Intelligent Computational Transportation

Transportation is commonplace around our world. Numerous researchers dedicate great efforts to vast transportation research topics. The purpose of this dissertation is to investigate and address a couple of transportation problems with respect to geographic discretization, pavement surface automatic examination, and traffic ow simulation, using advanced computational technologies. Many applications require a discretized 2D geographic map such that local information can be accessed efficiently. For example, map matching, which aligns a sequence of observed positions to a real-world road network, needs to find all the nearby road segments to the individual positions. To this end, the map is discretized by cells and each cell retains a list of road segments coincident with this cell. An efficient method is proposed to form such lists for the cells without costly overlapping tests. Furthermore, the method can be easily extended to 3D scenarios for fast triangle mesh voxelization. Pavement surface distress conditions are critical inputs for quantifying roadway infrastructure serviceability. Existing computer-aided automatic examination techniques are mainly based on 2D image analysis or 3D georeferenced data set. The disadvantage of information losses or extremely high costs impedes their effectiveness iv and applicability. In this study, a cost-effective Kinect-based approach is proposed for 3D pavement surface reconstruction and cracking recognition. Various cracking measurements such as alligator cracking, traverse cracking, longitudinal cracking, etc., are identified and recognized for their severity examinations based on associated geometrical features. Smart transportation is one of the core components in modern urbanization processes. Under this context, the Connected Autonomous Vehicle (CAV) system presents a promising solution towards the enhanced traffic safety and mobility through state-of-the-art wireless communications and autonomous driving techniques. Due to the different nature between the CAVs and the conventional Human- Driven-Vehicles (HDVs), it is believed that CAV-enabled transportation systems will revolutionize the existing understanding of network-wide traffic operations and re-establish traffic ow theory. This study presents a new continuum dynamics model for the future CAV-enabled traffic system, realized by encapsulating mutually-coupled vehicle interactions using virtual internal and external forces. A Smoothed Particle Hydrodynamics (SPH)-based numerical simulation and an interactive traffic visualization framework are also developed

PySimFrac: A Python Library for Synthetic Fracture Generation, Analysis, and Simulation

In this paper, we introduce Pysimfrac, a open-source python library for generating 3-D synthetic fracture realizations, integrating with fluid simulators, and performing analysis. Pysimfrac allows the user to specify one of three fracture generation techniques (Box, Gaussian, or Spectral) and perform statistical analysis including the autocorrelation, moments, and probability density functions of the fracture surfaces and aperture. This analysis and accessibility of a python library allows the user to create realistic fracture realizations and vary properties of interest. In addition, Pysimfrac includes integration examples to two different pore-scale simulators and the discrete fracture network simulator, dfnWorks. The capabilities developed in this work provides opportunity for quick and smooth adoption and implementation by the wider scientific community for accurate characterization of fluid transport in geologic media. We present Pysimfrac along with integration examples and discuss the ability to extend Pysimfrac from a single complex fracture to complex fracture networks

Design of decorative 3D models: from geodesic ornaments to tangible assemblies

L'obiettivo di questa tesi è sviluppare strumenti utili per creare opere d'arte decorative digitali in 3D. Uno dei processi decorativi più comunemente usati prevede la creazione di pattern decorativi, al fine di abbellire gli oggetti. Questi pattern possono essere dipinti sull'oggetto di base o realizzati con l'applicazione di piccoli elementi decorativi. Tuttavia, la loro realizzazione nei media digitali non è banale. Da un lato, gli utenti esperti possono eseguire manualmente la pittura delle texture o scolpire ogni decorazione, ma questo processo può richiedere ore per produrre un singolo pezzo e deve essere ripetuto da zero per ogni modello da decorare. D'altra parte, gli approcci automatici allo stato dell'arte si basano sull'approssimazione di questi processi con texturing basato su esempi o texturing procedurale, o con sistemi di riproiezione 3D. Tuttavia, questi approcci possono introdurre importanti limiti nei modelli utilizzabili e nella qualità dei risultati. Il nostro lavoro sfrutta invece i recenti progressi e miglioramenti delle prestazioni nel campo dell'elaborazione geometrica per creare modelli decorativi direttamente sulle superfici. Presentiamo una pipeline per i pattern 2D e una per quelli 3D, e dimostriamo come ognuna di esse possa ricreare una vasta gamma di risultati con minime modifiche dei parametri. Inoltre, studiamo la possibilità di creare modelli decorativi tangibili. I pattern 3D generati possono essere stampati in 3D e applicati a oggetti realmente esistenti precedentemente scansionati. Discutiamo anche la creazione di modelli con mattoncini da costruzione, e la possibilità di mescolare mattoncini standard e mattoncini custom stampati in 3D. Ciò consente una rappresentazione precisa indipendentemente da quanto la voxelizzazione sia approssimativa. I principali contributi di questa tesi sono l'implementazione di due diverse pipeline decorative, un approccio euristico alla costruzione con mattoncini e un dataset per testare quest'ultimo.The aim of this thesis is to develop effective tools to create digital decorative 3D artworks. Real-world art often involves the use of decorative patterns to enrich objects. These patterns can be painted on the base or might be realized with the application of small decorative elements. However, their creation in digital media is not trivial. On the one hand, users can manually perform texture paint or sculpt each decoration, in a process that can take hours to produce a single piece and needs to be repeated from the ground up for every model that needs to be decorated. On the other hand, automatic approaches in state of the art rely on approximating these processes with procedural or by-example texturing or with 3D reprojection. However, these approaches can introduce significant limitations in the models that can be used and in the quality of the results. Instead, our work exploits the recent advances and performance improvements in the geometry processing field to create decorative patterns directly on surfaces. We present a pipeline for 2D and one for 3D patterns and demonstrate how each of them can recreate a variety of results with minimal tweaking of the parameters. Furthermore, we investigate the possibility of creating decorative tangible models. The 3D patterns we generate can be 3D printed and applied to previously scanned real-world objects. We also discuss the creation of models with standard building bricks and the possibility of mixing standard and custom 3D-printed bricks. This allows for a precise representation regardless of the coarseness of the voxelization. The main contributions of this thesis are the implementation of two different decorative pipelines, a heuristic approach to brick construction, and a dataset to test the latter

Image Space Tensor Field Visualization Using a LIC-like Method

Tensors are of great interest to many applications in engineering and in medical imaging, but a proper analysis and visualization remains challenging. Physics-based visualization of tensor fields has proven to show the main features of symmetric second-order tensor fields, while still displaying the most important information of the data, namely the main directions in medical diffusion tensor data using texture and additional attributes using color-coding, in a continuous representation. Nevertheless, its application and usability remains limited due to its computational expensive and sensitive nature. We introduce a novel approach to compute a fabric-like texture pattern from tensor fields on arbitrary non-selfintersecting surfaces that is motivated by image space line integral convolution (LIC). Our main focus lies on regaining three-dimensionality of the data under user interaction, such as rotation and scaling. We employ a multi-pass rendering approach to estimate proper modification of the LIC noise input texture to support the three-dimensional perception during user interactions

Modeling and hexahedral meshing of cerebral arterial networks from centerlines

Computational fluid dynamics (CFD) simulation provides valuable information on blood flow from the vascular geometry. However, it requires extracting precise models of arteries from low-resolution medical images, which remains challenging. Centerline-based representation is widely used to model large vascular networks with small vessels, as it encodes both the geometric and topological information and facilitates manual editing. In this work, we propose an automatic method to generate a structured hexahedral mesh suitable for CFD directly from centerlines. We addressed both the modeling and meshing tasks. We proposed a vessel model based on penalized splines to overcome the limitations inherent to the centerline representation, such as noise and sparsity. The bifurcations are reconstructed using a parametric model based on the anatomy that we extended to planar n-furcations. Finally, we developed a method to produce a volume mesh with structured, hexahedral, and flow-oriented cells from the proposed vascular network model. The proposed method offers better robustness to the common defects of centerlines and increases the mesh quality compared to state-of-the-art methods. As it relies on centerlines alone, it can be applied to edit the vascular model effortlessly to study the impact of vascular geometry and topology on hemodynamics. We demonstrate the efficiency of our method by entirely meshing a dataset of 60 cerebral vascular networks. 92% of the vessels and 83% of the bifurcations were meshed without defects needing manual intervention, despite the challenging aspect of the input data. The source code is released publicly

Computational fluid dynamics indicators to improve cardiovascular pathologies

In recent years, the study of computational hemodynamics within anatomically complex vascular regions has generated great interest among clinicians. The progress in computational fluid dynamics, image processing and high-performance computing haveallowed us to identify the candidate vascular regions for the appearance of cardiovascular diseases and to predict how this disease may evolve. Medicine currently uses a paradigm called diagnosis. In this thesis we attempt to introduce into medicine the predictive paradigm that has been used in engineering for many years. The objective of this thesis is therefore to develop predictive models based on diagnostic indicators for cardiovascular pathologies. We try to predict the evolution of aortic abdominal aneurysm, aortic coarctation and coronary artery disease in a personalized way for each patient. To understand how the cardiovascular pathology will evolve and when it will become a health risk, it is necessary to develop new technologies by merging medical imaging and computational science. We propose diagnostic indicators that can improve the diagnosis and predict the evolution of the disease more efficiently than the methods used until now. In particular, a new methodology for computing diagnostic indicators based on computational hemodynamics and medical imaging is proposed. We have worked with data of anonymous patients to create real predictive technology that will allow us to continue advancing in personalized medicine and generate more sustainable health systems. However, our final aim is to achieve an impact at a clinical level. Several groups have tried to create predictive models for cardiovascular pathologies, but they have not yet begun to use them in clinical practice. Our objective is to go further and obtain predictive variables to be used practically in the clinical field. It is to be hoped that in the future extremely precise databases of all of our anatomy and physiology will be available to doctors. These data can be used for predictive models to improve diagnosis or to improve therapies or personalized treatments.En els últims anys, l'estudi de l'hemodinàmica computacional en regions vasculars anatòmicament complexes ha generat un gran interès entre els clínics. El progrés obtingut en la dinàmica de fluids computacional, en el processament d'imatges i en la computació d'alt rendiment ha permès identificar regions vasculars on poden aparèixer malalties cardiovasculars, així com predir-ne l'evolució. Actualment, la medicina utilitza un paradigma anomenat diagnòstic. En aquesta tesi s'intenta introduir en la medicina el paradigma predictiu utilitzat des de fa molts anys en l'enginyeria. Per tant, aquesta tesi té com a objectiu desenvolupar models predictius basats en indicadors de diagnòstic de patologies cardiovasculars. Tractem de predir l'evolució de l'aneurisma d'aorta abdominal, la coartació aòrtica i la malaltia coronària de forma personalitzada per a cada pacient. Per entendre com la patologia cardiovascular evolucionarà i quan suposarà un risc per a la salut, cal desenvolupar noves tecnologies mitjançant la combinació de les imatges mèdiques i la ciència computacional. Proposem uns indicadors que poden millorar el diagnòstic i predir l'evolució de la malaltia de manera més eficient que els mètodes utilitzats fins ara. En particular, es proposa una nova metodologia per al càlcul dels indicadors de diagnòstic basada en l'hemodinàmica computacional i les imatges mèdiques. Hem treballat amb dades de pacients anònims per crear una tecnologia predictiva real que ens permetrà seguir avançant en la medicina personalitzada i generar sistemes de salut més sostenibles. Però el nostre objectiu final és aconseguir un impacte en l¿àmbit clínic. Diversos grups han tractat de crear models predictius per a les patologies cardiovasculars, però encara no han començat a utilitzar-les en la pràctica clínica. El nostre objectiu és anar més enllà i obtenir variables predictives que es puguin utilitzar de forma pràctica en el camp clínic. Es pot preveure que en el futur tots els metges disposaran de bases de dades molt precises de tota la nostra anatomia i fisiologia. Aquestes dades es poden utilitzar en els models predictius per millorar el diagnòstic o per millorar teràpies o tractaments personalitzats.Postprint (published version

Thermal Lattice Boltzmann Methods for the Simulation of Turbulent Flows with Conjugate Heat Transfer – Application to Refrigerated Vehicles

In dieser Arbeit wird eine thermische Lattice-Boltzmann-Methode (TLBM) für die instationäre Simulation turbulenter Strömungen mit natürlicher Konvektion und konjugierter Wärmeübertragung vorgestellt. Turbulente Strömungen mit ihren chaotischen Druck- und Geschwindigkeitsschwankungen stellen eine besondere Herausforderung für numerische Simulationen dar, wobei turbulente Strömungen, angetrieben durch thermische Auftriebskräfte, eine besonders schwierige Aufgabe darstellen. Wie in dieser Arbeit gezeigt wird, ermöglicht TLBM Large Eddy Simulationen (LES) solcher Probleme im industriellen und technischen Maßstab unter Verwendung eines Smagorinsky-Feinstruktur-Modells und unter Ausnutzung seiner intrinsischen Parallelisierbarkeit sowie der Möglichkeit, mehrere tausend Prozessorkerne zu verwenden. Die Eignung der vorliegenden Methode wird in dieser Arbeit anhand von Anwendungen zur Simulation der Innenluftströmung und der Isolationseffizienz eines Kühlwagens, des Wärmetransports im Luftspalt zwischen Rotor und Stator bei Elektromotoren, der Weiterentwicklung hocheffizienter Isolation auf der Basis von Vakuumisolationspaneelen (VIP) und Latentwärmespeichern sowie deren Anwendung in Kühlwagen gezeigt. Eine umfassende Validierung der Methode und ihrer Implementierung im Open-Source-Framework OpenLB wird durchgeführt. Gitterkonvergenz zweiter Ordnung wird gegen das analytische Porous Plate Problem demonstriert, während stabile Simulationen auch bei grober Diskretisierung mit hohen Reynolds- und Rayleigh-Zahlen erreicht werden. Eine sehr gute Übereinstimmung wird für natürliche Konvektion in einem quadratischen Hohlraum, ein bekannter Benchmark-Fall, vom laminaren zum turbulenten Regime mit 10^3 <= Ra <= 10^10 und bei Auflösungen von y+ ~ 2 gezeigt. Im ersten Teil der Ergebnisse werden Simulationen eines leeren Kühlaufbaus für einen Kühllastwagen vorgestellt. Das Strömungsfeld und der Wärmeübergang innerhalb eines gegebenen Kühllastwagens zeigt eine sehr gute Übereinstimmung mit den Messergebnissen, insbesondere den experimentellen Daten für ein Kühlfahrzeug bei Re ~ 53000 an vier charakteristischen Geschwindigkeits- und 13 Temperaturpositionen im Lastwagen. Die Wärmeübertragung durch die Wände wird in den Simulationen durch konjugierte Wärmeübertragung aufgelöst. Dies ermöglicht nun die präzise Vorhersage von Wärmeströmen nahe von Nusselt-Korrelationen für den gegebenen Aufbau, aber - im Gegensatz zu gewöhnlichen Nusselt-Korrelationen - wird der Wärmestrom in der Simulation räumlich aufgelöst. Im zweiten Teil der Ergebnisse wird die Strömung und der Wärmeübergang in einem Ringspalt mit innen rotierendem Zylinder untersucht. Die besondere Herausforderung bei der Simulation dieser Taylor-Couette-Strömung ist die Bildung von Taylor-Wirbeln, die durch ihre Rotation senkrecht zur Hauptströmungsrichtung den entsprechenden Wärmeübergang deutlich erhöhen. Detaillierte instationäre Simulationen werden über einen weiten Drehzahlbereich von fast schleichender Strömungen bis hin zum Auftreten von Taylor-Wirbeln durchgeführt. Es wird eine gute Übereinstimmung mit bisherigen Ergebnissen für die Strömungsstrukturen und die Verbesserung des Wärmeübergangs durch Taylor-Wirbel festgestellt. Insbesondere wird die vorliegende Methode mit Messungen, einer Korrelation und Simulationen unter Verwendung des Scherspannungstransport-Turbulenzmodells (SST) verglichen. Besonderes Augenmerk wird auf die Vorhersage der kritischen Taylor-Zahl gelegt. Während direkte numerische Simulationen (DNS) mit LBM die kritische Taylor-Zahl aus den Experimenten nahezu identisch vorhersagen, wird sie von LBM-LES leicht und vom SST-Modell weiter überschätzt, was auf die übermäßig dissipative Natur der Turbulenzmodelle für die Transition zurückzuführen ist. Im dritten Teil der Ergebnisse werden innovative Konzepte für verbesserte, nachhaltigere Kühlfahrzeuge numerisch untersucht. Um den Kraftstoffverbrauch und die damit verbundenen Emissionen zu reduzieren, werden zwei Ansätze als vielversprechend angesehen: (a) der Einbau von Vakuum-Isolationspaneelen (VIP) in die Wände des Kühlkoffers und (b) die Einführung eines Latentwärmespeichers (LHS) zum Austausch der kraftstoffbetriebenen Klimaanlage (AC). Die Verwendung des vorliegenden TLBM erlaubt in den Simulationen die Auflösung der durch die AC und die natürliche Konvektion induzierten turbulenten Luftströmung, des Wärmeflusses innerhalb der Isolierwände und der tiefgefrorenen Ladung. Dies liefert neue Erkenntnisse über den Einfluss der Konzepte auf die Wärmeübertragung in verschiedenen Kühlaufbauten. Die Simulationen zeigen einen stark reduzierten und homogenisierten einströmenden Wärmestrom für das kombinierte PUR- und VIP-Isoliermaterial im Vergleich zu einer reinen PUR-Isolierung. Die Dämmung des Kühlaufbaus mit VIPs halbiert daher die erforderliche Kühlenergie. Dies ermöglicht den Ersatz der AC durch einen LHS in Dachnähe und ein zusätzliches Lüftungssystem mit deutlich geringerer Gesamtleistung. Unter Berücksichtigung der Temperaturhomogenität von Tiefkühlprodukten wird eine leichte Umströmung des Kühlgutes als notwendig erachtet. Die maximal zulässige Ausfallzeit der AC wird in den Simulationen mit jeweils ca. 3,3 min (PUR), 8 min (PUR+VIP) und 11 min (PUR+VIP+LHS) ermittelt. Im vierten Teil der Ergebnisse wird eine LBM zur Simulation des Schmelzens und des konjugierten Wärmeübergangs auf der Basis des Transports der Gesamtenthalpie vorgestellt, welche bei Validierung gegen die analytische Lösung des zeitabhängigen Stefan-Problems präzise Ergebnisse liefert. Die in dieser Arbeit entwickelte Methode zeigt geringe Grenzflächendiffusion für einen weiten Bereich von Relaxationszeiten und Stefan-Zahlen. Weiterhin wird eine enge Übereinstimmung für das Schmelzen von Gallium einschließlich der natürlichen Konvektion in 2D und 3D mit Messungen und Simulationen mit unterschiedlichen Ansätzen gezeigt. Das Modell wird ferner auf das Schmelzen von Paraffin in zwei komplexen Metallschaumgeometrien angewendet. Es wird eine Voxel-basierte parallele Vernetzung vorgestellt, die eine schnelle und automatisierte Verarbeitung der komplexen Geometrie in wenigen Minuten ermöglicht. Die Simulationen erfassen erfolgreich den materialübergreifenden Wärmetransfer in 3D, wobei die Wärmeleitfähigkeit des Schaums mehr als 1000-mal größer als die des Paraffins ist. Die Form der Schmelzfront und der Einfluss der spezifischen Oberfläche der verschiedenen Metallschäume stehen in enger Übereinstimmung mit früheren Simulationen

Frame Fields for Hexahedral Mesh Generation

As a discretized representation of the volumetric domain, hexahedral meshes have been a popular choice in computational engineering science and serve as one of the main mesh types in leading industrial software of relevance. The generation of high quality hexahedral meshes is extremely challenging because it is essentially an optimization problem involving multiple (conflicting) objectives, such as fidelity, element quality, and structural regularity. Various hexahedral meshing methods have been proposed in past decades, attempting to solve the problem from different perspectives. Unfortunately, algorithmic hexahedral meshing with guarantees of robustness and quality remains unsolved. The frame field based hexahedral meshing method is the most promising approach that is capable of automatically generating hexahedral meshes of high quality, but unfortunately, it suffers from several robustness issues. Field based hexahedral meshing follows the idea of integer-grid maps, which pull back the Cartesian hexahedral grid formed by integer isoplanes from a parametric domain to a surface-conforming hexahedral mesh of the input object. Since directly optimizing for a high quality integer-grid map is mathematically challenging, the construction is usually split into two steps: (1) generation of a feature-aligned frame field and (2) generation of an integer-grid map that best aligns with the frame field. The main robustness issue stems from the fact that smooth frame fields frequently exhibit singularity graphs that are inappropriate for hexahedral meshing and induce heavily degenerate integer-grid maps. The thesis aims at analyzing the gap between the topologies of frame fields and hexahedral meshes and developing algorithms to realize a more robust field based hexahedral mesh generation. The first contribution of this work is an enumeration of all local configurations that exist in hexahedral meshes with bounded edge valence and a generalization of the Hopf-Poincaré formula to octahedral (orthonormal frame) fields, leading to necessary local and global conditions for the hex-meshability of an octahedral field in terms of its singularity graph. The second contribution is a novel algorithm to generate octahedral fields with prescribed hex-meshable singularity graphs, which requires the solution of a large non-linear mixed-integer algebraic system. This algorithm is an important step toward robust automatic hexahedral meshing since it enables the generation of a hex-meshable octahedral field. In the collaboration work with colleagues [BRK+22], the dataset HexMe consisting of practically relevant models with feature tags is set up, allowing a fair evaluation for practical hexahedral mesh generation algorithms. The extendable and mutable dataset remains valuable as hexahedral meshing algorithms develop. The results of the standard field based hexahedral meshing algorithms on the HexMesh dataset expose the fragility of the automatic pipeline. The major contribution of this thesis improves the robustness of the automatic field based hexahedral meshing by guaranteeing local meshability of general feature aligned smooth frame fields. We derive conditions on the meshability of frame fields when feature constraints are considered, and describe an algorithm to automatically turn a given non-meshable frame field into a similar but locally meshable one. Despite the fact that local meshability is only a necessary but not sufficient condition for the stronger requirement of meshability, our algorithm increases the 2% success rate of generating valid integer-grid maps with state-of-the-art methods to 57%, when compared on the challenging HexMe dataset