Browsing by Author "Weishaupt, Kilian"

Now showing 1 - 5 of 5

Open Access
Experimental and simulation study on validating a numerical model for CO2 density-driven dissolution in water
(2020) Class, Holger; Weishaupt, Kilian; Trötschler, Oliver
Carbon dioxide density-driven dissolution in a water-filled laboratory flume of the dimensions 60~cm length, 40~cm height, 1~cm thickness was visualized using a pH-sensitive color indicator. We focus on atmospheric pressure conditions, like in caves where CO2 concentrations are typically higher. Varying concentrations of carbon dioxide were applied as boundary conditions at the top of the experimental setup, leading to the onset of convective fingering at differing times. The data were used to validate a numerical model implemented in the numerical simulator Dumux. The model solves the Navier-Stokes equations for density-induced water flow with concentration-dependent fluid density and a transport equation including advective and diffusive processes for the carbon dioxide dissolved in water. The model was run in 2D, 3D, and pseudo-3D on two different grids. Without any calibration or fitting of parameters, the results of the comparison between experiment and simulation show satisfactory agreement with respect to the onset time of convective fingering as well as the number and the dynamics of the fingers. Grid refinement matters in particular in the uppermost part where fingers develop. The 2D simulations consistently overestimated the fingering dynamics. This successful validation of the model is the prequisite for employing it in situations with background flow and for a future study of karstification mechanisms related to CO2-induced fingering in caves.
Open Access
Model concepts for coupling free flow with porous medium flow at the pore-network scale : from single-phase flow to compositional non-isothermal two-phase flow
(Stuttgart : Eigenverlag des Instituts für Wasser- und Umweltsystemmodellierung der Universität Stuttgart, 2020) Weishaupt, Kilian; Helmig, Rainer (Prof. Dr.-Ing.)
Open Access
Modeling of two phase flow in a hydrophobic porous medium interacting with a hydrophilic structure
(2022) Michalkowski, Cynthia; Weishaupt, Kilian; Schleper, Veronika; Helmig, Rainer
Fluid flow through layered materials with different wetting behavior is observed in a wide range of applications in biological, environmental and technical systems. Therefore, it is necessary to understand the occuring transport mechanisms of the fluids at the interface between the layered constituents. Of special interest is the water transport in polymer electrolyte membrane fuel cells. Here, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. This is crucial to choose optimal operating conditions and improve the overall cell performance. Pore-scale modeling of gas diffusion layers (GDLs) and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the hydrophobic porous GDL and the hydrophilic gas distributor, a particular challenge is the combination and interaction of the different material structures and wetting properties at the interface and its influence on the flow. In this paper, a modeling approach is presented which captures the influence of a hydrophilic domain on the flow in a hydrophobic porous domain at the interface between the two domains. A pore-network model is used as the basis of the developed concept which is extended to allow the modeling of mixed-wet interactions at the interface. The functionality of the model is demonstrated using basic example configurations with one and several interface pores and it is applied to a realistic GDL representation in contact with a channel-land structured gas distributor.
Open Access
A surrogate-assisted uncertainty-aware Bayesian validation framework and its application to coupling free flow and porous-medium flow
(2023) Mohammadi, Farid; Eggenweiler, Elissa; Flemisch, Bernd; Oladyshkin, Sergey; Rybak, Iryna; Schneider, Martin; Weishaupt, Kilian
Existing model validation studies in geoscience often disregard or partly account for uncertainties in observations, model choices, and input parameters. In this work, we develop a statistical framework that incorporates a probabilistic modeling technique using a fully Bayesian approach to perform a quantitative uncertainty-aware validation. A Bayesian perspective on a validation task yields an optimal bias-variance trade-off against the reference data. It provides an integrative metric for model validation that incorporates parameter and conceptual uncertainty. Additionally, a surrogate modeling technique, namely Bayesian Sparse Polynomial Chaos Expansion, is employed to accelerate the computationally demanding Bayesian calibration and validation. We apply this validation framework to perform a comparative evaluation of models for coupling a free flow with a porous-medium flow. The correct choice of interface conditions and proper model parameters for such coupled flow systems is crucial for physically consistent modeling and accurate numerical simulations of applications. We develop a benchmark scenario that uses the Stokes equations to describe the free flow and considers different models for the porous-medium compartment and the coupling at the fluid-porous interface. These models include a porous-medium model using Darcy’s law at the representative elementary volume scale with classical or generalized interface conditions and a pore-network model with its related coupling approach. We study the coupled flow problems’ behaviors considering a benchmark case, where a pore-scale resolved model provides the reference solution. With the suggested framework, we perform sensitivity analysis, quantify the parametric uncertainties, demonstrate each model’s predictive capabilities, and make a probabilistic model comparison.
Open Access
Umgang mit Forschungssoftware an der Universität Stuttgart
(2020) Flemisch, Bernd; Hermann, Sibylle; Holm, Christian; Mehl, Miriam; Reina, Guido; Uekermann, Benjamin; Boehringer, David; Ertl, Thomas; Grad, Jean-Noël; Iglezakis, Dorothea; Jaust, Alexander; Koch, Timo; Seeland, Anett; Weeber, Rudolf; Weik, Florian; Weishaupt, Kilian
Wir empfehlen die Einrichtung einer Organisationseinheit Forschungssoftware-Entwicklung an der Universität Stuttgart und eines daran angegliederten Stellenpools von Research Software Engineers (RSEs). Dazu schlagen wir Maßnahmen zur Schaffung und Finanzierung entsprechender neuer RSE-Stellen, zur Integration bestehender Stellen sowie zur Gewinnung und Förderung geeigneter Personen vor. RSEs sind Personen, die sich um Konzeption, Organisation, Implementierung, Testen, Dokumentation und Wartung von Forschungssoftware kümmern. Die institutionelle Förderung von Forschungssoftware-Entwicklung ist notwendig, da die Bedeutung von Software für die Forschung und Anforderungen an die entsprechende Software, u.a. durch die DFG, stetig zunimmt.