1,720,961 research outputs found
Thermoelasticity-based modal damage identification
No full textThe response of linear dynamic structures can be decomposed into modal components, where each natural frequency is also represented by a corresponding mode shape and damping ratio. While vibration-fatigue-damage identification was recently expanded using modal decomposition, this research proposes a modal-decomposition-based thermoelastic damage identification method. With the proposed method, a thermal camera can be used to identify the damage intensity of a particular mode shape. The proposed method is presented using a randomly excited structure exposed to multiaxial loads. With this, the intensity of a particular fatigue source is clearly related to the underlying structural dynamics
Non-stationarity index in vibration fatigue: Theoretical and experimental research
No full textRandom vibrations induce damage in structures, especially when they are operating close to their natural frequencies. The stationarity of the input excitation is one of the fundamental assumptions required for frequency-domain fatigue-damage theory. However, for real applications, excitation is frequently non-stationary and the identification of this non-stationarity is not easy. This study researches run-tests to identify the index of non-stationarity. Further, using excitation signals with different rates of amplitude-modulated non-stationarity, the index of non-stationarity is experimentally and theoretically researched with regards to the fatigue life. The experimental research was performed on a flexible structure that was excited close to a natural frequency. The experimental fatigue life is compared to the theoretical fatigue life under the stationarity assumption. The analysis of the experimental results reveals a close relation between the identified non-stationarity in the excitation signal and the fatigue life of the structure. It was found that amplitude-modulated non-stationary excitation results in a significantly shorter fatigue life if compared to a similar level of stationary excitation
Strain proportional damping in Bernoulli-Euler beam theory
No full textIn structural dynamics, different damping models are used; however, due to modal decomposition, those models typically result in the use of the damping ratio as the modal damping parameter. If proportional viscous damping is used, the damping ratio can be related to the mass and stiffness parameters of a particular dynamic system, i.e. the damping is structure-specific. Lord Rayleigh introduced the idea of proportional damping based on the global kinetic and potential energies of a dynamic system. This global or system-wide approach becomes questionable at the local scale, i.e., at a particular location of the researched system: for a particular mode, the potential energy is related to the strain mode shape and the kinetic energy is related to the displacement mode shape. As the strain and displacement mode shapes have different spatial distributions, also the spatial distributions of the potential and kinetic energies differ. Based on the Bernoulli-Euler beam theory, this research proposes an extension to the proportional damping approach, which results in a material-specific damping parameter. It is shown that using this material damping parameter and the assumption of damping energy proportionality to the local modal strain energy, the modal damping ratio of each mode can be obtained theoretically. This finding was confirmed against several experimental test-cases. The proposed material-specific damping parameter opens up the possibility to obtain the structure-specific damping parameters using the theoretical/numerical mode shapes
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
Non-stationarity and non-gaussianity in vibration fatigue
No full textIn vibration fatigue the frequency contents of dynamic loading and structure’s dynamic response overlap, resulting in amplified stress loads of the structure. Time domain fatigue approach does not give a good insight into the underlying mechanics of failure and therefore recently vibration fatigue in frequency domain is getting a lot of scientific attention. Gaussianity and stationarity assumptions are applied in frequency-domain methods for obtaining dynamic structure’s response and frequency-domain methods for calculating damage accumulation rate. However, in application, the structures are excited with non-Gaussian and non-stationary loads and this study addresses the effects of such dynamic excitation to experimental time-to-failure of a structure. The influence of non-Gaussian, but stationary excitation, is experimentally studied via excitation signals with equal power density spectrum and different values of kurtosis. The non-Gaussianity was found not to significantly change the structure’s time-to-failure and therefore, the study focuses on the non-stationary excitation signals that are also inherently non-Gaussian. The non-stationarity of excitation was achieved by amplitude modulation and significantly shorter times-to-failure were observed when compared to experiments with stationary non-Gaussian excitation. Additionally, the structure’s time-to-failure varied with the rate of the amplitude modulation. To oversee this phenomenon the presented study proposes a non-stationarity index which can be obtained from the excitation time history. The non-stationarity index was experimentally confirmed as a reliable estimator for severity of non-stationary excitation. The non-stationarity index is used to determine if the frequency-domain methods can safely be applied for time-to-failure calculation
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
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