Transient water table influence upon Light Non-Aqueous Phase Liquids (LNAPLs) redistribution: laboratory and modelling studies

Fluctuating water table conditions influence capillary-held LNAPL(Light Non-Aqueous Phase Liquids) mass above and below the water table. Risks posed by such dynamic source zones vary over time as water tables oscillate from tidal effects, seasonality or anthropogenic interferences. In this study, the first automated multiphase flow dynamic water table experimental system comprising both hardware and software, was developed to: i) automatically implement programmable cyclic water table fluctuations via Raspberry Pi$^T$$^M$ based inexpensive electronics; ii) dynamically monitor the real-time saturation distributions of all fluids (red-dyed-LNAPL, blue-dyed-water and air) in 2-D sand tank, using high-temporal-and-spatial resolution automated multi-spectral photography; and iii) accurately interpret large detailed datasets via advanced multi-spectral imaging. Such automated data acquisition and processing permit LNAPL releases and their redistributions under oscillating water table to be demonstrated in videos of photographic records, interpreted 2-D saturation contours and 1-D profiles. Eight experimental scenarios were undertaken to discern the influencing mechanisms of cyclic fluctuations incorporating with other influential factors including aquifer media and heterogeneities, volume and timing of releases, etc. Applicability of standard modelling by NAPL simulator was exercised, which provided a good general match of overall features of the release and oscillation dynamics. The high-resolution-and-frequency detailed quantitative dataset harvested was expected to supplement and expand the theories of multiphase flow distribution in porous media, where owing to the realization of the automated system, unprecedented processes were captured; and serve as a robust validation source of numerical and conceptual models which are essential tools in contamination site characterization, prediction, and remediation

Research and Education in Computational Science and Engineering

This report presents challenges, opportunities, and directions for computational science and engineering (CSE) research and education for the next decade. Over the past two decades the field of CSE has penetrated both basic and applied research in academia, industry, and laboratories to advance discovery, optimize systems, support decision-makers, and educate the scientific and engineering workforce. Informed by centuries of theory and experiment, CSE performs computational experiments to answer questions that neither theory nor experiment alone is equipped to answer. CSE provides scientists and engineers with algorithmic inventions and software systems that transcend disciplines and scales. CSE brings the power of parallelism to bear on troves of data. Mathematics-based advanced computing has become a prevalent means of discovery and innovation in essentially all areas of science, engineering, technology, and society, and the CSE community is at the core of this transformation. However, a combination of disruptive developments---including the architectural complexity of extreme-scale computing, the data revolution and increased attention to data-driven discovery, and the specialization required to follow the applications to new frontiers---is redefining the scope and reach of the CSE endeavor. With these many current and expanding opportunities for the CSE field, there is a growing demand for CSE graduates and a need to expand CSE educational offerings. This need includes CSE programs at both the undergraduate and graduate levels, as well as continuing education and professional development programs, exploiting the synergy between computational science and data science. Yet, as institutions consider new and evolving educational programs, it is essential to consider the broader research challenges and opportunities that provide the context for CSE education and workforce development

Experimental Investigations on Multiphase Phenomena in Porous Media

Modeling of waterflow and solute transport in porous media is typically based on the water dynamics only, while the gaseous phase is neglected. Since the two fluids share the same pore space a particular investigation of the gaseous phase is mandatory to understand its influence on the basic processes (continuity, hysteresis, entrapment,. . . ) especially near water saturation. For the multiphase measurements an existing multistep outflow setup for determination of hydraulic properties with laboratory sized columns, was improved by an additional air-flow measurement device where gas phase continuity and conductivity could be measured simultaneously. Measured hydraulic data was analyzed by inverse modeling on which the pneumatic data analysis was based. Several gas conductivity models were tested. The possibilities of a combined measurement of hydraulic and pneumatic properties were demonstrated with artificial porous media made of sintered glass. The comparison of measurement and simulations of air conductivity showed the necessity of a rescaling of the effective air saturation for predictions. The influence of the sample structure on the hydraulic and pneumatic properties was illustrated with several homogenous and heterogeneous samples of repacked sands. The differences between purely hydraulic and combined measurement could be shown with experiments carried out with two pathologic structures. For this samples the basic structure elements could be detected by the combination of hydraulic and pneumatic measurements

Microstructural and mechanical property modelling for the processing of Al-Si alloys

The components of a modem internal combustion engine are required to give extreme reliability over extended periods of operation and none is exposed to more arduous conditions than the piston, especially in the pin boss and crown regions of pistons for diesel engines. The increasing emissions requirements and performance targets demanded of direct injection diesel engines has resulted in steep increases in both specific powers and maximum cylinder pressures. This has in turn lead to greater temperatures and pressures being felt by the piston. The adaptation of the piston design to these increasingly demanding load and temperature conditions has required a continuous improvement and innovation in the field of materials and process technologies. The vast majority of the internal combustion engine pistons produced globally are made by a gravity die casting process using Al-Si based alloys. Although Al-Si alloys have been the subject of a great deal of research over the last 30 years, the majority of work has been based on fairly rudimentary characterisation of the microstructures as a function of alloy chemistry and cooling rate. Most of the attention has been paid to the silicon morphology and distribution rather than on a fundamental knowledge of the development of the complex microstructures and intermetallic phases that arise in commercial alloys. However, the properties of cast near-eutectica: luminium-silicon alloys are very strongly influenced by the microstructure, i.e. the primary aluminium, and the interdendritic microconstituents, such as secondary phases, intermetallics, inclusions and porosity. A fine and uniform grain size is often desired as it improves mechanical properties of castings such as tensile strength, ductility and fatigue resistance, and at the same time aids castability, improves porosity distributions and reduces hot tearing susceptibility. A thorough phase characterisation has been carried out using a number of techniques including optical and electron microscopy with electron backscatter diffraction (EBSD), and image analysis. Use was also made of thermodynamic modelling to predict the volume fraction and distribution of phases within the microstructure as a function of chemical composition and process parameters. From this analysis a detailed understanding of the phases occuffing in multicomponent Al-Si alloys was established. Furthermore, additions associated with grain refining, i.e. Ti, Zr and V, have been investigated systematically using commercial and model alloy systems. All three additions were observed to refine the structure of the castings through the formation of the phase A13Ti, although combined additions with Zr were found to be less efficient due to a 'poisoning' effect on the A13Ti. It was also established that there is a strong competition between the effects of grain refiners and P, with the formation of AbTi reducing the nucleating efficiency of AIP to silicon. The nucleation and growth of the primary silicon phase were thus examined by EBSD. AIP was confirmed as nucleating the silicon epitaxially, after which growth continues by surface nucleation, although the presence of twins were seen to influence the shape of the crystal. Finally, suggestions have been made as a consequence of this work for the future development of piston alloys

ALERT Doctoral School 2012: advanced experimental techniques in geomechanics

The twenty-second session of the European Graduate School 2012 (called usually ALERT Doctoral School) entitled Advanced experimental techniques in geomechanics is organized by Cino Viggiani, Steve Hall and Enrique Romero.Postprint (published version

Experimental and Numerical Studies of Burden Layers at Blast Furnace Charging

The blast furnace (BF) is the main production unit in the processing of iron ore to molten iron (“hot metal”) in the steelmaking industry. It is a large process with huge throughput and energy consumption, so even a slight improvement of its efficiency can lead to considerable reductions in costs and harmful emissions. The charging system is the only way by which the initial distribution of the raw materials can be controlled. This distribution not only determines the structure of the arising burden bed, but also the chemical and thermal efficiency of the gas. These are crucial factors for achieving a low rate of reductants, a long life length and a more sustainable operation of the furnace. Focusing on the behavior of particles forming heaps and layers in granular systems, this thesis has studied some questions related to burden-layer formation, burden bed properties, burden descent and gas flow distribution in the blast furnace throat and shaft. Firstly, the effects of particle shape and physical parameters on the porosity and angle of repose of iron ore particle heaps were simulated by discrete element method (DEM). Models of non-spherical particles (cylinders and cones) were established using the sphere-cluster method. For comparison and model validation, small-scale experiments were undertaken with particles of the same shapes prepared in the laboratory. The consistency of the simulated and experimental results demonstrate that the established DEM model can be used for the prediction of the porosity of a particle system. Some key physical parameters of the main burden materials (pellets, sinter and coke) were measured and validated by experiments. The experimentally determined parameters were the Young’s modulus, Shear modulus, Poisson’s ratio, particle density, coefficient of restitution, as well as coefficients of static and rolling friction. The experimental and calculated results were found to exhibit good agreement, which confirmed that the measured DEM parameters were of sufficient accuracy to be used in simulation of the burden distribution and descent in the blast furnace. DEM models describing the porosity distribution and radial ore-to-coke mass ratio of the burden layers in the blast furnace shaft were successfully established based on a bell-less burden charging system with 2D slot and 3D sector throat models. An experimental bell-less charging system with a scale of 1:10 compared to an industrial BF was designed and operated in a set of experiments. DEM simulations of the corresponding system showed results in general agreement with the empirical findings, validating the numerical models. Two kinds of non-uniform descent of burden in the upper part of the blast furnace were considered in a numerical DEM-based model, where the descent rate in the furnace center is greater than the descent rate at the wall or vice versa. The results showed that the ore-to-coke ratio decreases where the burden descent rate is low and increases where the descent rate is high. Finally, the effect of intermittent charging on the thermal and flow conditions in the upper shaft was analyzed by Computational Fluid Dynamics (CFD) combined with DEM. A model of the counter-current flow of gas and solids and the temperature of the two phases in a simplified setup was developed. The results clarified how the temperature and velocity of the ascending gas are affected by the intermittent charging.Masugnen är den huvudsakliga processenheten vid produktion av råjärn för stålframställning. Den är en industriell reaktor med mycket stor genomströmning av material. Ugnen har en hög energiförbrukning, vilket innebär att redan små relativa förbättringar i driften kan har stora implikationer för material- och energiåtgång samt för de utsläpp som förorsakas av processen. Masugnens chargering, d.v.s. inmatningen av det fasta råmaterialet vid toppen, är av stor betydelse för styrningen av råmaterialets radiella fördelning i ugnens övre del. Chargeringen bestämmer beskickningens struktur imasugnsschaktet, vilket påverkar ugnens termiska och kemiska verkningsgrad. Dessa faktorer är centrala för att uppnå driftpunkter med låg förbrukning av reduktionsmedel, lång ugnskampanj samt en hållbar järnframställning. Föreliggande avhandling studerar beteendet hos partiklar som bildar högar och lager i granulära system. Avhandlingen behandlar frågor av speciell relevans för bäddens egenskaper i masugnsschaktet, där lager av olika beskickningsmaterial bildas vid chargeringen och efter det långsamt sjunker nedåt i ugnen. För att beskriva hur gasen fördelas i schaktet måste även porositeten hos materialbädden vara känd. I den första delen av arbetet studerades inverkan av partikelform och fysikaliska parametrar på porositeten och rasvinkeln för högar av järnbärare. Systemet simulerades med diskreta element-metoden (DEM), där partiklar med annan form är sfärisk skapades genom att klumpa ihop överlappande sfärer (eng. sphere-cluster). För jämförelse och för validering av den matematiska modellen utfördes småskaliga laboratorie-experiment med partiklar av samma typ. Överensstämmelsen mellan de simulerade och experimentella resultaten visade att DEM-modellen kan användas för att prediktera porositeten hos partikelsystemet. Några viktiga fysikaliska parametrar hos de huvudsakliga beskickningsmaterialen (pelletar, sinter och koks) uppmättes och validerades med hjälp av experiment. De parametrar som bestämdes experimentellt var elasticitetsmodulen, skjuvmodulen Poissons konstant, partikeldensitet, restitutionskoefficienter, samt statiska och rullnings-friktionskoefficienter. De experimentella och simulerade resultaten befanns överensstämma väl, vilket bekräftade att DEM-parametrarna som bestämts var tillräckligt noggranna för att kunna utnyttjas vid simulering av beskickningsfördelning och -sjunkning i masugnen. DEM-modeller som beskriver bäddporositetens och den radiella malm-koksfördelningen hos beskickningen i masugnsschaktet skapades för ett system med s.k. Paul Wurth-chargeringsmål med två- eller tredimensionella modeller för masugnens gikt. Ett experimentellt klocklöst (eng. bell-less) uppsättningsmål i laboratorieskala i 1:10-skala jämfört med en industriell ugn byggdes och utnyttjades i experiment. DEM-simuleringar av motsvarande system gav resultat som generellt överensstämde med de experimentella resultaten, vilketvaliderade de matematiska modellerna. Två typer av ojämn sjunkning av beskickningen i schaktet studerades även numeriskt med hjälp av en DEM-modell, där bädden simulerades sjunka snabbare eller långsammare i masugnens centrala del. Resultaten visade att malm/koks-förhållandet avtar i regioner där bädden sjunker långsamt, medan kvoten ökar i regioner där sjunkhastigheten är hög. I arbetets sista del studerades hur en satsvis chargering påverkar det termiska och flödesmässiga dynamiska tillståndet hos den översta delen av masugnsschaktet med hjälp av flödessimulering (eng. Computational Fluid Dynamics, CFD) kombinerad med DEM, s.k. CFD-DEM-teknik. En förenklad och nerskalad modell utvecklades, som beskriver motströmsflödet av gas och beskickningsmaterial och temperaturerna hos de två faserna. Modellen klargjorde hur temperaturerna och gashastigheten påverkades av den oregelbundna chargeringen, vilket förklarar fenomen som man kan observera vid ugnstoppen i den verkliga driften av masugn

Microstructural stability of a nickel-based alloy overlay on a 2.25Cr1Mo steel substrate

Ni-based superalloy weld overlays are widely used in electricity generating plants to significantly reduce high temperature corrosion problems of ferritic steel components under service conditions. Welding a nickel alloy similar to IN625 onto the outer bore of a 2.25Cr1Mo steel tube enhances its service life as a superheater tube in the highly corrosive environment of a Waste-to-Energy boiler. For the purposes of studying the effects of high temperature service on the microstructure of this laid tube with a weld overly, a series of thermal exposure tests at 650˚C was performed for different times from 1 day up to 128 days. The microstructural evolution was studied using a combination of analytical techniques along with changes in hardness profile across the interface. Changes in the microstructure were examined using OM, SEM, EPMA, EBSD and FIB-STEM. Hardness survey results indicate significant changes in the interfacial region during ageing. Formation of a soft zone ~300 μm wide and its subsequent re-hardening was observed in the steel side while the hardness of the bulk steel remained unchanged. Development of a hard band ~30 μm wide adjacent to the interface in the weld overlay region and hardening of the bulk overlay material occurs in the early stages of ageing and remained unchanged with ageing time. Thermodynamic calculations were performed using Thermo-Calc software and TCFE6 and TTNI7 databases to aid interpretation of experimental data. Microstructural evolution in the steel region is related to the carbide transformation process and carbon migration. In the bulk of the steel tube, the bimodal microstructure is stable and in the tempered martensite/bainite areas, the initial M3C transform to M23C6 through a series of metastable carbides while in the ferrite grains, M2C carbide precipitates and transforms directly to the equilibrium carbide. The main process for supply of carbon atoms is transformation of carbides and the rates of transformation are related to the as-welded microstructure. On the steel side of interfacial region where bainite was formed after welding, the stability of metastable carbides is related to the carbon content. Long term ageing causes Mo replenishment in the coexisting ferrite and fine grains have formed in this region following long term ageing. Experimental observations confirmed that a network of alloyed M23C6 carbide precipitates was formed at the interface in the steel side which are believed to interrupt the carbon migration across the interface. Moreover, there is a carbide precipitation region within ~100 μm from the interface in the weld overlay. Beyond this region intermetallic phases like Mo-rich μ and Nb-rich δ were formed in the interdendritic regions and along the grain boundaries. Hard band formation is related to precipitation of the σ phase