricultural area indicated that Stone-curlews preferred recently harvested crops (mainly forage and wheat) and piles of farmyard manure. These habitat preferences are closely linked to the predominant agricultural activity of the study area, which is characterized by a high density of dairy farms for the production of Parmigiano Reggiano cheese. It seems likely that the proximity of gravel riverbed and farmland habitats is one of the main causes of the high breeding density recorded in the study area. We propose that the conservation of Stone-curlews at this site could potentially be achieved only by a synergistic management of both natural and agricultural habitats
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
Dynamic Stability in Ground Effect of a non Conventional UAV in Antisubmarine Surveillance Operations
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Trajectory tracking for an Ultralight WIG
No full textIn this paper we present our research about a particular ultralight WIG. We have carried out the design of a Flight Control System that has to fix the control variables trend through a non-linear mathematical model, because of the particular geometric and aerodynamic configuration of this WIG. So, the non-linear mathematical model design has to reproduce exactly the aircraft behaviour either OGE or IGE. In particular, through classical semi-empirical relations, analytical equations have been obtained in order to evaluate incidence variations, downwash and upwash angles due to the ground. In the present paper only longitudinal dynamic is considered, because of its peculiarity in WIG's aircraft dynamic. A mathematical general model has been built to evaluate aerodynamic coefficients variation laws due to altitude. This general equations system can be used in order to evaluate stability and control derivatives so it affords to simulate all the flight phases either out or in ground effect. A Simulink model has been realized and LQG/LTR robust control technique has been applied to design the controller. The simulation results have shown the accuracy of the mathematical model and that it is possible to control the studied UAV either OGE or IGE utilizing a single control system
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