1,721,111 research outputs found
Acoustic detection and tracking of a pipeline inspection gauge
Full text linkPipeline Inspection Gauges (PIGs) are widely used for monitoring and managing pipeline integrity. During a pigging operation it is fundamental to have a continuous measurement of the PIG position and movement, in order to achieve the best inspection and to have an early warning in the case the device is stuck. Currently, the tracking is performed by installing on the PIG “active” systems (e.g. acoustic pingers or electromagnetic emitters) that communicate with a set of receivers, making it possible the localization of the travelling gauge. Another solution is the deployment of an appropriately dense network of sensors along the pipe track, or the utilization of a dedicated system/crew that moves close to the pipe, so to physically perceive the vibrations generated by the nearby passage of the device. In fact, the moving PIG produces pressure transients and vibro-acoustic noise due to the velocity fluctuations, to the friction against the internal walls and to the crossing of the welding dents. It is important to mention that the conduit acts like an acoustic waveguide and the “sound” generated by the PIG, in many practical situations, can be sensed within the fluid at several kilometres from the originating point. This paper presents three different tracking procedures that exploit the noise generated by the PIG to locate it, remotely and passively, without requiring any additional equipment to be mounted on the gauge. The key points of the procedures are the availability of pressure measurements at a small number of positions along the pipeline, at relative distances of tens of kilometres, an accurate synchronization of the measurements, the real time transmission and multichannel processing of the data. The first method locates the PIG by performing a crosscorrelation analysis between the acoustic signal recorded on opposite sides of the moving gauge, the second method is based on the counting of the transients generated at known positions, the third one describes the pipe section between the PIG and the arrival terminal like a resonant structure, and obtains the length of this section (the distance of the PIG to the arrival) from the resonance frequency. All the methods are presented starting from real examples, in order to highlight their effective applicability. Moreover, the localization results are in agreement with the output of more sophisticated technological solutions
Pipeline digital monitoring based on vibroacoustic measurements
No full textReal time monitoring of a fluid transportation system is still a challenging matter, due to the complexity of the asset and a continuous demand of sustainability. The current frontier is a re-design of the information management during the asset lifecycle, with the digitalization and collection of large datasets which are used to infer “data driven” solutions. This paper presents a monitoring strategy based on the medium/long term detection and tracking of “smart indicators” of the oil & gas transportation system operations. The indicators exploit the digital vibroacoustic signals recorded by proprietary stations located on the conduit at an inter-distance of around 20 km. The collected data are analysed on a long-term basis, together with the measurements coming from other instruments (i.e. temperature, density, flow rate), in order to highlight small variations in the pipeline, which move the operational parameters to new states. As an example, sound speed, and attenuation are inverted for the fluid composition and the inner pipe condition. The correlation analysis of the signals recorded in consecutive pipeline segments, interpreted as an equivalent acoustic channel, reveals pipe deformations and/or flow anomalies. We show a case history of an oil trunkline in Nigeria, conveying a variable ratio water-oil mixture, with an inter-distance between the stations along the pipeline at about 17 km. We derive from the long-term and medium-term database some key parameters, which are the actual input for automatic digital monitoring algorithms
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
Linearized Elastic inversion in the k-w domain
No full textElastic inversion aims to give a detailed description of earth parameters. We explore the implementation aspects of the elastic linearized inversion in the k-ω domain introduced by Rocca and De Nicolao (1993). The hypothesis of small contrasts enables to use the Born approximation and to linearize the scattering properties of point diffractors. Operating in the k-ω domain we gain the additional advantage of the simplicity of the theory: perturbations of a uniform background are decomposed in sinusoidal components. The Bragg resonance condition links plane monochromatic incident and reflected waves to the medium wavenumber, so we obtain a simple relation between data and parameters. Inversion and analysis of the information is achieved by means of singular value decomposition of the data-parameters relation. The ill conditioning of the inverse problem (De Nicolao et al. 1993) does not allow a good estimation of all three elastic parameters. Even small numerical errors can deteriorate the quality of inversion and produce interferences between parameter estimates. Similar effects come from the practical aspects of data collection and processing. Truncations due to the finite length of the cable, the finite number of sources and receivers and the limited bandwidth of the wavelet produce aliasing and a distorted reconstruction of the initial model. Particular care is applied in choosing the processing sequence that minimizes these disturbances
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
Practical Aspects in mCSEM Migration
No full textIt is widely known that the main framework for mCSEM imaging is the mathematical inversion of data,
that in real applications (thus 3D model geometries) require great computational resources to be
accomplished in reasonable time. It is also known from literature that non-inversion based imaging,
through migration algorithms, both iterative or not, are feasible with a computational cost far lower with
respect to inversion, although yielding images of resistivity contrasts or an apparent resistivity, but not a
reliable resistivity estimation and associated uncertainty. Here some practical aspects of one-pass mCSEM
migration and suggestions for some imaging improvement are analyzed
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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