1,720,983 research outputs found
INVESTIGATION ON SMART SENSORS TO PREDICT FLUTTER AND AEROLASTIC RESPONSE
No full textThis research is devoted to the identification of non-linear aeroelastic systems in real time. The proposed studies will be related to develop new sensory techniques to identify aeroelastic modes and unsteady aerodynamics in fixed and rotary wings. These studies are important because the interaction of the vibration natural modes of the aircraft structure with the unsteady aerodynamic loading may become unstable under certain flight conditions, leading to the flutter phenomenon. Moreover, in a less severe scenario, these loads generate high levels of aircraft forced vibration that cause passenger discomfort and lead to structural fatigue and even failure. All these studies, although ultimately directed to helicopter blades, will be initially conducted with fixed-wing configurations, and will include both numerical simulations and experimental work conducted in still air and wind tunnel. From the project originality point-of-view, it is well known that the main line of research on aeroelasticity today is associated with non-linear phenomena. In the low speed range, the non-linearity is often associated with the structure alone (free play of control surfaces in most cases). However, in the high-speed transonic regime, non-linearities are also generated from the aerodynamics unsteadiness, and these are normally associated with localized shocks on supercritical airfoil configurations. There is no efficient method that can be used in the industry today to deal analytically with non-linear phenomena. The development of reliable and computationally efficient analytical methods is of fundamental importance for the industry. However, this development can only be done with the existence of carefully controlled wind tunnel tests to serve as a source of comparison data. As wind tunnel tests are very expensive, reliable experimental data must be acquired in the shortest period of time. The objective of this research is, therefore, to develop new sensory techniques based on smart materials to maximize the efficiency of wind tunnel tests to produce accurate data pertinent to aeroelasticity. In fact, Carleton University is engaged to pursue with several international partners a collaborative project on an experimental investigation to determine the aeroelastic flutter and forced vibration characteristics of a model of a typical commuter aircraft configuration using the National Research Council Canada (NRCC) Institute for Aerospace Research 5-foot square test section of their blow-down wind tunnel facility. The main investigation will be performed in the high-speed transonic regime where non-linear aerodynamic behavior occurs. Notwithstanding the panned NRCC tests, this research will be complemented with low-speed wind tunnel tests on a full-aircraft configuration to be carried out by partners at CTA (Centro Tecnico Aeroespacial) in Brazil to investigate the effect of structural non-linearities on flutter characteristics. This collaborative project is seen of strategic interest in terms of advancing the general knowledge as well as the partners' expertise in a research area that is of great and timely interest for the aerospace industry. It is further proposed that "La Sapienza" becomes a partner in this international research effort. One of the proposed wind tunnel models is a reflection plane wing-body model where a fairing allows a smooth transition between the wing and the fuselage. The model includes a swept-tapered wing, which supports a nacelle and a jet engine modeled as a hollow cylinder. Under terms of this collaboration, the wind tunnel model will be designed and fabricated at Carleton University. The model will be tested for flutter in the NRCC blow-down wind tunnel in the transonic regime for different pitch angles, Reynolds and Mach numbers. A mass damper ("flutter stopper") will be incorporated inside the wing structure to prevent flutter bifurcation and model accidental destruction. This is usually achieved using a mechanical device that is traditionally a small weight that is suddenly moved inside the structure by the release of a spring. The change in the wing mass distribution provided by the device stabilizes the onset of flutter. The wing structure deformation is traditionally measured using two mini-accelerometers mounted near the wing tip in the chord-wise direction. The accelerometers pick up the bending and torsion deformations of the wing, as the sum and difference of the individual signals. However, accelerometers are localized sensors that do not bring enough information to a generalized structural phenomenon such as flutter and aeroelastic response. Hence, piezoelectric fiber (Active Fiber Composite - AFC) sensors will be suitably embedded in the wing to measure its generalized modal deformations as well. This will be one of the main and novel aspects of this research project. These embedded geometric sensors are expected to allow for the first time a better determination of the flutter characteristics, as (distributed) modal sensors can identify the aeroelastic phenomena much more precisely in terms of the "modal participation". This work will be an extension of the studies on AFC-related geometric modal sensors developed in a present collaboration involving EMPA, ETH in Switzerland and Carleton University. It is suggested that Prof. Nitzsche and Prof. Coppotelli will join research efforts during Prof. Nitzsche's proposed tenure at "La Sapienza" to perform feasibility studies aiming to develop advanced smart sensors using AFC-related techniques for aeroelastic modal identification in the transonic regime for immediate application in the programmed wind tunnel tests, including the feasibility of measuring unsteady aerodynamic loads at certain wing cross-sections. In summary, the objective of the planned research is the development of analytical techniques to identify fundamental aspects of aeroelastic phenomena from AFC-generated signals. In this context, advanced studies, performed at "La Sapienza", on the identification of dynamic systems vibrating in the actual operating conditions represent an excellent starting point for the proposed project. This research is seen of great value for the organizations involved, not only for its novelty that will surely allow the publication of a number of joint papers, but also for its special and timely relevance in face of the planned wind tunnel tests, the potential industrial applications, and the basis of a established long-term collaboration
Identification of the smart spring properties from FRFs measurements
No full textThe objective of this paper is the dynamic identification of a reduced-scale helicopter
blade system that incorporates an active pitch link or smart spring for vibration control.
The identification of the Smart Spring parameters, in terms of the masses and stiffnesses
associated to its components, is carried out in the frequency domain using a developed
sensitivity-based updating method. This method, called Predictor-Corrector, iteratively
minimizes a residual vector of correlation functions, defined on the Frequency Response
Functions (FRFs), in order to obtain the unknown values of the parameters that well rep-
resent the dynamic behavior of the smart spring. In the paper the accuracy of the solution
provided by the developed technique is assessed through several numerical analyses. For
this purpose, a lumped parameter numerical model of the Smart Spring was developed
and the effects of various mass and stiffness distribution scenarios on the modal properties
of the system are presented. Due to the nonlinear dynamic behavior of the smart spring
system, a linear approximation of the system around a prescribed operative working con-
dition is considered. Finally, the developed approach is applied for the identification of the
dynamic parameters of a real smart spring system. It is shown that acceptable values of
the equivalent lumped parameters were achieved also considering experimental data such
as those recorded during a test campaign carried out at the Smart Rotor Laboratory of
the Carleton University, thus validating the identification approach
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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