<p dir="ltr">The continuous advancements in material science and manufacturing engineering have revolutionized the material design and fabrication techniques therefore drastically accelerating the development of complex structured materials. These novel materials, such as micro/nano-structures, composites, porous media, and metamaterials, have found important applications in the most diverse fields including, but not limited to, micro/nano-electromechanical devices, aerospace structures, and even biological implants. Experimental and theoretical investigations have uncovered that as a result of structural and architectural complexity, many of the above-mentioned material classes exhibit non-negligible nonlocal effects (where the response of a point within the solid is affected by a collection of other distant points), that are distributed across dissimilar material scales.</p><p dir="ltr">The recognition that nonlocality can arise within various physical systems leads to a challenging scenario in solid mechanics, where the occurrence and interaction of nonlocal elastic effects need to be taken into account. Despite the rapidly growing popularity of nonlocal elasticity, existing modeling approaches primarily been concerned with the most simplified form of nonlocality (such as low-dimensional, isotropic, and homogeneous nonlocal problems), which are often inadequate to identify the nonlocal phenomena characterizing real-world problems. Further limitations of existing approaches also include the inability to achieve a mathematically well-posed theoretical and physically consistent framework for nonlocal elasticity, as well as the absence of numerical approaches to achieving efficient and accurate nonlocal simulations. </p><p dir="ltr">The above discussion identifies the significance of developing theoretical and numerical methodologies capable of capturing the effect of nonlocal elastic behavior. In order to address these technical limitations, this dissertation develops an advanced continuum mechanics-based approach to nonlocal elasticity by using fractional calculus - the calculus of integrals and derivatives of arbitrary real or even complex order. Owing to the differ-integral definition, fractional operators automatically possess unusual characteristics such as memory effects, nonlocality, and multiscale capabilities, that make fractional operators mathematically advantageous and also physically interpretable to develop advanced nonlocal elasticity theories. In an effort to leverage the unique nonlocal features and the mathematical properties of fractional operators, this dissertation develops a generalized theoretical framework for fractional-order nonlocal elasticity by implementing force-flux-based fractional-order nonlocal constitutive relations. In contrast to the class of existing nonlocal approaches, the proposed fractional-order approach exhibits significant modeling advantages in both mathematical and physical perspectives: on the one hand, the mathematical framework only involves nonlocal formulations in stress-strain constitutive relationships, hence allowing extensions (by incorporating advanced fractional operator definitions) to model more complex physical processes, such as, for example, anisotropic and heterogeneous nonlocal effects. On the other hand, the nonlocal effects characterized by force-flux fractional-order formulations can be physically interpreted as long-range elastic spring forces. These advantages grant the fractional-order nonlocal elasticity theory the ability not only to capture complex nonlocal effects, but more remarkably, to bridge gaps between mathematical formulations and nonlocal physics in real-world problems.</p><p>An efficient nonlocal multimesh finite element method is then developed to solve partial integro-differential governing equations in the fractional-order nonlocal elasticity to further enable nonlocal simulations as well as practical applications. The most remarkable consequence of this numerical method is the mesh-decoupling technique. By separating the numerical discretization and approximation between the weak-form integral and nonlocal integral, this approach surpasses the limitations of existing nonlocal algorithms and achieves both accurate and efficient finite element solutions. Several applications are conducted to verify the effectiveness of the proposed fractional-order nonlocal theory and the associated multimesh finite element method in simulating nonlocal problems. By considering problems with increasing complexity ranging from one-dimensional to three-dimensional problems, from isotropic to anisotropic problems, and from homogeneous to heterogeneous nonlocality, these applications have demonstrated the effectiveness and robustness of the theory and numerical approach, and further highlighted their potential to effectively model a wider range of nonlocal problems encountered in real-world applications.</p>

<p dir="ltr">Modeling and simulation play a pivotal role in engineering and research, enabling cost effective solutions for design, manufacturing, and failure analysis, especially where physical testing is infeasible. This work explores numerical methods for multi-scale domains, where structures span diverse length scales, presenting unique challenges in meshing and accuracy. Advanced approaches such as domain decomposition and global-local methods are discussed, with an emphasis on their application in heterogeneous integration (HI) for advanced packaging. HI, which addresses the limitations of Moore’s Law, integrates diverse components into 2.5D and 3D architectures but introduces complex mechanical and thermo-mechanical challenges. This research addresses gaps in multi-scale numerical frameworks, proposing novel methods to handle non-linear physical evolution while maintaining compatibility with existing tools. A non-intrusive global-local inspired methodology that couples the local subdomain back to the global subdomain was implemented to increase the accuracy in non-linear multi-scale simulations involving evolution at local scale. The developed framework was then generalized to solve rate dependent and rate independent phenomenon. The work further extends into numerical methods for design of HI packages as well. Unlike detailed analysis, the design stage analysis prioritizes speed of computation with a first order accuracy of results. This is achieved using machine learning techniques for efficient design space exploration in HI. The study overall aims to advance computational frameworks tailored for accuracy in reliability analysis and speed in design stages, focusing on semiconductors and advanced packaging applications.</p>

<h4>This thesis explores the feasibility of <b>injecting waste plastic particles</b> and two compositions of <b>hot syngas</b>, produced from a gasification reactor utilizing waste plastics and natural gas, as alternative fuel sources in <b>ironmaking blast furnace</b><b>s.</b> Computational fluid dynamics <b>(CFD) analysis</b> is employed to assess the viability of these fuels. The study investigates impacts of these novel alternative injected fuels on flame temperature, quenching impact, hot metal temperature, coke replacement ratio, and furnace stability</h4><p></p>

<p dir="ltr">Shape memory alloys (SMAs) belong to the category of smart materials due to their unique shape memory properties induced by a thermomechanically-triggered phase transformation. This phase changing process is also associated with a pronounced energy dissipation capacity. In recent years, the shape-recovery and energy-dissipating capabilities of SMAs have been object of extensive studies with particular focus on the opportunities they offer for the design of smart composites. The restoring stress of constrained SMAs as well as the modulus change, following thermal loading, can be leveraged to improve the static and dynamic performance, such as the pre/post-bulking behavior, the aerodynamic stability, and the impact resistance of composite materials embedded with SMA wires or fibers. The nonlinear damping resulting from the nonlinear material behavior associated with the ferro-elastic and pseudo-elastic phases was explored in a few studies focusing on vibration suppression in composites. Nonetheless, existing research mainly focused on either SMA wire or fiber reinforced composites, while the understanding of the dynamics of hybrid composites integrating SMA layers still presents several unexplored areas. In part, this technological gap might be explained by the fact that the most common SMA alloy, the so-called Nitinol, is expensive and hence not amenable to be deployed in large scale applications. With the most recent advancements in low-cost SMAs (e.g. Fe-based and Cu-based alloys), new applications that make more extensive use of SMAs are becoming viable. It follows that the understanding of the dynamic response of composites integrating SMA laminae becomes an important topic in order to support the development of innovative hybrid composite structures.</p><p dir="ltr">This dissertation explores the design and the nonlinear dynamic response of hybrid composites integrating SMA laminae, with a particular emphasis on the damping performance under different operating conditions. The dynamic properties of SMA monolithic beams and hybrid composite beams integrated with SMA laminae are investigated via one-dimensional constitutive models. Monolithic SMA beams are investigated to understand the fundamental aspects of the damping capacity of the material as well as possible bifurcation phenomena occurring under different types of harmonic excitations and different levels of pre-strain. The study then focuses on hybrid composite beams, highlighting the effects of design parameters, such the thickness, position, and pre-strain level of SMA layers on the transient and forced dynamic characteristics.</p><p dir="ltr">To further explore the potential of embedding SMA laminae to tailor the damping capacity of the hybrid composite and optimize the distribution of SMA materials, hybrid composite plates (HCPs) assembled by stacking fiber composites and SMA layers (either monolithic or patterned) are explored. The damping capacity of the HCP is assessed under different operating conditions, with emphasis on the effect of pre-strain levels in the SMA layers. The optimization study focuses on understanding the distribution of SMA materials and the synergistic role of patterning and pre-straining individual SMA layers within the HCP. The damping capacity of the HCP is also estimated as a function of the SMA total transformed volume fraction in order to identify the types of patterns and the pre-strain profiles capable of improving the overall damping capacity of the HCP.</p><p dir="ltr">The investigation on the dynamics of SMA hybrid composites continues with the optimal design of sandwich composite beams with elastic face sheets and SMA cellular cores. A deep learning-based surrogate model is proposed to efficiently predict the nonlinear mechanical response of the SMA sandwich beams subject to transverse loading, hence enabling the optimization of the SMA cellular core. The multi-objective optimization of the energy-dissipating capacity and of the overall stiffness is then performed by taking advantage of evolutionary algorithms. Once the optimal geometric parameters of the SMA cellular cores are obtained, finite element simulations are conducted to numerically validate the optimal configurations of the sandwich beams.</p><p dir="ltr">Finally, the numerical models are validated via experimental measurements conducted on monolithic SMA beams. Tests include both tensile and vibration measurements in both the ferro-elastic and pseudo-elastic regimes. The stress-strain relations obtained from tensile tests are used to calibrate the constitutive model of SMAs. Subsequently, experimental vibration tests are performed on clamped-clamped SMA beams to assess the effect of pre-strain levels on the damping capacity of SMA beams via a dedicated experimental setup to apply and maintain the pre-strain levels. The theoretical, numerical, and experimental results provided in this dissertation can serve as important guidelines to design lightweight SMA smart composites with customizable dynamic behavior.</p>

Yes / Three-dimensional finite element models were executed and validated to investigate the performance of buried flexible high-density Polyethylene (HDPE) pipes, in unreinforced and multi-geogrid-reinforced sand beds, while varying pipe burial depth, number of geogrid-layers, and magnitude of applied cyclic loading. Geogrid-layers were simulated considering their geometrical thickness and apertures, where an elasto-plastic constitutive model represented its behaviour. Soil-geogrid load transfer mechanisms due to interlocked soil in-between the apertures of the geogrid-layer were modelled. In unreinforced and reinforced cases, pipe burial depth increase contributed to decreasing deformations of the footing and pipe, and the crown pressure until reaching an optimum value of pipe burial depth. On the contrary, the geogrid-layers strain increased with increasing pipe burial depth. A flexible slab was formed due to the inclusion of two-geogrid-layers, leading to an increase in the strain in the lower geogrid-layer, despite its lower deformation. Inclusion of more than two geogrid-layers formed a heavily reinforced system of higher stiffness, and consequently, strain distribution in the geogrid-layers varied, where the upper layer experienced the maximum strain. In heavily reinforced systems, increasing the amplitude of cyclic loading resulted in a strain redistribution process in the reinforced zone, where the second layer experienced the maximum strain.

<p dir="ltr">This study investigates airflow patterns and contaminant concentration in elevator-related areas, highlighting their critical role in indoor air quality and infection control. Despite widespread reliance on elevators, limited research addresses airflow patterns and contaminant behavior in these confined, high-density spaces. Using a full-scale elevator mockup connected to a lobby, this study conducted static and dynamic experiments to measure air velocity, temperature, and contaminant concentration. Static tests analyzed closed cabins with mixed ventilation, while dynamic tests examined the impact of passenger movement on airflow and contaminant dispersion.</p><p dir="ltr">Experimental data validated a Computational Fluid Dynamics (CFD) model, which revealed relatively uniform air conditions during elevator transit and notable wake effects associated with passenger movement. The CFD model simulated scenarios involving an index patient engaging in various respiratory activities, such as talking and coughing. Results showed that while the infection risk during short elevator rides is generally low, proximity to an infected individual during activities like talking increases transmission risk.</p><p dir="ltr">The findings underscore CFD’s value in studying both static and dynamic indoor airflow, though complexities in dynamic cases necessitate refined models and experimental methods. Additionally, the study enhances traditional displacement ventilation systems with induction panels and emphasizes the importance of integrated design for elevators and adjacent spaces to optimize ventilation performance and reduce infection risks during airborne crises, such as pandemics. This research advances understanding of indoor air quality in confined environments, providing insights for safer and more effective ventilation design.</p>

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The Zambezi River is the largest east-draining river in Africa. It captures runoff from 8 different countries before draining into the Indian Ocean in Mozambique through the Zambezi Delta which is recognised as a (Ramsar) Wetland of international importance. The Zambezi River flows are currently regulated by four large hydropower dams within its catchment. Much attention has been given in recent literature to the detrimental effects of the altered flow regime as a result of dams on the Zambezi River and the Delta in particular. Existing research relating to these negative effects includes many detailed ecological, hydrological and qualitative morphological studies but to date no detailed morphological modelling studies have been conducted in this regard. In this thesis a two-dimensional coupled hydrodynamic and morphological numerical model of the Zambezi Delta is created using topographical information obtained from a navigational study (Rio Tinto, 2011). The model hydrodynamics are calibrated using recorded water levels and flows at two gauging stations within the model domain. The bed load sediment transport is calibrated using field measurements (ASP, 2012b). The effects of dams on the Zambezi Delta are investigated by performing two 10 year simulations, one representing the current (post-dam) scenario and the other representing a pre-dam scenario. These simulation results show a significant decrease in flooded areas and sediment movement on the floodplains as a result of dams. Additional effects on channel widths and depth, on bed gradings, and on tidal water level variations are analysed. The model is then used to simulate a proposed environmental flood release scenario. Such releases have been recommended as a means to partially mitigate the negative impacts of dams on the Zambezi River. In this case an annual flood release supplying a peak flow of 8500 m3/s (slightly less than the pre-dam mean annual flood of 10 000 m3/s) was found to cause slightly more flooding of the close floodplains and to have small effects on the river channel width. The model predicts hydrodynamics and bed sediment transport of non-cohesive sediments with suitable accuracy but an issue with the suspended transport of cohesive sediments was identified. Recommendations are made for addressing the suspended sediment transport inaccuracy. The model, in its current form, can provide quantitative information regarding the hydrodynamics and course sediment transport of the general delta region on a coarse scale. With additional computational resources and accurate topographical information the model can be refined to give accurate predictions for localised areas within the delta. Such information would be valuable to specialist studies addressing the environmental effects of various proposed flooding scenarios or future dams. / AFRIKAANSE OPSOMMING: Die Zambezirivier is die grootste oos-dreineerende rivier in Afrika. Dit ontvang afloop van ag verskillende lande voor dit in die Indiese Oseaan in Mozambiek uitmond. Die Zambezidelta work erken as 'n RAMSAR vleiland van internasionale belang. Die vloei in die rivier word tans gereguleer deur vier groot hidro-elektriese damme binne sy opvangsgebied. Baie aandag is in die onlangse literatuur gegee aan die nadelige gevolge van die veranderde vloei as gevolg van damme op die Zambezi Rivier en spesifiek op die Delta. Bestaande navorsing met betrekking tot hierdie negatiewe effekte sluit in detail ekologiese, hidrologiese en kwalitatiewe morfologiese studies, maar tot op datum is geen gedetailleerde morfologiese modelleringstudies gedoen nie. In hierdie tesis is 'n twee-dimensionele gekoppelde hidrodinamiese en morfologiese numeriese model van die Zambezi Delta geskep met behulp van topografiese inligting wat verkry is uit 'n navigasiestudie (Rio Tinto, 2011). Die model hidrodinamika is gekalibreer deur teen watervlakke en vloei by twee meetstasies in die model domein. Die bedvrag sedimentvervoer is gekalibreer met behulp van veldmetings (ASP, 2012b). Die ȉnvloed van die damme op die Zambezi Delta is ondersoek deur twee 10-jarige simulasies, een wat die huidige ( na-dam ) scenario en die ander wat 'n voor-dam scenario ondersoek. Hierdie simulasie resultate toon 'n beduidende afname in die oorstroomde gebiede en sedimentbeweging op die vloedvlaktes as gevolg van damme. Bykomende effekte op kanaalbreedtes en -diepte, op die bedgraderings , en op getywatervlak variasies is ontleed. Die model is vervolgens gebruik om 'n voorgestelde omgewingings vloedloslaating te ondersoek. Sodanige loslaatings is aanbeveel om die negatiewe impak van damme op die rivier gedeeltelik te verminder. In hierdie geval gee 'n jaarlikse vloedloslaating met 'n piekvloei van 8500 m3/s (effens minder as die voor-dam gemiddelde jaarlikse vloed van 10 000 m3/s) effens meer oorstromings van die vloedvlaktes en het 'n klein uitwerking op die rivierkanaalbreedte. Die model voorspel die hidrodinamika en bedsedimentvervoer van nie-kohesiewe sedimente met betroubaarheid, maar 'n probleem met die vervoer van kohesiewe sedimente is geïdentifiseer. Aanbevelings word gemaak vir die aanspreek van die kohesiewe sedimentvervoer onakkuraatheid. Die model, in sy huidige vorm, kan kwantitatiewe inligting oor die hidrodinamika en natuurlik sedimentvervoer van die algemene delta streek by benadering verskaf. Met bykomende rekenaar hulpbronne en akkurate topografiese inligting kan die model verfyn word om akkurate voorspellings vir plaaslike gebiede binne die delta te gee. Sulke inligting kan waardevol wees vir spesialis-studies van die omgewingsimpakte van verskillende voorgestelde vloedloslaatings of toekomstige damme.

Aujourd’hui, la technologie du béton ayant fortement évolué, il est, sous certaines conditions, réaliste de construire des éléments structuraux en béton ayant à la compression une résistance de 90N/mm² voire nettement plus. En conséquence, l’ingénieur concepteur peut être amené dans le cadre du dimensionnement des colonnes à en diminuer les dimensions transversales pour des raisons esthétiques ou d’encombrement. Inévitablement, cette diminution de la section transversale induit une augmentation de l’élancement et augmente ainsi les risques des instabilités de flambement. A cette question de flambement, il faut adjoindre l’influence d’une préconception qui veut qu’une structure en béton à haute résistance soit moins ductile qu’une structure construite avec un béton normal ! De ceci résulte la question à la base de ce travail : « Peut-on arriver à diminuer la section transversale d’une colonne en utilisant des résistances de béton plus élevées tout en imposant la même valeur de capacité portante et en ne réduisant pas leur ductilité ? » Afin de répondre à cette question, le travail s’est articulé autour de deux axes essentiels qui sont d’une part une campagne d’essais (afin d’obtenir des résultats fiables) sur 12 colonnes en béton armé à haute résistance (90N/mm²) d’élancement 74 et 82 dont l’excentricité de la charge est une variable, et d’autre part l’implémen- tation de deux programmes informa- tiques utilisant le principe de l’analyse au second ordre en vue de réaliser une étude paramétrique dont l’excentricité, la hauteur des colonnes, la proportion d’acier, la résistance du béton sont les variables. Trop souvent encore, les ingénieurs de bureau d’études hésitent à effectuer un calcul au second ordre et placés devant la question des dimensions de section à donner à une colonne de hauteur et de capacité portante imposées, déterminent celles-ci pour se satisfaire d’un calcul au 1er ordre. Au terme de notre étude, nous avons montré que cette approche est loin d’être optimale, qu’il est possible, au prix d’un calcul au second ordre (mais il est fait à l’ordinateur), de tirer profit d’une augmentation de la résistance du béton pour réduire les dimensions des sections et aboutir en toute sécurité à un dimensionnement plus économique en consommation de matériaux (acier, béton, ciment).

This study addressed the numerical modelling of flow and diffusion in packed beds of mono-sized spheres. Comprehensive research was conducted in order to implement various numerical approaches in explicit1 and implicit2 simulations of flow through packed beds of uniform spheres. It was noted from literature that the characterization of a packed bed using porosity as the only geometrical parameter is inadequate (Van Antwerpen, 2009) and is still under much deliberation due to the lack of understanding of different flow phenomena through packed beds. Explicit simulations are not only able to give insight into this lack of understanding in fluid mechanics, but can also be used to develop different flow correlations that can be implemented in implicit type simulations. The investigation into the modelling approach using STAR-CCM+®, presented a sound modelling methodology, capable of producing accurate numerical results. A new contact treatment was developed in this study that is able to model all the aspects of the contact geometry without compromising the computational resources. This study also showed, for the first time, that the LES (large eddy simulation) turbulence model was the only model capable of accurately predicting the pressure drop for low Reynolds numbers in the transition regime. The adopted modelling approach was partly validated in an extensive mesh independency test that showed an excellent agreement between the simulation and the KTA (1981) and Eisfeld and Schnitzlein (2001) correlations' predicted pressure drop values, deviating by between 0.54% and 3.45% respectively. This study also showed that explicit simulations are able to accurately model enhanced diffusion due to turbulent mixing, through packed beds. In the tortuosity study it was found that the tortuosity calculations were independent of the Reynolds number, and that the newly developed tortuosity tests were in good agreement with techniques used by Kim en Chen (2006), deviating by between 2.65% and 0.64%. The results from the TMD (thermal mixing degree) tests showed that there appears to be no explicit link between the porosity and mixing abilities of the packed beds tested, but this could be attributed to relatively small bed sizes used and the positioning and size of the warm inlet. A multi-velocity test showed that the TMD criterion is also independent of the Reynolds number. It was concluded that the results from the TMD tests indicated that more elaborate packed beds were needed to derive applicable conclusions from these type of mixing tests. The explicit BETS (braiding effect test section) simulation results confirmed the seemingly irregular temperature trends that were observed in the experimental data, deviating by between 5.44% and 2.29%. From the detail computational fluid dynamics (CFD) results it was possible to attribute these irregularities to the positioning of the thermocouples in high temperature gradient areas. The validation results obtained in the effective thermal conductivity study were in good agreement with the results of Kgame (2011) when the same fitting techniques were used, deviating by 5.1%. The results also showed that this fitting technique is highly sensitive for values of the square of the Pearson product moment correlation coefficient (RSQ) parameter and that the exclusion of the symmetry planes improved the RSQ results. It was concluded that the introduction of the new combined coefficient (CC) parameter is more suited for this type of fitting technique than using only the RSQ parameter. / Thesis (M.Ing. (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2012

Flood inundation is a major natural hazard that can have very severe socio-economic consequences. This thesis presents an enhanced numerical model for flood simulation. After setting the context by examining recent large-scale flood events, a literature review is provided on shallow flow numerical models. A new version of the hyperbolic horizontal variable density shallow water equations with source terms in balanced form is used, designed for flows over complicated terrains, suitable for wetting and drying fronts and erodible bed problems. Bed morphodynamics are included in the model by solving a conservation of bed mass equation in conjunction with the variable density shallow water equations. The resulting numerical scheme is based on a Godunov-type finite volume HLLC approximate Riemann solver combined with MUSCL-Hancock time integration and a non-linear slope limiter and is shock-capturing. The model can simulate trans-critical, steep-fronted flows, connecting bodies of water at different elevations. The model is validated for constant density shallow flows using idealised benchmark tests, such as unidirectional and circular dam breaks, damped sloshing in a parabolic tank, dam break flow over a triangular obstacle, and dam break flow over three islands. The simulation results are in excellent agreement with available analytical solutions, alternative numerical predictions, and experimental data. The model is also validated for variable density shallow flows, and a parameter study is undertaken to examine the effects of different density ratios of two adjacent liquids and different hydraulic thrust ratios of species and liquid in mixed flows. The results confirm the ability of the model to simulate shallow water-sediment flows that are of horizontally variable density, while being intensely mixed in the vertical direction. Further validation is undertaken for certain erodible bed cases, including deposition and entrainment of dilute suspended sediment in a flat-bottomed tank with intense mixing, and the results compared against semi-analytical solutions derived by the author. To demonstrate the effectiveness of the model in simulating a complicated variable density shallow flow, the validated numerical model is used to simulate a partial dam-breach flow in an erodible channel. The calibrated model predictions are very similar to experimental data from tests carried out at Tsinghua University. It is believed that the present numerical solver could be useful at describing local horizontal density gradients in sediment laden and debris flows that characterise certain extreme flood events, where sediment deposition is important.