1,720,957 research outputs found
Effect of initial Out-of-Straightness (OOS) on predeformed pipeline for controlling lateral buckling
No full textA novel method of controlling lateral buckling, which involves pre-deforming a pipeline continuously into specific wavelength and amplitude prior to installation on the seabed, is reported in this paper. This paper first introduces the concept of pre-deforming pipe and then presents the results of FE analysis of different initial pre-deformation shapes that can influence the buckling behaviour of this pipeline system. Several random distributions of out-of-straightness are applied along the predeformed pipeline to investigate the sensitivity of the system to one of the largest uncertainty factors in pipeline designs – the exact as-laid configuration. Results show that with suitable selection of an initial pre-deformed shape and dimension, the system will only buckle at temperature and pressure levels that are unrealistically high for currently developed gas fields. It is found that both the buckle initiation load and the longitudinal strain are not sensitive to the inherent distribution of OOS. This makes a continuously pre-deformed pipeline a reliable, robust and safe lateral buckling management system. <br/
Effects of variability in lateral pipe-soil interaction and pipe initial out-of-straightness on controlled lateral buckling of pre-deformed pipeline
No full textThe state-of-the-art method for controlling temperature-induced global lateral buckling of a subsea pipeline is to engineer deliberate buckles at widely spaced locations. These buckles are engineered either by the installation process – i.e. ‘snake-laying’ or by installing subsea structures known as buckle initiators at each intended buckle location. The pre-deformed pipeline is new alternative method that involves continuously pre-deforming the pipeline prior to installation onto the seabed. This pre-deformation causes a significant reduction in axial stiffness and therefore significantly increases the buckle initiation temperature. It also allows thermal expansion to be accommodated throughout the pipe length via expansion of the pre-deformed curvatures, rather than being concentrated at specific buckle locations. This paper presents the influence of two of the variabilities in a pre-deformed pipeline design on the buckling performance: the initial out-of-straightness and the lateral pipe-soil interaction. The results show that the concept of a pre-deformed pipeline is robust and the success of the scheme is not affected by these two uncertainties. The pre-deformed pipeline is shown to be a self-governing system where the maximum strain is self-limited at any location. Pipeline pre-deformation is therefore proven to be a cost effective, safe and valuable tool for controlling pipeline lateral buckling.</p
The reliability of pre-deformation to control lateral buckling of pipelines: an evaluation based on observed embedment trends
No full textPre-deformation of a pipeline into a continuous sinusoidal wave-like form has been shown to be effective at controlling lateral buckling of subsea pipelines due to a substantially lower axial stiffness and the limiting of maximum strain at any location. This paper explores the feasibility and reliability of using such an approach, with an existing operating pipeline, which was installed using zero-radius bend (ZRB) initiator structures, used for comparison. Survey data of the pipeline profile and seabed bathymetry are adopted along with the pipe-soil interaction (PSI) inputs from the original design allowing a like-for-like comparison of the two approaches to management of lateral buckling. The comparison shows that, for the assumptions made in the numerical modelling, use of a pre-deformed pipeline results in lower strain than using ZRBs. Furthermore, the performance of the pre-deformed pipeline is robust, and shown to be unaffected by uncertainties in horizontal out-of-straightness, PSI input and seabed features. This study shows that pre-deformed pipelines can be an effective alternative for controlling the lateral buckling of subsea pipelines, which eliminates the need for buckle initiation structures to be installed along the pipeline route. This provides impetus for further work on installation methodologies to create the required level of pre-deformation.</p
Effect of lateral pipe-soil interaction on controlled lateral buckling using pre-deformed pipeline
No full textA novel approach to eliminate the onset of global buckling in pipelines is investigated in the paper. The method is based on pre-deforming a pipeline continuously with a specific wavelength and amplitude prior to installation on the seabed. The response of the pipeline to applied high temperature and pressure was studied in conjunction with variations in the lateral pipe-soil interaction (PSI) – both as uniform friction along the pipe and also with locally varying friction. Pipe and seabed parameters representing a typical wet-insulated infield flow line on soft clay are used. The pre-deformed pipeline has a higher buckle initiation temperature compared to a straight pipeline due to the reduced effective axial force build-up resulting from the low axial stiffness generated by the predeformed lobes along the pipeline. The results from this paper show that the strains in the predeformed pipeline are not significantly affected by the local variability of lateral PSI but rather by the global mean PSI. At a typical lateral soil resistance, i.e. a friction coefficient of 0.5, lateral buckling occurs at a very high temperature level that is not common in the subsea operation. At a very low friction, i.e. 0.1, lateral buckling occurs at a lower operating temperature but the strain is insignificant. The longitudinal strain of the pipeline is not highly sensitive to the lateral PSI, which is a quite different response to an initially straight pipeline. Therefore, this method could prove to be a valuable tool for the subsea industry as it enables the pipeline to be installed and operated safely at very high temperatures without the need for lateral buckling design and installation of expensive structures as buckle initiators. Even if the pre-deformed pipeline buckles at a very high temperature, during cycles of heat-up and cool-down the buckle shape ‘shakes down’ by geometric rearrangement to minimize the energy, and in doing so creates a series of ‘short pipelines’ in which the longitudinal strain is self-controlled. The system is therefore shown to be very robust in the conditions investigated and not affected by one of the biggest unknowns in seabed pipeline engineering, which is the local variability in lateral PSI
Controlling lateral buckling of subsea pipeline with sinusoidal shape pre-deformation
No full textIt is common for subsea pipelines to operate at high pressures and high temperatures (HPHT) conditions. The build-up of axial force along the pipeline due to temperature and pressure differences from as-laid conditions coupled with the influence of the seabed soil that restricts free movement of the pipeline can result in the phenomenon called ‘lateral buckling’. The excessive lateral deformation from lateral buckling may risk safe operation of the pipeline due to local axial strains that potentially could be severe enough to cause fracture failure of welds or collapse of the pipeline. Engineered buckles may be initiated reliably during operation by using special subsea structures or lay methods which are expensive. This paper introduces and exemplifies a novel method that involves continuously deforming the pipeline prior to or during installation with prescribed radius and wavelength to control lateral buckling that could be a valuable modification of the practical design of offshore pipelines. Previous published work has shown that installation of a pipeline with such continuous deformations is feasible. The results from an example pipeline case described here show that the pipeline can be installed and operated safely at elevated temperatures without the need for other expensive buckle initiation methods.</p
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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