Simulation-Oriented Methodology for Distortion Minimisation during Laser Beam Welding

Distortion is one of the drawbacks of any welding process, most of the time needed to be suppressed. One doubtful factor that could affect welding deformation is the shape of the liquid melt pool, which can be modified via variation of process parameters. The aim of this work was to numerically study the dynamics of the weld pool and its geometrical influence on welding distortion during laser beam welding. To achieve such a goal, a promising novel process simulation model, employed in investigating the keyhole and weld pool dynamics, has successfully been invented. The model incorporated all distinctive behaviours of the laser beam welding process. Moreover, identification of the correlation between the weld pool geometry and welding distortion as well as, eventually, weld pool shapes that favour distortion minimisation has also been simulatively demonstrated

Simulation-Oriented Methodology for Distortion Minimisation during Laser Beam Welding

Distortion is one of the drawbacks of any welding process, most of the time needed to be suppressed. One doubtful factor that could affect welding deformation is the shape of the liquid melt pool, which can be modified via variation of process parameters. The aim of this work was to numerically study the dynamics of the weld pool and its geometrical influence on welding distortion during laser beam welding. To achieve such a goal, a promising novel process simulation model, employed in investigating the keyhole and weld pool dynamics, has successfully been invented. The model incorporated all distinctive behaviours of the laser beam welding process. Moreover, identification of the correlation between the weld pool geometry and welding distortion as well as, eventually, weld pool shapes that favour distortion minimisation has also been simulatively demonstrated

Exploring Attacks and Defenses in Additive Manufacturing Processes: Implications in Cyber-Physical Security

Many industries are rapidly adopting additive manufacturing (AM) because of the added versatility this technology offers over traditional manufacturing techniques. But with AM, there comes a unique set of security challenges that must be addressed. In particular, the issue of part verification is critically important given the growing reliance of safety-critical systems on 3D printed parts. In this thesis, the current state of part verification technologies will be examined in the con- text of AM-specific geometric-modification attacks, and an automated tool for 3D printed part verification will be presented. This work will cover: 1) the impacts of malicious attacks on AM using geometrically-modified 3D models, 2) a 3D part reconstruction approach from medical imaging scans, 3) a mesh alignment technique based on point set registration, de- signed to handle abnormal part geometries, and 4) an automatic error detection and defect visualization tool for comparing the geometric similarity of 3D printed parts to their intended geometries

Edge-elements formulation of 3D CSEM in geophysics : a parallel approach

Electromagnetic methods (EM) are an invaluable research tool in geophysics whose relevance has increased rapidly in recent years due to its wide industrial adoption. In particular, the forward modelling of three-dimensional marine controlled-source electromagnetics (3D CSEM FM) has become an important technique for reducing ambiguities in the interpretation of geophysical datasets through mapping conductivity variations in the subsurface. As a consequence, the 3D CSEM FM has application in many areas such as hydrocarbon/mineral exploration, reservoir monitoring, CO2 storage characterization, geothermal reservoir imaging and many others due to there quantities often displaying conductivity contrasts with respect to their surrounding sediments. However, the 3D CSEM FM at real scale implies a numerical challenge that requires an important computational effort, often too high for modest multicore computing architectures, especially if it fuels an inversion process. On the other hand, although the HPC code development is dominated by compiled languages, the popularity of high-level languages for scientific computations has increased considerably. Among all of them, Python is probably the language that has shown more interest, mainly because of flexibility and its simple and clean syntax. However, its use for HPC geophysical applications is still limited, which suggests a path for research, development and improvement. Therefore, this thesis reports the attempts at designing and implementing a methodology that has not been systematically applied for solving 3D CSEM FM with an HPC application baked upon Python. The net contribution of this effort is the development and documentation of a new open-source modelling code for 3D CSEM FM in geophysics, namely, the Parallel Edge-based Tool for Geophysical Electromagnetic Modelling (PETGEM). The importance of having this modelling tools lies in the fact that they provide synthetic results that can be compared with real data which has a practical use both in the industry and academia. Still, available 3D CSEM FM codes are usually written in low-level languages whose implemented methods are often innaccessible to the scientific community since they are commercial. PETGEM is written mostly in Python and relies on mpi4py and petsc4py packages for parallel computations. Other scientific Python packages used include Numpy andScipy. This code is designed to cope with the main challenges encountered within the numerical simulation of the problem under consideration: tackle realistic problems with accuracy, efficiency and flexibility. It uses the Nédélec Edge Finite Element Method (EFEM) as discretisation technique because its divergence-free basis is very well suited for solving Maxwell¿s equations. Furthermore, it supports completely unstructured tetrahedral meshes which allows the representation of complex geometries and local refinement, positively impacting the accuracy of the solution. The parallel implementation of the code using shared/distributed-memory architectures is investigated and described throughout this document. In addition, the thesis deals with the numerical and physical challenges of the 3D CSEM FM problem. Through this work, frequency-domain Maxwell's equations have been discretised using EFEM and validated by comparison with analytical solutions and published data, proving that modelling results are highly accurate. Moreover, this work discusses an automatic mesh adaptation strategy and the convergence rate of the iterative solvers that are widely used in the literature for solving the EM problem is presented. In summary, this thesis shows that it is possible to integrate Python and HPC for the solution of 3D CSEM FM at large scale in an effective way. The new modelling tool is easy to use and the adopted algorithms are not only accurate and efficient but also have the possibility to easily add or remove components without having to rewrite large sections of the code.Los métodos electromagnéticos (EM) son una herramienta de investigación inestimable en geofísica, cuya relevancia ha aumentado rápidamente en los últimos años debido a su amplia adopción industrial. En particular, el modelado electromagnético de fuente controlada (3D CSEM FM) se ha convertido en una técnica importante para reducir las ambigüedades en la interpretación de datos geofísicos a través del mapeo de las variaciones de conductividad en el subsuelo. Como resultado, el 3D CSEM FM tiene aplicación en muchas áreas como la exploración de hidrocarburos/minerales, monitoreo de yacimientos, caracterización de almacenamiento de CO2, imágenes de yacimientos geotérmicos, entre otros, debido a que éstos muestran contrastes de conductividad con respecto a sus sedimentos circundantes. Sin embargo, el 3D CSEM FM a escala real implica un desafío numérico que requiere un esfuerzo computacional importante, a menudo demasiado exigente para arquitecturas multicore modestas, especialmente si éste forma parte de un proceso de inversión. Por otra parte, aunque el desarrollo aplicaciones HPC está dominado por lenguajes compilados, la popularidad de los lenguajes de alto nivel para cómputo científico ha aumentado considerablemente. Entre todos ellos, Python es probablemente el idioma que ha mostrado más interés, principalmente a su flexibilidad y sintaxis simple. Sin embargo, su uso para geocómputo con HPC sigue siendo limitado, lo que sugiere un camino para la investigación, el desarrollo y la mejora. Por lo tanto, esta tesis describe el diseño e implementación de una metodología que hasta ña fecha no se ha aplicado sistemáticamente para resolver el 3D CSEM FM con una aplicación HPC basada en Python. La contribución neta de este esfuerzo es el desarrollo y documentación de un nuevo código open-source para el modelado 3D CSEM FM en geofísica, es decir, Parallel Edge-based Tool for Geophysical Electromagnetic Modelling (PETGEM). La importancia del desarrollo de estas herramientas radica en el hecho de que proporcionan resultados sintéticos que pueden ser comparados con datos reales, lo cual tiene un uso práctico en la industria y el mundo académico. A pesar de ello, los códigos disponibles para 3D CSEM FM suelen estar escritos en lenguajes de bajo nivel, y en muchos casos sus métodos no son accesibles a la comunidad científica ya que son comerciales. PETGEM ha sido principalmente escrito en Python y se basa en paquetes mpi4py y petsc4py para cálculos paralelos. El código está diseñado para hacer frente a los principales desafíos que se encuentran en la simulación numérica del problema en cuestión: abordar problemas realistas con precisión, eficiencia y flexibilidad. Además, utiliza el Método de Elementos Finitos de Borde (EFEM) como técnica de discretización ya que sus bases son muy adecuadas para resolver las ecuaciones de Maxwell. Además, soporta mallas tetraédricas no estructuradas que permiten la representación de geometrías complejas y refinamiento local, impactando positivamente la precisión de la solución. A lo largo del documento se investiga la implementación paralela en arquitecturas de memoria compartida/distribuida. Además, la tesis revisa los desafíos numéricos y físicos del problema 3D CSEM FM. A través de este trabajo, las ecuaciones de Maxwell en el dominio de la frecuencia se han discretizado utilizando EFEM y validado contra soluciones analíticas y datos previamente publicados, lo que demuestra que los resultados del modelado son precisos. Por otra parte, este trabajo discute una estrategia de adaptación automática de malla y la tasa de convergencia de los solvers iterativos que se utilizan ampliamente en la literatura. En resumen, esta tesis muestra que es posible integrar Python y HPC para la solución de 3D CSEM FM a gran escala de una manera efectiva. La nueva herramienta de modelado es fácil de usar y los algoritmos adoptados no sólo son precisos y eficientes, sino también flexibles

Visual Techniques for Geological Fieldwork Using Mobile Devices

Visual techniques in general and 3D visualisation in particular have seen considerable adoption within the last 30 years in the geosciences and geology. Techniques such as volume visualisation, for analysing subsurface processes, and photo-coloured LiDAR point-based rendering, to digitally explore rock exposures at the earth’s surface, were applied within geology as one of the first adopting branches of science. A large amount of digital, geological surface- and volume data is nowadays available to desktop-based workflows for geological applications such as hydrocarbon reservoir exploration, groundwater modelling, CO2 sequestration and, in the future, geothermal energy planning. On the other hand, the analysis and data collection during fieldwork has yet to embrace this ”digital revolution”: sedimentary logs, geological maps and stratigraphic sketches are still captured in each geologist’s individual fieldbook, and physical rocks samples are still transported to the lab for subsequent analysis. Is this still necessary, or are there extended digital means of data collection and exploration in the field ? Are modern digital interpretation techniques accurate and intuitive enough to relevantly support fieldwork in geology and other geoscience disciplines ? This dissertation aims to address these questions and, by doing so, close the technological gap between geological fieldwork and office workflows in geology. The emergence of mobile devices and their vast array of physical sensors, combined with touch-based user interfaces, high-resolution screens and digital cameras provide a possible digital platform that can be used by field geologists. Their ubiquitous availability increases the chances to adopt digital workflows in the field without additional, expensive equipment. The use of 3D data on mobile devices in the field is furthered by the availability of 3D digital outcrop models and the increasing ease of their acquisition. This dissertation assesses the prospects of adopting 3D visual techniques and mobile devices within field geology. The research of this dissertation uses previously acquired and processed digital outcrop models in the form of textured surfaces from optical remote sensing and photogrammetry. The scientific papers in this thesis present visual techniques and algorithms to map outcrop photographs in the field directly onto the surface models. Automatic mapping allows the projection of photo interpretations of stratigraphy and sedimentary facies on the 3D textured surface while providing the domain expert with simple-touse, intuitive tools for the photo interpretation itself. The developed visual approach, combining insight from all across the computer sciences dealing with visual information, merits into the mobile device Geological Registration and Interpretation Toolset (GRIT) app, which is assessed on an outcrop analogue study of the Saltwick Formation exposed at Whitby, North Yorkshire, UK. Although being applicable to a diversity of study scenarios within petroleum geology and the geosciences, the particular target application of the visual techniques is to easily provide field-based outcrop interpretations for subsequent construction of training images for multiple point statistics reservoir modelling, as envisaged within the VOM2MPS project. Despite the success and applicability of the visual approach, numerous drawbacks and probable future extensions are discussed in the thesis based on the conducted studies. Apart from elaborating on more obvious limitations originating from the use of mobile devices and their limited computing capabilities and sensor accuracies, a major contribution of this thesis is the careful analysis of conceptual drawbacks of established procedures in modelling, representing, constructing and disseminating the available surface geometry. A more mathematically-accurate geometric description of the underlying algebraic surfaces yields improvements and future applications unaddressed within the literature of geology and the computational geosciences to this date. Also, future extensions to the visual techniques proposed in this thesis allow for expanded analysis, 3D exploration and improved geological subsurface modelling in general.publishedVersio

Brain and Human Body Modeling

This open access book describes modern applications of computational human modeling with specific emphasis in the areas of neurology and neuroelectromagnetics, depression and cancer treatments, radio-frequency studies and wireless communications. Special consideration is also given to the use of human modeling to the computational assessment of relevant regulatory and safety requirements. Readers working on applications that may expose human subjects to electromagnetic radiation will benefit from this book’s coverage of the latest developments in computational modelling and human phantom development to assess a given technology’s safety and efficacy in a timely manner. Describes construction and application of computational human models including anatomically detailed and subject specific models; Explains new practices in computational human modeling for neuroelectromagnetics, electromagnetic safety, and exposure evaluations; Includes a survey of modern applications for which computational human models are critical; Describes cellular-level interactions between the human body and electromagnetic fields

System-specific parameter optimization for non-polarizable and polarizable force fields

The accuracy of classical force fields (FFs) has been shown to be limited for the simulation of cation-protein systems despite their importance in understanding the processes of life. Improvements can result from optimizing the parameters of classical FFs or by extending the FF formulation by terms describing charge transfer and polarization effects. In this work, we introduce our implementation of the CTPOL model in OpenMM, which extends the classical additive FF formula by adding charge transfer (CT) and polarization (POL). Furthermore, we present an open-source parameterization tool, called FFAFFURR that enables the (system specific) parameterization of OPLS-AA and CTPOL models. The performance of our workflow was evaluated by its ability to reproduce quantum chemistry energies and by molecular dynamics simulations of a Zinc finger protein.Comment: 62 pages and 25 figures (including SI), manuscript to be submitted soo

Interactive CFD simulations

This project is about the development of an implementable Interactive Computer Fluid Dynamics methodology -- The range of this work begins with an overview of the current status of computational fluid dynamics simulation software and methodologies, continues with an introduction to what interactive and interactivity mean, develops an all original interactive CFD methodology to follow for the solution of fluid scenarios and finally, the description of the implementation of an interactive solver for CFD using the earlier developed methodology -- The project was developed entirely at the EAFIT University’s Applied Mechanics Laboratory in Medellin and is part of a collaboration effort in companionship with the University of Aberta in Canada and Los Andes University in Bogota, Colombi