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  • Upscaling
Type of Medium
  • 1
    Language: English
    In: Advances in Water Resources, August 2012, Vol.44, pp.101-112
    Description: ► New averaging approach that conserves hydraulic non-equilibrium during rapid infiltration of water. ► New indicators to describe hydraulic non-equilibrium quantitatively. ► Direct link between front morphology and hydraulic non-equilibrium. ► Insights into how structural connectivity affects hydraulic non-equilibrium. ► Shortcomings of an upscaled Richards model extended by hydraulic non-equilibrium. Water infiltration into heterogeneous, structured soil leads to hydraulic non-equilibrium across the infiltration front. That is, the water content and pressure head are not in equilibrium according to some static water retention curve. The water content increases more rapidly in more conductive regions followed by a slow relaxation towards an equilibrium state behind the front. An extreme case is preferential infiltration into macropores. Since flow paths adapt to the structural heterogeneity of the porous medium, there is a direct link between structure and non-equilibrium. The aim of our study is to develop an upscaled description of water dynamics which conserves the macroscopic effects of non-equilibrium and which can be directly linked to structural properties of the material. A critical question is how to define averaged state variables at the larger scale. We propose a novel approach based on flux-weighted averaging of pressure head, and compare its performance to alternative methods for averaging. Further, we suggest some meaningful indicators of hydraulic non-equilibrium that can be related to morphological characteristics of infiltration fronts in quantitative terms. These methods provide a sound basis to assess the impact of structural connectivity on hydraulic non-equilibrium. We demonstrate our approach using numerical case studies for infiltration into two-dimensional heterogeneous media using three different structure models with distinct differences in connectivity. Our results indicate that an increased isotropic, short-range connectivity reduces non-equilibrium, whereas anisotropic structures that are elongated in the direction of flow enforce it. We observe a good agreement between front morphology and effective hydraulic non-equilibrium. A detailed comparison of averaged state variables with results from an upscaled model that includes hydraulic non-equilibrium outlines potential improvements in the description of non-equilibrium dynamics including preferential flow in simplified, upscaled models based on Richards equation.
    Keywords: Transient Flow ; Upscaling ; Pressure Head Averaging ; Hydraulic Non-Equilibrium ; Preferential Flow ; Connectivity ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 2
    Language: English
    In: Frontiers in Microbiology, 01 August 2018, Vol.9
    Description: Over the last 60 years, soil microbiologists have accumulated a wealth of experimental data showing that the bulk, macroscopic parameters (e.g., granulometry, pH, soil organic matter, and biomass contents) commonly used to characterize soils provide insufficient information to describe quantitatively the activity of soil microorganisms and some of its outcomes, like the emission of greenhouse gasses. Clearly, new, more appropriate macroscopic parameters are needed, which reflect better the spatial heterogeneity of soils at the microscale (i.e., the pore scale) that is commensurate with the habitat of many microorganisms. For a long time, spectroscopic and microscopic tools were lacking to quantify processes at that scale, but major technological advances over the last 15 years have made suitable equipment available to researchers. In this context, the objective of the present article is to review progress achieved to date in the significant research program that has ensued. This program can be rationalized as a sequence of steps, namely the quantification and modeling of the physical-, (bio)chemical-, and microbiological properties of soils, the integration of these different perspectives into a unified theory, its upscaling to the macroscopic scale, and, eventually, the development of new approaches to measure macroscopic soil characteristics. At this stage, significant progress has been achieved on the physical front, and to a lesser extent on the (bio)chemical one as well, both in terms of experiments and modeling. With regard to the microbial aspects, although a lot of work has been devoted to the modeling of bacterial and fungal activity in soils at the pore scale, the appropriateness of model assumptions cannot be readily assessed because of the scarcity of relevant experimental data. For significant progress to be made, it is crucial to make sure that research on the microbial components of soil systems does not keep lagging behind the work on the physical and (bio)chemical characteristics. Concerning the subsequent steps in the program, very little integration of the various disciplinary perspectives has occurred so far, and, as a result, researchers have not yet been able to tackle the scaling up to the macroscopic level. Many challenges, some of them daunting, remain on the path ahead. Fortunately, a number of these challenges may be resolved by brand new measuring equipment that will become commercially available in the very near future.
    Keywords: Soil Microbiology ; Biodiversity ; Upscaling ; Tomography ; X-Ray Computed ; Nanosims Imaging ; Biology
    E-ISSN: 1664-302X
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  • 3
    In: Water Resources Research, March 2007, Vol.43(3), pp.n/a-n/a
    Description: Large‐scale models of transient flow processes in the unsaturated zone require, in general, upscaling of the flow problem in order to capture the impact of heterogeneities on a small scale, which cannot be resolved by the model. Effective parameters for the upscaled models are often derived from second‐order stochastic properties of the parameter fields. Such properties are good quantifications for parameter fields, which are multi‐Gaussian. However, the structure of soil does rarely resemble these kinds of fields. The non‐multi‐Gaussian field properties can lead to strong discrepancies between predictions of upscaled models and the averaged real flow process. In particular, the connected paths of parameter ranges of the medium are important features, which are usually not taken into account in stochastic approaches. They are determined here by the Euler number of one‐cut indicator fields. Methods to predict effective parameters are needed that incorporate this type of information. We discuss different simple and fast approaches for estimating the effective parameter for upscaled models of slow transient flow processes in the unsaturated zone, where connected paths of the material may be taken into account. Upscaled models are derived with the assumption of capillary equilibrium. The effective parameters are calculated using effective media approaches. We also discuss the limits of the applicability of these methods.
    Keywords: Richards Equation ; Unsaturated Flow ; Upscaling
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 4
    Text Resource
    Text Resource
    Universitäts- und Landesbibliothek Sachsen-Anhalt
    Description: Fluss und Transport in natürlichen porösen Medien werden durch die Strukturheterogenität des Untergrunds bestimmt. Konnektivität ist ein wichtiger Aspekt jener Strukturheterogenität, der richtig erfasst werden muss, um Modelvorhersagen zu verschiedenen physikalischen Prozessen zu ermöglichen oder zu verbessern. Die vorliegende Arbeit präsentiert neue Erkenntnisse über die quantitative Beschreibbarkeit von Strukturkonnektivität und die komplexe Beziehung zwischen struktureller und funktionaler Konnektivität in Bezug auf die Hydrologie der ungesättigten Zone. Funktionale Konnektivität beschreibt dabei das effektive hydraulische Verhalten in Bezug auf stationären Fluss, Stofftransport und hydraulisches Ungleichgewicht. Numerische Simulationen zeigen, dass eine gute Reproduktion von Strukturkonnektivität auch zu einer guten Reproduktionen funktionaler Konnektivität führt. Strukturkonnektivität beeinflusst jedoch effektiven Fluss, Transport und hydraulisches Ungleichgewicht auf unterschiedliche Weise. Funktionale Konnektivität muss daher als ein prozess- und zustandsabhängiges Konzept aufgefasst werden.... ; Flow and transport in the subsurface are determined by the structural heterogeneity of natural porous media. Connectivity is known to be an important facet of structural heterogeneity that has to be captured adequately in order to facilitate or improve model predictions on diverse physical processes in porous formations. This thesis presents some novel insights into the approaches to quantify structural connectivity and the complex relationship between structural and functional connectivity in the realm of vadose zone hydrology. Functional connectivity is expressed as effective hydraulic behavior with respect to stationary flow, solute transport and hydraulic non-equilibrium during infiltration. Numerical simulations demonstrate that a good reproduction of structural connectivity also entails a good reproduction of functional connectivity metrics. However, structural connectivity affect upscaled flow, transport and hydraulic non-equilibrium behavior differently. Thus, functional connectivity has to be considered as a process and state-dependent concept....
    Keywords: Bodenphysik ; Stoffübertragung ; Online-Publikation ; Hochschulschrift ; Konnektivitätsmaße; Stochastische Rekonstruktion; Stationärer Fluss; Stofftransport; Hydraulisches Ungleichgewicht; Upscaling ; Connectivity Metrics; Stochastic Reconstruction; Stationary Flow; Solute Transport; Hydraulic Nonequilibrium; Upscaling ; Ddc::600 Technik, Medizin, Angewandte Wissenschaften::630 Landwirtschaft::631 Technik, Ausstattung, Materialien
    Source: DataCite
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