Die Entwicklung neuer Materialien und neuer Werkstoffe wird heute international als Schlüsseltechnologie mit Querschnittscharakter und Schrittmacherfunktion für viele industrielle Bereiche eingestuft. Die Wirtschaftskraft der hoch entwickelten Industriegesellschaften hängt zunehmend von Erfolgen in der Materialwissenschaft und der Werkstofftechnologie ab. Die Forschungsaktivitäten in der Profillinie 1 sind gekennzeichnet durch Interdisziplinarität und Vernetzung von Forschungsvorhaben. Von besonderer Bedeutung ist darüber hinaus die zusätzliche Verzahnung mit der Profillinie 6 der TU Chemnitz “Modellierung, Simulation, Hochleistungsrechnen“, um die Material- und Werkstoffforschung durch den intelligenten Einsatz leistungsstarker Rechentechnik weniger kostenintensiv gestalten zu können.

This thesis reports recent numerical investigation of the rheological behavior of fresh concrete using the Distinct Element Method (DEM). Some relevant questions of the concrete rheology e.g. the influence of the concrete composition on the rheological behavior of the fresh concrete, the experimental determination of the Bingham rheological constants as well as the use of these constants in the numerical simulation were discussed thoroughly. An important topic of the performed investigation was the development of the numerical model for fresh concrete which enables simple, fast and stable predictive simulation of different technological operations with fresh concrete. Firstly, in a literature survey, the state-of-the-art of the numerical simulation of fresh concrete was presented and critically discussed in order to show advantages and disadvantages of other methods and modeling approaches. Open (unsolved) questions were highlighted and the basis for their investigation is created within this thesis. Fundamental concepts of the rheology were then presented and the basic rheological models of viscoelastic materials were considered; the rheological behaviors of different types of concretes were presented and its influencing factors were discussed. Additionally main methods for scientific investigation and testing of the fresh concrete were shown. The test methods were critically discussed in order to select the test, which has been used as a reference experimental test for the numerical simulations. Chosen reference experimental test was the slump flow test. The slump flow test was thoroughly analyzed and an analytical solution was developed which helps to interpret the results of measurements and provides a link between rheological constants and measured quantities. In a further step an extensive experimental program was carried out in order to investigate the rheological behavior of fresh concrete and get the input data for numerical simulation. Firstly, the experiments on macrolevel were performed. Here the rheological behavior of the fresh concrete flow in different tests was investigated (slump and slump flow tests, L-Box). Further, the experiments on mesolevel with polymer on Carbopol basis and mortar were developed and performed in order to investigate the interaction between distinct particles suspended in a fluid matrix. The necessary material parameters, especially those representative of the fluid suspension micromechanical behavior, i.e. the force-displacement relationship, yield force and bond strength, were determined by these experiments. The slump flow test was used as the basic test to calibrate the model for fresh concrete (key data: slump value, slump flow diameter (for concretes with a soft consistency) and the time of spreading). Thus, the decisive phenomena of the fresh concrete flow were highlighted, control points for a contact model were selected and the initial input data for the development of the contact model was obtained. Next, the user-defined contact model was developed and implemented into the Particle Flow Code ITASCA. The contact model was completely described and its limitations discussed. Then, the set of numerical tools was developed, which enable simplified and stable numerical simulation of the fresh concrete with particular behavior, i.e. automatic generation of the concrete with given particle grading, amount of fibers and air, automatic recalculation of the micromechanical parameters of the contact model from given initial yield stress and plastic viscosity. The model was calibrated by slump flow test simulations and validated by corresponding analytical approach. Further, the role of different model parameters was investigated by simulating the slump flow test. Furthermore, for verification of the model several additional experiments were simulated, i.e. L-Box and LCPC-box test. The results of modeling were compared with experimental results and discussed in detail. All numerical simulations provide qualitatively as well as quantitatively correct results and hence adequately represent the phenomena observed in real experiments. The thesis closes with general conclusions and outlook of the work. In the future, the developed contact model and tools of the “Virtual concrete laboratory” could be modified in order to extend the potential of the laboratory to cover such properties as thixotropic behavior of fresh concrete or simulating hardening of the concrete and behavior of the hardened concrete.

Um die wirtschaftliche Relevanz und die Flexibilität des Formdrückens zu erweitern, ist ein Maschinen- und Steuerungskonzept entwickelt worden, dass auch die Herstellung von nichtrotationssymmetrischen Bauteilen erlaubt. Neben experimentellen Untersuchungen zur Verfahrensentwicklung wurde ebenfalls eine numerische Verfahrensoptimierung des neu entwickelten Prozesses „Unrunddrücken“ durchgeführt, um unrunde Bauteile falten- und rissfrei sowie mit geringer Blechdickenreduktion herstellen zu können. In ersten experimentellen Untersuchungen wurden die technologischen Haupteinflussgrößen auf die Versagensformen Falten- und Rissbildung sowie die Blechausdünung ermittelt. Aufbauend auf diesen Ergebnissen ist ein kalibriertes Simulationsmodell erarbeitet worden, mit dem es möglich ist, das Prozessverständnis zu erhöhen und somit die Versagensfälle ganzheitlich über den Prozess zu betrachten. Die daraus gewonnenen Erkenntnisse wurden genutzt, um Optimierungsmaßnahmen für das Unrunddrücken abzuleiten. Es konnte experimentell nachgewiesen werden, dass sowohl die Falten- und Rissbildung als auch die Blechdickenreduktion durch die Optimierungsmaßnahmen deutlich reduziert werden können. Das in der vorliegenden Arbeit entwickelte Verfahren des Unrunddrückens stellt einen effizienten, kostengünstigen und vor allem flexiblen Fertigungsprozess für die Herstellung von nichtrotationssymmetrischen Bauteilen mit nahezu konstantem Blechdickenverlauf dar.

In dem aktuellen Beitrag wird eine kurze Einführung in die Mischung bzw. Entmischung hochviskoser inkompressibler Fluide gegeben. Hierzu wird die Methode der Phasenfeldmodellierung und ihre numerische Diskretisierung vorgestellt. Anhand eines konkreten Beispiels wird die technische Relevanz des vorgestellten Ansatzes demonstriert.

The present thesis focusses on two main issues: (i) the development of a multi-phase simulation tool for the characteristics of tight-gas reservoirs, and (ii) the investigation of advanced stimulation techniques. The latter mainly implies the analysis of certain damaging mechanisms, as well as the derivation of general modelling guidelines for fractured wells and underbalanced drilling. A special simulation tool is developed, realised in a Fortran-MATLAB coupling. The numerical model is based on the control-volume method with finite differences. It accounts for inertial non-Darcy effects, non-Newtonian fluid rheology and stress dependency of permeability via a simplified approach. The discretisation framework is fully unstructured, using the connection list approach and the common two-point flow stencil. Wells and boundary conditions can be handled very flexible in the code. Contrary to conventional treatment in simulators, wells are discretely included in the simulator. Inertial non-Darcy flow and stress dependency of reservoir permeability are shown to affect the accuracy of simulation models, despite low gas rates. Considering a realistic scenario, with non-Darcy flow and permeability (stress) dependent non-Darcy flow coefficients, stress dependency of reservoir permeability and fracture closure, a total reduction of 40 % is possible in a 10 year production period under realistic conditions. New type-curves are presented for non-Darcy flow in fracture and reservoir, allowing for the determination of non-Darcy flow related parameters. The stress sensitivity of tight-gas rocks is crucial when simulating such reservoirs. The stress dependency of the reservoir permeability impacts the productivity to a much higher degree than the fracture closure. A two-phase model is presented for the simulation of cleanup processes in terms of load water recovery. The fracturing fluid is treated as the water phase. The load water, causing hydraulic damage, hardly curtails productivity. To get considerable reductions in productivity, permeability in the fracture vicinity needs to be severely impaired. Due to the flow pattern, fractured wells are generally less sensitive against near wellbore damage than radial wells. An enhanced three-phase cleanup model is presented for the investigations of the polymer gel cleanup, incorporating a yield power law rheology (the Herschel-Bulkley model). The combined occurrence of loadwater recovery including capillary forces and the gel cleanup, are investigated for the first time. First results indicate that both processes are only weakly coupled. A new simulation methodology is presented to investigate underbalanced drilling, taking into account multi-phase reservoir flow with capillary forces. A sensitivity analysis points out that the degree of water encroachment is the key factor for a successful UBD operation. Countercurrent imbibition, causing water encroachment is also analysed. Hydraulic damage turns out to be far more pronounced in tight-gas formations.

Dieser Beitrag untersucht die Gültigkeit von 2,5D und 3D Simulationsmodellen des Füllvorgangs beim Spritzgießen. Zur numerischen Approximation dieser Ansätze wird für das 2,5D Verfahren die Software Cadmould 3D-F und für das 3D Verfahren Ansys CFX verwendet. Um das nicht newtonsche Viskositätsverhalten der Polymerschmelze abzubilden, wird in beiden Simulationen ein geeignetes Viskositätsmodell verwendet. Die Ergebnisse des numerischen Füllvorgangs werden anschließend mit experimentellen Daten validiert. / This article examines the validity of 2.5D and 3D simulation models of the filling process in injection molding. To numerically approximate these approaches, the software Cadmould 3D-F is used for the 2.5D method and Ansys CFX for the 3D method. To represent the non-Newtonian viscosity behavior of the polymer melt, a suitable viscosity model is used in both simulations. The results of the numerical filling process are then validated with experimental data.

Die additiven Fertigungstechnologien erleben seit einigen Jahren einen enormen Zuspruch bei der Herstellung von Einzelteilserien mit komplexen, endkonturnahen Geometrien und der Verarbeitung von Sonder- oder hybriden Werkstoffen. Prinzipiell lassen sich die Verfahren gemäß VDI- Richtlinie 3404 in drahtbasierte und pulverbasierte unterteilen. Eine weitere Unterteilung erfolgt hinsichtlich der Ausschmelztechnologie. Allen Verfahren ist gleich, dass schichtweise der Grundwerkstoff an den Stellen aufgetragen wird, wo er gemäß Endkontur benötigt wird. Damit ist ein immer wiederkehrender Wärmeeintrag verbunden, der somit Einfluss auf die Mikrostruktur der Bauteile und gleichzeitig auch auf die mechanischen Endeigenschaften ausübt. Die so erzeugten Komponenten sollten wenig Verzug oder Eigenspannungen als auch keine Porosität aufweisen, um die Gebrauchseigenschaften nicht negativ zu beeinflussen. Das Ziel ist es mittlerweile, diese verschiedenen Technologien numerisch abzubilden, um die Bauteileigenschaften vorherzusagen und ggf. Optimierungspotenziale zu eruieren. Der untersuchte Prozess ist das drahtbasierte Mehrlagenschweißen mittels des Metallschutzgasschweißens, bei dem neben der Simulation auch die Validierung im Fokus hinsichtlich Geometrie und Gefügeausbildung in den Schweißlagen stand. Diesbezüglich wurden im vorliegenden Fall zum einen alle, für die numerische Simulation notwendigen Materialparameter (mechanische und thermophysikalische Kenngrößen) des Schweißzusatzwerkstoffes G4Si1 bestimmt und in ein kommerzielles FEM-Programm (MSC Marc Mentat) implementiert. Zum anderen erfolgt zukünftig die wissenschaftliche Analyse der Verbesserung der Bauteileigenschaft, in dem die Schweißnaht unter Ausnutzung der Schweißhitze warmumgeformt wird. Erste Ergebnisse numerischer Simulationsergebnisse zeigen positive Effekte. Diese zeigen mikrostrukturelle Veränderungen (Kornfeinung durch Rekristallisation) und führten letztendlich zur Steigerung der mechanischen Eigenschaften. Der Vorteil dieser Verfahrenskombination ist außerdem die Kompensation des Verzuges durch die gezielte Umformung und einem gleichzeitigen „Richten“.

Melt flow plays an important role in directional solidification of multicrystalline silicon influencing the temperature field and the crystallization interface as well as the transport of impurities. This work investigates the potential of a traveling magnetic field (TMF) for an active control of the melt flow. A system of 3D numerical models was developed and adapted based on open-source software for calculations of Lorentz force, melt flow, and related phenomena. Isothermal and non-isothermal model experiments with a square GaInSn melt were used to validate the numerical models by direct velocity measurements. Several new 3D flow structures of turbulent TMF flows were observed for different melt heights. Further numerical parameter studies carried out for silicon melts showed that already a weak TMF-induced Lorentz force can stir impurities near to the complete mixing limit. Simultaneously, the deformed temperature field leads to an increase of the deflection of crystallization interface, which may exhibit a distinct asymmetry. The numerical results of this work were implemented in a research-scale silicon crystallization furnace. Scaling laws for various phenomena were derived allowing a limited transfer of the results to the industrial scale.

Gas-Partikel-Stroemungen finden sich in weiten Bereichen der Energie- und Verfahrenstechnik. Beispiele fuer haeu- fig anzutreffende Problemstellungen sind der Transport, die Separation oder die Injektion eines Gemisches aus festen Partikeln und einem Traegergas. Fuer die numerische Simulation solcher disperser Mehr- phasenstroemungen hat sich das Lagrange-Verfahren als besonders geeignet erwiesen. Andererseits stellt die An- wendung dieses Berechnungsverfahrens hoechste Anforderun- gen an die Ressourcen der verwendeten Rechner. Dies gilt im besonderen Masse fuer die Simulation von Stroemungen mit einer moderaten bis hohen Partikelbeladung, in denen die Partikel-Partikel-Kollisionen einen grossen Einfluss auf das Stroemungsverhalten haben. Um das grosse Leistungspotential, das heutige massiv par- allele Hochleistungsrechner bieten, effizient zu nutzen, wurden im Rahmen dieser Arbeit parallele Simulationsalgo- rithmen fuer die numerische Berechnung kollisionsbehafte- ter Gas-Partikel-Stroemungen entwickelt. Die Effizienz dieser Algorithmen wurde anhand verschiedener Testfaelle untersucht. Auf der Grundlage der dabei erzielten Ergeb- nisse wurden Vorschlaege fuer weitere Entwicklungsmoeg- lichkeiten erarbeitet. / Gas-particle-flows can be found widely in the field of energy production and process engineering. Examples for applications of such kind of flows are transport, se- paration or injection of a mixture of solid particles and a gaseous phase. The Lagrangian approach has proved to be a suitable means for the numerical simulation of disperse multiphase flows. On the other hand its application requires a large amount of computational power, especially when flows with a mo- derate or high particle loading are computed and particle- particle collisions have a significant influence on the flow. In order to use efficiently the large computational power that parallel computers provide nowadays, parallel algo- rithms for the numerical simulation of gas-particle flows including particle-particle collisions were developed in the cource of this work. The algorithms' efficiency was investigated considering different test cases. On the basis of the results suggestions for further developments were made.

Reactive transport modelling has wide applications in geosciences. In the field of hydrogeology, it has been utilised to simulate the biogeochemical processes that disperse and degrade contaminants in the aquifer. For geotechnical applications, such as geological CO2 sequestration, the reaction of CO2 with the ambient saline aquifer determines the final success of storage. In a radioactive waste repository, scientists rely on reactive transport models to predict the mobilisation of hazardous radionuclides within space and time. In this work, the multi-component mass transport code OpenGeoSys, was coupled with two geochemical solvers, the Gibbs Energy Minimization Selektor (GEM) and the Biogeochemical Reaction Network Simulator (BRNS). Both coupled codes were verified against analytical solutions and simulation results from other numerical models. Moreover, the coupling interface was developed for parallel simulation. Test runs showed that the speed-up of reaction part had a very good linearity with number of nodes in the mesh. However, for three dimensional problems with complex geochemical reactions, the model performance was dominated by solving transport equations of mobile chemical components. OpenGeoSys-BRNS was applied to a two dimensional groundwater remediation problem. Its calculated concentration profiles fitted very well with analytical solutions and numerical results from TBC. The model revealed that natural attenuation of groundwater contaminants is mainly controlled by the mixing of carbon source and electron donor. OpenGeoSys-GEM was employed to investigate the retardation mechanism of radionuclides in the near field of a nuclear waste repository. Radium profiles in an idealised bentonite column was modelled with varying clay/water ratios. When clay content is limited, Ba-Sr-Ra sulfate solid solutions have a very strong retardation effect on the aqueous radium. Nevertheless, when clay mineral is abundant, cation exchange sites also attract Sr and Ba, thus dominates the transport of Ra.