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Turbulent fluid flow in rough rock fractures
No full textThis thesis is dedicated to the study of the turbulent fluid flow in rough-walled rock fractures. Fracture models were generated from 3D scans of fractured rock samples, while fluid flow was simulated numerically by means of FVM-based open-source CFD toolbox OpenFOAM, employing the high-performance computing cluster for the more demanding 3D models.
First part of the thesis addresses the issue of fracture geometry. Realistic 2D and 3D fracture models were constructed from 3D scans of upper and lower halves of a fractured rock sample, taking both shear displacement and contact spots into account. Furthermore, we discuss the shortcomings of the available fracture aperture metrics and propose a new aperture metric based on the Hausdorff distance; imaging performance of the new metric is shown to be superior to the conventional vertical aperture, especially for rough fracture surfaces with abundant ridges and troughs.
In the second part of the thesis we focus on the fluid flow through the rock fracture for both 2D and 3D cases. While previous studies were largely limited to the fully viscous Darcy or inertial Forchheimer laminar flow regimes, we chose to investigate across the widest possible range of Reynolds numbers from 0.1 to 10^6, covering both laminar and turbulent regimes, which called for a thorough investigation of suitable turbulence modeling techniques. Due to narrow mean aperture and high aspect ratio of the typical fracture geometry, meshing posed a particularly challenging problem. Taking into account limited computational resources and a sheer number of model geometries, we developed a highly-optimised workflow, employing the steady-state RANS simulation approach to obtain time-averaged flow fields. Our findings show that while flow fields remain mostly stationary and undisturbed for simpler contactless geometries, emergence of contact spots immediately triggers a transition to non-stationary flow starting from Re ∼ 10^2, which is reflected by the streamline tortuosity data. This transition disrupts the flow pattern across the fracture plane, causing strong channeling and large separation bubbles, with area of the latter being much larger than the generating contact spots. Adverse influence of the contact spots on the overall permeability is strong enough to override any benefits of aperture increase during shear and dilation. Contactless 3D models can to a certain degree be approximated by their 2D counterparts. Lastly, we investigate the influence of both shearing and contact spots on the overall permeability and friction factor of the fracture, drawing a parallel to the well-studied area of turbulent flow in rough-walled pipes and ducts. Unlike the latter, 3D curvilinear fracture geometries exhibit a gapless laminar–turbulent transition, behaving as a hydraulically rough channel in the turbulent range as the shear displacement increases
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Turbulent fluid flow in rough rock fractures
Get PDFThis thesis is dedicated to the study of the turbulent fluid flow in rough-walled rock fractures. Fracture models were generated from 3D scans of fractured rock samples, while fluid flow was simulated numerically by means of FVM-based open-source CFD toolbox OpenFOAM, employing the high-performance computing cluster for the more demanding 3D models.
First part of the thesis addresses the issue of fracture geometry. Realistic 2D and 3D fracture models were constructed from 3D scans of upper and lower halves of a fractured rock sample, taking both shear displacement and contact spots into account. Furthermore, we discuss the shortcomings of the available fracture aperture metrics and propose a new aperture metric based on the Hausdorff distance; imaging performance of the new metric is shown to be superior to the conventional vertical aperture, especially for rough fracture surfaces with abundant ridges and troughs.
In the second part of the thesis we focus on the fluid flow through the rock fracture for both 2D and 3D cases. While previous studies were largely limited to the fully viscous Darcy or inertial Forchheimer laminar flow regimes, we chose to investigate across the widest possible range of Reynolds numbers from 0.1 to 10^6, covering both laminar and turbulent regimes, which called for a thorough investigation of suitable turbulence modeling techniques. Due to narrow mean aperture and high aspect ratio of the typical fracture geometry, meshing posed a particularly challenging problem. Taking into account limited computational resources and a sheer number of model geometries, we developed a highly-optimised workflow, employing the steady-state RANS simulation approach to obtain time-averaged flow fields. Our findings show that while flow fields remain mostly stationary and undisturbed for simpler contactless geometries, emergence of contact spots immediately triggers a transition to non-stationary flow starting from Re ∼ 10^2, which is reflected by the streamline tortuosity data. This transition disrupts the flow pattern across the fracture plane, causing strong channeling and large separation bubbles, with area of the latter being much larger than the generating contact spots. Adverse influence of the contact spots on the overall permeability is strong enough to override any benefits of aperture increase during shear and dilation. Contactless 3D models can to a certain degree be approximated by their 2D counterparts. Lastly, we investigate the influence of both shearing and contact spots on the overall permeability and friction factor of the fracture, drawing a parallel to the well-studied area of turbulent flow in rough-walled pipes and ducts. Unlike the latter, 3D curvilinear fracture geometries exhibit a gapless laminar–turbulent transition, behaving as a hydraulically rough channel in the turbulent range as the shear displacement increases
Turbulent fluid flow in rough rock fractures
No full textThis thesis is dedicated to the study of the turbulent fluid flow in rough-walled rock fractures. Fracture models were generated from 3D scans of fractured rock samples, while fluid flow was simulated numerically by means of FVM-based open-source CFD toolbox OpenFOAM, employing the high-performance computing cluster for the more demanding 3D models.
First part of the thesis addresses the issue of fracture geometry. Realistic 2D and 3D fracture models were constructed from 3D scans of upper and lower halves of a fractured rock sample, taking both shear displacement and contact spots into account. Furthermore, we discuss the shortcomings of the available fracture aperture metrics and propose a new aperture metric based on the Hausdorff distance; imaging performance of the new metric is shown to be superior to the conventional vertical aperture, especially for rough fracture surfaces with abundant ridges and troughs.
In the second part of the thesis we focus on the fluid flow through the rock fracture for both 2D and 3D cases. While previous studies were largely limited to the fully viscous Darcy or inertial Forchheimer laminar flow regimes, we chose to investigate across the widest possible range of Reynolds numbers from 0.1 to 10^6, covering both laminar and turbulent regimes, which called for a thorough investigation of suitable turbulence modeling techniques. Due to narrow mean aperture and high aspect ratio of the typical fracture geometry, meshing posed a particularly challenging problem. Taking into account limited computational resources and a sheer number of model geometries, we developed a highly-optimised workflow, employing the steady-state RANS simulation approach to obtain time-averaged flow fields. Our findings show that while flow fields remain mostly stationary and undisturbed for simpler contactless geometries, emergence of contact spots immediately triggers a transition to non-stationary flow starting from Re ∼ 10^2, which is reflected by the streamline tortuosity data. This transition disrupts the flow pattern across the fracture plane, causing strong channeling and large separation bubbles, with area of the latter being much larger than the generating contact spots. Adverse influence of the contact spots on the overall permeability is strong enough to override any benefits of aperture increase during shear and dilation. Contactless 3D models can to a certain degree be approximated by their 2D counterparts. Lastly, we investigate the influence of both shearing and contact spots on the overall permeability and friction factor of the fracture, drawing a parallel to the well-studied area of turbulent flow in rough-walled pipes and ducts. Unlike the latter, 3D curvilinear fracture geometries exhibit a gapless laminar–turbulent transition, behaving as a hydraulically rough channel in the turbulent range as the shear displacement increases
Variations on the Author
Get PDF“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
Get PDFWe 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
Get PDFWe 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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