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  • 1
    Language: English
    In: Journal of Contaminant Hydrology, March 1, 2011, Vol.120-121, p.141(16)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jconhyd.2010.08.001 Byline: Insa Neuweiler, Alexandros Papafotiou, Holger Class, Rainer Helmig Keywords: Upscaling; Two-phase flow; Buoyancy driven flow; Structure; Heterogeneity; Effective parameters; Non-Gaussian fields Abstract: In this paper we discuss estimates of effective parameters for an upscaled model for buoyant counter flow of DNAPL and water in a closed box filled with heterogeneous porous material. The upscaling procedure is based on the assumption that the flow is dominated by capillary forces on the small scale and that the fluids are segregated. The upscaled model has the same form as the usual two-phase flow model with an effective capillary pressure function and an effective mobility function I. Effective parameters are then estimated in two different ways. Stochastic theory can be applied to calculate the effective parameters to first order in the parameter fluctuations. This approach does not take into account that different parameter ranges of the heterogeneous field may be connected or isolated, yielding very different macroscopic residual saturations. Therefore, the second estimate of effective parameters takes connectivity of parameter ranges into account. In this case, the univariate parameter distribution of the heterogeneous field and the values that mark connected materials are the only information about heterogeneity that is used. Effective parameters are then estimated using mean field theory (the Maxwell approach). The upscaled model and the estimation of effective parameters are applied to a numerical test case. Buoyant counter flow in heterogeneous parameter fields with different structures is simulated numerically and compared to the solutions of the quasi-1d upscaled model with differently estimated parameters. It is demonstrated that connectivity of the different parameter ranges is an important information that determines typical time scales for the flow process and the macroscopic residual saturation. Even simple estimates of effective parameters based on little information may capture the typical time scales, provided that information about connected parameter ranges is taken into account. Article History: Received 11 November 2009; Revised 24 July 2010; Accepted 4 August 2010
    Keywords: Flow (Dynamics) -- Analysis
    ISSN: 0169-7722
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Journal of Hydrology, December 2017, Vol.555, pp.569-585
    Description: In urban water pipe networks, pipe leakage may lead to subsurface contamination or to reduced waste water treatment efficiency. The quantification of pipe leakage is challenging due to inaccessibility and unknown hydraulic properties of the soil. A novel physically-based model for three-dimensional numerical simulation of pipe leakage in variably saturated soil is presented. We describe the newly implemented coupling between the pipe flow simulator HYSTEM-EXTRAN and the groundwater flow simulator OpenGeoSys and its validation. We further describe a novel upscaling of leakage using transfer functions derived from numerical simulations. This upscaling enables the simulation of numerous pipe defects with the benefit of reduced computation times. Finally, we investigate the response of leakage to different time-dependent pipe flow events and conclude that larger pipe flow volume and duration lead to larger leakage while the peak position in time has a small effect on leakage.
    Keywords: Pipe Leakage ; Model Coupling ; Numerical Model ; Opengeosys ; Hystem-Extran ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 3
    Language: English
    In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 05 May 2017, Vol.520, pp.532-543
    Description: Due to the complexity of flow conditions as well as solid matrix and colloid surface properties, solid knowledge about the transport of iron oxide colloids in soils remains scarce. In order to analyze the influence of flow conditions on iron oxide colloid transport and retention, breakthrough behavior of negatively charged, organic matter-coated goethite (OMCG) colloids in saturated quartz sand columns was investigated under continuous and stagnant flow conditions. Classic DLVO and extended DLVO (XDLVO) interaction energies including Lewis acid/base parameters were evaluated using measurements of sessile drop contact angles and zeta potentials of OMCG colloids and quartz. Results elucidated that under continuous flow conditions, OMCG colloids were highly mobile, which was in agreement with calculated unfavorable attachment conditions revealed by predictions of both DLVO approaches. In contrast, during intervals of flow interruption, significant amounts of OMCG colloids were retained in the solid matrix and could not be remobilized via re-establishment of flow. The magnitude of colloid retention increased with the duration of flow interruption; OMCG colloids were almost completely immobilized after 112 h. Further experiments were conducted in order to determine possible colloid retention mechanisms. Results indicated that the major cause for retention during flow stagnation was OMCG colloid capture at locations with attractive DLVO/XDLVO interactions, promoted by fast gravitational settling of colloids onto the solid matrix. We compared breakthrough curves to model predictions, where we demonstrated that an attachment term with a stagnant fluid switch was required in the mass balance in order to reproduce the measurements. We conclude that high mobility of OMCG colloids and prediction of that transport behavior with the applied DLVO approaches were only valid under continuous flow conditions. Under more discontinuous hydraulic conditions relevant in natural soils, such as flow interruption, OMCG colloid transport behavior was modified significantly.
    Keywords: Iron Oxide Colloids ; Flow Interruption ; Dlvo ; Engineering ; Chemistry
    ISSN: 0927-7757
    E-ISSN: 1873-4359
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  • 4
    In: Water Resources Research, March 2017, Vol.53(3), pp.1784-1791
    Description: Models for flow in environmental systems are subject to uncertainty. Models can thus be interpreted as hypotheses on the validity of the underlying model assumptions. One important source of uncertainty in models for flow and transport processes in the subsurface is the model concept. While uncertain model parameters or forcing terms can be captured as random processes and random fields, this type of uncertainty cannot be included into a model in a straightforward manner. This is particularly true if established model descriptions of a given process are not known or are still being debated. In this contribution, we outline several examples of subsurface flow and transport modeling where uncertainty of the model concept plays an important role. We discuss the need for the development of methods and standards to deal with this type of uncertainty in model hypothesis testing. Uncertainty about processes in a model is a key source of uncertainty in many subsurface models Ongoing research on alternative modeling approaches for flow and transport should be taken up in formulations of structural model errors Methods are needed to deal with uncertainty about model concepts
    Keywords: Model Hypotheses ; Subsurface Flow Modeling ; Model Development
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 5
    Language: English
    In: Advances in Water Resources, December 2015, Vol.86, pp.257-259
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.advwatres.2015.10.010 Byline: Harrie-Jan Hendricks Franssen, Insa Neuweiler Author Affiliation: (a) Forschungszentrum Julich GmbH, Agrosphere (IBG-3), Wilhelm Johnen Strasse, 52428 Julich, Germany (b) Institute of Fluid Mechanics, University of Hannover, Appelstrasse 9a, 30167 Hannover, Germany Article History: Received 15 October 2015; Accepted 15 October 2015
    Keywords: Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 6
    Language: English
    In: Journal of Hydrology, June 2016, Vol.537, pp.A1-A4
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jhydrol.2016.03.013 Byline: Demetris Koutsoyiannis, Gunter Bloschl, Andras Bardossy, Christophe Cudennec, Denis Hughes, Alberto Montanari, Insa Neuweiler, Hubert Savenije
    Keywords: Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 7
    Language: English
    In: Advances in Water Resources, Dec, 2013, Vol.62, p.475(13)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.advwatres.2013.05.012 Byline: Jan Tecklenburg, Insa Neuweiler, Marco Dentz, Jesus Carrera, Sebastian Geiger, Christian Abramowski, Orlando Silva Abstract: acents Two-scale expansion for upscaling two-phase flow. acents Derivation of non-local single equation model for large scale two-phase flow. acents Parametrization in terms of hydraulic properties and medium geometry.
    Keywords: Flow (Dynamics) -- Analysis
    ISSN: 0309-1708
    Source: Cengage Learning, Inc.
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  • 8
    Language: English
    In: PAMM, 12/2018, Vol.18(1), p.e201800244
    Description: We present a time-space flux-corrected transport (FCT) finite element formulation for solving the linear time-dependent advection dominated advection-diffusion equation. Solving advection dominated transport equations with conventional finite element (FE) methods suffers from drawbacks of excessive numerical dispersion which results in non-physical, non-monotonic solutions. The FCT algorithm is an effective method which suppresses the non-monotonic behavior of the solution by applying a limited anti-diffusion operator to a first order scheme. Applying the FCT algorithm to time-space FE formulation, such as the time-discontinuous Galerkin (TDG) method, benefits from the advantages of both the TDG scheme and the FCT algorithm. In another word, the time-space FCT-FE formulation achieves arbitrary odd order accuracy in time at the discontinuous time nodes. Large time steps can be applied and the scheme ensures monotonic solution when linear interpolation is used for spatial discretization.
    Keywords: Interpolation ; Finite-Elemente-Methode ; Mathematics;
    ISSN: PAMM
    E-ISSN: 16177061
    Source: Wiley (via CrossRef)
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  • 9
    Language: English
    In: PAMM, December 2018, Vol.18(1), pp.n/a-n/a
    Description: We present a time‐space flux‐corrected transport (FCT) finite element formulation for solving the linear time‐dependent advection dominated advection‐diffusion equation. Solving advection dominated transport equations with conventional finite element (FE) methods suffers from drawbacks of excessive numerical dispersion which results in non‐physical, non‐monotonic solutions. The FCT algorithm is an effective method which suppresses the non‐monotonic behavior of the solution by applying a limited anti‐diffusion operator to a first order scheme. Applying the FCT algorithm to time‐space FE formulation, such as the time‐discontinuous Galerkin (TDG) method, benefits from the advantages of both the TDG scheme and the FCT algorithm. In another word, the time‐space FCT‐FE formulation achieves arbitrary odd order accuracy in time at the discontinuous time nodes. Large time steps can be applied and the scheme ensures monotonic solution when linear interpolation is used for spatial discretization.
    ISSN: 1617-7061
    E-ISSN: 1617-7061
    Source: John Wiley & Sons, Inc.
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  • 10
    Language: English
    In: Journal of contaminant hydrology, 2011, Vol.120, pp.141-156
    Description: In this paper we discuss estimates of effective parameters for an upscaled model for buoyant counter flow of DNAPL and water in a closed box filled with heterogeneous porous material. The upscaling procedure is based on the assumption that the flow is dominated by capillary forces on the small scale and that the fluids are segregated. The upscaled model has the same form as the usual two-phase flow model with an effective capillary pressure function and an effective mobility function Λ. Effective parameters are then estimated in two different ways. Stochastic theory can be applied to calculate the effective parameters to first order in the parameter fluctuations. This approach does not take into account that different parameter ranges of the heterogeneous field may be connected or isolated, yielding very different macroscopic residual saturations. Therefore, the second estimate of effective parameters takes connectivity of parameter ranges into account. In this case, the univariate parameter distribution of the heterogeneous field and the values that mark connected materials are the only information about heterogeneity that is used. Effective parameters are then estimated using mean field theory (the Maxwell approach). The upscaled model and the estimation of effective parameters are applied to a numerical test case. Buoyant counter flow in heterogeneous parameter fields with different structures is simulated numerically and compared to the solutions of the quasi-1d upscaled model with differently estimated parameters. It is demonstrated that connectivity of the different parameter ranges is an important information that determines typical time scales for the flow process and the macroscopic residual saturation. Even simple estimates of effective parameters based on little information may capture the typical time scales, provided that information about connected parameter ranges is taken into account. ; Includes references ; p. 141-156.
    ISSN: 0169-7722
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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