scholarly journals TORTUOSIMETRIC OPERATOR FOR COMPLEX POROUS MEDIA CHARACTERIZATION

2019 ◽  
Vol 38 (1) ◽  
pp. 25 ◽  
Author(s):  
Johan Chaniot ◽  
Maxime Moreaud ◽  
Loïc Sorbier ◽  
Thierry Fournel ◽  
Jean-Marie Becker
Keyword(s):  
Porous Media ◽  
Entry And Exit ◽  
Boolean Models ◽  
Topological Information ◽  
Physicochemical Processes ◽  
Topological Descriptor ◽  
Porous Part ◽  
Topological Characteristics ◽  
Definition Of ◽  
Arbitrary Propagation

Geometric tortuosity is one of the foremost topological characteristics of porous media. Despite the various definitions in the literature, to our knowledge, they are all linked to an arbitrary propagation direction. This article proposes a novel topological descriptor, named M-tortuosity, by giving a more straightforward definition, describing the data regardless of physicochemical processes. M-tortuosity, based on the concept of geometric tortuosity, is a scalable descriptor, meaning that information of several dimensions (scalar, histograms, 3D maps) is available. It is applicable on complex disconnected structures without any arbitrary definition of entry and exit. Topological information can be represented by aggregation into a unique scalar descriptor for classification purposes. It is extended by iterative erosions to take into account porous structure narrowness, especially bottleneck effects. This new descriptor, called M-tortuosity-by-iterative-erosions, describes tortuosity of the porous part as seen by a spherical particle of given size walking along the network. Boolean models are used to simulate different porous media structures in order to test the proposed characterization.

scholarly journals Geometric and Topological Bases of a New Classification of Wood Vascular Tissues Part 1: Shape and Arrangement Classifications of Vessels

2021 ◽  
Vol 13 (14) ◽  
pp. 7545
Author(s):  
Nikolai Bardarov ◽  
Vladislav Todorov ◽  
Nicole Christoff
Keyword(s):  
Computer Vision ◽  
Detailed Analysis ◽  
Tree Species ◽  
Complete Solution ◽  
New Classification ◽  
Topological Characteristics ◽  
Definition Of ◽  
Wood Science ◽  
Quantitative Indicators

The need to identify wood by its anatomical features requires a detailed analysis of all the elements that make it up. This is a significant problem of structural wood science, the most general and complete solution of which is yet to be sought. In recent years, increasing attention has been paid to the use of computer vision methods to automate processes such as the detection, identification, and classification of different tissues and different tree species. The more successful use of these methods in wood anatomy requires a more precise and comprehensive definition of the anatomical elements, according to their geometric and topological characteristics. In this article, we conduct a detailed analysis of the limits of variation of the location and grouping of vessels in the observed microscopic samples. The present development offers criteria and quantitative indicators for defining the terms shape, location, and group of wood tissues. It is proposed to differentiate the quantitative indicators of the vessels depending on their geometric and topological characteristics. Thus, with the help of computer vision technics, it will be possible to establish topological characteristics of wood vessels, the extraction of which would be used to develop an algorithm for the automatic classification of tree species.

A stress sensitivity model for the permeability of porous media based on bi-dispersed fractal theory

2018 ◽  
Vol 29 (02) ◽  
pp. 1850019 ◽  
Author(s):  
X.-H. Tan ◽  
C.-Y. Liu ◽  
X.-P. Li ◽  
H.-Q. Wang ◽  
H. Deng
Keyword(s):  
Porous Media ◽  
Fractal Dimension ◽  
Fractal Theory ◽  
Stress Sensitivity ◽  
Maximum Diameter ◽  
Proposed Model ◽  
Fractal Parameters ◽  
Stress Changes ◽  
Capillary Bundle ◽  
Definition Of

A stress sensitivity model for the permeability of porous media based on bidispersed fractal theory is established, considering the change of the flow path, the fractal geometry approach and the mechanics of porous media. It is noted that the two fractal parameters of the porous media construction perform differently when the stress changes. The tortuosity fractal dimension of solid cluster [Formula: see text] become bigger with an increase of stress. However, the pore fractal dimension of solid cluster [Formula: see text] and capillary bundle [Formula: see text] remains the same with an increase of stress. The definition of normalized permeability is introduced for the analyzation of the impacts of stress sensitivity on permeability. The normalized permeability is related to solid cluster tortuosity dimension, pore fractal dimension, solid cluster maximum diameter, Young’s modulus and Poisson’s ratio. Every parameter has clear physical meaning without the use of empirical constants. Predictions of permeability of the model is accordant with the obtained experimental data. Thus, the proposed model can precisely depict the flow of fluid in porous media under stress.

Das Handwerk – Zur definitorischen und statistischen Abgrenzung eines Querschnittsbereichs

2019 ◽  
Vol 67 (1) ◽  
pp. 67-79 ◽  
Author(s):  
Katarzyna Haverkamp
Keyword(s):  
Empirical Research ◽  
Market Entry ◽  
Empirical Studies ◽  
Causal Effects ◽  
Economic Research ◽  
Entry And Exit ◽  
Definition Of

Zusammenfassung In der empirischen Wirtschaftsforschung zeigt sich ein zunehmendes Interesse an der Untersuchung der Fragen der Gründungsdynamik und des Gründungserfolgs im Kontext der deutschen Handwerkswirtschaft. Eine besondere Herausforderung für diese Analysen besteht jedoch darin, dass eine statistische Abgrenzung des juristisch definierten Handwerkssektors in den vorliegenden Sekundärdatensätzen meist nur mit Einschränkungen möglich ist. Vor diesem Hintergrund analysiert dieser Beitrag Möglichkeiten und Grenzen einer statistischen Abgrenzung des Handwerks in Mikrodatensätzen und untersucht unterschiedliche, bislang verwendete Identifikationsverfahren im Hinblick auf die Repräsentativität der jeweils gewonnen Stichproben. Im Ergebnis zeigt der Beitrag die Stärken und Schwächen unterschiedlicher Identifikationsverfahren und formuliert Empfehlungen hinsichtlich ihrer Verwendung in der Entrepreneurship-Forschung. Abstract Recently, several empirical studies investigate the causal effects of regulation on market entry and exit using the example of the German crafts sector. However, since the definition of the sector is made on legal- and not statistical basis, the identification of crafts companies and employees in microdata records is an intricate process. This paper examines different identification strategies that have been used so far in empirical research and investigates whether the resulting samples are consistent with the overall population in question. The paper contributes to existing economic research by providing an understanding for the potential pitfalls when analyzing sub-groups in larger datasets and by formulating an explicit recommendation for the case of the research on regulation and entry in the German crafts sector.

A Micro-Sized Generic Demonstrator for Studying Synthetic Biological Processes

2011 ◽  
Author(s):  
Marc-Florian Uth ◽  
Heinz Herwig
Keyword(s):  
Porous Media ◽  
Synthetic Biology ◽  
Chemical Production ◽  
Computational Costs ◽  
Interdisciplinary Field ◽  
Micro Channels ◽  
Working Groups ◽  
Definition Of ◽  
Micro Reactors ◽  
Enzymatic Pathways

In the field of synthetic biology, enzymatic pathways are used to enhance the efficiency of chemical production processes. These pathways consist of micro reactors that are filled with porous media and enzymes that catalyze the partial reactions. In the present study we summarize the requirements of the micro reactors used for these applications and give an overview of the different problems that have to be solved. Furthermore we present the idea of a generic demonstrator as a research tool. In the interdisciplinary field of synthetic biology it can enhance the interaction between different groups. It will serve as a common base for numerically as well as for experimentally working groups. We propose a definition of a generic demonstrator for a micro fluidic reactor as it is typically used in this field. Besides, present work of our group is presented, that analyzes the flow field in the micro channels of the reaction zone that is filled with porous media. We show how computational costs can be saved by studying the entry lengths of these channels.

What is the role of tortuosity in the Kozeny-Carman equation?

2017 ◽  
Vol 5 (1) ◽  
pp. SB57-SB67 ◽  
Author(s):  
Nattavadee Srisutthiyakorn ◽  
Gerald M. Mavko
Keyword(s):  
Porous Media ◽  
Pore Space ◽  
Flow Simulation ◽  
Weighted Average ◽  
Rock Physics ◽  
Sample Length ◽  
Pore Throat ◽  
Binary Images ◽  
The Difference ◽  
Definition Of

Hydraulic tortuosity is an important parameter in characterizing fluid-flow heterogeneity in porous media. The most basic definition of tortuosity is the ratio of the average flow path length to the sample length. Although this definition seems straightforward, the lack of understanding and the lack of proper ways to measure tortuosity make it one of the most abused parameters in rock physics. Hydraulic tortuosity is often treated merely as a fitting factor, or worse, it is neglected by being combined with a geometric factor in the Kozeny-Carman (KC) equation. Often, the tortuosity is obtained from laboratory measurements of porosity, permeability, and specific surface area by inverting the KC equation. This approach has a major pitfall because it treats tortuosity as a fitting factor, and the inverted tortuosity is often unphysically high. In contrast, we obtained the tortuosity from 3D segmented binary images of porous media using streamlines extracted from a local flux, the output from the lattice Boltzmann method (LBM) flow simulation. After obtaining streamlines from each sample, we calculated the distribution of tortuosities and flux-weighted average tortuosity. With the tortuosity measurement from streamlines, every parameter in the KC equation can be measured accurately from 3D segmented binary images. We found, however, that the KC equation is still missing some important geometric information needed to predict permeability. With known parameters and without a fitting factor, the KC equation predicts permeability higher by one to two orders of magnitude than that predicted by the LBM. We searched for a missing parameter by exploring various concepts such as connected pore space and pore throat distribution. We found that the connected pore space does not contribute to the difference between the KC permeability and LBM permeability, whereas, as we learn with sinusoidal pipe examples, the pore throat distribution captures what is missing from the KC equation.

Determination of Forchheimer Term in Porous Media Consisting of Obstacles of Different Sizes

2012 ◽  
Vol 594-597 ◽  
pp. 2537-2540
Author(s):  
Ren Xing Liu ◽  
Akira Nakayama ◽  
Xiao Lan Haung
Keyword(s):  
Porous Media ◽  
Numerical Models ◽  
Pressure Gradients ◽  
Two Dimensional ◽  
Reasonable Estimate ◽  
Pressure Drops ◽  
Pressure Fields ◽  
Definition Of ◽  
Average Size

As a sequel to the study in determining the permeability of the porous media composed of obstacles of different sizes, exhaustive numerical calculations were conducted using the same two-dimensional numerical models of square rods as in the previous study. The models consist of collections of square rod obstacles of two-, three-, four- and five-different sizes. Computations were carried out to reveal the details of microscopic velocity and pressure fields. There results are integrated to find the macroscopic pressure gradients for collections of multi-sized obstacles. The Ergun type general formula has been proposed along with a definition of an effective average size, which, when substituted into the formula, yields a reasonable estimate for the macroscopic pressure drops in multi-sized obstacles.

scholarly journals Studying the Topology of Transportation Systems through Complex Networks: Handle with Care

2018 ◽  
Vol 2018 ◽  
pp. 1-17 ◽  
Author(s):  
Massimiliano Zanin ◽  
Xiaoqian Sun ◽  
Sebastian Wandelt
Keyword(s):  
Complex Network ◽  
Real World ◽  
Paradigm Shift ◽  
Transportation Networks ◽  
Transportation Systems ◽  
Node Ranking ◽  
Targeted Attacks ◽  
Topological Characteristics ◽  
Definition Of ◽  
Random Failures

The introduction of complex network concepts in the study of transportation systems has supposed a paradigm shift and has allowed understanding different transport phenomena as the emergent result of the interactions between the elements composing them. In spite of several notable achievements, lurking pitfalls are undermining our understanding of the topological characteristics of transportation systems. In this study, we analyse four of the most common ones, specifically related to the assessment of the scale-freeness of networks, the interpretation and comparison of topological metrics, the definition of a node ranking, and the analysis of the resilience against random failures and targeted attacks. For each topic we present the problem from both a theoretical and operational perspective, for then reviewing how it has been tackled in the literature and finally proposing a set of solutions. We further use six real-world transportation networks as case studies and discuss the implications of these four pitfalls in their analysis. We present some future lines of work that are stemming from these pitfalls and that will allow a deeper understanding of transportation systems from a complex network perspective.

scholarly journals Mean-intercept anisotropy analysis of porous media. I. Analytic formulae for anisotropic Boolean models

2017 ◽  
Vol 44 (7) ◽  
pp. 3650-3662
Author(s):  
Michael A. Klatt ◽  
Gerd E. Schröder-Turk ◽  
Klaus Mecke
Keyword(s):  
Porous Media ◽  
Boolean Models
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