1,720,981 research outputs found
Aerodynamics for a Sub-Orbital Reusable Experimental Vehicle
No full textIn this work an aerodynamic model for the calculation of the aerodynamic force and moment coefficients for a Sub-Orbital Reusable Experimental Vehicle is proposed. The aerodynamic model, which is based on physical properties of the flows around obstacles, provides the mathematical expression for each aerodynamic coefficient. These analytical forms incorporate various free parameters which have to be identified through opportune data elaborations. These free parameters are here identified by means of a best fitting procedure applied to data which are the result of wind tunnel testing and computational fluid dynamics. The aerodynamic model is applied to a vehicle developed and realized at the Italian Center of Aerospace Research (CIRA). The study is motivated by the fact that the aerodynamics of a reentry vehicle is characterized by complex flow structure about the aircraft which in turn cause great variations of all the aerodynamic coefficients with Mach number and angle of attack. Due to this complexity, these coefficients vary in a complicate fashion, therefore the modeling of the vehicle aerodynamics in the transonic regime is a difficult task which requires the accounting for the compressibility effects which happen for the various combinations of angles of attack and flight Mach number
A hybrid approach to robustness analyses of flight control laws in re-entry applications
Get PDFThe present paper aims at improving the efficiency of the robustness analyses of flight control laws with respect to conventional techniques, especially when applied to vehicles following time-varying reference trajectories, such as in an atmospheric re-entry. A nonlinear robustness criterion is proposed, stemming from the practical stability framework, which allows dealing effectively with such cases. A novel approach is presented, which exploits the convexity of linear time varying systems, coupled to an approximate description of the original nonlinear system by a certain number of its time-varying linearizations. The suitability of the approximating systems is evaluated in a probabilistic fashion making use of the unscented transformation technique. The effectiveness and potentials of the method are ascertained by application to the robustness analysis of the longitudinal flight control laws of the Italian Aerospace Research Center (CIRA) experimental vehicle USV
A linear time-varying approach for robustness analyses of a re-entry flight technology demonstrator
Get PDFA novel robustness analysis technique is proposed for atmospheric re-entry applications. The problem is stated as a finite time stability (FTS) analysis of linear time-varying (LTV) systems on a compact time domain, subject to bounded variations in initial state and unknown parameters. The FTS property is formulated as the inclusion of all the possible system trajectories into a pre-specified time-varying subset of the state space. Based on assuming the involved sets are polytopes, the proposed approach allows deducing the system FTS from the property verification on a limited number of numerically computed system trajectories. An additional result is presented which allows determination of a conservative estimate of the maximum norm-bound of time-varying perturbations under which the LTV system remains finite time stable. Results of the application of the proposed technique to a re-entry technology demonstrator are presented which demonstrate its effectiveness in complementing conventional linear time invariant-based analyses. Results also show that it is computationally viable and allows linking the system robustness to a quantitative analysis of the system trajectory dispersion around the nominal one due to concurrent initial state dispersion and uncertain parameters effects, which aids in evaluating mission objectives fulfillment
MU-SYNTHESIS FOR A SMALL COMMERCIAL AIRCRAFT: DESIGN AND SIMULATOR VALIDATION
No full textThe potential benefits deriving from the application of modern multivariable techniques to the flight control laws design for a fly-by-wire small commercial aircraft are evaluated by means of a practical benchmark problem. For such a class of airplanes, a unified set of flying qualities requirements is not available; therefore, a first effort has been made to formulate a suitable set of requirements to be followed during the design phase. On the basis of such requirements, a reference dynamic model of the aircraft has been chosen. Then a model matching H-inf, control problem has been solved via the mu-synthesis approach, which allows disturbance rejection and robustness specifications to be taken into account. Finally, the designed flight control laws have been evaluated by means of both numerical off-line simulations and pilot-in-the-loop simulations performed via the ground-based simulator located at the National Aerospace Laboratory in Amsterdam. The research activity has been performed within the framework of the research project Affordable Digital Fly-By-Wire Flight Control Systems funded by the IV Framework Program (1997-2000) of the European community
A Tool For Space Vehicle Uncertainty Ranges Estimation
No full textA key aspect in the success of a space project is the capability to detect as soon as possible the problems that can arise during the project development. This approach allows to optimise mission reliability, project costs and temporal delays. In this paper a design tool, named PARAN, is proposed for parametric analysis of uncertain systems. This tool can be used in the very early design phase of the system, allowing to define the maximum extent of relevant parameter uncertainty ranges in which required system properties are guaranteed. A system requirement can be often represented by a Boolean property, as a function of a set of relevant design parameters. Given a method for checking that property, PARAN efficiently allows to estimate a multi-dimensional uncertainty region in the parameters space, in which the system satisfies the property. Main feature of the proposed tool lies in the efficient underlying algorithm for finding the uncertainty region, which minimizes the total number of property evaluations. In the paper a case study is presented, applying PARAN to estimate the maximum allowable aerodynamic uncertainty region where the CIRA USV is trimmable and manoeuvrable. Evaluation of PARAN efficiency with respect to usual industrial gridding techniques is reported
Performance Assessment of LiDAR-Visual-Inertial Fusion for GNSS-Resilient Aerial Navigation
No full textThis work proposes an innovative LiDAR-Visual-Inertial navigation algorithm specifically conceived to face the challenges offered by a flying platform in a GNSS-denied environment. An Extended Kalman Filter is employed and loose integration of exteroceptive sensors measurement is considered. LiDAR and camera measurements are coupled altogether to build a joint pose estimate which exploits the LiDAR to associate depth information to image features detected by the camera. Particular attention is paid to the integrity of the multi-sensor-based solution. To this aim, a set of gating criteria is introduced to assess the validity of each measurement to be used within the filter and thus to improve its resiliency against anomalous pose estimates. The strategy is assessed using a simulation environment based on MATLAB/Simulink and Unreal Engine, which allows to retrieve realistic visual and LiDAR data by simulating different aircraft trajectories, geometries and scenes. Results on simulated data show a maximum percentage error on the position estimate, computed with respect to the vehicle traveled distance, of 4.6%, and a maximum error on the attitude angles estimate of 1.6°. The paper also introduces the experimental setup that has been developed to collect experimental data. Flight experiments are being conducted using a customized heavy lift quadcopter equipped with high performance Inertial Measurement Unit, color camera with a narrow Field Of View, a color fisheye camera, a scanning LiDAR and a GNSS receiver
Design process and real-time validation of an innovative autonomous mid-air flight and landing system
No full textThis paper describes the design process and the real-time validation of an innovative autonomous mid-air flight and landing system developed by the Italian Aerospace Research Center in the framework of the Italian national funded project TECVOL (Technologies for the Autonomous Flight). In the paper it is provided an insight of the whole development process of the system under study. In particular, the project framework is illustrated at first, then the functional context and the adopted design and testing approach are described, and finally the on-ground validation test rig on purpose designed is addressed in details. Furthermore, the hardware-in-the-loop validation of the autonomous mid-air flight and landing system by means of the real-time test rig is described and discussed
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
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