1,720,975 research outputs found
OMA analysis for the identification of the damping properties of a sloshing fluid
No full textIn this paper, the modal characteristics of a sloshing fluid at different operating conditions are estimated using Operational Modal Analysis (OMA) methods. The chosen system is characterized by a plexiglass tank filled with water mimicking the fuel tank inside an aircraft wing. Specifically, the considered tests are aimed at evaluating the sensitivity of the eigen-properties of the fluid to the random excitation levels and the liquid filling levels. Such experimental investigations are carried out at the environmental test facility available at the Department of Mechanical and Aerospace Engineering of the University of Rome “La Sapienza” which provided the closed-loop control vibrations at the base of the tank. Because the chosen tank system can be considered fully uncoupled with the dynamics of the sloshing fluid, these tests can be considered as a preliminary laboratory representation of the fluid sloshing inside an actual aircraft wing, thus contributing to the formation of the experimental database for the European funded project SLOshing Wing Dynamics (SLOWD)
Structural damping models for passive aeroelastic control
No full textAeroelastic qualification requirements are typically met by sizing aircraft to achieve adequate stability margins and keep peak gust responses below specified thresholds. A possible alternative approach is delaying flutter and alleviating gust response by embedding dissipative materials into structural components. This approach requires accurate damping models applicable to the analysis of complex configurations. In this paper, the effect of damping models in the evaluation of flutter boundaries and gust response of an aeroelastic test-bed is studied. In particular, three damping models completely different in frequency are considered to model the presence of skin patches for passive aeroelastic control: viscous damping, hysteretic damping and Biot damping models. In order to make them comparable the three models are tuned in order to dissipate the same amount of power at the flutter frequency by means of the introduction and definition of a generalized loss factor. The damping models are compared by evaluating their effect on flutter suppression and gust load alleviation. Finally, the sensitiveness of the stability and response aeroelastic analyses to the considered damping models are outlined and the obtained results are compared to provide modeling recommendations for passive flutter suppression and gust alleviation studies. The proposed methodology is applicable to any linear material model for which the related complex stiffness can be expressed in the frequency domain meeting the Hilbert restriction
Quasi-steady aeroelastic analysis of the semi-aeroelastic hinge including geometric nonlinearities
No full textA recent consideration in aircraft design is the use of folding wingtips, with the aim of enabling higher-aspect-ratio wings with less induced drag but also meeting airport gate limitations. A formulation is introduced to account for finite rotations of rigid folding wingtips attached through hinges on a flexible airframe structure including also aerodynamic follower forces for the folding wingtip components. This study investigates the effects of geometric nonlinearities on the quasi-steady aeroelastic response of floating wingtips. It is found that the wingtip response can vary significantly when geometric nonlinearities are accounted for; however, a small impact was observed on the main airframe structure
Proper orthogonal decomposition, dynamic mode decomposition, wavelet and cross wavelet analysis of a sloshing flow
No full textInternal hydrodynamics and its coupling with structural dynamics are non-negligible processes in the design phase of aerospace systems. An improved understanding of the nature of this coupling would allow for greater flexibility in modeling and design of such systems, and could lead eventually to the development of suitable active and/or passive control strategies for enhanced performances. In this manuscript we apply a number of data analysis techniques: proper orthogonal decomposition, dynamic mode decomposition and wavelet transform and their combination to time-resolved images of a liquid sloshing within an enclosure. We use these techniques to identify fluid-dynamic modes in space and time and to verify their coupling with the structural dynamics of vibrating structures. In particular we consider the transient case of a water tank mounted on a free oscillating cantilever. As the acceleration amplitude decays, we observe and quantify the transition from incoherent flow to standing waves. Our results show that the content of the images is very informative and can be used for quantitative analysis. As the main outcome, the hydrodynamic modes are identified using POD and DMD, and related to known features of sloshing flow, such as the frequency of the first symmetric free surface mode. Additionally we perform a comparison of wavelet transforms of POD time coefficients and measured acceleration signals at the tank base. Viewing the latter as the input and the former as the output of the fluid-dynamic system, we are able to correlate the enhanced damping of the cantilever oscillation to the different regimes of the hydrodynamic field
Surrogate finite-element modelling for launch vehicle multidisciplinary optimization
No full textA multi-disciplinary optimization approach is crucial to reduce development time and costs for new launch vehicle configurations, especially in light of the imminent increase in demand for launch services. This paper aims to present a methodology for obtaining a launch vehicle structural model that can be used for multidisciplinary design optimization through the use of genetic algorithms and radial basis functions. Specifically, a finite-element model generator is developed and used to create a solid rocket-based launch vehicle model, whose input parameters (geometry and loads) are affected by the selected payload and mission. To determine the critical load cases needed to size the structural components, the trajectory profile from takeoff to orbit insertion is of paramount importance. The use of surrogate models enhances the process of identifying the optimal design by enabling reductions in the running time of the optimization procedure, making the finite-element analysis suited for conceptual studies
Sloshing reduced-order models for aeroelastic analyses of innovative aircraft configurations
No full textThe present paper introduces the sloshing effects on aeroelastic stability and response of flying wing configurations. Using reduced order model based on data provided by computational fluid dynamics data, the description of the slosh dynamics is introduced into an integrated modelling that accounts for both rigid and elastic behaviour of flexible aircraft. The fully unsteady aerodynamics, modelled in the frequency domain via doublet lattice method, is recast in time-domain state-space form through the rational function approximation. The reference aircraft is the Body Freedom Flutter equipped with a single tank of cylindrical geometry, partially filled with water, and located underneath the center of mass. The results of the stability and response analyses are compared with the frozen fluid case with the final aim of showing how the fluid movement affects the complete aircraft behaviour
Damping modelling in aircraft flutter analyses
No full textThe aeronautic industry is moving towards the research for more and more performing materials in order to make the aircrafts increasingly lightweight, and to get a decrease in consumption and atmospheric pollution. These materials result in viscoelastic behavior that is difficult to analyze with traditional structural damping models typically used in design stage. In particular, appropriate description of the damping may become critical for the study of flutter stability margins which may ultimately lead to the initiation of limit-cycle behavior. This paper aims to introduce a first-principle-based viscoelastic damping formulation to be applied to aeroelastic systems describing highly flexible aircraft in order to critically assess its influence into flutter and stability analyses
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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