130,379 research outputs found
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
Identification of the Dynamic Properties of Active Twist Rotor Model Blade Using Output-Only Data
No full textn this paper, an approach to estimate the dynamic characteristics of a rotating
blade using response data is proposed. A test campaign devoted to demonstrate the capability
of the Smart Spring device to alter the dynamic properties of the rotating blade is carried out in
the framework of the Smart Hybrid Active Rotor Control System, SHARCS, project. Within this
project, the key factor is an active vibration control concept that uses piezoceramic actuators to
preferentially vary dry friction and stiffness of a structure. This device, if located at the blade
root, could adaptively vary the dynamic stiffness of the blade to change its flexural characteristics,
thus allowing control of the aeroelastic response of the entire blade. In this paper it is shown how
the modal parameters will be estimated from the time histories recorded, by a distributed array
of sensors, at different rotational speed of the blade and for different values of the stiffness of the
Smart Spring device. Both time domain and frequency domain methods were applied in order
to quantify the effects on the modal properties of different operating conditions of a prototype
version of the Smart Spring device. This device was attached to the push rod of an Active Twist
Rotor blade developed at the German Aerospace Center (DLR). From the performed experimental
investigation, carried out at the DLR’s whirl tower test facility, it was possible first to draw the
typical fan plots of the rotating blade, from which useful information about the dynamic behavior
of the system could be achieved. Then, a validation of the numerical model of the smart spring
device was obtained
Whirl Tower Demonstrations of the SHARCS Hybrid Control Concept
No full textElements of the SHARCS (Smart Hybrid Active Rotor Control System) Hybrid Control concept are demonstrated via two sets of whirl tower tests. Hybrid Control stands for combining a flow control (such as an Actively Controlled Flap or Active Twist Rotor) and of a structural (or stiffness) control device on a helicopter blade. A Hybrid Control system promises to reduce vibration and noise on helicopters simultaneously as well as to improve the efficiency of the flow control device. For the structural control system, a unique and entirely original Active Pitch Link has been developed at Carleton University, which is capable of dynamically controlling the torsional stiffness of a blade. Design, prototyping, static and whirl tower testing of this device is presented in the paper. A second set of whirl tower tests of an Active Twist Rotor equipped with a range of springs instead of the conventional pitch link, demonstrates that the Active Pitch Link shall indeed be capable of lowering the torsional stiffness of the blade. For these tests, the modal parameters of the blade were evalu-ated via a novel “Output-Only” method, which represents the first application of such methodology for rotary-wing applications
MeSH term explosion and author rank improve expert recommendations
No full textInformation overload is an often-cited phenomenon that reduces the productivity, efficiency and efficacy of scientists. One challenge for scientists is to find appropriate collaborators in their research. The literature describes various solutions to the problem of expertise location, but most current approaches do not appear to be very suitable for expert recommendations in biomedical research. In this study, we present the development and initial evaluation of a vector space model-based algorithm to calculate researcher similarity using four inputs: 1) MeSH terms of publications; 2) MeSH terms and author rank; 3) exploded MeSH terms; and 4) exploded MeSH terms and author rank. We developed and evaluated the algorithm using a data set of 17,525 authors and their 22,542 papers. On average, our algorithms correctly predicted 2.5 of the top 5/10 coauthors of individual scientists. Exploded MeSH and author rank outperformed all other algorithms in accuracy, followed closely by MeSH and author rank. Our results show that the accuracy of MeSH term-based matching can be enhanced with other metadata such as author rank
The SHARCS project: Smart hybrid active rotor control system for noise and vibration attenuation of helicopter rotor blades
No full textThe SHARCS project aims to develop an actively controlled helicopter rotor for the simultaneous suppression of vibration and noise. The proposed rotor will incorporate three subsystems of active control: an active impedance control device, which will replace the classical pitch link rods to reduce vibrations transmitted to the rotor hub, an actively controlled trailing edge flap to reduce vibrations due to dynamic stall and BVI as well as to reduce noise, and an actively controlled anhedral tip for the reduction of noise. The project is an international effort of seven partner institutions from Canada, Italy and Greece, which goal is to design, build and wind tunnel test a scaled rotor incorporating all three subsystems. The present paper describes the project structure and the progress made in the individual areas of research and design in the first year of the project
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Scholarly Communication and Publishing Lunch and Learn Talk #11: The ULS Open Access Author Fee Fund
No full textAt the May 2014 talk, you will learn about the ULS Open Access Author Fee Fund--what it is, why we do it, how it works, and how the program is going so far
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