Spatial Distribution of Local Permeabilities in Fibrous Networks

1992 ◽  
Vol 62 (3) ◽  
pp. 151-161 ◽  
Author(s):  
Susan M. Montgomery ◽  
Bernard Miller ◽  
Ludwig Rebenfeld
Keyword(s):  
Spatial Distribution ◽  
Spatial Heterogeneity ◽  
Heterogeneous Networks ◽  
Flow Direction ◽  
Time Dependent ◽  
Dependent Development ◽  
Fabric Structure ◽  
Elliptical Flow ◽  
Fluid Boundary ◽  
Liquid Flows

The shape of a developing radial fluid boundary in the plane of a fabric is a reflection of the structure of the fabric. Homogeneous fabrics, with permeabilities independent of position, yield circular or elliptical flow fronts, depending on the existence of a universally preferred flow direction. Heterogeneous networks yield flow fronts that deviate from this elliptical shape due to spatial variations in permeability. The time-dependent development of the fluid front that occurs when liquid flows radially in the plane of a fabric may be analyzed using Darcy's law to calculate local fabric permeabilities. The resulting spatial distribution of permeabilities is representative of the spatial heterogeneity of the fabric structure. Sample permeability distributions of geotextile fabrics are discussed.

scholarly journals How spatial heterogeneity shapes multiscale biochemical reaction network dynamics

2015 ◽  
Vol 12 (104) ◽  
pp. 20141106 ◽  
Author(s):  
Peter Pfaffelhuber ◽  
Lea Popovic
Keyword(s):  
Spatial Distribution ◽  
Spatial Heterogeneity ◽  
Reaction Network ◽  
Stochastic Averaging ◽  
Multiscale Model ◽  
Point Of View ◽  
Rigorous Results ◽  
Biochemical Reaction Network ◽  
Molecular Movement ◽  
Heterogeneous Multiscale

Spatial heterogeneity in cells can be modelled using distinct compartments connected by molecular movement between them. In addition to movement, changes in the amount of molecules are due to biochemical reactions within compartments, often such that some molecular types fluctuate on a slower timescale than others. It is natural to ask the following questions: how sensitive is the dynamics of molecular types to their own spatial distribution, and how sensitive are they to the distribution of others? What conditions lead to effective homogeneity in biochemical dynamics despite heterogeneity in molecular distribution? What kind of spatial distribution is optimal from the point of view of some downstream product? Within a spatially heterogeneous multiscale model, we consider two notions of dynamical homogeneity (full homogeneity and homogeneity for the fast subsystem), and consider their implications under different timescales for the motility of molecules between compartments. We derive rigorous results for their dynamics and long-term behaviour, and illustrate them with examples of a shared pathway, Michaelis–Menten enzymatic kinetics and autoregulating feedbacks. Using stochastic averaging of fast fluctuations to their quasi-steady-state distribution, we obtain simple analytic results that significantly reduce the complexity and expedite simulation of stochastic compartment models of chemical reactions.

scholarly journals Detection of Gas-Solid Two-Phase Flow Based on CFD and Capacitance Method

2018 ◽  
Vol 8 (8) ◽  
pp. 1367 ◽  
Author(s):  
Wanting Zhou ◽  
Yue Jiang ◽  
Shi Liu ◽  
Qing Zhao ◽  
Teng Long ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Cfd Simulation ◽  
Fluid Model ◽  
Flow Direction ◽  
Solid Particles ◽  
Drilling Process ◽  
Sources Of Information ◽  
Discrete Phase Model ◽  
Horizontal Drilling ◽  
Annular Channels

Multiphase flow in annular channels is complex, particularly in the region where the flow direction abruptly changes between the inner pipe and the outer pipe, as the cases in horizontal drilling and pneumatic conveying. Simplified models and experience are still the main sources of information. First, to understand the process more deeply, Computational Fluid Dynamics (CFD) package Fluent is used to simulate the gas-solid flow in the horizontal and the inclined section of an annular pipe. Discrete Phase Model (DPM) is adopted to calculate the trajectories of solid particles of different sizes at different air velocities. Also, the Two-Fluid model is used to simulate the sand flow in the inclined section for the case of air flow stoppage, for which an experiment is also conducted to verify the CFD simulation. Simulation results reveal the behaviour of the solid particles showing the dispersed spatial distribution of small particles near the entrance. On the other hand, larger particles manifest a distinct sedimented flow pattern along the bottom of the pipe. The density distribution of the particles over a pipe cross section is demonstrated at a variety of air velocities. The results also show that the large airspeed tends to generate swirls near the outlet of the inner pipe. In addition, Electrical Capacitance Tomography (ECT) technology is used to reconstruct the spatial distribution of particles, and the cross-correlation algorithm to detect velocity. Both the distribution and the velocity measurement by electric sensors agree reasonably well with the CFD predictions. The details revealed by CFD simulation and the mutual-verification between CFD simulation and the ECT method of this study could be valuable for the industry in drilling process control and equipment development.

scholarly journals Identification of Dominant Factors Affecting Soil Erosion and Water Yield within Ecological Red Line Areas

2020 ◽  
Vol 12 (3) ◽  
pp. 399 ◽  
Author(s):  
Jiangbo Gao ◽  
Yuan Jiang ◽  
Huan Wang ◽  
Liyuan Zuo
Keyword(s):  
Land Use ◽  
Spatial Distribution ◽  
Soil Erosion ◽  
Spatial Heterogeneity ◽  
Remote Sensing Data ◽  
Vegetation Coverage ◽  
Water Yield ◽  
Land Use Type ◽  
Functional Areas ◽  
Red Line

Soil conservation and water retention are important metrics for designating key ecological functional areas and ecological red line (ERL) areas. However, research on the quantitative identification of dominant environmental factors in different ecological red line areas remains relatively inadequate, which is unfavorable for the zone-based management of ecological functional areas. This paper presents a case study of Beijing’s ERL areas. In order to objectively reflect the ecological characteristics of ERL areas in Beijing, which is mainly dominated by mountainous areas, the application of remote sensing data at a high resolution is important for the improvement of model calculation and spatial heterogeneity. Based on multi-source remote sensing data, meteorological and soil observations as well as soil erosion and water yield were calculated using the revised universal soil loss equation (RUSLE) and integrated valuation of ecosystem services and tradeoffs (InVEST) model. Combining the influencing factors, including slope, precipitation, land use type, vegetation coverage, geomorphological type, and elevation, a quantitative attribution analysis was performed on soil erosion and water yield in Beijing’s ERL areas using the geographical detector. The power of each influencing factor and their interaction factors in explaining the spatial distribution of soil erosion or water yield varied significantly among different ERL areas. Vegetation coverage was the dominant factor affecting soil erosion in Beijing’s ERL areas, explaining greater than 30% of its spatial heterogeneity. Land use type could explain the spatial heterogeneity of water yield more than 60%. In addition, the combination of vegetation coverage and slope was found to significantly enhance the spatial distribution of soil erosion (>55% in various ERL areas). The superposition of land use type and slope explained greater than 70% of the spatial distribution for water yield in ERL areas. The geographical detector results indicated that the high soil erosion risk areas and high water yield areas varied significantly among different ERL areas. Thus, in efforts to enhance ERL protection, focus should be placed on the spatial heterogeneity of soil erosion and water yield in different ERL areas.

The two faces of time

2001 ◽  
Vol 9 (1) ◽  
pp. 11-18
Author(s):  
JAN SOKOL
Keyword(s):  
Linear Time ◽  
Human Experience ◽  
Time Dependent ◽  
Scientific Concept ◽  
Dependent Development ◽  
The Common ◽  
Two Sides

Speaking of a ‘lack of time’, do we mean the same ‘thing’ as the variable ‘t’ in a graph of some time-dependent development? The following article tries to show that both concepts are extreme examples of the two sides, or faces, of the single phenomenon of time, as common and trivial as it is mysterious. Scientific, numerical time is considered first, followed by the time of the common human experience, the time in the present. It is on the basis of this curious ability to ‘keep in presence’ various events that follow one another, that the scientific concept of linear time has been established and, with it, the possibility to measure the time for scientific and practical purposes.

Expression of ectonucleotidases in the prosencephalon of melatonin-proficient C3H and melatonin-deficient C57Bl mice: spatial distribution and time-dependent changes

2015 ◽  
Vol 362 (1) ◽  
pp. 163-176 ◽  
Author(s):  
Moran Homola ◽  
Martina Pfeffer ◽  
Claudia Fischer ◽  
Herbert Zimmermann ◽  
Simon C. Robson ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Time Dependent ◽  
C57bl Mice

Rim Seal Ingestion Characteristics for Axial Gap Rim Seals in a Closely-Spaced Turbine Stage From a Numerical Simulation

2006 ◽  
Author(s):  
Cheng-Zhang Wang ◽  
Bruce V. Johnson ◽  
David F. Cloud ◽  
Roger E. Paolillo ◽  
T. K. Vashist ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Pressure Field ◽  
Flow Direction ◽  
Tangential Velocity ◽  
Leading Edge ◽  
Time Dependent ◽  
Flow Parameters ◽  
Pressure Fields ◽  
Bow Wave ◽  
Dependent Flow

Turbine rim seal ingestion in gas turbines is influenced by many geometric and flow parameters. For turbine stages where the vanes and blades are closely spaced, the time-dependent pressure and flow fields near the seal strongly influence the rim seal ingestion. Numerical simulations of a close-spaced configuration, similar to that used in previous experiments, were made to determine the complex 3-D, time-dependent flow and ingestion characteristics of an axial gap rim seal. The calculated pressure fields were in general agreement with previously published experimental data. The radial velocities inward and outward in the axial gap seal were appreciable fractions of the hub tangential velocity and varied with position across the airfoil pitch and the axial location in the seal. The tangential velocities in the gap varied with flow direction, generally greater than hub velocity for flow ingress and less than hub velocity for flow ingress and less than hub velocity for flow egress. Velocity jets upstream of the blade leading edge penetrated into the disk cavity approximately 10 times the seal width. The ingestion velocities for this configuration were dominated by the blade bow wave pressure field. One conclusion of the authors is that the blade pressure field can be as or more significant than the vane trailing pressure field in influencing rim seal ingestion.

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