Over the past century, great strides have been made in the advancement of mine fire knowledge since the 1909 Cherry Mine Fire Disaster, one of the worst in U.S. history. However, fire hazards remain omnipresent in underground coal mines in the U.S. and around the world. A precise fire numerical analysis (simulation) before any fire events can give a broad view of the emergency scenarios, leading to improved emergency response, and better health and safety outcomes. However, the simulation cost of precise large complex dynamical systems such as fire in underground mines makes practical and even theoretical application challenging. This work details a novel methodology to reduce fire and airflow simulation costs in order to make simulation of complex systems around fire and mine ventilation systems viable. This study will examine the development of a Reduced Order Model (ROM) to predict the flow field of an underground mine geometry using proper orthogonal decomposition (POD) to reduce the airflow simulation cost in a nonlinear model. ROM proves to be an effective tool for approximating several possible solutions near a known solution, resulting in significant time savings over calculating full solutions and suitable for ensemble calculations. In addition, a novel iterative methodology was developed based on the physics of the fluid structure, turbulent kinetic energy (TKE) of the dynamical system, and the vortex dynamics to determine the interface boundary in multiscale (3D-1D) fire simulations of underground space environments. The proposed methodology was demonstrated to be a useful technique for the determination of near and far fire fields, and could be applied across a broad range of flow simulations and mine geometries. Moreover, this research develops a methodology to analyze the tenable limits in a methane fire event in an underground coal mine for bare-faced miners, mine rescue teams, and fire brigade teams in order to improve safety and training of personnel trained to fight fires. The outcomes of this research are specific to mining although the methods outlined might have broader impacts on the other fields such as tunneling and underground spaces technology, HVAC, and fire protection engineering industries. / Ph. D. / With the rapid advancement of technology, the mine fire knowledge has progressed significantly. Atmospheric monitoring and early sensing of heating has improved; the numerical analysis has been expedited with the usage of supercomputers, and more regulations and standards have been set to increase health and safety of miners. In spite of advancements in these areas, fire hazards remain a critical hazard in underground mines. Developing an emergency plan for the safe escape and for fighting the fire is one of the most important issues during a fire event in underground space environments such as mines. A precise fire numerical analysis (simulation) before any fire events can give a broad view of the emergency situation that leads to improving the health and safety issues in the mining industry. Unfortunately, the precise simulation of the large complex dynamical system such as a fire in underground spaces is costly. This work details a cutting edge approach to reduce the fire and airflow simulation costs in order to make simulation of complex systems around fire and mine ventilation systems viable. The main focus of this proposal is to develop novel methodologies to decrease the time of the fire and airflow simulations. The developed methodologies prove to be useful techniques for the reduction of fire simulation and airflow simulation costs. In addition, this study will examine the development of a comprehensive methodology to analyze the tenable limits in a fire event in an underground coal mine in order to improve safety and training of personnel trained to fight fires. These simulations, applied to training, will result in more efficient evacuations (e.g., the decision to leave can be made quickly and with less delay), as well as safe and effective firefighting under certain situations. The target of this research is specific to mining industry although the methods outlined might have broader impacts on the other fields such as tunneling and underground spaces technology, HVAC, and fire protection engineering industries. Therefore, this research may have an immense contribution on the improvement of health and safety associated with firefighting.

<p dir="ltr">This dissertation develops a comprehensive multiscale framework to predict microstructural evolution and associated mechanical response of materials by employing mechanistic finite element models or data-driven neural networks techniques. First, a novel approach is presented for simulating microstructural evolution during severe plastic deformation (SPD) in multiphase alloys, integrating dislocation density-based models with Crystal Plasticity Finite Element Modeling (CPFEM) to efficiently capture grain refinement across different phases in multiphase material. Second, a data-driven predictive model leveraging Artificial Neural Networks (ANN) is developed to link morphological attributes of microstructure—such as grain and cell structure—with material properties in additively manufactured AISI 316L, enhancing the ability to accurately predict material performance from microstructural details. Finally, dynamic recrystallization (DRX) is modeled through a finite element approach high-temperature deformation with the cell switching strategy of cellular automata, capturing key phenomena such as grain growth and nucleation events within a scalable multiscale approach. Together, these studies advance predictive capabilities for material deformation, promoting more efficient design and manufacturing processes.</p>

This study introduces numerical frameworks for simulating the interactions within soil systems subjected to freezing and thawing processes, crucial for addressing geotechnical challenges in cold regions. By integrating robust thermo-hydro-mechanical (THM), this research offers a general understanding and specific insights into the deformation, thermal, and moisture transport behaviors of freezing-thawing soils. The first part of this study presents a soil freezing characteristic curve (SFCC) adaptable to various computational frameworks, including THM models. The SFCC, enhanced by an automatic regression scheme and a smoothing algorithm, accommodates the dynamic changes in soil properties due to phase transitions. This model effectively captures the unique behaviors of different soil types under freezing conditions, addressing key factors such as freezing temperature, compaction, and mechanical loading. Building on this foundation, the second framework employs the phase-field method (PFM) coupled with THM to model the behavior of ice-rich saturated porous media. This approach advances the field by enabling distinct representations of the mechanical behaviors of ice and soil through a diffused interface, introducing anisotropic responses as the soil undergoes freezing. By integrating a transversely isotropic plastic constitutive model for ice, this method provides a tool for capturing the phase transition processes and the resulting mechanical responses of frozen soil. The third part extends these methodologies to model thaw consolidation in permafrost regions using a THM framework combined with phase field methods. This model incorporates internal energy functions and a multiscale modified Cam-Clay model within a damage phase field framework, adept at capturing the simultaneous effects of phase change and particle rearrangement. Through validation against experimental scenarios, this model demonstrates its effectiveness in understanding the microstructural evolution and plastic softening in thaw-sensitive soils, which is vital for enhancing infrastructure resilience under thaw conditions. Together, these integrated approaches represent a leap in the modeling and simulation of geotechnical behaviors in cold regions, offering potential applications in predicting and mitigating the impacts of climate change on permafrost and other freeze-thaw affected terrains. / Thesis / Doctor of Science (PhD)

The main objective of this dissertation was to investigate the impacts of human activities and climate control on hydrologic responses using the Integrated Hydrologic Model (IHM), which dynamically couples HSPF and MODFLOW. The study first evaluated the impacts of land use change and rainfall variability on hydrologic responses—such as streamflow, evapotranspiration (ET), groundwater ET, recharge, and groundwater heads—in the Anclote River basin (ARB), Florida. The results provided insights into the uncertainties in hydrologic responses due to rainfall variability. Secondly, hydrologic response flux changes were partitioned into anthropogenic causes, including groundwater pumping, irrigation, and land use change, by the IHM in the Trout Creek Watershed, Florida. Hydrologic response flux changes per unit of human stress flux change were calculated and assessed at mean annual and monthly scales, offering insights for projecting hydrologic changes due to anthropogenic stressors. For climate control, a three-stage precipitation partitioning framework was proposed to study climate impacts on mean annual groundwater ET across 33 gauged watersheds in west-central Florida using the IHM. The roles of groundwater ET in long-term water balance were quantified through four ratios, and the contributions of various climate variabilities to groundwater ET were determined, providing new insights into sustainable groundwater management. Moreover, the dissertation explored the development and application of a multi-scale framework for the IHM, enhancing simulation accuracy and efficiency across different spatial scales and facilitating better water resource management. Applied to the ARB, this framework demonstrated improved model performance in capturing hydrologic changes due to local human activities and climate variability. This research underscored the significance of integrated surface-groundwater models in accurately assessing hydrologic impacts for water resource management, especially in regions with shallow water tables. It advanced the understanding of human and climate impacts on hydrologic systems, offering valuable tools and methodologies for integrated water resource management.

This thesis presents the development of a new multiscale stochastic fracture mechanics modelling framework informed by in-situ X-ray Computed Tomography (X-ray CT) tests, which can be used to enhance the quality of new designs and prognosis practices for fibre reinforced composites. To reduce the empiricism and conservatism of existing methods, this PhD research systematically has tackled several challenging tasks including: (i) extension of the cohesive interface crack model to multi-phase composites in both 2D and 3D, (ii) development of a new in-house loading rig to support in-situ X-ray CT tests, (iii) reconstruction of low phase-contrast X-ray CT datasets of carbon fibre composites, (iv) integration of X-ray CT image-based models into detailed crack propagation FE modelling and (v) validation of a partially informed multiscale stochastic modelling method by direct comparison with in-situ X-ray CT tensile test results.

<p>This study is concerned with the predictive modeling of the machining and the mechanical behaviors of additive manufactured (AMed) Ti6AlV/TiC composites and Ti6Al4V, respectively, using microstructure-based hierarchical multiscale modeling. The predicted results could constitute as a basis for optimizing the parameters of machining and AM of the current materials.</p> <p>Through hierarchical flow of material behaviors from the atomistic, to the microscopic and the macroscopic scales, multiscale heterogeneous models (MHMs) coupled to the finite element method (FEM) are employed to simulate the conventional and the laser assisted machining (LAM) of Ti6AlV/TiC composites. In the atomistic level, molecular dynamics (MD) simulations are used to determine the traction-separation relationship for the cohesive zone model (CZM) describing the Ti6AlV/TiC interface. Bridging the microstructures across the scales in MHMs is achieved by representing the workpiece by macroscopic model with the microscopic heterogeneous structure including the Ti6Al4V matrix, the TiC particles, and their interfaces represented by the parameterized CZM. As a result, MHMs are capable of revealing the possible reasons of the peculiar high thrust forces behavior during conventional machining of Ti6Al4V/TiC composites, and how laser assisted machining can improve this behavior, which has not been conducted before.</p> <p>Extending MHMs to predict the mechanical behaviors of AMed Ti6Al4V would require including the heterogeneous microstructure at the grain level, which could be computational expensive. To solve this issue, the extended mechanics of structure genome (XMSG) is introduced as a novel multiscale homogenization approach to predict the mechanical behavior of AMed Ti6Al4V in a computationally efficient manner. This is realized by embedding the effects of microstructure heterogeneity, porosity growth, and crack propagation in the multiscale calculations of the mechanical behavior of the AMed Ti6Al4V using FEM. In addition, the XMSG can predict the asymmetry in the Young’s modulus of the AMed Ti6Al4V under tensile and compression loading as well as the anisotropy in the mechanical behaviors. The applicability of XMSG to fatigue life prediction with valid results is conducted by including the energy dissipations associated with cyclic loading/unloading in the calculations of the cyclic response of the material.</p>

Fotogrammetri är en viktig metod för att skapa 3D-representationer av terräng och strukturer, men utmaningar kvarstår när det gäller noggrannheten på grund av faktorer som bildkvalitet, kamerakalibrering och positionsdata. Användningen av drönare för byggnadsdetaljmätning möjliggör snabb och kostnadseffektiv datainsamling, men noggrannheten kan påverkas av bildkvalitet och skuggning. Avhandlingen syftar till att jämföra noggrannheten och kvaliteten hos punktmoln genererade med två olika tekniker: terrester laserskanning (TLS) och struktur-från-rörelse (SfM) fotogrammetri med drönare. För att testa båda metodernas osäkerhet och noggrannhet vid detaljmätning av bostäder. Genom att utföra mätningar på en villa har data samlats in med både TLS och drönare utrustade med 48 MP kamera, samt georeferering med markstöd (GCP). SfM-punktmoln bearbetades med Agisoft Metashape. Jämförelser gjordes mellan SfM- och TLS-punktmoln avseende täckning, lägesskillnad och lägesosäkerhet. Genom att följa riktlinjer från HMK - Terrester Laserskanning och tillämpa HMK Standardnivå 3 säkerställs hög noggrannhet i mätningarna. Kontroll av lägesosäkerhet av båda punktmolnen resulterade i en lägesosäkerhet som understeg toleranser satta enligt HMK - Terrester laserskanner Standardnivå 3.  Kontrollen av lägesosäkerheten visade att kvadratiska medelfelet(RMSE) i plan och höjd var 0.011m respektive 0.007m för TLS-punktmolnet, och 0.02m respektive 0.015m för drönar-SfM-punktmolnet, vilket låg under toleransen enligt HMK- Terrester Detaljmätning 2021. Resultaten tyder på att Structure-from-Motion fotogrammetri med drönare kan generera punktmoln med god detaljrikedom, inte lika noggrann som med terrester laserskanner på sin lägsta inställning. TLS uppvisade mindre osäkerhet enligt kontrollen av lägesosäkerhet, ungefär en halvering av RMSE i både plan och höjd. I studien framgick det att TLS presterar sämre vid svåråtkomliga ytor med skymd sikt och ogynnsamma infallsvinklar, där effekten blir en lägre punkttäthet för punktmolnet. Vid gynnsamma förhållanden erbjuder TLS en högre noggrannhet och detaljnivå jämfört med SfM punktmoln. Enligt M3C2 punktmoln analys, med TLS punktmolnet som referens, antydde det att SfM punktmolnet genererade största felen vid takfot samt vid buskage. De större felen vid takfot tyder på att SfM presterar sämre gällande detaljnivå och fel vid buskageområdet varierar inte från det som dokumenterats om fotogrammetriska fel vid mappning av vegetation. SfM kan utföra en effektiv datainsamling för större samt svåråtkomliga ytor men kräver lång bearbetningstid med diverse hjälpmedel för att uppnå hög noggrannhet. TLS kräver istället en lång datainsamlingsprocess men kan generera ett detaljerat och noggrant punktmoln direkt utan långa bearbetningsprocesser. Val av metod styrs därmed baserat på specifika projektkrav. Långsiktiga implikationer inkluderar förbättrad effektivitet och säkerhet inom bygg- och anläggningsprojekt, samt potentialen för kostnadsbesparingar och mer detaljerade inspektioner. / Photogrammetry is a crucial method for creating 3D representations of terrain and structures, yet challenges remain regarding accuracy due to factors such as image quality, camera calibration, and positional data. The use of drones for building detail measurements enables rapid and cost-effective data collection, but accuracy can be affected by image quality and shading. This thesis aims to compare the accuracy and quality of point clouds generated using two different techniques: terrestrial laser scanning (TLS) and Structure-from-Motion (SfM) photogrammetry with drones. The objective is to test the uncertainty and accuracy of both methods in residential surveying. Data collection was performed on a villa using both TLS and a drone equipped with a 48 MP camera, along with georeferencing with ground control points (GCP). SfM point clouds were processed with Agisoft Metashape. Comparisons were made between SfM and TLS point clouds in terms of coverage, positional difference, and positional uncertainty. By following guidelines from HMK - Terrester laserskanning 2021 and applying HMK Standard Level 3, high measurement accuracy was ensured. Positional uncertainty checks of both point clouds resulted in positional uncertainty within tolerances set by HMK - Terrestrial Laser Scanning Standard Level 3. The positional uncertainty, with a sample of 41 points showed that the root mean square error (RMSE) in plane and height was 0.011m and 0.007m respectively for the TLS point cloud, and 0.02m and 0.015m for the drone-SfM point cloud, both within the tolerance according to HMK - Terrestrial Detail Measurement 2021. The results suggest that Structure-from-Motion photogrammetry with drones can generate point clouds with good detail, although not as accurate as terrestrial laser scanning at its lowest setting. TLS showed less uncertainty according to the positional uncertainty check, with approximately half the RMSE in both plan and height. The study found that TLS performs worse on difficult-to-access surfaces with obstructed views and unfavorable angles, resulting in lower point cloud density. Under favorable conditions, TLS offers higher accuracy and detail compared to SfM point clouds. According to M3C2 point cloud analysis, using the TLS point cloud as a reference, SfM point clouds showed the largest errors at eaves and shrubbery. The larger errors at eaves indicate that SfM performs worse in terms of detail level, and errors in the shrubbery area are consistent with documented photogrammetric errors in vegetation mapping. SfM can effectively collect data for larger and difficult-to-access areas but requires extensive processing time with various aids to achieve high accuracy. Conversely, TLS requires a long data collection process but can generate a detailed and accurate point cloud directly without lengthy processing. The choice of method thus depends on specific project requirements. Long-term implications include improved efficiency and safety in construction and infrastructure projects, as well as potential cost savings and more detailed inspections.

Titanium (Ti) foams of different densities 1622-4100 Kgm-3 made by a powder sintering technique were studied as to their structural and mechanical properties. The foams were tested under static and dynamic loading. The material was tested quasi statically and dynamically under strain rates in the range of 0.001-2500 s-1 and under different loading modes. It was found that strain rate sensitivity is more pronounced in lower density foams. Experiments were complimented by virtual testing. Based on the Voronoi tessellations a computational method was developed to generate stochastic foam geometries. Statistical control was applied to produce geometries with the microstructural characteristics of the tested material. The generated structures were numerically tested under different loading modes and strain rates. Voronoi polyhedrals were used to form the porosity network of the open cell foams. The virtually generated foams replicated the geometrical features of the experimentally tested material. Meshes for finite element simulations were produced. Existing material models were used for the parent material behaviour (sintered Ti) and calibrated to experiments. The virtual foam geometries of different densities were numerically tested quasi statically under uniaxial, biaxial and triaxial loading modes in order to investigate their macroscopic behaviour. Dynamic loading was also applied for compression. Strain rate sensitive and insensitive models were used for the parent material model in order to examine the influence of geometry and material strain rate sensitivity under high rates of deformation. It was found that inertial effects can enhance the strain rate sensitivity for low density foams and numerical predictions for the generated foam geometries were in very good agreement with experimental results. Power laws were established in scaling material properties with density. The study includes: 1. Information on the material behaviour and data for macroscopically modelling this type of foams for a range of densities and under different strain rates. 2. A proposed method for virtually generating foam geometries at a microscopic scale and examine the effect of geometrical characteristics on the macroscopic behaviour of foams.

The size and conformational complexity of proteins and other large systems represent major challenges for today's methods of quantum chemistry.This thesis is centered around the development of new computational tools to gain molecular-level insight into electronic transitions in such systems. To meet this challenge, we focus on the polarizable embedding (PE) model, which takes advantage of the fact that many electronic transitions are localized to a smaller part of the entire system.This motivates a partitioning of the large system into two regions that are treated at different levels of theory:The smaller part directly involved in the electronic process is described using accurate quantum-chemical methods, while the effects of the rest of the system, the environment, are incorporated into the Hamiltonian of the quantum region in an effective manner. This thesis presents extensions of the PE model with theaim of expanding its range of applicability to describe electronic transitions in large molecular systemsin the optical and X-ray regions. The developments cover both improvements with regardto the quantum region as well as the embedding potential representing the environment.Regarding the former, a damped linear response formulation has been implemented to allow for calculations of absorption spectra of large molecular systems acrossthe entire frequency range. A special feature of this development is its abilityto address core excitations that are otherwise not easily accessible.Another important development presented in this thesis is the coupling of the PE model to a multi-configuration self-consistent-field description of the quantum region and its further combination with response theory. In essence, this extends the PE model to the study of electronic transitions in large systems that are prone to static correlation --- a situation that is frequently encountered in biological systems. In addition to the direct environmental effects on the electronic structure of the quantum region, another important component of the description of electronic transitions in large molecular systems is an accurate account of the indirect effects of the environment, i.e., the geometrical distortions in the quantum region imposed by the environment. In thisthesis we have taken the first step toward the inclusion of geometry distortions in the PE frameworkby formulating and implementing molecular gradients for the quantum region. To identify critical points related to the environment description, we perform a theoretical analysis of the PE model starting from a full quantum-mechanicaltreatment of a composite system. Based on this, we present strategies for an accurate yet efficient construction of the embedding potentialcovering both the calculation of ground state and transition properties. The accurate representation of the environment makes it possible to reduce the size of the quantum region without compromising the overall accuracy of the final results. This further enables use of highly accurate quantum-chemical methods despite their unfavorable scaling with the size of the system. Finally, some examples of applications will be presented to demonstrate how the PE model may be applied as a tool to gain insight into and rationalize the factors influencing electronic transitions in large molecular systems of increasing complexity. / <p>The dissertation was awarded the best PhD thesis prize 2016 by the Danish Academy of Natural Sciences.</p><p></p><p>QC 20170209</p>

Les structures planaires de grandes tailles sont de plus en plus utilisées dans les applications des satellites et des radars. Deux grands types de ces structures à savoir les FSS et les Reflectarrays sont particulièrement les plus intéressants dans les domaines de la conception RF. Mais en raison de leur grande taille et de la complexité des cellules élémentaires, l‘analyse complète de ces structures nécessite énormément de mémoire et des temps de calcul excessif. Par conséquent, les techniques classiques basées sur maillage linéaire soit ne parviennent pas à simuler de telles structures soit, exiger des ressources non disponibles à un concepteur d'antenne. Une technique appelée « technique par changement d'échelle » tente de résoudre ce problème par partitionnement de la géométrie du réseau par de nombreux domaines imbriqués définis à différents niveaux d'échelle du réseau. Le multi-pôle par changement d'échelle, appelé « Scale changing Network (SCN) », modélise le couplage électromagnétique entre deux échelles successives, en résolvant une formulation intégral des équations de Maxwell par une technique basée sur la méthode des moments. La cascade de ces multi-pôles par changement d'échelle, permet le calcul de la matrice d'impédance de surface de la structure complète qui peut à son tour être utilisées pour calculer la diffraction en champ lointain. Comme le calcul des multi-pôles par changement d'échelle est mutuellement indépendant, les temps d'exécution peuvent être réduits de manière significative en parallélisant le calcul. Par ailleurs, la modification de la géométrie de la structure à une échelle donnée nécessite seulement le calcul de deux multi-pôles par changement d'échelle et ne requiert pas la simulation de toute la structure. Cette caractéristique fait de la SCT un outil de conception et d'optimisation très puissant. Des structures planaires uniformes et non uniformes excité par un cornet ont étés modélisés avec succès, avec des temps de calcul délais intéressants, employant les ressources normales de l'ordinateur. / Large sized planar structures are increasingly being employed in satellite and radar applications. Two major kinds of such structures i.e. FSS and Reflectarrays are particularly the hottest domains of RF design. But due to their large electrical size and complex cellular patterns, full-wave analysis of these structures require enormous amount of memory and processing requirements. Therefore conventional techniques based on linear meshing either fail to simulate such structures or require resources not available to a common antenna designer. An indigenous technique called Scale-changing Technique addresses this problem by partitioning the cellular array geometry in numerous nested domains defined at different scale-levels in the array plane. Multi-modal networks, called Scale-changing Networks (SCN), are then computed to model the electromagnetic interaction between any two successive partitions by Method of Moments based integral equation technique. The cascade of these networks allows the computation of the equivalent surface impedance matrix of the complete array which in turn can be utilized to compute far-field scattering patterns. Since the computation of scale-changing networks is mutually independent, execution times can be reduced significantly by using multiple processing units. Moreover any single change in the cellular geometry would require the recalculation of only two SCNs and not the entire structure. This feature makes the SCT a very powerful design and optimization tool. Full-wave analysis of both uniform and nonuniform planar structures has successfully been performed under horn antenna excitation in reasonable amount of time employing normal PC resources.