1,720,959 research outputs found
Overhead crane subjected to impulse loading
Full text linkOverhead cranes are machines designed to lift and transport heavy equipment and materials. For this reason, their design is regulated by rigorous standards (for example, the series EN13000 in Europe). However, the standards do not take into account the effect of cyclic loading due to, for example, rapid successions of short commands to place heavy machines and structures in a required position. Therefore, the aim of this research is to study the structural effect of rapid successions of command impulses. The preliminary results show that the displacement of the structure over time increases when the command impulses have a frequency equal or close to the natural frequency of the structure
Condition Monitoring of Rolling Bearings for Automotive Water Pumps
No full textThe paper presents a study aimed at comparing the results of the classification of the operating conditions of rolling bearings for automotive water pumps based on different methods, all of which are experimental in nature and based on different features and different classification and clustering techniques. Various operating conditions of the bearings were taken into account. Vibration measurements on rolling bearing housings were experimentally recorded using a dedicated test rig and also analysed in the time and frequency domain. The statistical indices (Standard Deviation, Skewness, Kurtosis, Mean, Peak, and Crest Factor) were calculated for the analysis in the time domain, while the FFT was used for the frequency analysis. The indicators Standard Deviation and Skewness were used as input for a clustering procedure to perform an automatic identification of the health status of the rolling element bearing. A self-organizing-map is used for non-supervised clustering. A feed-forward back-propagation neural network and the DTW technique are used for supervised classification. The proposed approaches are compared with each other based on the results and their different characteristics
Dynamic Analysis of a Quay Crane Using Lumped Parameter Models
No full textThe objective of this research activity is to evaluate the extent to which models with lumped parameters might be appropriate for the development of lifting devices. The models we used have only one or two degrees of freedom, but the parameters of the crane were derived by a FEM analysis of its structure, while the viscoelastic parameters of the ropes took into account their time-varying behavior. The results showed that it is useful to consider the length of the ropes in order to calculate more accurately the dynamics of the crane, since the stiffness and the damping change during the load movement. According to the results, higher stress values were also obtained using the model with one degree of freedom for the ropes. This implies that the model can be useful for rope selection as it ensures a conservative estimate of their coefficient of safety. In the case of the two-degree-of-freedom model, the same is true for the structure
Comparison of signal processing techniques for condition monitoring based on artificial neural networks
No full textThe paper presents the results of a study aimed to compare different signal processing techniques for the condition monitoring of a mechanical system for indexing motion. Artificial feed-forward neural networks (ANN) are used as classifiers. The mechanical system can work in different conditions (variable loads and velocities, lubricant oil with different viscosity) and the ANN identifies the working condition. The monitored variable is the acceleration signal of the rotating table, opportunely pre-processed. The signal processing techniques compared are: Power Spectral Density (PSD), Fast Fourier Transform (FFT), Wavelet, Amplitude Probability Density Function (PDF), Higher Order Spectra (HOS)
Generation of Alternative Motion with Adjustable Stroke by Deformation of an Elastic Ring
No full textMotion optimization of industrial robots and high performances prototypes design
No full textAtti del Dip. di Ing. Meccanica, Università degli Studi di Brescia - Vol. 4
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
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