1,721,021 research outputs found
Integrity assessment by cross correlated modal identification of steel structures
Full text linkDosadašnja istraţivanja u obasti integriteta čeličnih konstrukcija bazirana su uglavnom na analitičkim procenama veka strukture kroz numeričke proračune i ispitivanja konvencionalnim eksperimentima. Numeričke metode, ma koliko bile precizne, ne pruţaju pravu sliku o realnom ponašanju i stanju čelične konstrukcije. S druge strane, merenja na realnim konstrukcijama u uslovima redovne eksploatacije mogu biti veoma zahtevna za izvoĎenje.
Ubrzanim razvojem elektronskih ureĎaja i smanjenjem njihove cene, sistemi za akviziciju i višekanalna merenja postali su komercijalno dostupni, pa se došlo u situaciju da rezultati merenja budu ekstremno velike datoteke, koje je srazmerno teško analizirati i adekvatno protumačiti u realnom vremenu. Drugi nedostatak konvencionalnog pristupa u proceni integriteta čeličnih konstrukcija je to što se ispitivanja izvode na epruvetama, ili u najboljem slučaju, na umanjenim modelima koji predstavljaju čeličnu konstrukciju koja je predmet ispitivanja. Ovakvim eksperimentima, u laboratorijskom okruţenju, zanemareni su uticaji ambijentalnih uslova kao što su kiša, vetar, sneg, velike temperaturne promene, pomeranje tla, uticaj saobraćaja i drugi faktori.
Jedan od ciljeva ove disertacije je da se prevaziĎu nedostaci do sada primenjivanih metoda i da se unapredi postupak merenja i tumačenja digitalnih zapisa. Pošlo se od ideje da je moguće tako povezati ANSYS numeričku analizu čelične konstrukcije sa merenjima na realnoj strukturi, da se postigne egzaktno podešavanje modela i postavi usavršena metodologija za procenu integriteta konstrukcije. Numeričkim simulacijama dolazi se do okvirne slike odziva konstrukcije izloţene pobudi, prvenstveno u smislu definisanja sopstvene frekvencije oscilovanja konstrukcije, modalne mase, krutosti i prigušenja, kao i osnovnih modova oscilovanja. Poznavanjem tih modalnih parametara, uz 3D model date čelične konstrukcije, definiše se matrica mernih tačaka (koordinate, pravci merenja, način vezivanja senzora), broj potrebnih senzora i minimalna konfiguracija opreme za snimanje dinamičkih parametara. Obradom podataka prikupljenih na ovaj način, jasno se definiše odziv konstrukcije za postojeću pobudu. UvoĎenjem simulirane ambijentalne pobude u 3D model konstrukcije, proveravaju se rezultati prethodno uraĎene numeričke analize, kao i njihova korelacija sa rezultatima dobijenim realnim merenjem. Korekcijom 3D modela, sa ciljem potpunog usklaĎivanja analitičkih i empirijskih rezultata, dolazi se do 3D modela koji je potpuni ekvivalent stvarne čelične konstrukcije. To otvara mogućnost da se struktura ispita pod opterećenjima koja nije bilo moguće uvesti na realnoj kostrukciji (veći intenzitet opterećenja, kritična kombinacija opterećenja, zahtevniji ambijentalni uslovi...).
Metodologija koja je predmet ove disertacije primenjena je na dve čelične konstrukcije različite konfiguracije, namene i dimenzija. U pitanju su rešetkasta čelična konstrukcija dalekovodnog stuba i čelična struktura glavnog objekta termoelektrane.
Obe ove konstrukcije su specifične na odreĎeni način i zahtevaju odgovarajući pristup, kako u definiciji 3D modela tako i u programu ispitivanja.Early researches on steel structures integrity were mainly oriented on calculations and conventional experiments. Robust numerical methods of a high accuracy are usually less reliable in estimation of dynamical properties and a true condition of a steel structure. On the other hand, experiments on real structures, being in regular operation, could be very demanding to conduct.
Acquisition systems nowadays became more affordable than ever, due to fast development of commercial electronics. Therefore, data loggs are rather oversized and thus very difficult to analyse. Another problem is that the objects in experiments are usually simple items such as bars and plates, or simplified models of real structure. In such experiments contribution of harsh ambient conditions (snow, wind, ice, high humidity, extreme temperatures, excessive traffic, ...) is mostly neglected.
Main goal of this PhD thesis is improvement of renowned experimental methods. It is also addressed to implementation and justification of novel methodology in structural integrity analysis. The main idea is to correlate experimental results with those obtained applying ANSYS software package (based on Finite Element Method). Throughout a results cross-correlation and model adjustment the new presentation of the structure is created, in other words, a reliable base for further analysis. Structural properties which are in the focus of the correlation process are natural frequency, modal mass, stiffness and damping. By a proper definition of those parameters, and a 3D model of the structure, a preliminary map of measuring points and measuring configuration can be set.
Main point of the experiment concept is to determine dynamic behaviour of the structure, exposed to a known load. Truly correlated 3D model, with verified geometric, static and dynamic properties offers the opportunity to predict the structure behaviour under loads that can hardly apply on a living structure (extreme overloads, complex loads, harsh ambient conditions...). In the doctoral thesis, it is presented a consistent methodology applied in the analysis of different structural cases as follows: an electric grid transmission tower and grillage structure in the thermal power plant. Each one of the quoted items is steel made, having its own properties, and thus requires specific approach along the modelling process, experimental treatment and post event analysis
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
Vibration monitoring, analysis and damping at the hydro power plant
Full text linkVibration monitoring is well proven procedure for estimation of a condition of a machine system. Excessive vibrations indicate the unexpected problems in operation. Moreover, vibration analysis often can help to discover the cause of the problem. In this paper procedure for system monitoring, data logging, collected data analysis and necessary actions for vibration level dampening at the hydro power plant is described. In order to lower the level of vibration of an operating machine it is necessary to measure vibration intensity and frequency first. Then, through the Fast Fourier Transformation (FFT), collected data is transformed from the time to the frequency domain. Frequency domain signal indicates the possible causes of elevated vibration amplitudes. Every cause of perturbation forces and high vibration levels has its own distinctive frequency domain graph. Frequency of dominant amplitudes (most commonly seven highest amplitudes are taken into consideration) determines the cause of the problem. Rotational machines most often have a problem with dynamic imbalance and/or shaft misalignment. These problems are discovered by excessive vibrations at the rotational frequency and double rotational frequency respectively. On the other hand static structures most commonly change their modal characteristics (natural frequency) due to loss of structural integrity. When the cause of the excessive vibrations is determined it is possible to design the optimal solution. In this case, it was provided through the tailor made modular lightweight steel construction, mounted in order to raise the stiffness of the oscillatory systemPredavanje po pozivu sa međunarodnog skupa štampano u izvod
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
- …
