02 Fakultät Bau- und Umweltingenieurwissenschaften
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3
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Item Open Access Comparing methods for permeability computation of porous materials and their limitations(2023) Krach, David; Steeb, HolgerEfficient numerical simulations of fluid flow on the pore scale allow for the numerical estimation of effective material properties of porous media, e.g. intrinsic permeability or tortuosity. These parameters are essential for various applications where hydro‐mechanical properties on larger scales have to be known. Numerical tools based intrinsically on pore scale simulations are known e.g. as Digital Rock Physics in geosciences and have even more and more replaced physical experiments. For these reasons, the validation of numerical methods as well as the establishment of clear limits regarding the application areas play an important role. Here, we compute single‐phase flow through a porous matrix, e.g. irregular sphere packings, sandstones, artificially created thin porous media, on the pore scale. Therefore we implement on the one hand a Smoothed Particle Hydrodynamics algorithm for solving the Navier‐Stokes equations and on the other hand a Finite Difference solver for the Stokes equations. Both methods work directly and seamlessly on voxel data of porous materials which are generated by µXRCT‐scans or by microfluidic experiments that have undergone segmentation and binarization. We compare both solvers from a parallel performance point of view as well as their results for flows in the Darcy regime. In addition, we investigate the limitations of the solvers using the example of a porous material whose pore geometry changes over time and precipitation affects the flow conditions.Item Open Access Investigation on the removal of selected organic micropollutants from municipal wastewater by trickling filters and sand filters(2019) Ghorban, ShimaRecently several different types of organic micropollutants are detected in the aquatic environment as a result of inadequate wastewater treatment. The adverse effects of the various micropollutants such as pharmaceuticals, personal care products, pesticides, herbicides and industrial chemicals with concentrations less than 1 μgL-1 on the ecosystem are challenging to be assessed. Thus, sufficient approaches are indispensable to curtail the negative impacts that these substances may have on the environment and human health. Much research was done especially in the recent years on the fate and removal of these emerging contaminants from wastewater by different measures. In this work, a systematic literature review (SLR) is conducted to determine the current state of research in micropollutant removal around the globe which discovers the existing approaches for micropollutant treatment and enables applying an unbiased evaluation. Then one of the identified approaches (sand filter and trickling filter) which is the objective of this study was investigated, and the removal behavior of micropollutants by this method was experimented. The influent and effluent of the trickling filters and sand filters in LFKW wastewater treatment plant were taken and the effect of biodegradation and sorption on the removal of the compounds was investigated. Micropollutant analysis regarding non-polar substances was performed bygas chromatography-mass spectrometry (GCMS) while high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MSMS) was applied instead for polar compounds. Furthermore, the molecular orbital energies of the substances were investigated. UV/Vis spectrophotometry and DOC analysis were other experimental approaches that have been used in order to shed some light on the behavior of these contaminants. As a result of this study, micropollutants are classified in different groups based on their physical-chemical properties, providing it as an essential factor affecting micropollutant removal behavior. Moreover, different correlations between the physical-chemical properties and the micropollutants elimination are assessed.Item Open Access Parameter identification and validation of shape-memory polymers within the framework of finite strain viscoelasticity(2021) Ghobadi, Ehsan; Shutov, Alexey; Steeb, HolgerShape-Memory Polymers (SMPs) can be stretched to large deformations and recover induced strains when exposed to an appropriate stimulus, such as heat. This emerging class of functional polymers has attracted much interest and found applications in medicine and engineering. Nevertheless, prior to any application, their physical and mechanical properties must be thoroughly studied and understood in order to make predictions or to design structures thereof. In this contribution, the viscoelastic behavior of a polyether-based polyurethane (Estane) and its rate- and temperature-dependent behavior have been studied experimentally and by the mean of simulations. The model-inherent material parameters are identified with the assumption of the thermo-rheological complexity. Here, the numerical results of uni-axial stress relaxations were compared with the associated experiments in conjucation with the Levenberg-Marquard optimization method to determine the parameters of the Prony equation. The ability of the model to simulate the thermo-mechanical properties of Estane was evaluated by data-rich experimental observations on tension and torsion in various temperature ranges. Heterogeneous tests are included into the experimental program to cover a broader spectrum of loading scenarios.Item Open Access Analysing the bone cement flow in the injection apparatus during vertebroplasty(2023) Trivedi, Zubin; Gehweiler, Dominic; Wychowaniec, Jacek K.; Ricken, Tim; Gueorguiev-Rüegg, Boyko; Wagner, Arndt; Röhrle, OliverVertebroplasty, a medical procedure for treating vertebral fractures, requires medical practitioners to inject bone cement inside the vertebra using a cannula attached to a syringe. The required injection force must be small enough for the practitioner to apply it by hand while remaining stable for a controlled injection. Several factors could make the injection force unintuitive for the practitioners, one of them being the non‐Newtonian nature of the bone cement. The viscosity of the bone cement varies as it flows through the different parts of the injection apparatus and the porous cancellous interior of the vertebra. Therefore, it is important to study the flow of bone cement through these parts. This work is a preliminary study on the flow of bone cement through the injection apparatus. Firstly, we obtained the rheological parameters for the power law model of bone cement using experiments using standard clinical equipment. These parameters were then used to obtain the shear rate, viscosity, and velocity profiles of the bone cement flow through the cannula. Lastly, an analysis was carried out to understand the influence of various geometrical parameters of the injection apparatus, in which the radius of the cannula was found to be the most influential parameter.Item Open Access Minimization of the influence of shear-induced particle migration in determining the rheological characteristics of self-compacting mortars and concretes(2020) Baumert, Christian; Garrecht, HaraldDetermining the exact rheological properties of cementitious materials in fundamental units is a crucial step in concrete science. It is undisputed that before measuring rheological properties in concrete rheometers, it is necessary to pre-shear the fresh mortar or concrete. Due to the migration of the coarse particles into areas with lower shear stress, however, segregation takes place. An experimental set-up was developed to determine the effects on the measured values of the concrete rheometer ICAR. This allows the active homogenization (pre-shearing) of the material before each change of speed. In the tests higher raw values (macroscopic data) could be measured. This clearly influences the calculated rheological Bingham parameters and modified Bingham parameters for a self-compacting concrete (SCC) with a maximum grain size of 16 mm. Therefore, the homogeneity of the material, a main hypothesis of rheological measurements, does not seem to be fulfilled with the coaxial rheometer used. The process of the indispensable pre-shearing therefore requires more attention in the future so that measurement errors can be minimized. Especially in numerical simulation, suitable rheological models and the realistic determination of parameters are crucial. Since the shear-induced particle migration is largely dependent on the maximum grain size, an ultra-high performance concrete (UHPC) with a maximum particle size of only 0.5 mm was also investigated in the laboratory mixer KNIELE KKM-RT. The integrated rheometer enables also the active homogenization of the fresh concrete during pre-shearing but without the danger of over-mixing, as it is the case for the experimental ICAR setup. This article proves that relevant differences can also be identified for such a material.Item Open Access Interlaboratory study on rheological properties of cement pastes and reference substances : comparability of measurements performed with different rheometers and measurement geometries(2020) Haist, Michael; Link, Julian; Nicia, David; Leinitz, Sarah; Baumert, Christian; Bronk, Tabea von; Cotardo, Dario; Eslami Pirharati, Mahmoud; Fataei, Shirin; Garrecht, Harald; Gehlen, Christoph; Hauschildt, Inga; Ivanova, Irina; Jesinghausen, Steffen; Klein, Christopher; Krauss, Hans-W.; Lohaus, Ludger; Lowke, Dirk; Mazanec, Oliver; Pawelczyk, Sebastian; Pott, Ursula; Radebe, Nonkululeko W.; Riedmiller, Joachim Jürgen; Schmid, Hans-Joachim; Schmidt, Wolfram; Secrieru, Egor; Stephan, Dietmar; Thiedeitz, Mareike; Wilhelm, Manfred; Mechtcherine, ViktorThis paper presents the results of an interlaboratory study of the rheological properties of cement paste and ultrasound gel as reference substance. The goal was to quantify the comparability and reproducibility of measurements of the Bingham parameters yield stress and plastic viscosity when measured on one specific paste composition and one particular ultrasound gel in different laboratories using different rheometers and measurement geometries. The procedures for both in preparing the cement paste and carrying out the rheological measurements on cement paste and ultrasound gel were carefully defined for all of the study’s participants. Different conversion schemes for comparing the results obtained with the different measurement setups are presented here and critically discussed. The procedure proposed in this paper ensured a reasonable comparability of the results with a coefficient of variation for the yield stress of 27% and for the plastic viscosity of 24%, despite the individual measurement series’ having been performed in different labs with different rheometers and measurement geometries.