1,720,961 research outputs found
A model for predicting pipeline sinkage induced by tunnel scour
No full textThe current design practice for subsea pipeline on-bottom stability (e.g. DNV-RP-F109) does not account the effect of sediment transport around a pipeline. Both field survey and small scale model test results show that seabed scour has a significant effect on pipeline embedment and therefore stability. Physical model tests carried out in an innovative large experimental facility, named the O-tube, at the University of Western Australia, have shown that tunnel scour and the subsequent pipe sinkage into the scour hole tend to stabilize a pipeline which might otherwise become unstable on an assumed stationary seabed, under ramping-up flow conditions. A simple calculation model that incorporates the three-dimensional scour and pipe sinkage due to the soil bearing capacity failure at the supporting span shoulders is proposed. The model parameters were calibrated using the O-tube experimental results. The model serves as a key element of a new pipeline stability analysis method that takes into account seabed mobility.</p
A new facility for studying ocean-structure-seabed interactions: The O-tube
No full textThis paper describes a unique new physical testing facility for studying ocean-structure-seabed interactions, and in particular pipeline on-bottom stability on erodible seabed under hydrodynamic loading. The facility, named the O-tube due to its shape, is a fully enclosed flume in which ambient and storm-induced near-seabed flows are generated by a computer-controlled flow pump. Combined steady and oscillatory flow can be generated by alternating pump flow directions in a controlled manner, and computer control also allows irregular flow to be generated. The design of the O-tube combines the capabilities of a conventional open channel flume (which provides steady current) with a U-tube (which provides oscillatory flow). The facility is designed to physically model severe storm conditions, as well as ambient or tidal flows. When studying pipeline stability on erodible seabed under severe hydrodynamic loading conditions, tests can be performed at a relatively large scale (typically 1/5) for large diameter pipelines (e.g. 40. in. gas trunklines) and at full scale for small diameter pipelines (<. 8. in.) to minimize potential scaling effects associated with movable bed model tests. The specifications of the O-tube, a model pipe and an actuator system that supports the model pipe are given in detail. Preliminary model testing results show that the facility has met its design expectations.</p
A re-examination of the hydrodynamic forces acting on partially-buried submarine pipelines
No full textThe hydrodynamic forces exerted on a pipeline partially buried in a permeable seabed subjected to combined random oscillatory flow are investigated experimentally. The tests were carried out in a re-circulating flume that can generate steady currents, oscillatory flow and combined flow, known as the O-tube. The performance of the testing facility was validated against published experimental data under regular oscillatory flow conditions. Four tests with different embedment depths, under random oscillatory flow conditions were then carried out. The flow velocity, hydrodynamic pressure around the model pipe and pore pressure in the soil were monitored. The hydrodynamic forces were calculated through pressure integration around the model pipe. The hydrodynamic force reduction due to embedment was compared with the model given in the most widely-used pipeline stability design guideline, DNV-RPF109. A horizontal load reduction of 55% was found for the fully buried pipe, which was lower than the 70% reduction suggested by DNV-RP-F109. The variation of the vertical hydrodynamic load with embedment ratio (embedment depth to pipe diameter) was also found to be different from the model suggested by DNV-RP-F109. It was found the fully buried pipe experienced a large vertical force, even higher than that of the fully exposed pipe, under low KC number conditions.</p
Calibration of UWA’s O-tube flume facility
No full textThe O-tube facility, designed and established at the University of Western Australia, is an innovative closed loop flume in which a random storm sequence can be reproduced via control of a large pump system. The O-tube facility is capable of simulating hydrodynamic conditions near the seabed and the interaction with seabed sediment and any infrastructure that is resting on it.The purpose of carrying out the O-tube calibration described in this paper is to obtain the relationship between the motor rotation movement and the flow velocity generated in the O-tube, such that any required storm history within the performance envelope of the O-tube can be reproduced. A range of flow velocities and the corresponding pump speeds were measured under steady current, oscillatory flow and combined flow conditions. It was found that the relationship between the pump speed and the flow velocity varies with the oscillatory flow period. Based on the pump characteristic curves and O-tube system curves, the correlation between the motor speed and the flow velocity was derived by applying hydraulic theory and the principle of energy conservation.The derived correlation is validated by reproducing a wide range of target storm series, including a (1:5.8) scaled 100-year return period storm from the North West Shelf of Western Australia in 40 m water depth
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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