1,720,978 research outputs found
Fatigue Damage Spectrum calculation in a Mission Synthesis procedure for Sine-on-Random excitations
Full text linkIn many real-life environments, certain mechanical and electronic components may be subjected to Sine-on-Random vibrations, i.e. excitations composed of random vibrations superimposed on deterministic (sinusoidal) contributions, in particular sine tones due to some rotating parts of the system (e.g. helicopters, engine-mounted components,...). These components must be designed to withstand the fatigue damage induced by the "composed" vibration environment, and qualification tests are advisable for the most critical ones. In the case of an accelerated qualification test, a proper test tailoring which starts from the real environment (measured vibration signals) and which preserves not only the accumulated fatigue damage but also the "nature" of the excitation (i.e. sinusoidal components plus random process) is important to obtain reliable results. In this paper, the classic time domain approach is taken as a reference for the comparison of different methods for the Fatigue Damage Spectrum (FDS) calculation in case of Sine-on-Random vibration environments. Then, a methodology to compute a Sine-on-Random specification based on a mission FDS is proposed
Smart localization of microphones inside an automotive cabin
No full textInterior sound measurements play an important role in vehicle development and refinement. Sometimes hundreds of microphones are installed in an automotive cabin. During test preparation and execution, a lot of time is spent in determining the microphone positions and in tracking cables to the data acquisition channel. A smart acoustic localization approach is presented to automate this process and to realize considerable time gains. It is based on estimating the distance between a microphone and (at least 4) sources by acoustic time-of-arrival measurements, combined with novel algorithms that cope with reflections and non-line-of-sight issues. The method will be illustrated using in-vehicle measurements
Synthesis of Sine-on-Random vibration profiles for accelerated life tests based on fatigue damage spectrum equivalence
No full textIn many real life environments, mechanical and electronic systems are subjected to vibrations that may induce dynamic loads and potentially lead to an early failure due to fatigue damage. Thus, qualification tests by means of shakers are advisable for the most critical components in order to verify their durability throughout the entire life cycle. Nowadays the trend is to tailor the qualification tests according to the specific application of the tested component, considering the measured field data as reference to set up the experimental campaign, for example through the so called “Mission Synthesis” methodology. One of the main issues is to define the excitation profiles for the tests, that must have, besides the (potentially scaled) frequency content, also the same damage potential of the field data despite being applied for a limited duration. With this target, the current procedures generally provide the test profile as a stationary random vibration specified by a Power Spectral Density (PSD). In certain applications this output may prove inadequate to represent the nature of the reference signal, and the procedure could result in an unrealistic qualification test. For instance when a rotating part is present in the system the component under analysis may be subjected to Sine-on-Random (SoR) vibrations, namely excitations composed of sinusoidal contributions superimposed to random vibrations. In this case, the synthesized test profile should preserve not only the induced fatigue damage but also the deterministic components of the environmental vibration. In this work, the potential advantages of a novel procedure to synthesize SoR profiles instead of PSDs for qualification tests are presented and supported by the results of an experimental campaign
Shaker testing simulation of non-gaussian random excitations with the fatigue damage spectrum as a criterion of mission signal synthesis.
No full textExperimental simulations of random excitations are nowadays performed digitally by applying the Inverse Fast Fourier Transform (IFFT) to the desired Power Spectral Density (PSD) profile, in combination with randomized IFFT phases. However, the excitations generated in this way will always have a Gaussian probability distribution, whereas real-life random excitations are typically non-Gaussian. For example, in the case of land transportation some distinctive peaks will occur which exceed the average level of vehicle vibration. The sta-tistical parameter known as kurtosis can characterize this feature and could be controlled in experimental simulations in addition to the PSD. The so-called “kurtosis control” can be achieved by special phase manipulation instead of selecting the phases randomly. By increasing the kurtosis, it is furthermore also possible to obtain an accelerated qualification test, whereby the time-to-failure (TTF) is decreased in a controlled manner. It is known that the response of a lightly-damped linear system is closer to Gaussian than the applied excitation. Therefore, in order to increase the response kurtosis in an accelerated test, the kurtosis control method must be able to effectively generate extra kurtosis. In this work a method was used which indeed achieves a high excitation kurtosis, which moreover passes into the re-sponse of the structure. According to the Fatigue Damage Spectrum (FDS) model, a single-degree-of-freedom system was hereby considered in order to calculate the structural response. Furthermore, the rainflow counting procedure and the Miner damage accumulation rule were employed to predict relative TTFs for operational excitation and accelerated test mission. Finally, the considered method of non-Gaussian shaker testing simulation was also advanced from kurtosis control to direct application of the FDS as a criterion for mission signal synthesis. An extensive experimental campaign was carried out, where an example of a real-life vibration excitation measured on the cabin floor of a car was considered. Shaker testing was performed for a cantilevered test specimen subjected to various simulated Gaussian, non-Gaussian, accelerated non-Gaussian, and real road excitations
Smart localization of microphones inside an automotive cabin
No full textInterior sound measurements play an important role in vehicle development and refinement. Sometimes hundreds of microphones are installed in an automotive cabin. During test preparation and execution, a lot of time is spent in determining the microphone positions and in tracking cables to the data acquisition channel. A smart acoustic localization approach is presented to automate this process and to realize considerable time gains. It is based on estimating the distance between a microphone and (at least 4) sources by acoustic time-of-arrival measurements, combined with novel algorithms that cope with reflections and non-line-of-sight issues. The method will be illustrated using in-vehicle measurements
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
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