Abstract The reinforcement of concrete with steel fibres changes the failure of the composite material from catastrophic brittle failure to pseudo-ductile behaviour as a result of crack-bridging by the fibres, and the additional work which is absorbed by fibre pull-out. A good understanding of the properties of the fibre-reinforced concrete depends on an understanding of the fibre pull-out process. The main aim of the current study is to investigate, both experimentally and numerically, the pull-out behaviour of a single hooked end steel fibre from epoxy matrix, where epoxy was chosen to replace concrete in order to enable visualisation of the pull-out process. The experimental and numerical results both contribute to the development of a physical understanding of the mechanism of pull-out. Experimental studies included the evaluation of the mechanical properties of hooked end steel fibre and epoxy matrix by means of tensile tests, the manufacturing of pull-out specimens consisting of a single hooked end steel fibre embedded in epoxy matrix, and the experimental characterisation of the fibre pull-out. The significant features (peaks and minima) of the load vs. displacement graph were correlated to stills taken from a video of the pull-out process, in which the plastic deformation of the fibre is evident. Small deformations (spalling) were also observed in the matrix. A model is proposed for the mechanisms which interact during the pull-out process. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Mechanical and Aeronautical Engineering / unrestricted

Managed aquifer recharge (MAR) is widely applied for sustainable groundwater management. Despite its apparent simplicity, the evaluation of MAR schemes can be challenging especially with regard to feasibility assessment, planning but also operation. The absence of proper evaluation methods hinders the optimal operational management, reduces the level of public trust and raises questions about the impact of MAR on the affected ecosystem. The development of appropriate tools could help water utilities to maximize the use of groundwater while satisfying physical, financial, and sustainability constraints. As overall objective, the application of new and advanced tools can increase the understanding of the underlying processes and in that way increase the confidence in MAR and foster the successful implementation of MAR schemes. The thesis consists of three main parts which objectives are to: 1) understand the role of modelling in MAR and identify information gaps by a review of available modelling studies; 2) increase the availability of efficient database and analytical tools including their development and web-based implementation; and 3) improve and contribute to new advances in numerical modelling of MAR. A survey of conducted modelling studies, mainly based on numerical methods, revealed that groundwater flow models are most frequently applied to assess MAR schemes. Modelling objectives comprise the planning and optimization of the design and operation of a MAR facility as well as its impact on the groundwater system. Simulations help to assess the achievable recovery efficiency and occurring geochemical processes to minimize the risk of failure of a planned facility, also with regard to long-term impacts. Furthermore, site-selection and the influence of MAR on seawater intrusion are frequently analysed by modelling. The literature review served as a basis for the MAR model selection tool which enables, dependent on objectives, methods and model types, to extract suitable models and case studies. Based on analytical equations to determine groundwater mounding, saltwater intrusion or the pumping-induced river drawdown, further tools were developed and compiled on a web-based platform for easy access and utilization. The web-based applications can be used as screening tools to assess MAR-related issues. For a more detailed analysis, numerical models represent useful instruments to analyse MAR schemes on various scales. On regional scale, the feasibility of MAR implementation at proposed locations is often a challenging question due to the lack of detailed knowledge of the local groundwater system and its response to MAR. Consequently, an approach combining numerical groundwater flow modelling and GIS-based multi-criteria decision-analysis (MCDA) was formulated and subsequently tested for the city centre of Hanoi, Vietnam. The results indicate that MAR could help to reduce the local overexploitation of groundwater and stop land subsidence. For existing MAR schemes on local scale, the residence time in the subsurface is a critical parameter determining e.g. the removal of pathogens. As the influence of viscosity on the seasonal residence time is not fully clear, a numerical groundwater flow and heat transport model was set up for a MAR scheme in Berlin, Germany to evaluate the seasonal impact of viscosity. The results suggest that the consideration of viscosity in the numerical modelling scheme has an influence on the subsurface travel time and results in shorter residence times. At point scale, clogging represents a critical issue with regard to the long-term viability of a MAR scheme which is frequently neglected in numerical models. The numerical unsaturated flow model HYDRUS-1D/2D was enhanced to enable the simulation of time-variable hydraulic conductivities as an approximation of clogging. With the help of the time-variable scaling factor in combination with the reservoir boundary condition, the increasing water head in the laboratory aquifer well and infiltration basin due to clogging was reproduced. The presented tools and numerical modelling approaches are useful to assess a wide range of MAR-specific issues, to manage the risks associated with implementation and operation and improve the overall performance and reliability of MAR schemes. Through the application of suitable data-based, analytical and numerical tools, the thesis contributes to the perception of MAR as a suitable and reliable technique for water resource management.:1 INTRODUCTION 1 2 ASSESSMENT OF MANAGED AQUIFER RECHARGE THROUGH MODELLING 11 3 WEB-BASED EMPIRICAL AND ANALYTICAL TOOLS FOR INITIAL MAR-RELATED ASSESSMENT 29 4 MANAGED AQUIFER RECHARGE FEASIBILITY ASSESSMENT USING GIS-BASED SUITABILITY MAPPING AND NUMERICAL MODELLING 53 5 INFLUENCE OF VISCOSITY ON THE SEASONAL RESIDENCE TIME DURING MAR OPERATION 73 6 SIMULATION OF HYDRAULIC CONDUCTIVITY CHANGES OVER TIME DURING MAR OPERATION 91 7 SCIENTIFIC IMPLICATIONS AND RESEARCH PERSPECTIVES...113 Bibliography 117 A Appendix 143 / Grundwasseranreicherung (engl. Managed Aquifer Reharge, MAR) wird oftmals für ein nachhaltiges Grundwassermanagement eingesetzt. Trotz der scheinbaren Einfachheit von MAR, kann die Bewertung insbesondere in Bezug auf Machbarkeitsstudien, Planung, aber auch Betrieb herausfordernd sein. Das Fehlen geeigneter Bewertungsmethoden hindert ein optimales Betriebsmanagement, reduziert das Vertrauen der Öffentlichkeit und wirft Fragen über die Auswirkungen von MAR auf das betroffene Ökosystem auf. Die Entwicklung geeigneter Instrumente könnte daher Wasserversorgern helfen, die Nutzung des Grundwassers zu maximieren und gleichzeitig physische, finanzielle und nachhaltige Bedingungen einzuhalten. Als übergeordnetes Ziel kann die Anwendung neuer und fortschrittlicher Instrumente das Verständnis für die zugrunde liegenden Prozesse verbessern und so das Vertrauen in MAR stärken und die erfolgreiche Umsetzung von MAR-Anlagen fördern. Die Arbeit besteht aus drei Hauptteilen, deren Ziele es sind: 1) die Rolle der Modellierung von MAR zu verstehen und Informationslücken durch eine Überprüfung der verfügbaren Modellierungsstudien zu identifizieren; 2) die Verfügbarkeit effizienter datenbankbasierter und analytischer Instrumente einschließlich ihrer Entwicklung und webbasierten Implementierung zu erhöhen; und 3) mit Hilfe von neuen Fortschritten die numerische Modellierung von MAR-Anlagen zu verbessern und zu unterstützen. Eine Literaturrecherche bereits durchgeführter Modellierungsstudien, die vor allem auf numerischen Modellen beruhen, ergab, dass Grundwasserströmungsmodelle am häufigsten zur Beurteilung von MAR-Anlagen eingesetzt werden. Die Modellierungsziele umfassen die Planung und Optimierung des Aufbaus und des Betriebs einer MAR-Anlage sowie deren Auswirkungen auf das Grundwassersystem. Simulationen helfen, die erreichbare Rückgewinnungseffizienz und die auftretenden geochemischen Prozesse zu beurteilen, um das Ausfallrisiko einer geplanten Anlage auch im Hinblick auf langfristige Auswirkungen zu minimieren. Darüber hinaus wird die Standortauswahl und der Einfluss von MAR auf das Eindringen von Meerwasser häufig durch Modellierung analysiert. Die Literaturrecherche diente als Grundlage für das MAR-Modellauswahl-Tool, bei dem in Abhängigkeit von Zielen, Methoden und Modelltypen geeignete Modelle und Fallstudien extrahiert werden können. Weitere Werkzeuge, die auf analytischen Gleichungen zur Bestimmung von Grundwasseraufwölbung, Salzwasserintrusion oder der pumpinduzierten Durchflussreduzierung im Fließgewässer basieren, wurden entwickelt und auf der webbasierten INOWAS-Plattform für einen einfachen Zugang und Nutzung zusammengestellt. Die webbasierten Anwendungen können als Screening-Instrumente zur Beurteilung von MAR-bezogenen Problemen eingesetzt werden. Für eine detailliertere Analyse stellen numerische Modelle nützliche Instrumente zur Analyse von MAR-Anlagen auf verschiedenen Skalen dar. Auf regionaler Ebene ist die Machbarkeit der Umsetzung von MAR an den vorgeschlagenen Standorten oft eine schwierige Frage, da das lokale Grundwassersystem und seine Reaktion auf die Anwendung von MAR nicht hinreichend bekannt sind. Dazu wurde ein Ansatz entwickelt, der numerische Grundwasserströmungsmodellierung und GIS-basierte multikriterielle Entscheidungsanalyse (MCDA) kombiniert, um die Machbarkeit und mögliche Auswirkungen der MAR-Implementierung zu bewerten. Der kombinierte Ansatz wurde im Stadtzentrum von Hanoi, Vietnam, getestet, wo die Ergebnisse darauf hindeuten, dass MAR dazu beitragen könnte, die lokale Übernutzung zu reduzieren und die Bodensenkung zu stoppen. Auf lokaler Ebene bei bestehenden MAR-Systemen ist die Verweilzeit im Untergrund ein kritischer Parameter, der z.B. die Entfernung von Krankheitserregern bestimmt. Da der Einfluss von Viskosität auf die saisonale Verweildauer nicht eindeutig ist, wurde für eine MAR-Anlage in Berlin ein numerisches Grundwasserströmungs- und Wärmetransportmodell erstellt, um die saisonalen Auswirkungen des Prozesses zu bewerten. Die Ergebnisse deuten darauf hin, dass Viskosität einen Einfluss auf die unterirdische Verweilzeit hat und zu einer Verkürzung der Aufenthaltszeiten führt. Auf kleiner Skala stellt die Kolmatierung ein wichtiges Thema dar, das den Erfolg eines MAR-Systems erheblich bestimmt, jedoch in numerischen Modellen häufig vernachlässigt wird. Das numerische ungesättigte Strömungsmodell HYDRUS-1D/2D wurde erweitert, um die Simulation von zeitlich variablen hydraulischen Leitfähigkeiten als vereinfachte Näherung von Kolmatierung zu ermöglichen. Mit Hilfe des zeitlich variablen Skalierungsfaktors in Kombination mit der Speicherrandbedingung konnte der im Labor gemessene, durch Kolmatierung verursachte, ansteigende Wasserspiegel im Brunnen und Infiltrationsbecken reproduziert werden. Die vorgestellten Werkzeuge und numerischen Modellierungsansätze sind nützlich, um eine breite Palette von MAR-spezifischen Fragen zu bewerten, um die mit der Implementierung und dem Betrieb verbundenen Risiken zu managen und die Gesamtleistung und Zuverlässigkeit von MAR-Anlagen zu verbessern. Durch den Einsatz geeigneter empirischer, analytischer und numerischer Werkzeuge trägt die Arbeit dazu bei, dass MAR als eine geeignete und zuverlässige Technik für das Wasserressourcenmanagement angesehen wird.:1 INTRODUCTION 1 2 ASSESSMENT OF MANAGED AQUIFER RECHARGE THROUGH MODELLING 11 3 WEB-BASED EMPIRICAL AND ANALYTICAL TOOLS FOR INITIAL MAR-RELATED ASSESSMENT 29 4 MANAGED AQUIFER RECHARGE FEASIBILITY ASSESSMENT USING GIS-BASED SUITABILITY MAPPING AND NUMERICAL MODELLING 53 5 INFLUENCE OF VISCOSITY ON THE SEASONAL RESIDENCE TIME DURING MAR OPERATION 73 6 SIMULATION OF HYDRAULIC CONDUCTIVITY CHANGES OVER TIME DURING MAR OPERATION 91 7 SCIENTIFIC IMPLICATIONS AND RESEARCH PERSPECTIVES...113 Bibliography 117 A Appendix 143

<div>Polymer bonded explosives (PBXs) consist of energetic material (EM) crystals embedded inside a polymeric binder. These are highly heterogeneous structures designed to explode under controlled conditions. However, accidental ignition of PBXs leading to deflagration, or even detonation, may take place due to non-shock stimulus such as low velocity impacts and vibration. Thus, assessing the safety of PBXs under non-shock stimulus is very important.</div><div><br></div><div>The ignition in PBXs depends on several microstructural features which include mechanical properties of EM particles and polymeric binder, as well as the adhesive properties of interface between EM particles and binder. It is also sensitive to initial defects in EM particles including cracks or voids. EM particle size distribution, distance between particles and their relative location are also shown to be affecting the ignition behavior of PBXs. This study focuses on PBX composition consisting of HMX as EM and Sylgard or HTPB as polymeric binder. Among several mechanisms of hot-spot formation, this study focuses on frictional heating at cracks or debonded surfaces.</div><div><br></div><div>Finite element simulations are performed on a domain containing a single EM particle embedded inside polymer binder under compressive and tensile loading at 10 m/s. The effect of the binder properties and the particle surface properties, on damage evolution and corresponding temperature rise due to frictional heat generation, is investigated. Two binders, Sylgard and HTPB, while two surface qualities for HMX particle, low and high, are compared. The adhesion strength of the particle-polymer interface is varied and damage evolution is qualitatively compared with experimental results to estimate interfacial energy release rate for HMX-Sylgard and HMX-HTPB interfaces. Simulations of two HMX particles inside Sylgard binder, subjected to vibration loading, are performed to analyze the effect of particle-particle distance and relative location of particles on the damage evolution and frictional heating in the particles.</div><div><br></div><div>The results of impact simulations show that the low surface quality HMX particle inside HTPB is likely to propagate cracks as compared to high surface quality particle. The HMX particle inside Sylgard shows crack propagation irrespective of particle surface quality. The impact simulations with the lower stiffness binder do not show a significant increase in temperature after impact. A polymer with higher stiffness induces more particle damage under impact contributing to a larger temperature rise. Furthermore, high quality surface and higher adhesion strength induces larger stresses and increase the temperature rise. The vibration simulations show that a small particle is less likely to damage when it is shielded by a large particle irrespective of its distance, within 40-200$\mu$m, from the large particle. However, the small particle is likely to damage when it is in parallel to the large particle with respect to loading. The temperature rise in the small particle is higher than the larger particle only in case of parallel configuration. The adhesion between the particles and the polymer has a direct effect on the formation of hot-spots due to friction and through local increase of compressive stresses that may cause a surge in heat generation.</div><div><br></div><div>The energetic materials often show anisotropy in elastic and crystalline properties. Fracture in HMX along the preferred cleavage plane is considered. Anisotropy in the elastic constants is also incorporated in the fracture model. The dependence of pressure on temperature is considered using Mie-Gruneisen equation of state which is shown to be important for damage evolution in HMX at impact velocity of 100 m/s.</div>

Up-to-date methods of numerical modelling of random fields were applied to investigate some features of solute transport in saturated porous media with stochastic hydraulic conductivity. The paper describes numerical experiments which were performed and presents the first results.

>Magister Scientiae - MSc / Several attempts have been made to assess the impact of post-fire soil erosion; however, erosion occurs as a result of the complex interplay between many factors, such as climate, land cover, soil and topography, making precise estimation difficult. Additionally, these factors are far from constant in space and time, and often interact with one another. To assess the impact of wildfire on soil erosion and factors influencing its variability, the post-fire soil erosion response of two mountainous headwater sub-catchments namely Langrivier and Tierkloof, with different vegetation cover in the Jonkershoek Valley was examined using a systematic approach that combines efforts in field and laboratory work, spatial analysis and process-based numerical modelling. Geospatial modelling shows high spatial variability in erosion risk, with 56 % to 67 % of surfaces being highly susceptible excluding rock cover. The model highlights the importance of terrain and vegetation indices, with predicted erosion being more severe on steep slopes with lower vegetation cover. / 2021-08-30

There are still uncertainties in the safety of existing embankment dams. For instance, the majority of embankment dams in Sweden were built between 1950s and 1970s, designed and constructed to standards that might be unacceptable nowadays. Particularly, Vattenfall’s records stated that 40% owned embankments dams developed sinkholes (Nilsson, 1999). Moreover, internal erosion and its failure mechanisms of initiation and development are still not fully understood (Bowles et al., 2013). Also, internal threats are difficult to detect and interpret even using new instrumentation techniques. The aim of this Master Thesis is to identify failure mechanisms of embankment dams prior to breaching and hence, verify the reliability of a risk analysis after the breaching of the dam. The methodology consisted of monitoring an embankment dam prone to fail by internal erosion mechanisms. Finally the results were modelled using FEM to identify the risk of internal erosion prior to breaching.

No description available.

The aim of the thesis is hydraulic computation of shallow water flow in floodplains with using 2D numerical modelling. Processing river is Dyje in the south of Moravia in location Břeclav. For model creation is necessary to know the software, accumulate input data and prepare model input parameters. Output data are process to form of maps water depths and maps water flow velocities.

<p>Continuous casting is a vital process in the production of semi-finished steel, converting molten metal into solid form. Primary cooling, a critical stage of this process, uses water to cool the solidifying shell as it descends through the mold. The quality of the final cast product is significantly influenced by the fluid flow characteristics during this phase. Given the inherent complexities and costs associated with experimental studies in this area, numerical modeling has emerged as a crucial tool for understanding, predicting, and optimizing fluid flow dynamics within the mold. This research focuses on the implications of argon injection within the mold during the primary cooling stage of the continuous casting process.</p><p>In this thesis, a comprehensive computational investigation of the transportation, entrapment, and fluid dynamic effects of argon injection is presented. Through an exploration of bubble sizes, SEN submergence depths, and slide gate openings, the study reveals how these parameters can significantly influence the casting process.</p><p>The research finds that argon bubble size plays a critical role in determining bubble trajectories and residence times, with smaller bubbles showing a longer residence time and increased boundary interaction due to the dominance of drag forces. The submergence depth of the submerged entry nozzle (SEN) also influences these factors, with deeper submergence resulting in longer bubble trajectories and greater residence times. The study highlights how bubble diameter impacts their entrapment probability, with bubbles ranging from 0.3mm to 0.6mm being most prone to entrapment.</p><p>The effects of argon injection on fluid flow within the SEN demonstrate an enhancement of turbulence, thus promoting a uniform outflow. However, excessively high argon flow rates risk a critical reduction in meniscus velocity, which could lead to overcooling. The research further elucidates the influence of argon on X-velocity near the mold's narrow faces, indicating a potential method for controlling dendritic growth and enhancing the final product quality.</p><p>This work underlines the complex and multifaceted impacts of argon injection on the continuous casting process. It suggests that through careful manipulation of argon bubble size, SEN submergence depth, and slide gate opening, it is possible to optimize the transportation and entrapment of argon bubbles, manage fluid flow dynamics, and ultimately, improve the quality of the cast product.</p>

<p>  </p> <p>In this study, we aimed to explore the potential of integrating wind turbines into tall buildings to harness wind energy in urban areas. Advanced computer simulations will be used to analyze the complex wind patterns and turbulence around tall buildings. We will also study the optimization of wind turbine placement to maximize energy production. We focus on two types of wind turbines, the savonius and a modified savonius, using the Myring formula. We evaluated their performance in turbulent urban areas using computational fluid dynamics simulations. The simulations will also help us understand the wind flow behavior around tall buildings, informing wind turbine placement optimization.</p> <p>Our findings contribute to the understanding of urban wind energy production. This may lead to further advancements in wind turbine design and application in urban environments, promoting sustainable and clean energy production in densely populated areas.</p> <p>We also evaluate the economic feasibility of wind power as an energy source and its potential for commercial applications. Our study's insights are significant for wind energy research, urban planning, and sustainable energy production in cities.</p> <p>To achieve our objectives, we will use state-of-the-art computational tools such as the ANSYS Fluent Student software and the Steady Reynolds Averaged Navier-Stokes (SRANS) K-ε model and K-ω SST models for simulating wind flow around tall buildings.</p> <p>In summary, the goal of this research is to develop a methodology for integrating wind turbines into tall urban buildings to harness wind energy potential. This will contribute to the understanding of urban wind energy production and its economic feasibility for commercial applications.</p>