1,720,959 research outputs found
Airborne acoustic emission of an abrasive waterjet cutting system as means for monitoring the jet cutting capability
Full text linkAbrasive waterjet cutting is a manufacturing technology making use of a high-speed waterjet with abrasive particles in suspension, for cutting materials with different mechanical properties. Product quality requirements are pushing towards an improvement of tracking and stabilization methods of the relevant process variables. Amongst those, the jet kinetic power defines the cutting capability and has a significant impact on the final cut features. This variable is subject to relevant fluctuations versus time. Besides, the current state of the art does not provide means for its in-line monitoring. The aim of this contribution is to monitor the airborne acoustic emission of an abrasive waterjet cutting head and investigate its correlation with the jet kinetic power. The investigation is carried out by means of factorial studies, in which the jet is fired at various water pressures and abrasive feed rates, providing different kinetic powers. The acoustic emission is synchronously monitored by means of a condenser microphone, installed on the cutting head. Data at frequencies above 40 kHz is found to constitute a robust and selective acoustic signature of the airborne jet. The acoustic signature is proven to be an effective in-line indicator of the jet kinetic power and its pressure-induced variations, whilst abrasive-induced variations remain undetected. A calibration procedure is presented, for translating the acoustic data into a jet kinetic power. The method is validated by means of further experiments that envisage its deployment in a real scenario. Overall, the presented method constitutes a robust tool for monitoring pressure-induced variations of the jet cutting capability
Operational vibration of a waterjet focuser as means for monitoring its wear progression
Full text linkAbrasive waterjet cutting is a competitive manufacturing technology in the aerospace, defense, and automotive industries. End-user requirements are currently pushing machine builders to improve the automation of their processes, in an effort to reduce costs and downtimes, as well as increase robustness and stability. On this regard, the waterjet focuser is a critical component, as its fast wear progression requires constant human supervision, for promptly detecting detrimental effects on the cutting performance. This paper describes an innovative approach for in-line monitoring the wear progression of a waterjet focuser, by means of an accelerometer installed on its tip. This result is allowed by two separate studies of the focuser, of which the first investigates the sensitivity of its first mode frequency to the wear progression, while the second demonstrates the possibility of tracking said frequency from the in-line vibration signal delivered by the accelerometer, during operation. The presented setup makes use of low-cost sensing hardware that can be easily retrofitted into the design of waterjet focusers. The information delivered is expected to tackle end-user requirements for improved process automation
Innovative data regression incorporating deterministic knowledge for soft sensing in the process industry
No full textSoft sensing is a monitoring technique for the indirect assessment of a target variable by means of direct measurements of others and the application of data mining on the historical log, as well as simplified models of the system. Due to technical and economic advantages respect to hardware sensing, soft sensing has been increasingly used in many scenarios, in particular within the process industry. Despite the literature being wide regarding the application of conventional regression techniques on data provided by the monitoring hardware, a systematic approach for supporting and improving data regression through the deterministic knowledge of the process is still missing. This contribution presents an innovative regression method based on first principle modeling. The method is introduced and tested under the case scenario of conventional clinker making process, for predicting the instantaneous fraction of the unburned calcium oxide. A second test case involves an innovative clinkering stage based on microwaves application
Exploiting Laser Doppler Vibrometry in Large Displacement Tests
No full textLarge-displacement vibration testing has assumed increasing importance to answer the need of predicting damages for excessive real life vibration. Moreover, the need for reducing weight is pushing towards the use of non-contact methods in such tests. Discrete Scanning Laser Doppler Vibrometry (SLDV) has resulted to be an important tool for contactless measuring the dynamic behavior of structures. However, the method suffers when high displacements are reached because the laser spot continuously moves on the target surface with an associated uncertainty on the actual measurement point location that increases proportionally to the increase of the deformation of the structure. Such a condition causes the vibration signal to look alike the one recorded by a Continuous Scanning Laser Doppler Vibrometry (CSLDV) approach, with sidebands that are more pronounced the higher the structure deformation is. This paper describes how SLDV can still be exploited for measuring on structures undergoing large displacements, with the further benefit of extracting information related to additional degrees of freedom deriving from the continuous scanning look-alike behavior of the measurement. This results in a better capability of the technique to extract incipient/potential damages on the structure under test. The concept is explored on simulated data representing a cantilever beam pushed to move at high displacements
Focusing tube operational vibration as a means for monitoring the abrasive waterjet cutting capability
Full text linkAbrasive waterjet cutting is a competitive manufacturing technology in the aerospace, defense and automotive industries which, as power users, require state of the art process performances in terms of stability and product assurance, due to their demanding quality standards. Meeting such requirements is a relevant technical challenge for abrasive waterjet cutting, due to insufficient monitored data and intrinsic process instability. The present paper describes an innovative approach based on non-invasive vibration sensors, for monitoring the jet cutting capability. This result is allowed by the experimental evidence proving that the operational vibration monitored by means of two accelerometers installed at the tip of the focusing tube is well related to the kinetic power of the abrasive particles, i.e. the only portion of the jet power that is responsible for the material removal in abrasive waterjet cutting. The approach is validated by means of an experimental investigation, in which the abrasive waterjet is fired at different water pressures and abrasive mass flow rates, providing different kinetic powers. The information delivered enriches the process knowledge, thus paving the way to significant improvements ranging from closed-loop control strategies for the water and abrasive feeding systems to actions for supporting operators in compensating drifts of the jet cutting capability. The expected impact is an improvement of process automation and stability, as well as an enhanced process traceability
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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