Browsing by Author "Steeb, Holger (Prof. Dr.-Ing.)"

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Open Access
Digital laboratory: X-ray computed tomography towards direct numerical simulations
(Stuttgart : Institute of Applied Mechanics, 2025) Uribe, David; Steeb, Holger (Prof. Dr.-Ing.)
A digital porous media laboratory comprises a set of techniques to analyse and characterize samples using computer simulations and digital measurements to predict or determine material properties. This thesis has implemented the complete workflow of this technique from sample preparation until reporting the gained information pertaining said sample. A complete design of an in house built X-ray computed tomographic system is described. All components of the system are listed and the way they are electrically and mechanically coupled is explained. Software architecture to control the system and the advantages it has to maintain the system is described at a cost of system complexity. The in-house tomographic system was used to characterize engineering, geologic and biological samples.
Open Access
Direct numerical simulation and analysis of solid body motion in dilute suspensions using Smoothed Particle Hydrodynamics
(Stuttgart : Institute of Applied Mechanics, 2024) Kijanski, Nadine; Steeb, Holger (Prof. Dr.-Ing.)
Suspensions and their applications are found in many engineering, environmental or medical fields. While the effective rheological behavior is well understood in the framework of non-Newtonian fluid mechanics, contributions in the field of pore-scale fully resolved numerical simulations with non-spherical particles are rare. The motion of single particles immersed in the fluid is still on-going research and depends on hydromechanical forces as well as on solid-solid interactions. Using Smoothed Particle Hydrodynamics, a modeling approach for Direct Numerical Simulations of a single-phase fluid containing non-spherically formed solid aggregates is presented. The motion of single particles in dilute suspensions are observed to analyze effects like shear-wall migration or rolling, as seen in experiments. To be able to simulate the behavior of for example fresh concrete or mud flow as realistic as possible, the simulations taking into account a Newtonian as well as a non-Newtonian material model for the carrier fluid.
Open Access
Experimental multi-scale characterization using micro X-ray computed tomography
(Stuttgart : Institute of Applied Mechanics, 2023) Ruf, Matthias; Steeb, Holger (Prof. Dr.-Ing.)
The effective mechanical and hydro-mechanical behavior of porous media, granular solids, and related materials with complex morphologies is intimately linked to their internal microstructure on the pore/grain scale. For microstructural characterization, transmission micro X-Ray Computed Tomography (µXRCT) has emerged as a crucial three-dimensional (3D) imaging technique that can provide structural information from the micrometer to centimeter scale. Due to its non-destructive nature, it can be excellently combined with time-dependent investigations, either ex situ or in situ. In particular, the possibility of coupling mechanical or hydro-mechanical characterization with µXRCT-based 3D imaging in situ allows many physical phenomena to be studied in more detail and consequently understood more comprehensively. For example, the microstructure evolution can be observed under various controlled boundary conditions and linked to measured effective quantities. New insights and improved understanding can ultimately positively influence modeling approaches. In order to be able to perform such multi-scale studies, a modular, open, and versatile lab-based µXRCT system was developed within the scope of this work. It provides a spatial resolution of down to less than 10 µm. The developed system has an integrated universal testing machine that enables in situ compressive, tensile, and torsional studies as well as their combinations, parallel or sequential. Furthermore, hydro-mechanical coupled phenomena can be investigated using appropriate equipment, such as triaxial flow cells. Thanks to the open and modular concept, the developed system can be used in the future for a wide variety of multiphysics research questions and can be considered as an open experimental platform. Employing the established system, various multi-scale phenomena from different material classes are motivated and partly investigated in more detail within this work. For this purpose, classical experimental characterization methods are combined with µXRCT-based 3D imaging ex situ as well as in situ. Among others, 3D imaging is combined with ultrasound wave propagation measurements to investigate the influence of artificially generated crack networks in Carrara marble by different thermal treatment protocols. Load-sequence effects are demonstrated on an open-cell foam sample. An in situ workflow is shown to investigate the not-well-understood effective stiffness behavior of biphasic monodisperse granular packings of stiff and soft particles of different volume fractions at different stress states. The fracturing of a rock sample in a triaxial flow cell shows possibilities of application in the context of fracture mechanics. All resulting data sets, including metadata, are available via the Data Repository of the University of Stuttgart (DaRUS).
Open Access
Hydro-mechanical coupling of flow in deformable high-aspect ratio fractures
(Stuttgart : Institute of Applied Mechanics, 2022) Schmidt, Patrick; Steeb, Holger (Prof. Dr.-Ing.)
Underground flow processes in fractured porous media possess a great significance regarding the optimization of energy production based on natural resources. Energy is stored in form of liquids, respectively heat in the underground and its excavation is highly impacted by discontinuities of the porous medium's transport characteristics such as induced by discrete fractures or fracture networks. Throughout the exploitation flow processes might become fairly complex, since fractures do not simply increase the permeability and induce preferential flow paths within the reservoir, they also reduce the stiffness of the surrounding rock mass. Therefore, the objective of this thesis is to derive a numerically efficient hydro-mechanical model for flow in fractured porous media in which the reduction of the fracture flow domain by one dimension increases the computational performance. The derived model is then applied to data obtained from field-scale pumping operations in fractured reservoirs to contribute to a better understanding of hydro-mechanical processes under in-situ conditions.
Open Access
Image-based characterization of multiphase flow in porous media
(Stuttgart : Institute of Applied Mechanics, 2024) Vahid Dastjerdi, Samaneh; Steeb, Holger (Prof. Dr.-Ing.)
Multiphase flow in porous media encompasses a wide range of applications, including groundwater management, resource extraction, and carbon dioxide sequestration. This interdisciplinary field intersects geophysics, hydrology, and environmental science and has the potential to revolutionize industrial applications. The dynamics of imbibition and drainage processes in porous media and the relevant underlying physics, as well as developing effective models to describe them, are among the main focuses of research in multiphase porous media flow. This work primarily revolves around equations to compute capillary pressure and accommodate features like hysteresis. To follow this aim, experimental observations are examined by integrating two continuum theories for phase flow in porous media. One theory extends the understanding of multiphase flow by incorporating essential elements in thermodynamic equations, namely phases, and their interfaces, formulating capillary pressure as a function of saturation and phases' specific interfacial area. The fact that interfaces are the locus of force exchange between all the present phases supports the necessity of considering them in describing a multiphase flow system. The other theory addresses limitations in conventional approaches by differentiating between percolating and non-percolating fluid clusters. This theory employs the fact that the distribution of forces is different in the percolating and non-percolating fluid elements. This research merges these theories to enhance the available comprehension of two-phase flow in porous media. In order to collect the pore-scale information necessary as the input parameters in the mentioned continuum theories, microfluidic experiments are carried out and visualized using a customized open-air microscope. The high-resolution recording of experiments provides real-time information on the two-phase flow process. Subsequently, the recorded snapshots are processed via a self-developed segmentation and parameter calculation code. The REV-scale parameters gathered from the experiments, among others, include saturation and specific interfacial area. The results from the experiments show that an approach that considers specific interfacial area when differentiating between percolating and non-percolating fluid elements proves valuable in modeling two-phase porous media flow. Moreover, a linear relation between saturation and specific interfacial area of percolating fluid phases is observed, which could help find more efficient models for multiphase fluid flow in a porous medium. Additionally, the formation of preferential flow paths after cyclic phase displacements is documented. These preferential flow paths, referred to as an effective porous medium, remain unaltered when enough fluid clusters are stranded. The stranded fluid clusters and the solid matrix form the effective porous medium, which constrains the flow to the preferential flow pathways for both fluids, regardless of the wetting properties of the flow system. This observation highlights the need to differentiate between primary and scanning events in applications. These results could contribute to advancing a two-phase flow theory capable of capturing dynamic conditions and hysteresis phenomena, emphasizing the importance of considering interfacial area and phase connectivity in continuum theories.
Open Access
Multiscale modelling of hydro-mechanical coupling in porous media
(Stuttgart : Institute of Applied Mechanics, 2021) Osorno Tejada, Maria Camila; Steeb, Holger (Prof. Dr.-Ing.)
Hydro-mechanical processes in porous media are phenomena that occurs at different length and time scales. This thesis presents a multiscale approach to model these phenomena with continuum approaches. On the pore scale, effective transport properties, e.g. the intrinsic permeability or the tortuosity, are numerically calculated. Further, on a Darcy or reservoir scale, the results of the Direct Numerical Simulations on the pore scale are applied to hydro-mechanically coupled (consolidation) problems and fluid-filled fractures.
Open Access
Saddle-point and minimization principles for diffusion in solids : phase separation, swelling and fracture
(Stuttgart : Institute of Applied Mechanics, 2020) Böger, Lukas; Steeb, Holger (Prof. Dr.-Ing.)
Liquid diffusion in solids plays a major role in countless biomedical, geotechnical and everyday applications. Modern continuum mechanics delivers suitable modeling approaches for both macroscopically observable material behavior and microstructural arrangements: multi-field formulations allow for different length scales and coupled physical effects. This work contributes to the theory and finite element discretization of diffusion phenomena in solids. Foundations of large strain kinematics, Newtonian balances and constitutive theory are outlined in conjunction with solute transport and essential non-equilibrium thermodynamics. This forms the basis for three applications. First, spinodal decomposition in rigid bodies is formulated in terms of an incremental variational formulation allowing for an efficient exploitation of its saddle-point structure. Then, a new minimization formulation for Fickian diffusion in hydrogels is shown to be the counterpart of the classical saddle-point principle and implemented with non-standard FE schemes. This model is extended by a phase-field approach to fracture to account for diffusion-induced material failure.
Open Access
Simulation of coupled transfer and transport phenomena in multi-phase materials with application to polymer gels
(Stuttgart : Institute of Applied Mechanics, 2021) Sauerwein, Malte; Steeb, Holger (Prof. Dr.-Ing.)
The use of polymers in fluid-saturated porous media has increased in relevance during the last years. Polymers, which exist in the pore space of a solid skeleton, are able to interact with the pore fluid as well as with the solid. The interactions cause changes in the macroscopic behavior, while especially transport and transfer processes within the pore space are affected. The precise knowledge of these processes over time is a key factor for developing innovative applications in petroleum engineering but also for innovative building materials. Therefore, the aim of this thesis is to develop a multi-phase model for simulating the coupled processes in such kind of material. With such model, the physical behavior of water-soluble polymers in petroleum engineering and the swelling behavior of hydrogels in polymer-enhanced building materials can be predicted over time. The coupled processes are simulated by solving the system's governing equations in a finite element framework and are validated through experimental results.